Weather





  • My Presentation to the Pacific Pension & Investment Institute
    by Roy W. Spencer, Ph. D. on February 17, 2020 at 8:56 am

    Last week I was privileged to present an invited talk (PDF here) to the Winter Roundtable of the the Pacific Pension & Investment Institute in Pasadena, CA. The PPI meeting includes about 120 senior asset managers representing about $25 Trillion in investments. Their focus is on long-term investing with many managing the retirement funds of

  • Corrected RCP Scenario Removal Fractions
    by Roy W. Spencer, Ph. D. on February 6, 2020 at 10:26 am

    Well, as I suspected (and warned everyone) in my blog post yesterday, a portion of my calculations were in error regarding how much CO2 is taken out of the atmosphere in the global carbon cycle models used for the RCP (Representative Concentration Pathway) scenarios. A few comments there said it was hard to believe such

  • UAH Global Temperature Update for January 2020: +0.56 deg. C
    by Roy W. Spencer, Ph. D. on February 5, 2020 at 12:11 pm

    The Version 6.0 global average lower tropospheric temperature (LT) anomaly for January, 2020 was +0.56 deg. C, unchanged from the December 2019 value of +0.56 deg. C. The linear warming trend since January, 1979 remains at +0.13 C/decade (+0.11 C/decade over the global-averaged oceans, and +0.18 C/decade over global-averaged land). Various regional LT departures from

  • Nature Has Been Removing Excess CO2 4X Faster than IPCC Models
    by Roy W. Spencer, Ph. D. on February 5, 2020 at 10:26 am

    Note: What I present below is scarcely believable to me. I have looked for an error in my analysis, but cannot find one. Nevertheless, extraordinary claims require extraordinary evidence, so let the following be an introduction to a potential issue with current carbon cycle models that might well be easily resolved by others with more

  • Limbaugh Receives the Presidential Medal of Freedom
    by Roy W. Spencer, Ph. D. on February 5, 2020 at 6:16 am

    Last night at the State of the Union Address, President Trump awarded radio talk show host and conservative commentator Rush Limbaugh the Presidential Medal of Freedom. If you haven’t heard, Rush was recently diagnosed with stage 4 lung cancer. I cannot think of a more deserving recipient of our country’s highest civilian honor. Rush has

  • Europe’s Anti-Science Plague Descends On Africa
    by Charles Rotter on February 20, 2020 at 2:00 pm

    From The GWPF Date: 19/02/20 European Scientist European activists are putting lives at risk in East Africa, turning a plague of insects into a real prospect of widespread famine. Map: FOA The fast-breeding desert locust has invaded Kenya, Somalia and Ethiopia, creating a state of emergency. The pests recently landed in Djibouti, Eritrea, Oman and…

  • NASA Flights Detect Millions of Arctic Methane Hotspots
    by Charles Rotter on February 20, 2020 at 10:00 am

    From NASA Feature | February 18, 2020 The image shows a thermokarst lake in Alaska. Thermokarst lakes form in the Arctic when permafrost thaws. Credit: NASA/JPL-Caltech By Esprit Smith, NASA’s Earth Science News Team The Arctic is one of the fastest warming places on the planet. As temperatures rise, the perpetually frozen layer of soil,…

  • Canadian Government: Anti-Pipeline Eco-Extremists Sabotaging Railway Lines
    by Eric Worrall on February 20, 2020 at 6:00 am

    Guest essay by Eric Worrall h/t Breitbart, Fox News; An intense situation in Canada as climate activists, environmentalists and other groups including Antifa appear to be edging towards committing acts of terrorism. But the conflict has deeper roots, an apparent power struggle between hereditary chiefs of the Wet’suwet’en Nation who oppose the Coastal GasLink natural…

  • Japan: Back to the Fossil Fueled Future!
    by David Middleton on February 20, 2020 at 2:00 am

    Guest MJaGA! by David Middleton MjaGA = Making Japan Great Again From the Midget Oligarch Reporting On News Service (MORONS)… EconomicsJapan Goes Into Reverse on Going GreenThe country abandoned nuclear energy and is building coal plants that will spew as much CO2 as all the cars in the U.S. By Noah SmithFebruary 5, 2020 Modern…

  • Global climate frameworks miss the ‘big picture’ on food, say scientists
    by Anthony Watts on February 19, 2020 at 10:00 pm

    Schemes may fall short of ambitions by dealing separately with food production, supply and consumption From the INTERNATIONAL MAIZE AND WHEAT IMPROVEMENT CENTER (CIMMYT) Global schemes to fight climate change may miss their mark by ignoring the “fundamental connections” in how food is produced, supplied and consumed, say scientists in a new paper published in…

  • A Midwinter Subtlety of Puget Sound Weather
    by noreply@blogger.com (Cliff Mass Weather Blog) on February 19, 2020 at 3:43 pm

    On the surface, today was a gloriously boring weather day over western Washington.Bright blue skies, light winds, agreeable, but cool temperatures.  A day you would think meteorologists would be taking a siesta.But like a fine wine, Northwest weather is often best appreciated in its subtleties....and today was no different.With clear skies and weak winds, the ground could radiate efficiently to space, and much of the region had its coldest morning in a month.  As shown by the low temperatures this (Tuesday) morning (below), temperatures ranged from the low to mid-30s near the Sound, to mid-20s in the eastern Seattle suburbs to even the single digits to a few sites  near Mt. Rainier.  Frost was found all over the region, with fog in river valleys and low spots.This morning on the way downtown for a breakfast lecture of the wonderful CleanTech Alliance, I saw a band of clouds down the center of Lake Washington.    And reaching the 49th floor of 1201 3rd Avenue Building, I saw a line of clouds extending north-south down Puget Sound.And I knew why is was there.....and like an experienced meteorological sommelier I was able to savior the moment.   Here is the cloud line as seen from the Space Needle PanoCam---not as dramatic a view as I had enjoyed while listening to a lecture about battery technologies, but perhaps you can see it (click on image to enlarge).The reason for the line is that there were intersecting land breezes from both sides of the Sound.  But let me explain.Everyone knows about sea breezes--onshore winds that occur when land gets warmer than water.  But when the opposite occurs, when the land is cooler than water, there is a rush of air from land to water called the land breeze. And such land breezes are best seen when the general winds are light...like last night.This morning there were land breezes on both sides of the Sound...both headed towards the center of the body of water.   This can be illustrated by a plot of the winds around 8 AM near Edmonds.Circles indicate calm winds and air temperatures are also plotted (the observations over the water were from a Washington State ferry).  The Sound is roughly 45F this time of the year...roughly 10-15F warmer than the adjacent land.  Enough to form a weak land breeze.As shown in the schematic below, as the land breezes convergence over the center of the Sound, air is forced to rise, forming a band of clouds.  This is what happened to today over Puget Sound and to a lesser extent over Lake Washington.  Take a careful look tomorrow morning...it may well happen again.

  • U.S. Operational Weather Prediction is Crippled By Inadequate Computer Resources
    by noreply@blogger.com (Cliff Mass Weather Blog) on February 17, 2020 at 2:58 pm

    U.S. global numerical weather prediction has now fallen into fourth place, with national and regional prediction capabilities a shadow of what they could be.There are several reasons for these lagging numerical weather prediction capabilities, including lack of strategic planning, inadequate cooperation between the research and operational communities, and too many sub-optimal prediction efforts.But there is another reason of equal importance: a profound lack of computer resources dedicated to numerical weather prediction, both for  operations and research. The bottom line:  U.S. operational numerical weather prediction resources used by the National Weather Service must be increased 10 times to catch up with leading efforts around the world and 100 times to reach state of the science.  Why does the National Weather Service require very large computer resources to provide the nation with world-leading weather prediction?Immense computer resources are required for modern numerical weather prediction.  For example, NOAA/NWS TODAY is responsible for running:A global atmospheric model (the GFS/FV-3) running at 13-km resolution out to 384 hours.Global ensembles (GEFS) of many (21 forecasts) forecasts at 35 km resolutionThe high-resolution Rapid Refresh and RAP models out 36 h.The atmosphere/ocean Climate Forecast System model out 9 month.sThe National Water Model (combined WRF and hydrological modeling)Hurricane models during the seasonReanalysis runs (rerunning past decades to provide calibration information)Running the North American mesoscale model (NAM)Running the Short-Range Ensemble Forecast System (SREF)This is not a comprehensive list.  And then there is the need for research runs to support development of the next generation systems.  As suggested by the world-leading European Center for Medium Range Weather Prediction, research computer resources should be at least five times greater than the operational requirements to be effective.NY Times Magazine: 10/23/2016How Lack of Computing Resources is Undermining NWS  Numerical Weather PredictionThe current modeling systems (some described above) used by the National Weather Service are generally less capable then they should be because of insufficient computer resources.  Some examples.1.  Data Assimilation.  The key reason the U.S. global model is behind the European Center and the other leaders is because they use an approach called 4DVAR, a resource-demanding technique that involves running the modeling systems forward and backward in time multiple times.  Inadequate computer resources has prevented the NWS from doing this.2.  High-resolution ensembles.   One National Academy report after another, one national workshop committee after another, and one advisory committee after another has told NWS management that the U.S. must have a large high-resolution ensemble system (at least 4-km grid spacing, 30-50 members) to deal with convection (e.g., thunderstorms) and other high-resolution weather features.  But the necessary computer power is not available.European Center Supercomputer3.  Global ensembles.  A key capability of any first-rate global prediction center is to run a large global ensemble (50 members at more), with sufficient resolution to realistically simulate storms and the major impacts of terrain (20 km grid spacing or better).  The European Center has a 52 members ensemble run at 18-km grid spacing.  The U.S. National Weather Service?  21 members at 35-km resolution.  Not in the same league.I spend a lot of time with NOAA and National Weather Service model developers and group leaders.  They complain continuously how they lack computer resources for development and testing.  They tell me that such resource deficiency prevents them from doing the job they know they could. These are good people, who want to do a state-of-the-art job, but they can't do to inadequate computer resources.NOAA/NWS computer resources are so limited that university researchers with good ideas cannot test them on NOAA computers or in facsimiles of the operational computing environment.  NOAA grant proposal documents make it clear:  NOAA/NWS cannot supply the critical computer resources university investigators need to test their innovations (below is quote from a recent NOAA grant document):So if a researcher has a good idea that could improve U.S. operational weather prediction, they are out of luck:  NOAA/NWS doesn't have the computer resources to help.  Just sad.U.S. Weather Prediction Computer Resources Stagnate While the European Center Zooms AheadThe NOAA/NWS computer resources available for operational weather prediction is limited to roughly 5 petaflops (pflops).   Until Hurricane Sandy (2010), National Weather Service management was content to possess one tenth of the computer resources of the European Center, but after the scandalous situation went public after that storm (including coverage on the NBC nightly news), NOAA/NWS management managed to get a major increment to the current level--which is just under what is available to the European Center.Image courtesy of Rebecca Cosgrove, NCEP Central Operations  But the situation is actually much worse than it appears.   The NWS computer resources are split between operational and backup machines and is dependent on an inefficient collection of machines of differing architectures (Dell, IBM, and Cray).  There is a bottleneck of I/O (input/output) from these machines (which means they can't get information into and out of them efficiently), and storage capabilities are inadequate.There is no real plan for seriously upgrading these machines, other than a 10-20% enhancement over the next few years.In contrast, the European Center now has two machines with a total of roughly 10 pflop peak performance, with far more storage, and better communication channels into and out of the machine.And keep in mind that ECMWP computers have far few responsibilities than the NCEP machines.  NCEP computers have to do EVERYTHING from global to local modeling, for hydrological prediction to seasonal time scales.  The ECMWF computers only have to deal with global model computing.To make things even more lopsided, the European Center is now building a new computer center in Italy and they recently signed an agreement to purchase a new computer system FIVE TIMES as capable as their current one.They are going to leave NOAA/NWS weather prediction capabilities in the dust.  And it did not have to happen.And I just learned today that the UKMET office, number two in global weather prediction, just announced that it will spend 1.2 BILLION pounds (that's 1.6 billion dollars) on a new weather supercomputer system, which will leave both the European Center and the U.S. weather service behind.   U.S. weather prediction will drop back into the third tier.Fixing the ProblemPast NOAA/NWS management bear substantial responsibility for this disaster, with Congress sharing some blame for not being attentive to this failure.  Congress has supplied substantial funding to NOAA/NWS in the past for model development, but such funding has not been used effectively.Importantly, there IS bipartisan support in Congress to improve weather prediction, something that was obvious when I testified at a hearing for the House Environment Subcommittee last November.  They know there is a problem and want to help.There is bipartisan support in Congress for better weather modelingA major positive is that NOAA is now led by two individuals (Neil Jacobs and Tim Gallaudet), who understand the problem and want to fix it. And the President's Science Adviser, Kelvin Droegemeier,  is a weather modeler, who understands the problem. So what must be done now?(1)  U.S. numerical prediction modeling must be reorganized, since it is clear that the legacy structure, which inefficiently spreads responsibility and support activities, does not work.  The proposal of NOAA administrator Neal Jacobs to build a new EPIC center to be the centerpiece of U.S. model development should be followed (see my blog on EPIC here).(2) NOAA/NWS must develop a detailed strategic plan that not only makes the case for more computer resources, but demonstrates how such resources will improve weather prediction.  Amazingly, they have never done this.  In fact, NOAA/NWS does not even have a document describing in detail the computer resources they have now (I know, I asked a number of NOAA/NWS managers for it--they admitted to me it doesn't exist).(3)  With such a plan Congress should invest in the kind of computer resources that would enable U.S. weather prediction to become first rate.  Ten times the computer resources (costing about 100 million dollars) would bring us up to parity, 100 times would allow us to be state of the science (including such things as running global models at convection-permitting resolution, something I have been working on in my research).Keep in mind that a new weather prediction computer system would be no more expensive that a single, high tech jet fighter.  Which do you think would provide more benefit to U.S. citizens?  And remember, excellent weather prediction is the first line of defense from severe weather that might be produced by global warming.82 million dollars a piece(4)  Future computer resources should divided between high-demand operational forecasting, which requires dedicated large machines, and less time-sensitive research/development runs, which could make use of cloud computing.  Thus, future NOAA computer resources will be a hybrid.(5)  Current operational numerical prediction in the National Weather Service has been completed at the NCEP Central Operations Center.  This center has not been effective, has unnecessarily slowed the transition to operations of important changes, and must be reorganized or replaced with more facile, responsive entity.U.S. citizens can enjoy far better weather forecasts, saving many lives and tens of billions of dollars per year.   But to do so will require that NOAA/NWS secure vastly increased computer resources, and reorganize weather model development and operations to take advantage of them.

  • A Weak El Nino Transitioning to La Nada
    by noreply@blogger.com (Cliff Mass Weather Blog) on February 15, 2020 at 4:40 am

    During the past few months we have moved from near neutral conditions (La Nada) to a weak El Nino (warmer than normal temperatures in the central and eastern tropic Pacific)--providing some insights into the weather later this year.Looking at the temperatures in the central tropical Pacific (the Nino 3.4 area), the water temperatures have moved from a bit cooler than normal in September to around .5C above normal.  This is a minimal El Nino.Next, viewing water temperatures in an east-west slice of the Pacific Ocean--from the surface to about 300 meters below the surface-- show warmer than normal conditions (red/orange colors). The trade winds have weakened as well--another marker of El Nino.  This is a very weak, minimal El Nino.  And the strength of the signal is important.Last month, the NOAA Climate Prediction Center was projecting that this spring we could move into neutral territory (tropical sea surface temps within .5C of normal)-- see belowAnd the January extended forecast from many modeling systems (see below) generally indicates neutral conditions, slightly weighted towards the warm side.  The latest European Center model is similar.The key point in all this, is that with a weak El Nino grading to neutral (normal, La Nada) conditions in the tropical Pacific, there is no reason to expect conditions in our area to be different from normal.  They could be, of course, but the tropical Pacific will not be weighting the atmospheric dice in any direction (something that a strong El Nino or La Nina would do).What about the BLOB?  How is it going?  The latest sea surface temperature anomaly map (difference from normal) shows cool water immediately off the West Coast, but evidence of a weak blob (1-2C above normal) off the coast.   Let's call it a junior blob...much, much weaker than the one we experienced a few years ago.

  • Extremely Favorable Water Supply Outlook for this Summer
    by noreply@blogger.com (Cliff Mass Weather Blog) on February 13, 2020 at 3:44 am

    If you enjoy drinking water, keeping your plants green, and appreciate an agricultural bounty--there is good reason to smile.  The water outlook is exceptionally favorable for this summerAs noted in my previous blog, the last two months have brought far wetter than normal conditions over the region, including a restored snowpack.The latter is illustrated by the SNOTEL snow water equivalent map, which indicates an overall state snowpack a bit more than 100% of normal.  The City of Seattle reservoir storage is way above normal-- in fact as high as the usual peak reservoir level in May and early June (and Seattle has been letting out plenty of water to prevent dams from being overtopped).   Similarly bountiful conditions are found for the Everett and Tacoma water systems.But the biggest water challenge is always on the eastern slopes of the Cascades, water that supplies the huge agricultural industry of the region.    One key source of water is the Yakima River and its associated reservoir system.  As shown in the graph below, the Yakima storage system went from well below normal in November to above normal today, with the water level now as high as early April last year.The other major sources of water for Columbia Basin agriculture is the Columbia River, whose water run-off volume for April to September is predicted to be 106% of normal by the National Weather Service's Portland River Forecast Center.  All good.And the precipitation is not over.  The latest UW WRF model 180 h forecast of accumulated precipitation (below) suggests 2-5 inches of water content in our mountains, with several feet of snow above roughly 4000 ft.And to top it off the latest NOAA Climate Prediction Center three months forecasts are for normal temperatures and normal to above normal precipitation over the region.The bottom line is that we are in exceptionally good shape regarding water for the upcoming summer and early fall, with no sign of drought or water shortages.  With well-filled reservoirs, lots of snow, and much more precipitation in our near future, there is little likelihood of water issues later this year.

  • The Record Breaking Blue Mountain Flooding of February 6-8, 2020
    by noreply@blogger.com (Cliff Mass Weather Blog) on February 11, 2020 at 6:33 pm

    There has been a lot of discussion about heavy rain and flooding around the Northwest, but one region really stands out, with river levels and flooding unmatched in many decades, if ever:  the region on and near the northwest side of the Blue Mountains of northeast Oregon.Walla Walla River from Hwy 12 Provided By Kevin Pogue of Whitman CollegeWalla Walla River Provided by Kevin PogueTo orient you, a topographic map of the region is shown below.  The Blue Mountain's slopes on the northeast side are oriented southwest to northeast--that is going to be very important in understanding what happened a few days ago.  Heavy rains on these northeast slopes flowed into rivers heading to the northwest, bringing most to flood stage and some to record flood levels not observed in a century.  I-84 and other roads were closed in places.I-84 West of Baker OregonThe rainfall totals for this precipitation event were extraordinary: some places received nearly 10 inches, and 3-6 inches were commonplace (see totals below for Feb 5-8).The 7-day total precipitation from the National Weather Service show the situation with a wider view (see below).  You can also the even larger amounts on the western side of the Cascades, but the larger rivers on the western side of the Cascades can handle huge amounts of rainfall better. Still there was plenty of flooding in western Washington.The intense precipitation on the northwest side of the Blue Mountains caused the rivers to surge, some to record-breaking levels.  Not for that day.  FOR ANY DAY ON RECORD.For example, the  discharge of the Umatilla River (Near Gibbon, Oregon)...see map below... blasted the previous all time record (black line) and far exceeded daily records (red triangle).So why was this event so extreme for northeast Blue Mountains?   Good question.The answer was that we had an unusual multi-day atmospheric river that came in from the west-northwest, with wind optimized to push directly up the northwest side of the Blue Mountains (see water vapor channel satellite picture last on February 6th).  The result was intense precipitation and flooding.

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  • What If: Hurricane Michael’s Extensive Wind Swath Would Devastate Houston, NWS says
    by Chris on January 15, 2020 at 11:15 pm

    “In summary, it’s going to be bad.” That’s how Jeff Evans with the NWS in Houston/Galveston began Wednesday’s presentation, “What if Hurricane Michael Struck Houston? An Examination of Inland Wind Damage,” at the AMS 100th Annual Meeting in Boston. He was boots on the ground after Hurricane Michael slammed the panhandle as a Category 5

  • 10-m Resolution Quarter-Trillion Gridpoint Tornadic Supercell Simulation Mesmerizes
    by Chris on January 14, 2020 at 7:00 pm

    An exceptionally high resolution simulation of a supercell thunderstorm fascinated conferees Tuesday at the AMS 100th Annual Meeting in Boston. Leigh Orf of the University of Wyoming presdented imagery and animations of the simulation that ran on the Blue Waters Supercomputer. With a 10 m grid spanning 11,200 X 11,200 X 2,000 (251 billion) grid

  • Record January Thaw for the 100th AMS Annual Meeting Adds to “Unconventional” Weather Trend
    by Chris on January 12, 2020 at 4:33 pm

    [UPDATED] You’ve heard it before: The convergence of thousands of meteorologists at AMS Annual Meetings brings unusual weather to the host city. Spring-like warmth this weekend in this year’s host city of Boston is continuing this trend. As of 2 pm ET Sunday, the temperature at Logan International Airport has climbed to at least 73

  • Students Converse with Air Force Hurricane Hunter Flight Meteorologists, Tornado Field Researcher
    by Chris on January 12, 2020 at 3:16 am

    Saturday’s Student Conference at the AMS 100th Annual Meeting kicking off in Boston featured a series of Conversations with Professionals to gain insight into a variety of career choices, the work these professionals in our field currently do, and how they got where they are today. This year’s series, in which short introductions are followed

  • In Celebration: American Weather Enterprise Collaborating to Protect Lives and Property
    by Jeff on December 19, 2019 at 10:15 pm

    By Mary M. Glackin, AMS President-Elect, and Dr. Joel N. Myers, Founder and CEO, AccuWeather In his acclaimed book, The Signal and the Noise, noted statistician Nate Silver examines forecasts of many categories and finds that most forecast types demonstrate little or no skill, and most predictive fields have made insignificant progress in accuracy over the

  • A simple model of convection to study the atmospheric surface layer
    by Katherine Fodor on September 20, 2019 at 9:10 am

    Since being immortalised in Hollywood film, “the butterfly effect” has become a commonplace concept, despite its obscure origins. Its name derives from an object known as the Lorenz attractor, which has the form of a pair of butterfly wings (Fig. 1). It is a portrait of chaos, the underlying principle hindering long-term weather prediction: just a small change in initial conditions leads to vastly different outcomes in the long run. The three-equation system that gives rise to the Lorenz attractor is often referred to as a simple model of atmospheric convection, yet amongst the atmospheric science community, attention is rarely paid to the original fluid flow that the Lorenz equations describe. Consisting of a fluid layer heated from below and cooled from above, Rayleigh-Bénard convection (Fig. 2) is a hallmark flow beloved by fluid dynamicists and mathematicians alike for its analytical tractability, yet rich behaviour. It is often cited as being of immediate relevance for many geophysical and astrophysical flows [1]. The success of turbulent Rayleigh-Bénard convection in leading to our understanding of chaos, as exemplified by the Lorenz attractor, suggests the enticing possibility of gaining other key conceptual insights into the behaviour of the Earth’s atmosphere through the use of this simple convective system.   In a recent study [2] we explored this potential by investigating to what extent turbulent Rayleigh-Bénard convection serves as an analogue of the daytime atmospheric boundary layer, also known as the convective boundary layer (CBL). In particular, we investigated whether statistical properties in the surface layer develop with height in a similar way in both systems. The surface layer is typically just a few tens of metres thick, but due to the strong turbulent mixing that takes place there, it is of primary importance for the development of the boundary layer. The surface boundary conditions of Rayleigh-Bénard convection and the CBL are the same, which might lead one to think that surface-layer properties should behave similarly in both cases. However, differences in the upper boundary conditions between the two systems modify the large-scale circulations that appear in both systems and this may have an impact in the surface layer. Indeed, despite the much-heralded relevance of Rayleigh-Bénard convection to geophysical flows, we find that its cooled upper plate modifies the large-scale structures in such a way that it substantially alters the behaviour of near-surface properties compared to the CBL. In particular, the downdrafts in Rayleigh-Bénard convection are considerably stronger than in the CBL and their impingement into the surface layer changes how velocity and temperature statistics develop with height. However, we also find that just an incremental change to the upper boundary condition of Rayleigh-Bénard convection is needed to closely match surface-layer statistics in the CBL. If instead of being cooled, the upper plate is made adiabatic, i.e. no heat is allowed to escape (Fig. 3), the influence of the strong, cold downdrafts is removed, resulting in surface-layer similarity between this modified version of Rayleigh-Bénard convection and the CBL. Rayleigh-Bénard convection with an adiabatic top lid has the advantage that it is a simpler experimental set-up than the CBL and provides a longer statistically steady state, allowing for greater statistical convergence to be achieved through long-time averaging. In the long term, the classical Rayleigh-Bénard system will continue to serve as a paradigm for studies of natural convection, though we are increasingly beginning to see that its practical application to geophysical and astrophysical [3] flows may not be as straightforward as past literature seems to suggest.  References [1] A. Pandey, J. Scheel, and J. Schumacher.  Turbulent superstructures in Rayleigh-Bénard convection.Nature Communications, 9:2118, 2018. [2] K.  Fodor,  JP  Mellado,  and  M.  Wilczek.   On the  Role  of  Large-Scale Updrafts and Downdrafts in Deviations From Monin-Obukhov Similarity Theory  in  Free  Convection. Boundary-Layer Meteorology,  2019. [3] F. Wilczynski, D. Hughes, S. Van Loo, W. Arter, and F. Militello.  Stability  of  scrape-off  layer  plasma:  a  modified  Rayleigh-Bénard  problem. Physics of Plasmas, 26:022510, 2019. Edited by Dasaraden Mauree Katherine Fodor is a PhD. candidate at the Max Planck Institute for Meteorology in Hamburg, Germany. She uses very high resolution computer simulations to study turbulence in the atmosphere. In particular, her research concerns interactions between large-scale structures and small-scale turbulence. You can find her on Twitter @FodorKatherine where, in addition to science, she also tweets about cycling.”    

  • A brighter future for the Arctic
    by Patrik Winiger on September 13, 2019 at 7:00 am

    This is a follow-up from a previous publication. Recently, a new analysis of the impact of Black Carbon in the Arctic was conducted within a European Union Action. “Difficulty in evaluating, or even discerning, a particular landscape is related to the distance a culture has traveled from its own ancestral landscape. As temperate-zone people, we have long been ill-disposed toward deserts and expanses of tundra and ice. They have been wastelands for us; historically we have not cared at all what happened in them or to them. I am inclined to think, however, that this landscape is able to expose in startling ways the complacency of our thoughts about land in general. Its unfamiliar rhythms point up the narrow impetuosity of Western schedules, by simply changing the basis of the length of the day. And the periodically frozen Arctic Ocean is at present an insurmountable impediment to timely shipping. This land, for some, is irritatingly and uncharacteristically uncooperative.”             -Barry Lopez, Arctic Dreams, 1986 Study Back in the 1980s the Arctic was a different place. It is one of the fastest changing regions of our planet and since then, Arctic sea ice volume has more than halved (Figure 1). Our study took place in the 2010s, when the Arctic moved into a new regime and sea ice volume showed unprecedented lows. In the last 3 years since our study ended this decline has just continued. During 4 years, we collected small airborne particles at 5 different sites around the Arctic; 1 to 2 years per site. Later, we measured  the concentrations and isotopic sources of black carbon (BC) aerosols, a product of incomplete combustion of biomass and fossil fuels, and a subfraction of the total collected aerosol. All living organisms have more or less the same relative amount of radiocarbon atoms. We call it a similar ‘isotopic fingerprint’. Through photosynthesis plants take up CO2. About 1 in 1012 CO2 molecules contains the naturally occurring (but unstable) radiocarbon atom (14C), which is formed high up in the atmosphere through solar radiation. Black carbon from biomass burning thereby has a contemporary radiocarbon fingerprint. When plants die, the radiocarbon atoms are left to decay, and no new radiocarbon is being built into the plant. Radiocarbon’s half-life is 5730 years, which means that fossils and consequentially soot from fossil fuels is completely depleted of radiocarbon. For the same periods and sites of our observations (see Figure 2), we also simulated black carbon concentration and sources. This was done with an atmospheric transport model (FLEXPART), using emission inventory data for fossil and biofuels (ECLIPSE), and biomass burning (GFED) (see Figure 3). Emission inventories like ECLIPSE calculate emissions of air pollutants and greenhouse gases in a consistent framework. They rely on international and national statistics of the  amount of consumed energy sources for e.g., energy use, industrial production, and agricultural activities. GFED uses MODIS satellite measurements of daily burnt area. This is used – together with ’emission factors’ (i.e. amount of emitted species per consumed energy source unit) – to calculated emissions of several different gas and particle species. The details and methodologies have also been described in a previous EGU ASxCR blogpost. Black carbon, a short live climate pollutant (SLCP), is the second or more likely third largest warming agent in the atmosphere after the greenhouse gases carbon dioxide and methane. Unlike the two gases, it is less clear how big the net warming effect of BC is. There are several open questions, that lead to the current uncertainty: 1. How much BC is exactly put into the atmosphere? 2. How long does it stay in the air and where is it located? 3. Where from and where to is it transported, and where and when is it deposited? 4. How does it affect the earths radiative balance by darkening snow and ice, and most importantly of all: how does it interact with clouds. We have a fair understanding of all these processes, but still, relatively large uncertainties remain to be resolved. Depending on how much BC is in the air and where it is located in the atmosphere, it can have different effects (e.g., strong warming, warming, or even cooling). And all these things need to be measured, and simulated correctly by computer models. Current multi-model best estimates by the Arctic Monitoring and Assessment Programme say that BC leads to increases of Arctic surface temperature of 0.6°C (0.4°C from BC in the atmosphere and 0.2°C from BC in snow) based on their radiative forcing (see Figure 4). It is important however to note, that our main focus on emission reduction should target (fossil-fuel) CO2 emissions, because they will affect the climate long after (several centuries) they have been emitted. And reduction in these sources means reduction in soot as well, since soot is also a combustion product. Reduction that targets soot specifically can be achieved by installation of particulate filters (retrofitting of old engines and stringent standard for new vehicles), shifting to cleaner fuels, burning techniques, or introduction and enforcement of inspection and maintenance programs to assure compliance with already existing legislation. It is recognized internationally that for effective implementation of the Paris Agreement (mitigation effort to hold the average global temperature well below 2°C relative to the preindustrial levels), mitigation measures of short live climate pollutants (such as BC and methane) need to be considered. As the Arctic environment is more sensitive to climate change, knowing exactly which origins (source types and regions) are contributing to black carbon in this part of the world is important for effective mitigation measures. Source attributions of black carbon depend on the altitude where the aerosol is located at the time of measurement or modelling. Wildfires are known to contribute more at higher elevations during the fire seasons (Paris et al., 2009) than at the Arctic surface. Several of the global chemical models have already approximately predicted the proportion of source influence but their accuracy depends on the emissions input and performance of the model. Part of this problem is, that these models get input from emission inventories. These inventories tell the model where, when and how much black carbon is emitted, kind of like instructions from a cookbook. But the different cook books don’t agree on the amount of black carbon that goes into our annual black carbon cake. Additionally, all the different cookbooks have different recipes for different years. If we take a best estimate of global black carbon emissions, our annual cake  has about the size (and weight; because of similar densities of limestone/granite and soot) of the great pyramid of Giza (7500 gigagrams). But the range of estimates vary immensely (2000-29000 gigagrams) (see Figure 5). And these numbers are only for man-made emissions (fossil fuels and biofuels) i.e. excluding wildfires and natural biomass burning. A recent multi-model analysis puts global annual BC fire emissions between 1000 and 6000 gigagrams. To correct these models and the emission inventories we rely on observational data to validate the model results. The model set-up we used did really well in simulating soot concentrations. A bit less well in simulating fuel types (sources) – better for fossil fuels than biofuels and biomass burning. The model simulated that 90% of BC emissions (by mass) – reaching surface level – in the Arctic originated form countries north of 42°N. In our isotope measurements, we found that black carbon sources had a strong seasonality, with high contributions of fossil fuels to black carbon in the winter (75%) and moderate (60%) in the summer. Black carbon concentrations where roughly four times higher in winter than in summer. Concentrations of black carbon at the different stations were also relatively different from each other. These surface level (<500m above sea level) Pan-Arctic results, based on our 14C method, were not very surprising. Few individual locations, as used in our latest study, have previously been published and had similar sources(e.g., Barrett et al., 2015. Winiger, et al, 2015, 2016). However, the sources in our study were relatively uniform for all stations and almost in seasonal sync with each other (high fossil winter, low fossil summer). This could have important implications for policy related questions. Uniform sources could mean that mitigation measures could have a stronger impact, if the right sources are tackled at the right time, to keep the Arctic from becoming a small ice floe, not large enough to stand on. There could be brighter days ahead of us. Edited by Dasaraden Mauree Patrik Winiger is Research Manager at the ETH Zürich and guest researcher at the Department of Earth Sciences, Vrije Universiteit Amsterdam. His research interest focuses on sources and impact of natural and anthropogenic Short Lived Climate Pollutants and Greenhouse Gases. He tweets as @PatrikWiniger.    

  • Water vapor isotopes: a never ending story!
    by Jean-Louis Bonne on April 9, 2019 at 7:00 am

    Water stables isotopes are commonly exploited in various types of archives for their information on past climate evolutions. Ice cores retrieved from polar ice sheets or high-altitude glaciers are probably the most famous type of climate archives. In ice cores, the message about past temperature variations is conserved in the ice, formed from the snow falls whose isotopic composition vary with the temperatures governing the snow crystals formation. However, deciphering the temperature variations from water isotopes is not always straightforward, as the temperature is not the only parameter which can have an imprint on the isotopic composition of the ice, but other variations like changes in origin of the moisture can also play a role. Water isotopic observations are useful tools to understand the water cycle, as the water masses keep in their isotopic composition a signal of the phase changes they have undergone. Many studies use complex atmospheric models representing the water isotopes to refine the analysis of paleoclimatic data. The same models are also used for future climate projections, a domain where large uncertainties are still linked to the prediction of the water cycle and the changes in precipitations. Water isotopes can be useful to benchmark such models and contribute to their improvement. To better understand the processes affecting the water isotopic composition in the atmosphere, our group at the Alfred Wegener Institut in Germany has been focusing on the first step of the atmospheric water cycle: the evaporation at the oceanic surface. For this purpose, we have been continuously measuring the water vapour isotopic composition since summer 2015 directly above the ocean surface, on-board the german research ice breaker Polarstern (Figure 1). We measured humidity level, δ18O and δ2H (representing the variations of the amount of water isotopes, H218O and H2H16O, compared to the most abundant isotope H216O) and calculated the second order parameter deuterium excess, defined as d-excess = δ2H – 8.δ18O. Our observations, newly published in Nature Communications, extend over all latitudes in the Atlantic sector, from the North Pole up to the coast of Antarctica (Figure 2), and could therefore also be exploited for many projects involving water isotopes at any latitude around the whole Atlantic basin. They allowed us to experimentally explore the interactions between the atmospheric moisture and the open sea as well as the sea ice. According to a commonly accepted theory proposed about 40 years ago (Merlivat and Jouzel, 1979), the meteorological conditions under which the oceanic evaporation takes place leave their fingerprint in the isotopic composition of the vapour. We have been able to test this theory on the field for the first time under such a large range of climatic conditions. Our observations indeed confirm the expected role of relative humidity and sea surface temperature in the isotopic composition of the evaporated flux. However, contrary to what was expected from this theory, our records reveal that the wind speed at which the evaporation takes place does not leaves its mark in the vapour isotopic composition above the oceans (Figure 3). In the sea ice covered areas of the polar oceans, the observations were showing highly different signals than above the open ocean. We have shown that an atmospheric model simulating the isotopic composition of water (ECHAM5-wiso) could at first not reproduce the intensity of these variations. We managed to identify the cause of this discrepancy, by adding a new source of humidity in the model. This model was already considering the sublimation of sea ice as a source of humidity. But so far, it was assuming that the sea ice was formed only from frozen oceanic water and therefore had the same isotopic composition as this oceanic water. However, the surface of the sea ice is also affected by snow falling on top of already formed sea ice. These snow falls having a totally different isotopic composition than the oceanic water, once integrated in the model as a new potential source of sublimation, they drastically changed the simulations of vapour isotopes in polar regions and the model now resolves our observations in these sectors much better (Figure 4). Our observations have shown their ability to benchmark atmospheric models of atmospheric water cycle. They highlight different processes having significant consequences on the simulation of water isotopic composition in vapour and precipitation at the global scale which should be considered in all atmospheric water cycle modelling experiments. They contribute to better understanding the creation of the first water isotopic signal during oceanic evaporation. This is particularly important as the oceanic evaporation will later determine the isotopic signal found in subsequent precipitation. The interpretation of past climate archives originally formed from precipitation can therefore be significantly affected by these results. Edited by Dasaraden Mauree Jean-Louis Bonne is an atmospheric scientist at the Alfred Wegener Institut, Bremerhaven in Germany. He prepaed his PhD at the LSCE, Gif-sur-Yvette, France. His research aims at understanding the contributions of local and remote sources to locally observed atmospheric composition by their combination with atmospheric simulations. He has been working on the atmospheric components of the water and carbon cycles, exploiting present-day observations of greenhouse gases and water vapour isotopic compositions. His current project, ISOARC, is focusing on the identification of the moisture sources of the eastern-Arctic. His personal blog can be reached here.

  • The puzzle of high Arctic aerosols
    by Julia Schmale, Andrea Baccarini, Paul Zieger on September 19, 2018 at 2:53 pm

    Current Position: 86°24’ N, 13°29’E (17th September 2018) The Arctic Ocean 2018 Expedition drifted for 33 days in the high Arctic and is now heading back south to Tromsø, Norway. With continuous aerosol observations, we hope to be able to add new pieces to the high Arctic aerosol puzzle to create a more complete picture that can help us to improve our understanding of the surface energy budget in the region. In recent years, considerable efforts have been undertaken to study Arctic aerosol. However, there are many facets to Arctic aerosol so that different kinds of study designs are necessary to capture the full picture. Just to name a few efforts, during the International Polar Year in 2008, flight campaigns over the North American and western European Arctic studied the northward transport of pollution plumes in spring and summer time [1,2,3]. More survey-oriented flights (PAMARCMIP) have been carried out over several years and seasons [4] around the western Arctic coasts. The NETCARE campaigns [5] have studied summertime Canadian Arctic aerosol in the marginal ice zone. And the Arctic Monitoring and Assessment Programme (AMAP) has issued reports on the radiative forcing of anthropogenic aerosol in the Arctic [6,7]. These and many other studies have advanced our understanding of Arctic aerosol substantially. Since the 1950s we are aware of the Arctic Haze phenomenon that describes the accumulation of air pollution in the Arctic emitted from high latitude sources during winter and early spring. In these seasons, the Arctic atmosphere is very stratified, air masses are trapped under the so-called polar dome and atmospheric cleansing processes are minimal. In springtime, with sunlight, when the Arctic atmosphere becomes more dynamic, the Arctic Haze dissolves with air mass movement and precipitation. Then, long-range transport from the mid-latitudes can be a source of Arctic aerosol. This includes anthropogenic as well as forest fire emissions. The latest AMAP assessment report [6] has estimated that the direct radiative forcing of current global black and organic carbon as well as sulfur emissions leads to a total Arctic equilibrium surface temperature response of 0.35 °C. While black carbon has a warming effect, organic carbon and particulate sulfate cool. Hence, over the past decades the reductions in sulfur emissions from Europe and North America have led to less cooling from air pollution in the Arctic [8]. Currently, much effort is invested in understanding new Arctic emission sources that might contribute to the black carbon burden in the future, for example from oil and gas facilities or shipping [9, 10, 11]. These studies contribute to a more thorough understanding of direct radiative effects from anthropogenic aerosol and fire emissions transported to the Arctic. However, neither long-range transported aerosol nor emissions within the lower Arctic contribute substantially to the aerosol found in the boundary layer of the high Arctic [12]. These particles are emitted in locations with warmer temperatures and these air masses travel north along isentropes that rise in altitude the further north they go. The high Arctic boundary layer aerosol, however, is important because it modulates the radiative properties of the persistent Arctic low-level clouds that are decisive for the surface energy budget (see first Arctic Ocean blog in August 2018). Currently, knowledge about sources and properties of high Arctic aerosol as well as their interactions with clouds is very limited, mainly because observations in the high Arctic are very rare. In principle, there are four main processes that shape the aerosol population in the high north: a) primary sea spray aerosol production from open water areas including open leads in the pack ice area, b) new particle formation, c) horizontal and vertical transport of natural and anthropogenic particles, and d) resuspension of particles from the snow and ice surface (snowflakes, frost flowers etc.). From previous studies, especially in the marginal ice zone and land-based Arctic observatories, we know that microbial emissions of dimethyl sulfide and volatile organic compounds are an important source of secondary aerosol species such as particulate sulfate or organics [13]. The marginal ice zone has also been identified as potential source region for new particle formation [14]. What is not known is to which degree these particles are transported further north. Several scavenging processes can occur during transport. These include coagulation of smaller particles to form larger particles, loss of smaller particles during cloud processing, precipitation of particles that acted as cloud condensation nuclei or ice nucleating particles, or sedimentation of large particles to the surface. Further north in the pack ice, the biological activity is thought to be different compared to the marginal ice zone, because it is limited by the availability of nutrients and light under the ice. Hence, local natural emissions in the high Arctic are expected to be lower. Similarly, since open water areas are smaller, the contribution of primary marine aerosol is expected to be lower. In addition, the sources of compounds for new particle formation that far north are not very well researched. To understand some of these sources and their relevance to cloud properties, an international team is currently measuring the aerosol chemical and microphysical properties in detail during the Arctic Ocean 2018 expedition on board the Swedish icebreaker Oden. It is the fifth expedition in a series of high Arctic field campaigns on the same icebreaker. Previous campaigns took place in 1991, 1996, 2001 and 2008 (see refs [15, 16, 17, 18] and references therein). The picture below describes the various types of air inlets and cloud probes that are used to sample ambient aerosol particles and cloud droplets or ice crystals. A large suite of instrumentation is used to determine in high detail the particle number concentrations and size distribution of particles in the diameter range between 2 nm and 20 µm. Several aerosol mass spectrometers help us to identify the chemical composition of particles between 15 nm and 1 µm as well as the clusters and ions that contribute to new particle formation. Filter samples of particles smaller than 10 µm will allow a detailed determination of chemical components of coarse particles. They will also give a visual impression of the nature of particles through electron microscopy. Filter samples are also used for the determination of ice nucleation particles at different temperatures. Cloud condensation nuclei counters provide information on the ability of particles to form cloud droplets. A multi-parameter bioaerosol spectrometer measures the number, shape and fluorescence of particles. Further instruments such as black carbon and gas monitors help us to distinguish pristine air masses from long-range pollution transport as well as from the influence of the ship exhaust. We can distinguish and characterize the particle populations that do or do not influence low-level Arctic clouds and fogs in detail by using three different inlets: i) a total inlet, which samples all aerosol particles and cloud droplets/ice crystals, ii) an interstitial inlet, which selectively samples particles that do not form droplets when we are situated inside fog or clouds, and iii) a counterflow virtual impactor inlet (CVI), which samples only cloud droplets or ice crystals (neglecting non-activated aerosol particles). The cloud droplets or ice crystals sampled by the CVI inlet are then dried and thus only the cloud residuals (or cloud condensation nuclei) are characterized in the laboratory situated below. To gain more knowledge about the chemical composition and ice nucleating activity of particles in clouds, we also collect cloud and fog water on the uppermost deck of the ship and from clouds further aloft by using tethered balloon systems. When doing vertical profiles with two tethered balloons, also particle number concentration and size distribution information are obtained to understand in how far the boundary layer aerosol is mixed with the cloud level aerosol. Furthermore, a floating aerosol chamber is operated at an open lead near the ship to measure the fluxes of particles from the water to the atmosphere. It is still unknown whether open leads are a significant source of particles. For more details on the general set-up of the expedition see the first two blogs of the Arctic Ocean Expedition (here and here). After 33 days of continuous measurements while drifting with the ice floe and after having experienced the partial freeze-up of the melt ponds and open water areas, it is now time for the expedition to head back south. We will use two stations in the marginal ice zone during the transit into and out of the pack ice as benchmarks for Arctic aerosol characteristics south of our 5-week ice floe station. As Oden is working her way back through the ice and the expedition comes to an end, we recapitulate what we have measured in the past weeks. What was striking, especially for those who have spent already several summers in the pack ice, is that this time the weather was very variable. There were hardly two days in row with stable conditions. Instead, one low pressure system after the other passed over us, skies changed from bright blue to pale grey, calm winds to storms… On average, we have experienced the same number of days with fog, clouds and sunshine as previous expeditions, but the rhythm was clearly different. From an aerosol perspective these conditions meant that we were able to sample a wide variety characteristics including new particle formation, absence of cloud condensation nuclei with total number concentrations as low as 2 particles per cubic centimeter, coarse mode particles, and size distributions with a Hoppel-minimum that is typical for cloud processed particles. Coming back home, we can hardly await to fully exploit our recorded datasets. Stay tuned! Do not hesitate to contact us for any question regarding the expedition and measurements. Check out this blog for more details of life during the expedition and our project website which is part of the Arctic Ocean 2018 expedition. Edited by Dasaraden Mauree Julia Schmale is a scientist in the Laboratory of Atmospheric Chemistry at the Paul Scherrer Institute, Switzerland. She has been involved in Arctic aerosol research for the past 10 years. Andrea Baccarini, is doing his PhD in the Laboratory of Atmospheric Chemistry at the Paul Scherrer Institute, Switzerland. He specializes in new particle formation in polar regions. Paul Zieger, is an Assistant Professor in Atmospheric Sciences at the University of Stockholm, Sweden. He is specialized in experimental techniques for studying atmospheric aerosols and clouds at high latitudes.

  • The perfect ice floe
    by Julia Schmale on August 28, 2018 at 8:07 pm

    Current position: 89°31.85 N, 62°0.45 E, drifting with a multi-year ice floe (24th August 2018) With a little more than three weeks into the Arctic Ocean 2018 Expedition, the team has found the right ice floe and settled down to routine operations. Finding the perfect ice floe for an interdisciplinary science cruise is not an easy task. The Arctic Ocean 2018 Expedition aims to understand the linkages between the sea, microbial life, the chemical composition of the lower atmosphere and clouds (see previous blog entry) in the high Arctic. This means that the “perfect floe” needs to serve a multitude of scientific activities that involve sampling from open water, drilling ice cores, setting up a meteorological tower, installing balloons, driving a remotely operated vehicle, measuring fluxes from open leads and sampling air uncontaminated from the expedition activities. The floe hence needs to be composed of multi-year ice, be thick enough to carry all installations but not too thick to allow for drilling through it. There should also be an open lead large enough for floating platforms and the shape of the floe needs to be such that the icebreaker can be moored against it on the port or starboard side facing all for cardinal directions depending on where the wind is coming from. The search for the ice floe actually turned out to be more challenging than expected. The tricky task was not only to find a floe that would satisfy all scientific needs, but getting to it north of 89°N proved exceptionally difficult this year. After passing the marginal ice zone north of Svalbard, see blue line on the track (Figure 2), progress through the first year ice was relatively easy. Advancing with roughly 6 knots, that is about 12 km/h, we advanced quickly. After a couple of days however, the ice became unexpectedly thick with up to three meters. This made progress difficult and slow, even for Oden with her 24,500 horse powers. In such conditions the strategy is to send a helicopter ahead to scout for a convenient route through cracks and thinner ice. However, persistent fog kept the pilot from taking off which meant for the expedition to sit and wait in the same spot. For us aerosol scientists looking at aerosol-cloud interactions this was a welcome occasion to get hand on the first exciting data. In the meantime, strong winds from the east pushed the pack ice together even harder, producing ridges that are hard to overcome with the ship. But with a bit of patience and improved weather conditions, we progressed northwards keeping our eyes open for the floe. As it happened, we met unsurmountable ice conditions at 89°54’ N, 38°32’ E, just about 12 km from the North Pole – reason enough to celebrate the farthest North. Going back South from there it just took a bit more than a day with helicopter flights and good visibility until we finally found ice conditions featuring multiple floes. And here we are. After a week of intense mobilization on the floe, the four sites on the ice and the instrumentation on the ship are now in full operation and routine, if you stretch the meaning of the term a bit, has taken over. A normal day looks approximately like this: 7:45:  breakfast, meteorological briefing, information about plan of the day; 8:30 – 9:00: heavy lifting of material from the ship to the ice floe with the crane; 9:00 (or later): weather permitting, teams go to the their sites, CTDs are casted from the ship if the aft is not covered by ice; 11:45: lunch for all on board and pick-nick on the floe; 17:30: end of day activities on the ice, lifting of the gangway to prevent polar bear visits on the ship; 17:45: dinner; evening: science meetings, data crunching, lab work or recreation. At the balloon site, about 200 m from the ship, one balloon and one heli-kite are lifted alternately to take profiles of radiation, basic meteorological variables and aerosol concentrations. Other instruments are lifted up to sit over hours in and above clouds to sample cloud water and ice nucleating particles, respectively. At the met alley, a 15 m tall mast carries radiation and flux instrumentation to characterize heat fluxes in the boundary layer. The red tent at the remotely operated vehicle (ROV) site houses a pool through which the ROV dives under the flow to measure physical properties of the water. The longest walk, about 20 minutes, is to the open lead site, where a catamaran takes sea surface micro layer samples, a floating platform observes aerosol production and cameras image underwater bubbles. The ice core drilling team visits different sites on the floe to take samples for microbial and halogen analyses. Importantly, all activities on the ice need to be accompanied by bear guards. Everybody carries a radio and needs to report when they go off the ship and come back. If the visibility decreases, all need to come in for safety reasons. Lab work and continuous measurements on the ship happen throughout the day and night. More details on the ship-based aerosol laboratory follow in the next contribution. Edited by Dasaraden Mauree Julia Schmale is an atmospheric scientist at the Paul Scherrer Institute in Switzerland. Her research focuses on aerosol-cloud interactions in extreme environments. She is a member of the Atmosphere Working Group of the International Arctic Science Committee and a member of the Arctic Monitoring and Assessment Programme Expert Group on Short-lived Climate Forcers .

  • The Physics of Fog
    by Met_Team on September 7, 2018 at 5:09 am

    By MetService Meteorologist Claire Flynn While the weather conditions that lead to the formation of fog are usually quite benign, fog itself can be very disruptive. In particular the aviation and marine industries are often interested in how fog or mist will affect the visibility for their journeys, though fog also affects road-users. Fog can also make for some excellent photography opportunities, creating an eerie backdrop (as you can see in some of the photos below!) A ‘fogbow’, photographed in the Waipa District by Peter Urich. To find out how a fogbow is formed, take a look at this blog on atmospheric optics. But what is fog, and how is it formed? Before we can talk about what fog is, we first need to define a key factor of fog: visibility. Visibility has a different definition at night time and at day time. The definition given by the International Civil Aviation Organisation (ICAO) is: During day time, visibility is the greatest distance at which a black object of suitable dimensions situated near the ground can be seen and recognised when observed against a bright background, During night time, visibility is given by the greatest distance through which light of around 1000 candelas can be seen and identified against an unlit black background. Fog and mist are created by microscopic water droplets suspended in the air. These tiny water droplets scatter any light that passes through or past them, meaning that objects in the fog become hard to see. Fog and mist are then defined by how much the visibility is reduced. The ICAO definitions are: Fog: a suspension of very small water droplets in air, reducing the visibility to 1000 metres or less. Mist: similar to fog, however visibility will be reduced to no less than 1000 metres. Haze is another phenomenon that can reduce visibility. However, this is a reduction in visibility caused by microscopic particles in the air, rather than by water droplets. For example, in New Zealand we sometimes get haze around our coastlines after we have had strong winds, as the wind can whip up sea spray and cause small particles of sea salt to be suspended in the air. So now we know what fog is, how is it formed? There are a number of processes that can cause fog, and fog is classified into different ‘types’ based on how it forms. The most common types are radiation fog and valley fog, followed by advection fog. We can also get post-frontal (or evaporation) fog and steaming fog. Let’s take a look at the different types of fog in more detail: Radiation Fog Radiation fog is so-called as the formation process depends upon a balance of “radiative heat fluxes” (I’ll explain what this means below). Radiation fog usually forms overnight or early morning during the coldest hours of the day, and then dissipates after the sun comes up. It primarily forms over land but has been observed to form over shallow inlets and harbours as well. It is the most common type of fog we see in New Zealand. Radiation Fog in Christchurch, photographed by Julienne Nacion. For radiation fog to form, we need several ingredients: Clear skies, Light winds, Sufficient moisture in the lowest layer of the atmosphere, near the ground. These conditions are most commonly met when we have high pressure over the country, but there are other situations where these conditions can be met too. In short, on a clear night with light winds, the air can cool down enough to reach its “dew point” (100% relative humidity) and water vapour in the air will start to condense into fog. Let’s have a look at this process in a little more detail. Radiative Heat Fluxes The process of radiation fog formation starts at sunset, when the balance of radiative heat fluxes changes. Everything radiates heat – with warmer objects emitting more radiation than cooler objects. On a sunny day, incoming solar radiation is greater than the radiation emitted by the Earth back to space – this causes the ground and the air directly above it to warm up. On a cloud-less night, the Earth continues to radiate heat away to space – but with no incoming solar radiation, this causes the ground, and the air directly above it, to cool quickly. Clear Skies Cloudy skies change the radiative heat balance described above. If there is cloud in the sky, it will absorb the heat emitted by the Earth’s surface and re-radiate it back towards the ground. This prevents the land surface from cooling as much as it would on a cloudless night. Clear skies allow the ground to cool quickly by emitting heat to space via radiation, allowing a ‘temperature inversion’ to form (this is when the temperature increases with height, rather than decreasing with height like it usually does – more on inversions here.) Radiative cooling is an essential part of the formation of radiation fog, so the less cloud around, the greater the chances that fog will form. Light winds If the wind is too strong, then this can cause warmer, drier air from aloft to be mixed up with the air near the ground, meaning that the land surface cannot cool as quickly. Conversely, if there is no wind at all, you are more likely to get a very heavy dew instead of fog – this is because very light winds help to mix the cool air through a shallow layer of air near the land surface. If there isn’t enough wind, the cooling will be restricted to the lowest few centimetres of the atmosphere, allowing dew but not fog. Sufficient moisture The relative humidity in the lowest layers of the atmosphere needs to be high enough that radiative cooling overnight will allow the air to reach its “dew point”. The dew point is a measure of how much water vapour is in the air – when the dew point is equal to the air temperature, this is equivalent to 100% relative humidity, and the air cannot hold any more water vapour. In addition, warm air can hold more water vapour than cool air. If the air cools to its dew point, and then continues to cool, the water vapour needs to go somewhere – initially it condenses on the ground as dew, but if we have sufficient radiative cooling and light winds to mix the cool air through a shallow layer as described above, the water vapour will begin to condense into fog as well. Shallow radiation fog by Addington Brook in Hagley Park, photographed by Don Gracia. The brook serves to provide a source of moisture in the lowest layer of the atmosphere, aiding the formation of fog. While having lots of water vapour in the lowest layer of the atmosphere helps fog to form, it is in fact beneficial for the air aloft to be quite dry. This is because water vapour in the air absorbs infra-red radiation, and, much like cloud, can re-radiate some of this heat back to Earth. This means that if the air aloft is dry, the land surface can cool much more efficiently. Many of our airports in New Zealand are prone to radiation fog, and our aviation forecasters spend a lot of time thinking about whether or not radiation fog is likely to affect each airport when night falls. Hamilton Airport is our foggiest airport in New Zealand, with an average of 92.4 nights a year when fog is reported. This is followed by Dunedin Airport, with 64 nights a year. Since it needs to be cool and damp for radiation fog to form, it is much more common during winter than summer. Auckland Airport shows a particularly strong seasonal trend – with only a couple of cases of fog occurring during the warmer months between September 20th and March 20th over the past ten years (all these cases were advection fog rather than radiation fog – you can find an explanation of advection fog later). Radiation fog can be particularly disruptive when it occurs at Auckland Airport, which has an average of 19.3 foggy nights a year. While some aircraft are equipped to land in low visibility, taxiing around the runway is still dangerous in fog, and fewer aircraft can land per hour during low visibility operations. Another type of fog that can affect Auckland Airport is post-frontal fog, which is a special case of radiation fog. Post-Frontal Fog (Evaporation Fog) Suppose a front moves over an area, bringing cloud and rain. Sometimes, after a front has moved over, the skies clear up and the winds ease. If this occurs at night then the radiation fog formation process can begin. In this case however we now also have water sitting on the ground, which can be evaporated into the air near the Earth’s surface, increasing the dew point of the air. This means that fog may start to form at slightly higher temperatures than it would have done had the ground been dry. The wet ground also means that fog can form without the need for dew. The satellite image above was taken at 4.40pm on 3rd August 2018. The frontal cloud had cleared away from Auckland Airport shortly before sunset (you can see that it is beginning to get dark in the bottom right hand corner of the image). Following the front, the air was relatively cloud-free. This meant that Auckland Airport had a ready supply of moisture (water on the ground due to the front that had just passed over) and clear skies. The winds had also died back overnight creating the perfect conditions for fog. In this case, fog formed between midnight and 2am, persisting until the sun came up the next day and clearing around 8am. Valley Fog Valley fog is another special case of radiation fog. The formation process also relies on the land surface cooling by emitting radiation to space, allowing the air to reach its dew point temperature and causing moisture to condense. Most people know that warm air rises. This is because warm air is less dense than cool air – it weighs less, and therefore becomes buoyant and rises above the cool air. Equally, cold air sinks. In hilly areas, on a calm and cloudless night, the land surface on the hills cools. This in turn cools the air directly above it. The cooler air then sinks down into the valleys, much like water flowing through a river. Pooling of cold air means that fog can form more quickly, and persist for longer, in valleys than over flat terrain. At times in the Winter, some valleys or basins (for example, the Mackenzie Basin) will see fog that persists for days, and does not even clear during the height of the day. This is because the weak sunshine is not enough to warm the extensive pool of cold air sitting in the valley. Valley fog, Dovedale River, Tasman District. Photographed by Sheryl Waters. Valley fog in the Wakatipu Basin, photographed by Marin Corinthian Kohn. Advection Fog The word ‘advection’ refers to the transfer of heat and moisture from one place to another by the wind. Advection fog primarily forms over the sea (also called sea fog), though we can get advection fog over the land sometimes as well. Let’s start with sea fog. Sea fog occurs when the wind pushes warm, moist air over a cooler sea surface. The sea surface cools the air directly above it, causing water vapour to condense into fog. Around New Zealand, high pressure to the east of the country is a good situation for sea fog to form – with northeasterly winds bringing air down from the sub-tropics, across cooler waters. If the high pressure stays in place for a long time (called a blocking high), then the sea fog can persist over the water for many days. We learnt above that radiation fog forms after the sun sets and the land cools, and then dissipates when the sun comes up again the next morning. Unlike the land, the ocean is deep and dark, and it does not warm up and cool down as the sun rises and sets. For this reason, sea fog can happen at any time of day (and this is also why radiation fog will not occur over the sea). But if sea fog doesn’t dissipate when the sun rises, what makes it go away? Essentially, we need an ‘air mass change’ – or another weather system to come along and push the sea fog away. Sea fog is most common during Spring, as the sea surface temperatures lag behind the increasingly warm land and air. The satellite image above shows an area of sea fog sitting along the coast of Canterbury on the morning of 7th August 2018. You can see Banks Peninsula sticking out above the fog. Christchurch Airport reported fog overnight, which began to lift to low cloud early in the morning. The satellite image below is an infra-red image of the same scenario. By measuring infra-red radiation, we can infer the temperature of the cloud tops or land surface. The red and green area to the west of the image indicates very cold temperatures of about -50°C. This is because this is part of a front, with cloud tops extending high into the atmosphere where it is very cold indeed. You’ll notice that the sea fog doesn’t appear on the infra-red image – this is because it is very low to the ground, and therefore it is similar in temperature to its surroundings. The front coming from the west moved over the country later in the day, pushing away the sea fog, and no fog was reported at Christchurch Airport the following night. Hybrid Radiation-Advection Fog Those who live along our coastlines likely will have found themselves engulfed in sea fog from time to time. When extensive sea fog forms around our coasts over the sea, it can sometimes advect onto the land as well, but tends to dissipate on warm days as it moves further inland. Once sea fog has advected onto the land, it will likely show a slight diurnal variation – thinning out during the afternoon and becoming denser again overnight – this is called hybrid radiation-advection fog. Wellington Airport is never affected by pure radiation fog but it is affected by sea fog on a handful of days a year. The graphs below compare the times of day when fog was observed at Wellington Airport (sea fog, though once it is over the airport it becomes hybrid radiation-advection fog) and Hamilton Airport (radiation fog alone). As you can see, Hamilton Airport has a very strong diurnal trend, with fog reported frequently at night, and very rarely in the afternoons. On the other hand, fog at Wellington Airport happens any time of day, with only a slight diurnal trend. You can read more about how fog occurs at Wellington airport here. While sea fog that moves onshore becomes hybrid radiation-advection fog, we can also get radiation fog that forms over land, and then later advects over another area. This is also hybrid radiation-advection fog. For example, radiation fog frequently forms up the Hutt Valley, north of Wellington. In rare cases the radiation fog then drifts southwards across the harbour and over Wellington Airport in a light northeasterly drift. Hybrid radiation-advection fog that occurs at Wellington Airport via this process tends to be very short-lived, whereas sea fog that moves onshore at Wellington Airport can persist for most of the day. Steaming Fog The final type of fog I will explain in this blog is steaming fog. Steaming fog is also the rarest type of fog in New Zealand, and only occurs under very specific conditions. It tends to be very shallow, so is not as troublesome as the likes of advection fog or radiation fog. The best example of steaming fog around New Zealand would be steam rising from hot pools in places like Rotorua. Steaming fog occurs when cold air lies over a much warmer water surface. Air close to the water surface is warmed and moistened by the water underneath. This makes the air buoyant (remember, “warm air rises” – this process is called convection). The air rises up and mixes with the cooler air slightly above it. If the increasing water content of the air outstrips the heating of the air from beneath, then the air can become supersaturated, and excess water vapour will condense into mist or fog. Here at MetService, we have dedicated marine and aviation meteorologists. There are also meteorologists who write the public weather forecasts on metservice.com, our app, the tv and newspapers. Each of these different disciplines have a different focus when it comes to forecasting fog, and forecasters spend a lot of time thinking about how fog will affect the people they are forecasting for. Marine forecasters look for situations where extensive sea fog is likely. Radiation fog is less of a concern for our marine forecasters, but sometimes radiation fog can form over the likes of Manakau Harbour. Meanwhile, aviation forecasters spend a lot of time thinking about radiation fog, but if sea fog is looking likely to move onto the coast, then they need to take this into consideration also. While the processes behind fog formation are generally well understood, it can still be very difficult to forecast. Any error in the temperature forecasts or humidity forecasts can drastically change the likelihood of fog forming. To forecast fog perfectly, you would also need a perfect forecast for the cloud cover, temperature, humidity, and wind speed. You also need to know whether the ground will be wet or frosty. Weather models alone are not currently able to resolve weather conditions on a small enough scale to accurately depict the risk of fog. Therefore it comes down to our meteorologists’ experience and knowledge, together with local observations of the conditions on the ground. Because of this, fog can be very challenging to forecast – but it also makes it more rewarding when you get a fog forecast just right!   Tags: fogradiation fogadvection fogvalley fogpost-frontal fogevaporation fogsteaming fog

  • Am I at risk of experiencing a thunderstorm?
    by Lisa Murray on May 14, 2018 at 3:19 am

    By MetService meteorologist April Clark. Whether you actively seek the thrill of a good lightning storm or you need to make sure your nervous dog is inside in your protective arms when a thunderstorm hits, MetService has got your back. MetService has an experienced team of specialist meteorologists who take care of what we call 'mesoscale forecasting' – that is, the forecasting of weather features that are very small in size but can be very intense in nature, e.g. thunderstorms, squalls etc. The relatively small size of these weather features is what makes it a challenge when communicating their potential threat to you and your nervous Labrador.    Thunderstorms, by nature are coy things. They require very specific conditions to ‘kick off’ and when they do it can be within localised areas. By localised we mean that a thunderstorm is small enough that, while you sip your cool lemonade under a sunny sky, 5km down the road a cumulonimbus cloud (thunderstorm cloud) could be throwing 5cm hail on your Aunt Betty’s house.   Below is a bit of an explainer of how we forecast thunderstorms, feel free to skip ahead a couple of paragraphs for the nitty gritty on our Thunderstorm Charts. For thunderstorms to form they first need an atmosphere that is conducive to vigorous updrafts (i.e. air rising very quickly from the ground). These conditions arise when warm/moist air near the ground is overlaid by cooler/drier air aloft – in meteorologist speak this is called an unstable atmosphere. These conditions can happen in a number of ways. A well-known example happens during summer, when strong heating from the sun creates a much warmer air layer just above the ground, producing an unstable atmosphere. If this layer of warm air is also moist (often moisture is provided from a water source like the sea) then the atmosphere is ‘extra ripe’ for thunderstorms. So, there is the potential for thunderstorms when an unstable atmosphere is present, but this doesn’t necessarily mean any will form. What we call a trigger is needed to ‘nudge’ off a thunderstorm. These thunderstorms are turning out to be quite hard work to get going! The trigger to start a thunderstorm can come from several sources. To name a few; fronts which create their own updraft, sea breeze wind convergences where ground level winds from two directions meet and are forced upwards, mountains which force the air up as it tries to pass over them, or features in the upper atmosphere which can create the uplift needed near the ground to generate a thunderstorm.  The trigger is often the trickiest part of thunderstorm forecasting as a very subtle change in wind, temperature or frontal strength can be the difference between a crack of lightning or a non-event. Now you have an idea of what ‘princess and the pea’ type conditions are needed to produce a thunderstorm let’s investigate how MetService relays the risks of a thunderstorm to you at home. Three different risk charts are produced at MetService, depending on the certainty, severity and how far ahead we expect a thunderstorm to affect an area. The first and most frequent type issued is called the Thunderstorm Outlook. These charts are issued every day in the morning with an update in the evening (or more frequently if required). As its name suggests the Thunderstorm Outlook chart has the longest forecast range, highlighting areas anywhere in New Zealand with the potential for thunderstorm formation (both moderate and severe) for today and tomorrow. Three risk levels convey the likelihood of thunderstorms forming over the whole area, ranging from low to high. If you live within a shaded area that happens to be under a moderate or high risk that day, though it is likely that within that whole shaded area a thunderstorm will form, it is possible that you, sitting on your patio, will not see one.  This is due to the small and confined ‘mesoscale’ nature of a localised thunderstorm. For example, thundery showers caused by summer sea breezes can be very isolated leading to the ‘sunny day at my place, hail at my Auntie’s 5km down the road’ situation (more on this ‘afternoon convection’ here http://blog.metservice.com/Convection). However, if we have an active squall that moves across a region you can expect more people to experience thunderstorm conditions. The second chart our meteorologists produce is called a Severe Thunderstorm Watch. This chart is much like the Thunderstorm Outlook but is only issued when severe thunderstorms are expected anywhere in New Zealand, and it usually has a shorter forecast outlook of 6-12 hours. Again, much like the Thunderstorm Outlook these Thunderstorm Watches are forecasts, created to alert people to the possibility of a severe thunderstorm forming in their area. So, what makes a thunderstorm severe you may be asking? For MetService, these heavyweights of the thunderstorm world must exhibit at least one of the following criteria; heavy rainfall of 25mm/h or more, hailstones with a diameter of 20mm or more, strong wind gusts of 110km/h or more, or damaging tornadoes. The third and final chart issued for thunderstorms is the Severe Thunderstorm Warning. This chart is different from the two previous charts as it is only issued after a thunderstorm has formed and is deemed severe through careful analysis of volumetric (3-dimensional) radar data. Mesoscale meteorologists need a thunderstorm to be within about 150 kilometres of the radar to fully probe the structure of the storm and therefore categorically define it as severe. For this reason, a Severe Thunderstorm Warning will only be issued inside the deep blue areas in the right-hand image below. When issued, a Severe Thunderstorm Warning will include the current location of the thunderstorm, a cone for its forecast path and an indication of where the storm will be in 30 and 60 minutes time. Due to how short the forecast time is on these warnings it will usually have a more specific area in which our mesoscale meteorologist has deemed at high risk of seeing a thunderstorm. This means if you are within the Severe Thunderstorm Warning area, keep your Labrador inside or get out the popcorn, you’re likely to see some lightning.  Though the chance of being caught under a severe thunderstorm in New Zealand is low, if you are unlucky enough to experience one unprepared, it can be dangerous, with lightning, large hail, flash flooding, and squally winds among some of the effects of a severe thunderstorm. What can you do if you have a lead time of an hour or so? Quite a lot in fact. A few simple examples are listed below. Torrential Rain: If you're in a narrow watercourse or working in a stormwater drain, get out of it. Very strong winds: If you're up on the roof, get down, secure loose roofing iron and other potentially dangerous flying objects. Lightning: Go inside, or at least stay away from trees which are out in the open, and consider unplugging electrical appliances. Hail:  If you're driving, be ready to slow down or stop, or put the car in the garage.   Thunderstorms are incredible forces of nature, which both fascinate and frighten. Although their effects are often very localised they can be extremely hazardous. Our highly skilled meteorologists use a range of charts to communicate thunderstorm risks and severity through a three-step alert process from Outlook to Watch to Warning. Now that you’ve read this blog, we hope you understand how we alert the public about the chance of thunderstorms from the forecasting bench! Tags: thunderstormthunderstormsdownburstdownpourthunderstorm Warningthunderstrom watchthunderstorm outlookupdraftsApril Clark

  • Tropical Cyclone Hola Update - 11/03/18
    by Met_Team on March 11, 2018 at 3:25 am

    Tropical Cyclone Hola Update - 11/3/2018 By Meteorologists, Andy Best and April Clark This blog is a look at what has changed from yesterdays update which can be found at  https://blog.metservice.com/node/1179 on this blog site. You can find further information on the Tropical cyclone page at http://bit.ly/TropicalCycloneActivity     CURRENT STATUS OF CYCLONE ACTIVITY Tropical Cyclone Hola (971hPa, Category 3) was analysed near 21.4S 169.0E (near the Loyalty Islands of New Caledonia) at 1300 New Zealand time this afternoon and is moving southeast at 14 knots. Tropical Cyclone Hola is expected to track southwards and start to gradually weaken as well as move out of the tropics on Sunday.The system is expected to undergo extra-tropical transition as it approaches 30S later on Sunday. Cyclone Hola is expected to be extra-tropical and track close to the upper North Island of New Zealand on Monday. Current models are predicting Cyclone Hola to swiftly skirt the northeast of the North Island during Monday, bringing Severe Weather to eastern parts of the upper North Island. Severe Weather Watches and Warnings have now been issued for Monday, with rain accumulations of as much as 150mm and wind gusts of up to 130km/h forecast for eastern regions from Northland to northern Hawkes Bay. You can find the latest information on the Severe Weather and impacts at http://bit.ly/AllWarnings Hola will bring severe gale force winds and heavy rain to northern and eastern parts of the North Island during Monday and the early hours of Tuesday, and could cause coastal inundation for eastern areas from Northland to western Bay of Plenty including Gisborne as well. The heaviest rain is expected in Northland, Great Barrier Island, Coromandel Peninsula and Gisborne, where a heavy rain Warning is now in force. In addition, gale southeasterlies are expected to develop from early Monday morning, then changing southwesterly during Monday afternoon and evening. The strongest winds are expected in Northland, Auckland, Coromandel Peninsula, Bay of Plenty and Gisborne, and a strong wind Warning is in force for these areas. This system is compact but fast moving, meaning that those expected to be impacted should expect weather conditions to change rapidly, so keeping updated with the forecast, Civil Defence and New Zealand Transport Agency is key. Another low is located near 6.7S 160.1E near the Solomon Islands at 1300 New Zealand time today. This low is expected to track into the northern Coral Sea over the next few days with the risk of it developing into a tropical cyclone being LOW, but increasing to MODERATE from Tuesday next week. Tags: TC holasevere weatherTC

  • Tropical Cyclone Hola Update - 10/3/18
    by Met_Team on March 10, 2018 at 3:04 am

    Tropical Cyclone Hola Update - 10/3/2018 By Meteorologist, Andy Best This blog is a look at what has changed from yesterdays update which can be found at  https://blog.metservice.com/TC-Hola-9-3-2018 on this blog site. You can find further information on the Tropical cyclone page at http://bit.ly/TropicalCycloneActivity   Severe Tropical Cyclone Hola remains at Category 3 TC at 2:10pm today New Zealand time with winds close to its centre of around 130km/h with gales extending up to 260km from the centre. The TC is currently moving southeast at 25km/h. By 1am Sunday morning (NZ time) it is expected to weaken to a category 2 TC and still lie north of Latitide 25S. This means that the winds near the centre are expected to weaken to around 120km/h and by 1am Monday morning to around 90km/h. TC Hola will continue southeast out of the Tropics, and is expected to pass close the the upper North Island as a deep low during Monday and Tuesday.   There is still some uncertainty with respect to Hola s focecast track. The affected areas and associated confidence levels depicted are highly dependent on Hola s track. Relevant authorities and the public are advised to keep up to date with the latest forecasts from MetService. Hola will cause significant damage and disruption if it tracks across, or very near, to the North Island. This includes wind damage to structures and powerlines, large amounts of rain causing flooding, slips and damage to roads, and large waves affecting low-lying coastal areas. Based on Hola s current forecast track, there is high confidence of heavy rain and severe gales in Northland, Auckland, Coromandel Peninsula, Waikato, Bay of Plenty and Gisborne from on early Monday through to overnight Monday.   The confidence for heavy rain and severe gales is moderate during Monday and early Tuesday for the central North Island from Waitomo, Taranaki across to Hawkes Bay,including the Tongariro National Park and the Whanganui Hill Country, while the confidence is low for heavy rain in Wairarapa over the same period. It is very likely that Warnings and Watches associated with Hola will be issued tomorrow (Sunday March 11th). The Severe Weather Outlook Map at http://bit.ly/SWOutlook on metservice.com shows the areas we are currently concerned about. The MetService TC Bench are keeping a close eye on developments 24/7 and will issue Severe Weather Watches and Warnings for any areas which could see any severe weather associated with this event, along with press releases and updates on social media. We’ll post further updates on TC Hola in the coming days, and as always, you can keep up to date with the latest forecasts and warnings at metservice.com You can also watch the latest Tropical Cyclone video at  http://bit.ly/metservicetv     Tags: TCTropical cyclone Holasevere weather

  • Tropical Cyclone Hola Update - 9/3/2018
    by Lisa Murray on March 9, 2018 at 2:01 am

    Tropical Cyclone Hola Update - 9/3/2018 By Meteorologist, Lisa Murray This blog is a look at what has changed from yesterdays update which can be found at http://bit.ly/TCHola_1 on this blog site. You can find further information on the Tropical cyclone page at http://bit.ly/TropicalCycloneActivity Tropical Cyclone Hola is currently a Category 3 TC with winds at its centre of around 150km/hr. It is slowly moving between Vanuatu and New Caledonia, but will pick up speed as it begins to move southeastwards.  In the next 40hours the winds at the centre of this TC are expected to continue to weaken to about 90km/h, but will still have some impact on the Loyalty Islands, New Caledonia and southern Vanuatu.    The global models have adjusted their tracks again and now the ECWMF and the GFS have given a similar solution to the potiental tracks bringing the low across the north of New Zealand, while the UK model still keeps the low to the north of New Zealand (this model is currently the outlayer). Each run of these models fine tune the position and run a selection of possible tracks, some of which can be seen in the image below.     The Severe Weather Outlook Map at http://bit.ly/SWOutlook on metservice.com shows the areas we are currently concerned about. Tropical Cyclone Hola, currently near Vanuatu, approaches the far north of the North Island on Monday while transitioning into an extra-tropical cyclone. Cyclone Hola is then expected to quickly move away to the southeast of New Zealand on Tuesday. A ridge builds over the North Island on Wednesday, while westerlies strengthen across the South Island. There is still a great deal of uncertainty with respect to the track and intensity of Hola. Relevant authorities and the public are advised to keep up to date with the latest forecasts from MetService, since Hola is expected to cause significant damage and disruption if it does affect the North Island. This may include wind damage to structures and powerlines, damage to roads due to floods and slips and coastal inundation. Based on the current forecast track of Hola, there is a high risk of heavy rain and severe gales in Northland, Auckland, Coromandel Peninsula, Waikato, Bay of Plenty and Gisborne from early Monday through to Tuesday. The risk for heavy rain and severe gales is moderate during Monday and Tuesday for the central North Island from Waitomo, Taranaki across to Hawkes Bay, inclduing the Tongariro National Park and the Whanganui Hill Country. The risk is low for heavy rain in Wairarapa over the same period. Please note that the above mentioned areas and associated risks can change significantly due to possible shifts in Hola's track affecting the timing, intensity and track of Hola as it nears New Zealand. There is enough information available that if you are in any area from Northland, through Firth of Thames, Coromandel to Bay of Plenty and northern Gisborne, you should start preparing for this event as you are in the high risk area for some severe winds, heavy rain and large waves, if the system crosses the upper North Island.  MetService meteorologists are monitoring TC Hola closely and provide tropical updates daily via the Tropical Cyclone Activity page  where you can also see hourly satellite imagery. As the cyclone moves closer to New Zealand and over colder waters, it will undergo transformation into a mid-latitude depression but will still have strong winds and heavy rain associated with it. The MetService TC Bench are keeping a close eye on developments 24/7 and will issue Severe Weather Watches and Warnings for any areas which could see any severe weather associated with this event, along with press releases and updates on social media. We’ll post further updates on TC Hola in the coming days, and as always, you can keep up to date with the latest forecasts and warnings at metservice.com You can also watch the latest Tropical Cyclone video at  http://bit.ly/metservicetv   Tags: Tropical cyclone HolaTC hola

 

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