CAPTION A computer simulation reveals how Langrangian coherent structures can serve as temporary scaffolding. CREDIT Vicente Perez-Munuzuri/U. Santiago de Compostela

Rivers of moist air transporting water vapor from tropics to Europe and other midlatitude lands may be linked to 'Lagrangian coherent structures' high in atmosphere

If you want to assign blame on an overcast day, then cast your eyes on the tropics. Water vapor originating from the Earth's tropics is transported to midlatitudes on long filaments of flowing air that intermittently travel across the world's oceans. When these airy tendrils make landfall, they can cause severe floods and other extreme weather events. Yet despite the importance of these "atmospheric rivers" for the global water and heat cycles, the mechanism behind their formation is still a mystery.

But a new study, published this week in the journal Chaos, from AIP Publishing, suggests that unusually persistent spatial structures that self-assemble high up in the atmosphere serve as "tracer patterns" around which atmospheric rivers grow. Based on simulations using real weather data in the Atlantic Ocean, the work was focused specifically on the transport of water from the tropics of the Caribbean to the Iberian Peninsula in Spain, but it suggests a more general way to study the transport of tropical water vapor globally.

These so-called Lagrangian coherent structures have been observed shaping other natural phenomena, including volcanic ash clouds and plankton blooms.

"Given that atmospheric rivers over the Atlantic and Pacific oceans appear as coherent filaments of water vapor lasting for up to a week, and that Lagrangian coherent structures have turned out to explain the formation of other geophysical flows, we wondered whether Lagrangian coherent structures might somehow play a role in the formation of atmospheric rivers," said study coauthor Vicente Perez-Munuzuri, a physicist at the University of Santiago de Compostela in Spain.

Through supercomputer simulations, Perez-Munuzuri and his colleagues have shown that Lagrangian coherent structures and atmospheric rivers could indeed be linked. Using publically available data about wind speed and water vapor flux from real-world atmospheric rivers over the Atlantic, the scientists created a supercomputer model consisting of thousands of moving virtual air particles and found a close match between the complex swirls -- the Lagrangian coherent structures -- made by the air particles and the patterns made by the real atmospheric rivers.

"The Lagrangian coherent structures serve as a kind of temporary scaffolding around which an atmospheric river can grow and lengthen," Perez-Munuzuri said.

The team thinks Lagrangian coherent structures could provide a better way of identifying and classifying atmospheric rivers. "To date, most methods used to identify atmospheric rivers are based on their water vapor flux or wind speed," Perez-Munuzuri said. "Here we show that the rivers can be classified by whether or not they start as Lagrangian coherent structures and also what shapes those structures take."

The recent floods in Texas have caused some of the worst flooding since Hurricane Ike in 2008, causing the rainiest month in the state's history. 

What lessons have been learned from Ike's devastation of the Galveston and Houston area, and how have they helped in the prediction of future such storms? 

Researchers at the Institute for Computational Engineering and Sciences at the University of Texas at Austin have been studying computational models and simulations of hurricanes like Ike in order to predict the consequences of such natural disasters and better prepare the Texas Gulf Coast for their effects. 

Environmental and coastal ocean engineering models yield complex systems that combine interdisciplinary techniques. Accurate and efficient simulation requires advanced tools in supercomputing. Watch the video below, where Jennifer Proft of UT Austin discusses new ideas for the high resolution modeling of extreme weather such as hurricane storm surge and floods: 

Hurricane forecasting evolving with new storm surge products, upgraded supercomputer modeling

NOAA’s Climate Prediction Center says the 2015 Atlantic hurricane season will likely be below-normal, but that’s no reason to believe coastal areas will have it easy.

For the hurricane season, which officially runs from June 1 to November 30, NOAA is predicting a 70 percent likelihood of 6 to 11 named storms (winds of 39 mph or higher), of which 3 to 6 could become hurricanes (winds of 74 mph or higher), including zero to 2 major hurricanes (Category 3, 4 or 5; winds of 111 mph or higher). While a below-normal season is likely (70 percent), there is also a 20 percent chance of a near-normal season, and a 10 percent chance of an above-normal season.

“A below-normal season doesn’t mean we’re off the hook. As we’ve seen before, below-normal seasons can still produce catastrophic impacts to communities,” said NOAA Administrator Kathryn Sullivan, Ph.D., referring to the 1992 season in which only seven named storms formed, yet the first was Andrew – a Category 5 Major Hurricane that devastated South Florida.

“The main factor expected to suppress the hurricane season this year is El Niño, which is already affecting wind and pressure patterns, and is forecast to last through the hurricane season,” said Gerry Bell, Ph.D., lead seasonal hurricane forecaster with NOAA’s Climate Prediction Center. “El Niño may also intensify as the season progresses, and is expected to have its greatest influence during the peak months of the season. We also expect sea surface temperatures in the tropical Atlantic to be close to normal, whereas warmer waters would have supported storm development.”

Included in today’s outlook is Tropical Storm Ana, but its pre-season development is not an indicator of the overall season strength. Ana’s development was typical of pre-season named storms, which often form along frontal boundaries in association with a trough in the jet stream. This method of formation differs from the named storms during the peak of the season, which originate mainly from low-pressure systems moving westward from Africa, and are independent of frontal boundaries and the jet stream.

With the new hurricane season comes a new prototype storm surge watch/warning graphic from NOAA’s National Hurricane Center, intended to highlight areas along the Gulf and Atlantic coasts of the United States that have a significant risk of life-threatening inundation by storm surge from a tropical cyclone.

The new graphic will introduce the concept of a watch or warning specific to the storm surge hazard. Storm surge is often the greatest threat to life and property from a tropical cyclone, and it can occur at different times and at different locations from a storm’s hazardous winds. In addition, while most coastal residents can remain in their homes and be safe from a tropical cyclone’s winds, evacuations are often needed to keep people safe from storm surge. Having separate warnings for these two hazards should provide emergency managers, the media, and the general public better guidance on the hazards they face when tropical cyclones threaten.

Also new this season is a higher resolution version (2 km near the storm area) of NOAA's Hurricane Weather Research and Forecasting model (HWRF), thanks to the upgrades to operational supercomputing. A new 40-member HWRF ensemble-based data assimilation system will also be implemented to make better use of aircraft reconnaissance-based Tail Doppler Radar data for improved intensity forecasts. Retrospective testing of 2015 HWRF upgrades demonstrated a five percent improvement in the intensity forecasts compared to last year.

This week, May 24-30, is National Hurricane Preparedness Week. To help those living in hurricane-prone areas prepare, NOAA offers hurricane preparedness tips, along with video and audio public service announcements at www.hurricanes.gov/prepare.

"It only takes one hurricane or tropical storm making landfall in your community to significantly disrupt your life,” said FEMA Deputy Administrator Joseph Nimmich. “Everyone should take action now to prepare themselves and their families for hurricanes and powerful storms. Develop a family communications plan, build an emergency supply kit for your home, and take time to learn evacuation routes for your area. Knowing what to do ahead of time can literally save your life and help you bounce back stronger and faster should disaster strike in your area."

NOAA will issue an updated outlook for the Atlantic hurricane season in early August, just prior to the historical peak of the season.

NOAA also issued its outlook for the Eastern Pacific and Central Pacific basins. For the Eastern Pacific hurricane basin, NOAA’s 2015 outlook is for a 70 percent chance of an above-normal hurricane season. That outlook calls for a 70 percent probability of 15 to 22 named storms, of which 7 to 12 are expected to become hurricanes, including 5 to 8 major hurricanes. For the Central Pacific hurricane basin, NOAA’s outlook is for a 70 percent chance of an above-normal season with 5 to 8 tropical cyclones likely.

DFG funds new Mathematical Collaborative Research Center on Wave Phenomena at KIT and new Transregio project on weather forecasting with KIT participation

The Karlsruhe Institute of Technology (KIT) has successfully acquired funding for a new collaborative research center (CRC). The German Research Foundation (DFG) will finance the CRC "Wave Phenomena: Analysis and Numerics" coordinated by KIT. This is the first CRC in the area of mathematics at KIT. Here, mathematicians in the areas of analysis and numerics cooperate to analytically understand, numerically simulate, and manipulate the propagation of waves. In addition, the DFG has approved the new CRC/Transregio "Waves to Weather", with KIT as one of the three main partners. It addresses a new generation of weather forecasts.

"Success in this recent CRC funding competition confirms the competence of the scientists involved and underlines the visibility of research at KIT," says KIT President Professor Holger Hanselka. "We encounter waves everywhere in daily life - even our body does not work without wave phenomena. The new CRC studies these wave phenomena in an comprehensive way."

Collaborative research centers (CRCs) are research programs of universities scheduled for a duration of up to twelve years (three times four years), in which researchers work on complex topics, crossing the boundaries of disciplines, institutes, and departments. "These CRCs contribute to defining the profiles of the participating universities and to supporting young scientists," explains KIT Vice President for Research and Information, Professor Detlef Löhe. "The research training group integrated in the "Wave Phenomena" CRC will give young mathematicians the opportunity to profit from stimulating interdisciplinary cooperation."

The CRC 1173 "Wave Phenomena: Analysis and Numerics" brings together 16 scientists from analysis and numeric of the KIT Department of Mathematics. Another four researchers of optics and photonics, biomedical technology, and applied geophysics work on the interfaces to applications. Two mathematicians from the Universities of Stuttgart and Tübingen will also contribute to the CRC. "Waves are everywhere. Seeing and hearing are based on the propagation of light and sound waves, the human heartbeat is driven by depolarization waves, and most modern communication is based on electromagnetic waves", says CRC spokesperson Professor Marlis Hochbruck, Head of the Numerical Analysis Research Group of the KIT Institute of Applied and Numerical Mathematics (IANM). "The propagation of waves can be described by differential equations and gives rise to a number of fascinating mathematical problems."

The goal of the CRC "Wave Phenomena: Analysis and Numerics" is to analytically understand, numerically simulate, and manipulate the propagation of waves under realistic scenarios. The scientists focus on typical wave phenomena such as the emergence of standing and travelling waves or wave fronts, oscillations and resonances, dispersion, wave guidance, reflection, refraction, and scattering of waves.

Transregio "Waves to Weather"

Enhancing the precision and reliability of weather forecasts is the objective of the new CRC/Transregio 165 "Waves to Weather" (W2W), in which scientists of KIT, Ludwig-Maximilians-Universität München (LMU) as coordinator, Technische Universität München (TUM), the German Aerospace Center (DLR) Munich, and Johannes Gutenberg University (JGU) Mainz cooperate in a transregional manner. "The socio-economical relevance of weather forecasts is increasing, which is not least due to the transformation of the energy system," explains Professor Peter Knippertz, Head of the Working Group on Atmospheric Dynamics within the Troposphere Research Division of the KIT Institute of Meteorology and Climate Research (IMK-TRO). W2W concentrates on the presently biggest challenge in weather forecasting: Identifying the limits of predictability in particular of wavelike air movements in various situations and making the physically best possible predictions.

The likelihood of record-breaking warm years in England is set to substantially increase as a result of the human influence on the climate, new research suggests.

In a study published today, 1 May, in IOP Publishing's journal Environmental Research Letters, an international team of researchers has shown that the chances of England experiencing a record-breaking warm year, such as the one seen in 2014, is at least 13 times more likely as a result of anthropogenic climate change.

This is according to climate model simulations and detailed analyses of the Central England Temperature (CET) record--the world's longest instrumental temperature record dating back to 1659.

The results of the study showed that human activities have a large influence on extreme warm years in England, which the researchers claim is remarkable given England is such a small region of the world.

Lead author of the study Dr Andrew King, from the ARC Centre of Excellence for Climate System Science at the University of Melbourne, said: "When you look at average annual temperatures over larger regions of the world, such as the whole of Europe, there is a lower variability in temperatures from year to year compared with smaller areas.

"As a result of this low variability, it is easier to spot anomalies. This is why larger regions tend to produce stronger attribution statements, so it is remarkable that we get such a clear anthropogenic influence on temperatures in a relatively small area across central England." 

To arrive at their results, the researchers firstly used climate model simulations to calculate the likelihood of very warm years when there is just natural forcings on the climate and no human influence, and then when there is both natural forcings and human influence. The change in the likelihood of warm years due to human influences on the climate was then calculated.

The researchers then observed the CET and picked out the warmest years from the record since 1900. The warmest years were then plotted onto a graph which the researchers used to calculate the likelihood of warm years happening now and warms years happening 100 years ago.

The model-based method suggested at least a 13-fold increase (with 90% confidence) due to human influences on the climate, whilst the observation-based approach suggested at least a 22-fold increase in the probability of very warm years in the climate of today compared with the climate of a century ago (again with 90% confidence).

"Both of our approaches showed that there is a significant and substantial increase in the likelihood of very warm years occurring in central England," Dr King Continued. 

According to the CET, 2014 was the warmest year on record in central England. It has been reported that during the last 60 years there has been rapid warming in the CET in line with the anthropogenic influence on the climate, with the highest average annual temperature of 10.93 °C recorded in 2014.

The Central England Temperature (CET) series, which is the longest instrumental time series of temperature in the world, has monthly recordings of average temperatures dating back to 1659 and recordings of average daily temperatures dating back to 1772.

The CET is designed to represent the climate of the English Midlands, which is approximated by a triangular area enclosed by Lancashire in the north, Bristol in the south-west and London in the south-east. The CET has undergone thorough and extensive quality control, making it an ideal resource for studying long-term temperature trends across the region.

As to whether these results can be seen to be representative of areas outside of central England, Dr King said: "I would expect that other areas near the UK would produce similar results. 

"For larger regions, stronger attribution statements can often be made. For example, we performed a similar attribution study for Europe as a whole and found a 35-fold increase in the likelihood of extremely warm years using model simulations."

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