Converging Satellites Unlock Sudden Demise Of Hurricane Lili

by Staff Writers
Atlanta GA (SPX) Feb 09, 2006
Using a fleet of NASA and other satellites as well as aircraft and other observations, scientists were able to unlock the secret of Hurricane Lili's unexpected, rapid weakening as she churned toward a Louisiana landfall in 2002. The data from multiple satellites enabled researchers to see dry air move into the storm’s low levels, partially explaining why Lili weakened rapidly.
This study focuses on the rapid weakening of Hurricane Lili over the Gulf of Mexico beginning early on Oct. 3, 2002. During this time span, Hurricane Lili rapidly weakened from a category 4 to a category 1 storm, with its maximum sustained winds decreasing by 45 knots (51.8 mph) in the 13-hour period, until she made landfall in Louisiana. Operational computer models failed to predict this rapid weakening, which is not well-understood.

The study is being presented at the 86th Annual Meeting of the American Meteorological Society in Atlanta, Ga., during the week of Jan. 30. It was conducted by researchers from Mississippi State University (MSU), Mississippi State, Miss., and the National Center for Atmospheric Research (NCAR), Boulder, Colo.

"Because a polar-orbiting satellite can only obtain regional observations once per day, the ability to combine observations from multiple satellites over the data-sparse ocean is a key to understanding tropical cyclone intensity change," says Dr. Pat Fitzpatrick, the principal investigator from MSU.

In order to dissect this complex puzzle, scientists turned to data from NASA's Terra, Aqua, QuikSCAT and Tropical Rainfall Measuring Mission (TRMM) satellites, as well as data from the National Oceanic and Atmospheric Administration's Advanced Very High Resolution Radiometer (AVHRR) aboard Geostationary Operational Environmental Satellite (GOES). They also looked at data from sensors called "dropsondes" that were dropped from hurricane hunter airplanes while flying over Hurricane Lili. Those dropsondes provided temperature, humidity and wind data.

The different satellites provided a variety of data to look at the hurricane's components. QuikSCAT provided surface winds; Aqua provided high-resolution temperature and moisture profile data; and GOES-8 supplied upper-level winds. Sea Surface Temperature data was also measured from Aqua, Terra, TRMM and AVHRR. Standard weather observations were also incorporated, including maritime surface data from the National Data Buoy Center.

All of these different components were fed into an NCAR computer model called MM5 that re-creates atmospheric and oceanic conditions in four dimensions (height, width, area and time). The data was combined using a "Four-Dimensional Variational Analysis" (4DVAR) system.

The MM5 computer model and 4DVAR system, developed by NCAR scientists, essentially re-created the conditions when Hurricane Lili weakened, so scientists could better understand the cause of the drop in strength. The model showed that low-level drier air, not observed in the conventional data, moved into the west side of Lili, at 00 Universal Time on Thursday, Oct. 3, 2002, (Wednesday, Oct. 2, at 8:00 p.m. ET), partially explaining the storm’s weakening.

That dry air created an "open eyewall" which is basically a break up in the powerful thunderstorms that circle the open air center (eye) of the hurricane. Once the eyewall starts to break down, the storm weakens quickly.

The computer model also showed that the GOES upper-level wind data and QuikSCAT satellite wind information can improve hurricane track forecasts. "These satellites, through the 4DVAR technique, improved the inner-core wind structure and also defined the steering currents better," Fitzpatrick said. When this additional wind data from those two satellites was input, the computer model was also able to better re-create Hurricane Lili's track at landfall.

A paper on this subject has been submitted for review to Monthly Weather Review on the 4DVAR experiments, titled "The Impact of Multi-satellite Data on the Initialization and Simulation of Hurricane Lili's (2002) Rapid Weakening Phase." The scientists involved in this project are Xiaoyan Zhang and Qingnong Xiao, of the NCAR; and Pat Fitzpatrick, Nam Tran, Yee Lau, Sachin Bhates, and Valentine Anantharaj of MSU.

Related Links
American Meteorological Society
Mississippi State University

www.terradaily.com/reports/...Lili.html

NASA Finds Intense Lightning Activity Around A Hurricane Eye

by Staff Writers
Huntsville AL (SPX) Jun 26, 2006
When you think of lightning, you think of a thunderstorm. Many people also assume that hurricanes have a lot of lightning because they are made up of hundreds of thunderstorms.
However, according to Dr. Richard Blakeslee of the NASA Marshall Space Flight Center (MSFC) in Huntsville, Ala., "Generally there's not a lot of lightning in the hurricane eye-wall region. So when people detect a lot of lightning in a hurricane, they perk up -- they say, okay, something's happening."

In 2005, scientists did perk up, because a very strong Hurricane Emily had some of the most lightning activity ever seen in a hurricane. Scientists are now trying to determine if the frequency of lightning is connected to the hurricane's strength.

In July of that year, NASA lightning researchers joined hurricane specialists from the National Oceanic and Atmospheric Administration (NOAA) and 10 universities for a month-long Tropical Cloud Systems and Processes (TCSP) field experiment in Costa Rica. The purpose of the mission was to determine what weather, climate and other factors that helped create tropical storms and hurricanes.

They also wanted to learn about what makes these storms strengthen. All of these organizations study lightning in hurricanes to get a better understanding of the strengthening or weakening (intensification) of the storms.

Hurricane Emily was one of three named storms (the others were Hurricane Dennis and Tropical Storm Gert) observed during the TCSP field experiment. Scientists flew NASA's ER-2 high-altitude weather plane above Emily, where they recorded some of the most powerful lightning activity ever seen in a hurricane’s eye-wall. Emily was one of the largest, most violent hurricanes ever to be documented by the ER-2 plane.

During the flights, scientists detected both cloud-to-ground lightning strokes and cloud-to-cloud lightning in the thunderstorms surrounding Emily's eye. They also found that the "electric fields," or areas of the atmosphere that contained electricity above Hurricane Emily, were some the strongest ever recorded.

"We observed steady fields in excess of 8 kilovolts (8,000 volts) per meter (3.2 feet)," says Blakeslee. "That is huge—and comparable to the strongest fields we would expect to find over a large land-based thunderstorm."

The field experiment concluded before the birth of hurricanes Katrina and Rita in 2005. However, scientists also observed significant lightning in the eye walls of hurricanes Katrina and Rita through long range ground-based lightning detection networks.

That similarity has generated more interest in trying to understand the connection between lightning activity and hurricane development, intensification and behavior.

Researchers at the National Space Science and Technology Center, a facility jointly managed and operated by NASA MSFC and Alabama research universities, are working with the NOAA to better understand the connection between lightning and hurricane intensity.

The month of June is typically known among meteorologists for promoting lightning safety awareness, because June is the first month of summer and brings thunderstorms.

Related Links
www.nasa.gov/centers/mar...e/index.html
www.lightningsafety.noaa.gov/
thunder.nsstc.nasa.gov/


www.terradaily.com/reports/..._Eye.html

Global Warming Surpassed Natural Cycles In 2005 Hurricane Season

by Staff Writers
Boulder CO (SPX) Jun 26, 2006
Global warming accounted for around half of the extra hurricane-fueling warmth in the waters of the tropical North Atlantic in 2005, while natural cycles were only a minor factor, according to a new analysis by Kevin Trenberth and Dennis Shea of the National Center for Atmospheric Research (NCAR).
The study will appear in the June 27 issue of Geophysical Research Letters, published by the American Geophysical Union. "The global warming influence provides a new background level that increases the risk of future enhancements in hurricane activity," Trenberth says. The research was supported by the National Science Foundation, NCAR's primary sponsor.

The study contradicts recent claims that natural cycles are responsible for the upturn in Atlantic hurricane activity since 1995. It also adds support to the premise that hurricane seasons will become more active as global temperatures rise. Last year produced a record 28 tropical storms and hurricanes in the Atlantic. Hurricanes Katrina, Rita, and Wilma all reached Category 5 strength.

Trenberth and Shea's research focuses on an increase in ocean temperatures. During much of last year's hurricane season, sea-surface temperatures across the tropical Atlantic between 10 and 20 degrees north, which is where many Atlantic hurricanes originate, were a record 1.7 degrees F above the 1901-1970 average.

While researchers agree that the warming waters fueled hurricane intensity, they have been uncertain whether Atlantic waters have heated up because of a natural, decades-long cycle, or because of global warming.

By analyzing worldwide data on sea-surface temperatures (SSTs) since the early 20th century, Trenberth and Shea were able to calculate the causes of the increased temperatures in the tropical North Atlantic. Their calculations show that global warming explained about 0.8 degrees F of this rise.

Aftereffects from the 2004-05 El Nino accounted for about 0.4 degrees F. The Atlantic multidecadal oscillation (AMO), a 60-to-80-year natural cycle in SSTs, explained less than 0.2 degrees F of the rise, according to Trenberth. The remainder is due to year-to-year variability in temperatures.

Previous studies have attributed the warming and cooling patterns of North Atlantic ocean temperatures in the 20th century—and associated hurricane activity—to the AMO. But Trenberth, suspecting that global warming was also playing a role, looked beyond the Atlantic to temperature patterns throughout Earth's tropical and midlatitude waters.

He subtracted the global trend from the irregular Atlantic temperatures—in effect, separating global warming from the Atlantic natural cycle. The results show that the AMO is actually much weaker now than it was in the 1950s, when Atlantic hurricanes were also quite active. However, the AMO did contribute to the lull in hurricane activity from about 1970 to 1990 in the Atlantic.

Global warming does not guarantee that each year will set records for hurricanes, according to Trenberth. He notes that last year's activity was related to very favorable upper-level winds as well as the extremely warm SSTs. Each year will bring ups and downs in tropical Atlantic SSTs due to natural variations, such as the presence or absence of El Nino, says Trenberth. However, he adds, the long-term ocean warming should raise the baseline of hurricane activity.

Related Links
www.ncar.ucar.edu/

www.terradaily.com/reports/...ason.html

Hurricane Katrina's waves felt in California
11:00 24 September 2006
From New Scientist

On 29 August 2005, as hurricane Katrina was rumbling towards New Orleans, a seismic hum more than 1000 times the strength of the average volcanic tremor was felt nearly 3000 kilometres away in southern California. Its source was the hurricane itself.

Hurricanes create large ocean waves, which send energy pulsing through the Earth as they pound the shoreline. To determine the power of Katrina's seismic waves, Peter Gerstoft of the University of California, San Diego, and colleagues analysed the signals recorded by a network of 150 seismic stations in southern California just before Katrina hit the Louisiana coast. They used a method known as beamforming, which preferentially picks up signals from a particular direction, to decipher the seismicity generated by Katrina (Geophysical Research Letters, vol 33, p L17805).

Seismic surface waves, which travel through the Earth's crust, were detected 30 hours before the hurricane made landfall, while body waves, which bounce down into the mantle, arrived some 18 hours later. "The body waves had travelled down to 1100 kilometres inside the Earth," Gerstoft says. This is the first time that a hurricane's seismic signal has been detected so far away.

Tree Rings Offer Insights to Hurricanes

-- Within the annual growth rings of old longleaf pines, scientists are discovering a previously unknown record of hurricane activity in the Southeast.

A University of Tennessee-led team has found that hurricane rain can leave a chemical mark in the woody tissue of these shallow-rooted trees that can date when storms occurred.


Full story: www.physorg.com/news78418930.html

NASA technology captures massive hurricane waves

A hurricane's fury can be relentless, from frightening winds, to torrential rains and flooding. These storms also create enormous ocean waves that are hazardous to ships. And through storm surges of up to 30 feet the storms can demolish shoreline structures, erode beaches and wash out coastal roads.

As part of its activities to better understand Earth's dynamic climate, NASA research is helping to increase knowledge about the behavior of hurricane waves. The NASA Scanning Radar Altimeter (SRA), designed to take measurements of the changing wave height and structure in and around hurricanes, flew through many storms on a National Oceanic and Atmospheric Administration (NOAA) WP-3D aircraft from 1998-2005. It captured unprecedented details on wave behavior that are helping improve sea height forecasts. Strong storms like Hurricane Bonnie in August 1998 - the first to be monitored by SRA - were found to produce severe ocean waves and dramatic changes in wave height and complexity over small distances.

The SRA measures waves by sweeping a radar beam across the ocean and measuring the distance to the sea at many points. Those distances are then subtracted from the aircraft altitude to produce a sea-surface elevation map that is displayed on a monitor in the aircraft.

While the flight portion of the SRA hurricane research program concluded with the 2005 hurricane season, the data gathered continue to help researchers develop and improve ocean wave computer models that simulate hurricane-generated ocean wave height, dominant wavelength, and wave direction.

These computer models allow wave behavior to be predicted at times and places where there are no observations. However, actual observations from SRA are essential because "they tell us how the wave field - the height, length and direction of waves in a given area – actually varies with a hurricane's wind speed, size, and forward motion so that we can improve the performance of the models that disaster managers and structural engineers rely on for guidance," said C. Wayne Wright, NASA Wallops Flight Facility, Wallops Island, Va.

Ongoing research efforts have shown that ocean wave height responds rapidly to changes in a storm's wind speed. But scientists believe the overall wave field is also driven by the size or radius of a storm's strongest winds, and its forward speed. In Hurricane Katrina in August 2005 the largest waves, up to 40 feet, were found near the strongest winds. In September 2004, scientists with the Naval Research Laboratory-Stennis Space Center, Bay St. Louis, Miss., measured a record-size ocean wave - a whopping 91 feet - when the eye wall of Hurricane Ivan passed over sensors in open water over the Gulf of Mexico.

"Ocean depth is another critical factor in wave height," said Edward Walsh, NASA Wallops Flight Facility, Wallops Island, Va. "Our observations from Hurricane Bonnie indicated that as soon as the waves encountered the continental shelf - the underwater extension of the coastal plain - their length began to shorten and they became steeper. As the water became shallow, wave height plummeted."

Similarly, with Hurricane Rita in September 2005, the wave height dropped dramatically and was only 9 feet when wave energy was lost due to the shoaling of water on the continental shelf - the process in which waves coming into shallow waters are slowed by friction and become closer together and steeper.

Fortunately, a storm's most massive waves usually decrease in size when they interact with the ocean's continental shelf and other land forms, like "barrier islands" that form a thin protective wall between the open sea and the mainland. The islands absorb the strongest waves, sheltering the mainland during large storms. But with powerful storms like Katrina, the constant battering of waves can take a toll on the land, leaving the islands reduced or gone altogether.

SRA's detailed and precise information, together with data to be gathered by a new operational SRA being built by NOAA to replace the NASA prototype, promises to provide additional insight into a hurricane's behavior. Such research is increasingly important as areas become more prone to higher storm surges as natural defenses like barrier islands and wetlands disappear.

Source: NASA/Goddard Space Flight Center


www.physorg.com/news78497161.html

NASA Looks at Sea Level Rise, Hurricane Risks to New York City

New York City has been an area of concern during hurricane season for many years because of the large population and logistics. More than 8 million people live in the city, and it has hundreds of miles of coastline that are vulnerable to hurricane threats. Using computer climate models, scientists at NASA have looked at rising sea levels and hurricane storm surge and will report on them at a science meeting this week.

Cynthia Rosenzweig and Vivien Gornitz are scientists on a team at NASA's Goddard Institute for Space Studies (GISS) and Columbia University, New York City, investigating future climate change impacts in the metropolitan area. Gornitz and other NASA scientists have been working with the New York City Department (DEP) of Environmental Protection since 2004, by using computer models to simulate future climates and sea level rise. Recently, computer modeling studies have provided a more detailed picture of sea level rise around New York by the 2050's.

During most of the twentieth century, sea levels around the world have been steadily rising by 1.7 to 1.8 mm (~0.07 in) per year, increasing to nearly 3 mm (0.12 in) per year within just the last decade. Most of this rise in sea level comes from warming of the world’s oceans and melting of mountain glaciers, which have receded dramatically in many places since the early twentieth century. The 2001 report of the Intergovernmental Panel on Climate Change found that a global warming of 1.4° to 5.8° C (2.5° -10.4° F) could lead to a sea level rise of 0.09-0.88 meters (4 inches to 2.9 feet) by 2100.

A study conducted by Columbia University scientists for the U.S. Global Change Research Program in 2001 looked at several impacts of climate change on the New York metropolitan area, including sea level rise. The researchers projected a rise in sea level of 11.8 to 37.5 inches in New York City and 9.5 to 42.5 inches in the metropolitan region by the 2080s.

"With sea level at these higher levels, flooding by major storms would inundate many low-lying neighborhoods and shut down the entire metropolitan transportation system with much greater frequency," said Gornitz.

With sea level rise, New York City faces an increased risk of hurricane storm surge. Storm surge is an above normal rise in sea level accompanying a hurricane. Hurricanes are categorized on the Saffir-Simpson scale, from 1 to 5, with 5 being the strongest and most destructive. The scale is used to give an estimate of the potential property damage and flooding expected along the coast from a hurricane landfall. Wind speed is the determining factor in the scale, as storm surge values are highly dependent on the slope of the continental shelf and the shape of the coastline, in the landfall region.

A recent study by Rosenzweig and Gornitz in 2005 and 2006 using the GISS Atmosphere-Ocean Model global climate model for the Intergovernmental Panel on Climate Change projects a sea level rise of 15 to 19 inches by the 2050s in New York City. Adding as little as 1.5 feet of sea level rise by the 2050s to the surge for a category 3 hurricane on a worst-case track would cause extensive flooding in many parts of the city. Areas potentially under water include the Rockaways, Coney Island, much of southern Brooklyn and Queens, portions of Long Island City, Astoria, Flushing Meadows-Corona Park, Queens, lower Manhattan, and eastern Staten Island from Great Kills Harbor north to the Verrazano Bridge. Gornitz will present these findings at the annual meeting of the Geological Society of America in Philadelphia during the week of Oct. 23.

To understand what hurricane storm surges would do to the city, surge levels for hurricanes of categories 1 through 4 were calculated by the U.S. Army Corps of Engineers for the 1995 Metro New York Hurricane Transportation Study using NOAA’s SLOSH computer model. SLOSH (Sea, Lake and Overland Surges from Hurricanes) is a computerized model run by the National Hurricane Center to estimate storm surge heights resulting from historical, hypothetical, or predicted hurricanes by taking into account pressure; size, forward speed, track and hurricane winds.

According to the 1995 study, a category three hurricane on a worst-case track could create a surge of up to 25 feet at JFK Airport, 21 feet at the Lincoln Tunnel entrance, 24 feet at the Battery, and 16 feet at La Guardia Airport. These figures do not include the effects of tides nor the additional heights of waves on top of the surge. Some studies suggest that hurricane strengths may intensify in most parts of the world as oceans become warmer. However, how much more frequently they will occur is still highly uncertain.

Hurricanes have hit New York City in the past. The strongest hurricane was a category four storm at its peak in the Caribbean, which made landfall at Jamaica Bay on Sept. 3, 1821 with a 13-foot storm surge. It caused widespread flooding in lower Manhattan. The “Long Island Express” or “Great Hurricane of 1938," a category three, tracked across central Long Island and ripped into southern New England on Sept. 21, 1938, killing nearly 700 people. The storm pushed a 25-35 foot high wall of water ahead of it, sweeping away protective barrier dunes and buildings.

The 1995 Transportation study was done to assess the vulnerability of the city's transportation system to hurricane surges. The 2001 Columbia study was one of the regional studies for the U.S. National Assessment of Climate Variability and Change; the recent study for the NYC DEP was to evaluate potential climate change impacts, including sea level rise, on the agency's mandated activities and infrastructure.

"This entire work is solutions oriented," said Rosenzweig. "It's about helping NYC DEP and other New York City agencies make better preparations for climate extremes of today, and changing extremes of the future. The report will help us determine how can we do better job now, as well as in the future."

Source: by Rob Gutro, Goddard Space Flight Center


www.physorg.com/news81007489.html

Looking at the Impact of Hurricane Ivan on Florida Coasts

Ivan was just one of four strong hurricanes to directly hit Florida coasts within a 1-month period in 2004. A new study has examined the poststorm impact and the short-term recovery from Ivan along a 200-km stretch of coast from Fort Walton Beach to St. George Island. The study is published in the latest issue of the Journal of Coastal Research.


Hurricane Ivan made landfall along the northwestern Florida and Alabama coast on September 16, 2004. It briefly reached Category 5 strength, persisting as a strong Category 4 hurricane in the Gulf of Mexico before being downgraded to a strong Category 3 at landfall by the U.S. National Hurricane Center.

A team of researchers from the University of South Florida conducted one prestorm and three poststorm beach-profile surveys to understand the morphological changes created by Ivan and also the poststorm recovery. Included in the assessment was an excavation of 46 trenches to study the characteristics and thickness of subaerial storm deposits.

Storm impact along barrier island coasts has been the subject of numerous studies. Because of the largely unpredictable nature of extreme storms like hurricanes, most studies concentrate on poststorm impact and behavior, whereas collection of prestorm data is typically not conducted, making it difficult to quantify the dramatic morphological impact of storms as well as poststorm recovery.

What the study found was apparent, and dramatic morphological and sedimentological impacts extended more than 300 km eastward from the center of the hurricane. Extensive inundation and overwash occurred within 100 km from the storm center at landfall. The highest elevation of beach erosion extended considerably above the measured storm-surge level, indicating that storm-wave setup and swash run-up played significant roles in controlling the elevation of beach erosion.

Beach recovery began immediately after the storm. Within 90 days, the berm crest recovered to its prestorm elevation, although it was now located 15 m landward.

To read the entire study, click here: www.allenpress.com/pdf/coas..._1402.pdf

Journal of Coastal Research is the bi-monthly journal of The Coastal Education and Research Foundation (CERF).

Source: Alliance Communications Group


www.physorg.com/news83860755.html

Busy Hurricane Season Forecast for 2007
Associated Press

Dec. 8, 2006 — The 2007 Atlantic hurricane season should have above-average activity, with three major hurricanes and a good chance at least one of them will make landfall, a top hurricane researcher said Friday.

Colorado State forecaster William Gray predicted 14 named storms and a total of seven hurricanes next year.

He and fellow researcher Philip Klotzbach said there is a 64 percent chance of one of the major hurricanes — with sustained winds of 111 mph or greater — coming ashore. The long-term average probability is 52 percent, they said.

Still, they said fewer hurricanes are likely to make landfall next year than in the devastating 2005 season, which had 28 named storms, including 15 hurricanes, four of which hit the U.S. The worst was Katrina, which leveled parts of the Gulf Coast.

The 2006 season had nine named storms and five hurricanes, two of them major. That was considered a "near normal" season but fell short of predictions by Gray and government scientists. None hit the U.S. Atlantic coast — only the 11th time that has occurred since 1945.

Gray and Klotzbach said last month that a surprise late El Nino contributed to the calmer June-to-November hurricane season this year.

El Nino — a warming in the Pacific Ocean — has far-reaching effects that include changing wind patterns in the eastern Atlantic, which can disrupt the formation of hurricanes there, Gray said.

Gray's team said Friday those conditions are likely to dissipate before the next season but Klotzbach cautioned, "this is an early prediction."

Gray said he believes the Atlantic basin is in an active hurricane cycle, despite the calm 2006 season.

"This active cycle is expected to continue for another decade or two at which time we should enter a quieter Atlantic major hurricane period like we experienced during the quarter-century periods of 1970-1994 and 1901-1925," he said.

Tropical Storm Risk, a London-based consortium of weather, insurance and risk-management experts, on Thursday forecast an active 2007 season, with up to 16 tropical storms including nine hurricanes, four of them intense.


dsc.discovery.com/news/2006...n_pla.html

Aircraft Captures Windy Details In Hurricane's Ups And Downs

Researchers employing some of the world's most sophisticated weather research equipment recently captured details on winds and other conditions in a rapidly intensifying hurricane. This data will help to advance the understanding of these complex storms.

While meteorologists have made considerable strides in forecasting a hurricane's track, intensity predictions have remained a more elusive challenge. Part of the difficulty is that the many factors that control intensity, particularly the speed, direction and spin of air throughout the atmosphere, are constantly changing and tricky to measure. Aircraft are able to gather detailed, precise measurements of winds in a hurricane that can help researchers understand what is going on inside the storm, allowing better forecasts to be made.

In July 2005, Hurricane Dennis experienced several periods of rapid intensity fluctuations, providing for several excellent opportunities to learn about tropical cyclone behavior. Dennis reached hurricane strength on July 7, 2005, in the eastern Caribbean Sea, and rapidly strengthened into a category 4 storm before making landfall in Cuba on July 8. After weakening considerably as the storm moved over Cuba, Dennis attained category 4 hurricane status again with a pressure drop of 11 millibars in under two hours, indicative of rapid intensification. A typical low-pressure system in the United States might intensify that much over the course of an entire day.

Flying over Hurricane Dennis with NASA's ER-2 aircraft and the National Oceanic and Atmospheric Administration's (NOAA) P-3 aircraft, scientists gathered data on the storm's internal structure, including the distribution of winds, rainfall, temperature and moisture. The aircraft information has provided insight into the evolution of a hurricane's warm inner core; one of the many factors that impact storm development.

The research flights were conducted as part of the Tropical Cloud Systems and Processes (TCSP) mission in Costa Rica, a NASA field experiment with cooperative participation from NOAA and several universities. This experiment was aimed at studying the birthing conditions for tropical storms and hurricanes and identifying the factors that cause them to strengthen or weaken.

"This campaign was particularly unique because two types of aircraft provided measurements on different atmospheric variables," said Joe Turk of the Naval Research Laboratory, Monterey, Calif. "The information is also being used to determine how accurately satellites capture storm details."

The aircraft data provide high resolution measurements with a level of detail far superior to current weather satellites. During the mission, the NASA ER-2 aircraft flew over Dennis at 65,000 feet while taking scientific measurements that probed downward through the cloud layers. At times, the NOAA P-3 flew identical and coordinated patterns, but from an altitude of 12,000 feet, probing the storm from the inside.

As the hurricane fluctuated in intensity, flights into the storm continued, taking critical measurements of wind, temperature, and moisture. "The erratic nature of the storm and the timing of the research mission allowed scientists to pierce through the core of the hurricane at many stages of its life cycle and for the first time map a hurricane's entire evolution," said Steve Guimond of Florida State University, Tallahassee, Fla.

NASA's ER-2 Doppler radar measured wind speed along the track of the aircraft including measurements indicative of the size and concentration of raindrops and ice particles, while another ER-2 instrument, the Advanced Microwave Precipitation Radiometer, gathered microwave imagery of the internal structure of rain clouds. By analyzing when and where strong winds are occurring, researchers can better determine when intensity changes may occur. Data on the storm's vertical temperature structure - indirectly related to wind speed and rainfall - was also examined from overpasses of NASA and NOAA satellites.

These key aircraft observations not only assist in understanding the rapid intensification of hurricanes, they can also help scientists recreate storms on computer models that are used in forecasting. Just small changes in wind speed and direction patterns can significantly rearrange a storm's rain and wind structure, altering the evolution of its predicted track and intensity.

Previous research has suggested that rapid hurricane intensification, like that seen in Dennis, is associated with "hot towers." These are columns of rapidly rising air that reach and in some cases overshoot the top of the troposphere - the lowest layer of the atmosphere - about nine miles high in the tropics. They are called "hot" because of the large amount of heat they release through condensation of water vapor, providing fuel for strong winds and heavy rainfall.

"With Dennis, it appears the hot towers played a major role in the rapid intensification of the storm, giving clues on how energy is concentrated and winds evolve at various stages of development," said Guimond. "The observations also helped place the storm's behavior in greater context and matched well with computer model simulations, suggesting that we are making progress in replicating hurricane development."

"Improved knowledge of how both the heating and rotation or 'spin' of air parcels associated with these hot towers interacts with the greater organized system is thought to be another key ingredient to improving hurricane intensity forecasts," said Steve Miller of the Naval Research Laboratory. "While our preliminary findings based on satellite views of Dennis support the idea that such physical links may in fact exist, additional insight requires the kind of three-dimensional detailed perspective on internal storm structure that is only available in a field experiment, such as the TCSP mission."

As researchers identify other factors most critical in hurricane development, those elements can be targeted for increased observation in future field missions to obtain the big pieces of the puzzle needed to solve the mysteries of hurricane behavior.

Note: This story has been adapted from a news release issued by NASA/Goddard Space Flight Center.


www.sciencedaily.com/release...634.htm#

Mega-Hurricanes Fueled by River Plumes
Larry O'Hanlon, Discovery News

Feb. 01, 2007 — The tepid waters of the Amazon and Orinoco rivers may be goading modest hurricanes into super storms, says a researcher studying the balmy river water at sea.

Oceanographer Amy Ffield overlayed the tracks of category 4 and 5 hurricanes from 1960 to 2000 on the bathtub-warm, less saline plumes that surge from the mighty rivers into the ocean off the coast of northeastern South America.

She found that more than two-thirds of all storms that reach category 5 status — the most powerful — pass right over the giant plume of warm river water.

"The Amazon is the largest (river) in the world and the Orinoco the third largest," explained Ffield, a researcher at Seattle-based Earth and Space Research as well as Columbia University's Lamont-Doherty Earth Observatory. "Together they create a huge plume. These plumes go way out."

Her new work is published in the January issue of the Journal of Climate.

The warmer, fresher water is about 30 to 200 feet deep over a vast swath of ocean, almost like a giant oil slick, Ffield told Discovery News. Because the river water is much less dense than the seawater, the two do not easily mix. Instead, the river water creates a barrier between cooler seawater below and the atmosphere above.

This is good news for ambitious hurricanes. When they spin over the river plumes they may be revved by the heat of the river water, or at the very least protected from being weakened by the cooler seawater, she explained.

"What's exciting about this research is that people who have been studying hurricanes look at sea surface temperatures, but not how sea surface temperatures are made," said Ffield. "I'm saying, let's look at what controls sea surface temperature."

The two great rivers are just one overlooked physical variable in the great North Atlantic hurricane factory, Ffield said, along with the interactions of plumes with the north Brazil current and other physical phenomena in the open ocean.

Other hurricane experts suspect that Ffield could be onto something.

Take the current state of affairs in hurricane forecasting, said Kerry Emanuel, a hurricane researcher at the Massachusetts Institute of Technology. Hurricane scientists have become pretty good at forecasting storm tracks, he said, but still have trouble predicting changes in intensity, which are closely related to water temperature.

"One of the Holy Grails of hurricane forecasting is intensity," said Emanuel. "Part of the reason for that is that in practice we don't have any good temperature and salinity profiles of the ocean in (hurricane) paths."

That data is needed and perfectly possible to gather, but the political will, and therefore the funding, just hasn't been there, Emanuel said. As a result, he said, "Our models don't know what's out there."



dsc.discovery.com/news/2007...e_pla.html

Hurricane can form new eyewall and change intensity rapidly

Hurricanes can gain or lose intensity with startling quickness, a phenomenon never more obvious than during the historic 2005 hurricane season that spawned the remarkably destructive Katrina and Rita.

Researchers flew through Rita, Katrina and other 2005 storms trying to unlock the key to intensity changes. Now, data from Rita is providing the first documented evidence that such intensity changes can be caused by clouds outside the wall of a hurricane's eye coming together to form a new eyewall.

"The comparison between Katrina and Rita will be interesting because we got excellent data from both storms. Rita was the one that showed the eyewall replacement," said Robert Houze Jr., a University of Washington atmospheric sciences professor and lead author of a paper detailing the work in the March 2 edition of the journal Science.

"The implication of our findings is that some new approaches to hurricane forecasting might be possible," he said.

Houze and Shuyi Chen, an associate professor of meteorology and physical oceanography at the University of Miami Rosenstiel School of Marine and Atmospheric Science, lead a scientific collaboration called the Hurricane Rainband and Intensity Change Experiment. The project is designed to reveal how the outer rainbands interact with a hurricane's eye to influence the storm's intensity. Chen is a co-author of the Science paper, as are Bradley Smull of the UW and Wen-Chau Lee and Michael Bell of the National Center for Atmospheric Research in Boulder, Colo.

The project is the first to use three Doppler radar-equipped aircraft flying simultaneously in and near hurricane rainbands. The project also uses a unique computer model developed by Chen's group at the Rosenstiel School.

"The model provided an exceptionally accurate forecast of eyewall replacement, which was key to guiding the aircraft to collect the radar data," Chen said.

A hurricane's strongest winds occur in the wall of clouds surrounding the calm eye. The researchers found that as the storm swirled into a tighter spin, a band of dry air developed around the eyewall, like a moat around a castle. But while a moat protects a castle, the hurricane's moat eventually will destroy the existing eyewall, Houze said. Meanwhile, outer rainbands form a new eyewall and the moat merges with the original eye and the storm widens, so the spin is reduced and winds around the eye are slowed temporarily, something like what happens as a figure skater's arms are extended. But the storm soon intensifies again as the new eyewall takes shape.

"The exciting thing about the data from Rita is that they show that the moat is a very dynamic region that cuts off the old eye and establishes a wider eye," Houze said. "It's not just a passive region that's caught in between two eyewalls."

Hurricane forecasters in recent years have developed remarkable accuracy in figuring out hours, even days, ahead of time what path a storm is most likely to follow. But they have been unable to say with much certainty how strong the storm will be when it hits land. This work could provide the tools they need to understand when a storm is going to change intensity and how strong it will become.

Scientists already knew that intensity can change greatly in a short time -- in the case of Rita the storm grew from a category 1, the least powerful hurricane, to a category 5, the most powerful, in less than a day. Aircraft observation of the moat allowed scientists to see Rita's rapid loss of intensity during eyewall replacement, which was followed by rapid intensification.

"Future aircraft observations focused in the same way should make it possible to identify other small-scale areas in a storm where the processes that affect intensity are going on, then that data can be fed into high-resolution models to forecast storm intensity changes," Houze said.

That understanding could prove valuable for coastal residents deciding whether a storm is powerful enough to warrant their seeking safety farther inland. Rita and Katrina, among the six most intense Atlantic hurricanes ever recorded in terms of the barometric pressure within the core of the storm, struck just three weeks apart in August and September 2005, together resulting in some 2,000 fatalities and more than $90 billion in damage along the Gulf of Mexico coastline. The most-intense Atlantic storm ever recorded, Wilma, also struck in the record-setting 2005 hurricane season, which produced 15 hurricanes, including a fourth category 5 storm, Emily, and a category 4 storm, Dennis.

The National Oceanic and Atmospheric Administration provided two research aircraft for the project and the third was provided by the U.S. Navy and funded by the National Science Foundation.

The planes flew several novel flight paths, including a circular track in Rita's moat, to gather information from the edges of rainbands and other structures in the hurricane.

"We used a ground-control system with a lot of data at our fingertips to focus the aircraft into places in the storm where there were processes happening related to intensity changes," Houze said.

Source: University of Washington


www.physorg.com/news91987629.html

Prehistoric Hurricane Activity Uncovered
Science Daily — Hurricanes Katrina and Rita focused the international spotlight on the vulnerability of the U.S. coastline. Fears that a "super-hurricane" could make a direct hit on a major city and cause even more staggering losses of life, land and economy triggered an outpouring of studies directed at every facet of this ferocious weather phenomenon. Now, an LSU professor takes us one step closer to predicting the future by drilling holes into the past.

Kam-biu Liu, George William Barineau III Professor in LSU's Department of Oceanography and Coastal Sciences, is the pioneer of a relatively new field of study called paleotempestology, or the study of prehistoric hurricanes. Liu, a long-time resident of Louisiana, became even more interested in the subject during the aftermath of Hurricane Katrina, when a national debate was sparked concerning hurricane intensity patterns and cycles.

"People were discussing the probability of a Category 5 hurricane making direct impact on New Orleans," said Liu. "That's tricky, because it's never actually happened in history. Even Katrina, though still extremely powerful, was only a Category 3 storm at landfall."

Currently, experts tend to agree that Atlantic hurricane activity fluctuates in cycles of approximately 20-30 years, alternating periods of high activity with periods of relative calm. But records of such events have only been kept for the last 150 years or so. What would happen, Liu wondered, if you looked back thousands of years? Would larger cycles present themselves?

How does a scientist study storms that happened during prehistoric times? "Basically, we worked under the assumption that the storm surge from these catastrophic hurricanes would have the capability to drive sand over beach barriers and into coastal lakes," said Liu. "This is called an overwash event. We believed that pulling sediment cores from coastal lakes and analyzing the sand layers might give us the information we needed." The same methodology can be used to find overwash sand layers in coastal marshes. Using radiocarbon analysis and other dating techniques, Liu and his research team worked to develop a chronology of prehistoric storms in order to analyze any emerging patterns or cycles.

This methodology has proven successful for the group. In an article printed in the March issue of American Scientist, the magazine of Sigma Xi, the Scientific Research Society, Liu states that evidence from the Gulf Coast drill sites shows that hurricanes of catastrophic magnitude directly hit each location only approximately 10 -- 12 times in the past 3,800 years. "That means the chances of any particular Gulf location being hit by a Category 4 or Category 5 hurricane in any given year is around 0.3 percent," said Liu.

After spending more that 15 years studying dozens of lakes and marshes along the U.S. Gulf and Atlantic Coasts, Liu and his students are moving on to a more tropical location. Liu was recently awarded more than $690,000 from the Inter-American Institute for Global Change Research, or IAI, for his new project titled "Paleotempestology of the Caribbean Region," which is slated to run for five years. He serves as the principal investigator for this international and multi-disciplinary project, which involves 12 other co-investigators from four different countries, including another contributor from LSU, Nina Lam, a professor in the Department of Environmental Studies.

Institutions participating in the study include: the Woods Hole Oceanographic Institution, Brown University, Boston College, the University of Tennessee, the University of Toronto, the Memorial University of Newfoundland, the University of Costa Rica, and the Instituto Mexicano de Tecnologia del Agua, or IMTA, in Mexico.

Liu's Caribbean research has attracted funding not only from the IAI but also from the U.S. National Science Foundation. He and his students have already engaged in three separate expeditions to the Caribbean, stopping in Anguilla, Barbuda and the Bahamas, in the summer and fall of 2006 to core coastal salt ponds in order to gather paleohurricane evidence for analysis. He has recently returned from a coring trip to the Mosquito Coast of Honduras, where he and his co-workers studied how Hurricane Mitch, a catastrophic hurricane that killed more than 12,000 people in Honduras and Nicaragua in 1998, impacted the local communities and environment. His students have also conducted coring fieldwork in Barbados, Nicaragua and Belize during the past year. With many future trips to the Caribbean in the planning stages, they hope to reproduce a prehistoric hurricane analysis as successful as their Gulf Coast study.

Note: This story has been adapted from a news release issued by Louisiana State University.


www.sciencedaily.com/release...0440.htm

Warning of bad hurricane season

Experts are again predicting a busy Atlantic hurricane season, with up to 17 named tropical storms forming - nine of which could become hurricanes.
At least one major storm is expected to make landfall in the US during the 1 June-30 November season, Colorado State University forecasters said.

Last year, leading forecasters wrongly predicted a bad hurricane season.

However the record-breaking 2005 season saw 15 hurricanes, including Katrina which devastated New Orleans.

Another forecaster, London-based Tropical Storm Risk, has likewise predicted 17 tropical storms, nine of them hurricanes, for the 2007 season.

'Very active season'

"We have increased our forecast for the 2007 hurricane season, largely due to the rapid dissipation of El Nino conditions," Colorado experts Philip Klotzbach and William Gray said in a statement.

"We are now calling for a very active hurricane season. Landfall probabilities for the 2007 hurricane season are well above their long-period averages," they said.

The researchers said the upsurge in storm activity could be anticipated because of an end of warm-water El Nino activity in the Pacific, which resulted in milder weather on the US Atlantic coast last year and a downturn in hurricane activity.

"Tropical and North Atlantic sea surface temperatures remain well above their long-period averages," they said.

The 2005 season broke records with a total of with 28 storms and 15 hurricanes. Hurricane Stan, which hit Guatemala, killed at least 2,000 people.



news.bbc.co.uk/1/hi/world...6524017.stm

NASA: Dust curbed hurricanes

Scientists say particles from Saharan storms blocked enough sunlight to cool ocean waters.

Lee Bowman / Scripps Howard News Service

Clouds of Saharan dust traveling west over the Atlantic early last summer blocked enough sunlight to significantly cool the ocean's surface waters, NASA scientists say.

By stealing heat from the ocean, the dust storms may well have contributed as much as, or more than, a developing El Nino pattern did to a quieter-than-expected hurricane season later in the summer, the researchers said.

After early forecasts suggested that the 2006 hurricane season might be only slightly less nasty than the record-setting round the year before, last summer and fall proved less active than a normal season. Only nine tropical storms formed, with just five reaching hurricane strength.

The 2005 season produced a record 27 tropical storms, with 15 strengthening to hurricanes, including the Gulf Coast-battering Katrina and Rita.

In assessing why the hurricane season fizzled last year, most long-range forecasters pointed to the sudden onset of a weak El Nino in the Pacific.

But William Lau, chief of the Laboratory for Atmospheres at NASA's Goddard Space Flight Center in Greenbelt, Md., says satellite data show that several major dust storms blew from the Sahara into the Atlantic in June and July, and that their dust particles were enough to block sunlight from the ocean's surface. He reported the findings in the American Geophysical Union journal Eos.

"This research is the first to show that dust does have a major effect on seasonal hurricane activity," Lau said.

Lau and Kyu-Myong Kim of Goddard found that sea-surface temperatures across the prime hurricane-breeding regions of the Atlantic and Caribbean were as much as 1.8 degrees Fahrenheit cooler than during the previous year.



www.detnews.com/apps/pbcs.dll/article

Dusty Hurricanes

Throw gasoline on a fire, and the flames swell to a raging inferno. Throw dirt on a fire, and the flames suffocate. But what happens when you throw dirt on a hurricane? It's a serious question.

Hurricanes are born in Atlantic waters just off the west coast of Africa. Thunderstorms gather there and, sometimes, for reasons no one fully understands, they merge into swirling monster storms that can cross the ocean to hit the United States thousands of miles away.

The place where hurricanes are born is very close to the Sahara desert—a prodigious source of fine dirt and dust—and Sahara dust storms can blow right into the hurricane genesis region. What does all that dry, dusty air do to a baby hurricane? This is a mystery of hurricane science.

"There are at least two possibilities," notes Bill Lapenta, an atmospheric scientist from NASA's Marshall Space Flight Center. On one hand, dust might strengthen a hurricane. Dust grains serve as nucleation points for clouds and raindrops. This could cause a young storm to intensify because rain is a key part of a hurricane's internal "heat engine." On the other hand, dry, dusty air might have the opposite effect, choking off a storm's development by altering atmospheric circulation patterns normal to a growing storm.

Which theory is true? Lapenta and colleagues recently gathered data that brings them closer to the answer. They did it by flying directly into a dusty hurricane.

Along with dozens of other scientists, Lapenta spent last fall in the Cape Verde Islands off the west coast of Africa. Their mission: to catch hurricanes in the act of being born. The name of the expedition was NASA African Monsoon Multidisciplinary Analyses—or NAMMA for short. NAMMA researchers monitored the ocean near Cape Verde for promising clusters of thunderstorms, and when they saw a group gathering into a potential hurricane, they sprang into action. NASA's DC-8 Airborne Laboratory flew in and around the storms equipped with instruments to measure wins, water vapor, moisture, atmospheric pressure and temperature. NASA and NOAA satellites, weather balloons and ground-based radar gathered even more data.

"We sampled one particular storm two days in a row," recalls Lapenta. "On the first day, our instruments detected very little dust in the storm system. It was clean and pristine. But the next day, using the same aircraft and the same instruments, we detected lots of dust." From one day to the next, the storm system had behaved like a dust mop, swooping up tiny particles from the atmosphere and pulling them in.

What happened next? The storm eventually went on to form a category three hurricane, Helene, one of the strongest of the 2006 Atlantic hurricane season.

So dust promotes hurricanes, right? Lapenta isn't ready to leap to that conclusion. "It's a very complicated problem," he explains. "Dust is one factor in hurricane formation, but there are many others, too." Atmospheric winds, humidity, sea-surface temperature—they all play a role. The effect of dust may be "situation dependent," meaning it depends on what the rest of the atmosphere is doing when the dust hits. "We're still analyzing our data to get the whole picture," he says.

So long after the aircraft has landed, the study continues. NAMMA is a three-year mission, with the first year dedicated to field research, followed by two years of data-analysis.

Source: by Sherrie Super and Dr. Tony Phillips, Science@NASA


www.physorg.com/news95952434.html

Hurricane-Warming Link Debated
Randolph Schmid, Associated Press

April 18, 2007 — The debate over whether global warming affects hurricanes may be running into some unexpected turbulence. Many researchers believe warming is causing the storms to get stronger, while others aren't so sure. Now, a new study raises the possibility that global warming might even make it harder for hurricanes to form.

The findings, by Gabriel A. Vecchi of the National Oceanic and Atmospheric Administration and Brian J. Soden of the University of Miami, are reported in Wednesday's issue of Geophysical Research Letters.

Vecchi and Soden used 18 complex computer climate models to anticipate the effects of warming in the years 2001-2020 and 2018-2100.

Included in the results were an increase in vertical wind shear over the tropical Atlantic and eastern Pacific oceans.

Vertical wind shear is a difference in wind speed or direction at different altitudes. When a hurricane encounters vertical wind shear the hurricane can weaken when the heat of rising air dissipates over a larger area.

On the other hand, warm water provides the energy that drives hurricanes, so warmer conditions should make the storms stronger.

"We don't know whether the change in shear will cancel out the increased potential from warming oceans, but the shear increase would tend to make the Atlantic and East Pacific less favorable to hurricanes," said Vecchi, of NOAA's Geophysical Fluid Dynamics Laboratory in Princeton, N.J.

"Which one of the two — warming oceans or increasing shear — will be the dominant factor? Will they cancel out? We and others are currently exploring those very questions, and we hope to have a better grasp on that answer in the near future," Vecchi said.

"What we can say is that the magnitude of the shear change is large enough that it cannot be ignored," he added.

Any decrease in strength or frequency of storms caused by shear would apply only if all else was equal, Vecchi said, "but all else is not equal, since the shear increase is being driven by global warming."

Soden, of Miami's Rosenstiel School for Marine and Atmospheric Science, added: "This study does not in any way undermine the widespread consensus in the scientific community about the reality of global warming."

The massive destruction caused by Hurricanes Katrina and Rita in 2005 focused attention on tropical cyclones — as these storms are also known — and some well-known researchers suggested the warming seas were fueling stronger storms.

Last year an El Nino — a warming of the water in the tropical Pacific that can affect weather worldwide — dampened the Atlantic hurricane season.

Now, just weeks before the traditional June 1 start of the hurricane season, forecasters and residents of hurricane-threatened regions nervously wait to see what this summer will bring.

The government's hurricane season forecast has yet to be issued, but a top storm researcher has predicted a very active 2007 Atlantic hurricane season. William Gray of Colorado State University expects at least nine hurricanes, with a good chance one will hit the U.S. coast.

While Vecchi and Soden's research indicates increased wind shear in the Atlantic and eastern Pacific, their models did not find the same thing elsewhere.

The models projected that the west and central Pacific should become more favorable to development of the storms, called typhoons in those areas.

Kerry Emanuel, a hurricane expert at the Massachusetts Institute of Technology, said he thinks storms' sensitivity to wind shear may be overestimated.

Emanuel, who was not involved in this research, said he published a study last year that calculated that increasing the potential intensity of a storm via warming by 10 percent increases hurricane power by 65 percent, whereas increasing shear by 10 percent decreases hurricane power by only 12 percent.

On the other hand, Christopher W. Landsea of NOAA's National Hurricane Center, called Vecchi's study "a very important contribution to the understanding of how global warming is affecting hurricane activity."

Landsea, who was not part of the research, said he believes it "provides evidence that the busy period we've seen in the Atlantic hurricanes since 1995 is due to natural cycles, rather than manmade causes."

The research was funded by the National Oceanic and Atmospheric Administration and the National Aeronautics and Space Administration.



dsc.discovery.com/news/2007...e_pla.html

Eye Of The Hurricane Reveals A New Power Source
Science Daily — In the eye of a furious hurricane, the weather is often quite calm and sunny. But new NASA research is providing clues about how the seemingly subtle movement of air within and around this region provides energy to keep this central "powerhouse" functioning.

Using computer simulations and observations of 1998's Hurricane Bonnie in southern North Carolina, scientists were able to get a detailed view of pockets of swirling, warm humid air moving from the eye of the storm to the ring of strong thunderstorms in the eyewall that contributed to the intensification of the hurricane.

The findings suggest that the flow of air parcels between the eye and eye wall - largely believed trivial in the past - is a key element in hurricane intensity and that there's more to consider than just the classic "in-up-and-out" flow pattern. The classic pattern says as air parcels flow "in" to the hurricane's circulation, they rise "up," form precipitating clouds and transport warm air to the upper atmosphere before moving "out" into surrounding environmental air.

"Our results improve understanding of the mechanisms that play significant roles in hurricane intensity," said Scott Braun, research meteorologist at NASA's Goddard Space Flight Center, Greenbelt, Md. "The spinning flow of air parcels - or vortices - in the eye can carry very warm, moist eye air into the eyewall that acts as a turbocharger for the hurricane heat engine." The research appears in the June 2007 issue of the American Meteorological Society's Journal of the Atmospheric Sciences.

"While the 'in-up-and out' pattern has been the prevailing paradigm for the past five decades, when you closely examine intense hurricanes it's apparent that a second family of moist air parcels often travels from the border of the eyewall to the eye, where it picks up moisture from the ocean surface," said co-author Michael Montgomery, professor of meteorology at the U.S. Naval Postgraduate School, Monterey, Calif. "These moisture-enriched air parcels then rather quickly return to the main eyewall and collectively raise the heat content of the lower eyewall cloud, similar to increasing the octane level in auto fuel."

The researchers analyzed thousands of virtual particles to track the movement of air between the eye and eyewall, and between the eyewall and its outside environment. To uncover the impact of these particles on storm intensity, they used a simulation of Hurricane Bonnie from a sophisticated computer model and data gathered during the NASA Convection and Moisture Experiment (CAMEX).

The simulation has also helped to explain the formation of deep "hot towers" observed in Bonnie and many other hurricanes by NASA's Tropical Rainfall Measuring Mission (TRMM) satellite. TRMM carries the first and only space-based precipitation radar that allows researchers to peer through clouds and get a 3-D view of storm structure. It captured a particularly deep hot tower in Bonnie as the storm intensified several days before striking North Carolina.

Hot towers are deep, thick clouds that reach to the top of the troposphere, the lowest layer of the atmosphere, usually about ten miles high in the tropics. The updrafts within these "towers" act like express elevators, accelerating the movement of energy that boosts hurricane strength, and are called "hot" because of the large amount of latent heat they release as water vapor is condensed into cloud droplets. Deep hot towers in the eyewall are usually associated with a strengthening storm.

In previous research, Braun, Montgomery, and Zhaoxia Pu of the University of Utah, Salt Lake City, found a direct relationship between these deep hot towers and the intense vortices inside the eye. "The vortices were shown to be especially crucial in providing the focus and lift needed for hot tower formation and add insight into when and where hot towers will develop in storms," said Braun. The study was published in the January 2006 CAMEX special issue of the Journal of the Atmospheric Sciences.

Vortices are created in response to the rapid change in wind speed from the fierce eyewall to the calm eye. Near the surface, air spiraling inward collides with these vortices to force air up, forming updrafts. Strong updrafts in the eyewall carry moisture much higher than normal and help create hot towers.

The current study suggests that in addition to providing lift, these vortices also feed high energy air from the low-level eye into the eyewall, boosting the strength of the updrafts. This transfer of energy allows the storm to remain stronger than expected, particularly when encountering weakening influences, including cooler ocean water temperatures and wind shear, the change in the direction and speed of winds with altitude.

"This discovery may help explain why strong storms can remain intense for several hours or longer after encountering conditions that usually bring weakening," said Montgomery. "Ongoing research will add to our understanding of the dynamics associated with storm intensity so that we can pinpoint the variables and processes that must be represented in numerical models to improve intensity forecasts."

When hurricane Bonnie finally began to lose strength a couple days before landfall, a significant amount of air in the eyewall was traced back - not to the eye - but to the middle levels of the atmosphere away from the storm. This inflow was caused by wind shear and brought much cooler, drier environmental air into Bonnie's circulation, acting like an anti-fuel to reduce energy in the storm and weaken its strong winds.

Despite these and other recent advances in understanding the internal workings of hurricanes, forecasting their intensity is still a significant challenge.

"Most of today's computer models that aid forecasters cannot sufficiently account for the extremely complex processes within hurricanes, and model performance is strongly dependent on the information they are given on the structure of a storm," said Braun. "We also typically only see small parts of a storm at a given time. That is why it is important to combine data from field experiments such as CAMEX with data from TRMM and other satellites. As observing technologies and models improve, so too will forecasts."

Note: This story has been adapted from a news release issued by NASA/Goddard Space Flight Center.


www.sciencedaily.com/release...2538.htm

Climate's remote control on hurricanes

Natural climate variations, which tend to involve localized changes in sea surface temperature, may have a larger effect on hurricane activity than the more uniform patterns of global warming, a report in this week's Nature suggests.


In the debate over the effect of global warming on hurricanes, it is generally assumed that warmer oceans provide a more favorable environment for hurricane development and intensification. However, several other factors, such as atmospheric temperature and moisture, also come into play.

Drs. Gabriel A. Vecchi of the NOAA Geophysical Fluid Dynamics Laboratory and Brian J. Soden from the University of Miami Rosenstiel School of Marine & Atmospheric Science analyzed climate model projections and observational reconstructions to explore the relationship between changes in sea surface temperature and tropical cyclone 'potential intensity' - a measure that provides an upper limit on cyclone intensity.

They found that warmer oceans do not alone produce a more favorable environment for storms because the effect of remote warming can counter, and sometimes overwhelm, the effect of local surface warming. "Warming near the storm acts to increase the potential intensity of hurricanes, whereas warming away from the storms acts to decrease their potential intensity," Vecchi said.

Titled “Effect of Remote Sea Surface Temperature Change on Tropical Cyclone Potential Intensity,” their study found that long-term changes in potential intensity are more closely related to the regional pattern of warming than to local ocean temperature change. Regions that warm more than the tropical average are characterized by increased potential intensity, and vice versa. “A surprising result is that the current potential intensity for Atlantic hurricanes is about average, despite the record high temperatures of the Atlantic Ocean over the past decade.” Soden said. “This is due to the compensating warmth in other ocean basins.”

“As we try to understand the future changes in hurricane intensity, we must look beyond changes in Atlantic Ocean temperature. If the Atlantic warms more slowly than the rest of the tropical oceans, we would expect a decrease in the upper limit on hurricane intensity,” Vecchi added. “This is an interesting piece of the puzzle.”

“While these results challenge some current notions regarding the link between climate change and hurricane activity, they do not contradict the widespread scientific consensus on the reality of global warming,” Soden noted.

Source: University of Miami


www.physorg.com/news116687408.html

Increased hurricane activity linked to sea surface warming


The link between changes in the temperature of the sea’s surface and increases in North Atlantic hurricane activity has been quantified for the first time. The research - carried out by scientists at UCL (University College London) and due to be published in Nature on January 31 - shows that a 0.5°C increase in sea surface temperature can be associated with a ~40 per cent increase in hurricane activity.

The study, conducted by Professor Mark Saunders and Dr Adam Lea of the Benfield UCL Hazard Research Centre and the UCL Tropical Storm Risk forecasting venture, finds that local sea surface warming was responsible for about 40 per cent of the increase in Atlantic hurricane activity (relative to the 1950-2000 average) between 1996 and 2005.

The study also finds that the current sensitivity of tropical Atlantic hurricane activity to sea surface warming is large, with a 0.5°C increase in sea surface temperature being associated with a ~40 per cent increase in hurricane activity and frequency.

The research focuses on storms that form in the tropical North Atlantic, Caribbean Sea and Gulf of Mexico – a region which produced nearly 90 per cent of the hurricanes that reached the United States between 1950 and 2005. To quantify the role of sea warming it was necessary to first understand the separate contributions of atmospheric circulation and sea surface temperature to the increase in hurricane frequency and activity.

Professor Saunders, the lead author of the study, explained how this was done. “We created a statistical model based on two environmental variables – local sea surface temperature and an atmospheric wind field - which replicated 75-80 per cent of the variance in tropical Atlantic hurricane activity and frequency between 1965 and 2005. By removing the influence of winds from the model we were able to assess the contribution of sea surface temperature and found that it has a large effect. “

“Our analysis does not identify whether greenhouse gas-induced warming contributed to the increase in water temperature and thus to the increase in hurricane activity. However, it is important that climate models are able to reproduce the observed relationship between hurricane activity and sea surface temperature so that we can have confidence in their reliability to project how hurricane activity will respond to future climate change.”

Source: University College London



www.physorg.com/news120919915.html

How strong is a hurricane? Just listen

Knowing how powerful a hurricane is, before it hits land, can help to save lives or to avoid the enormous costs of an unnecessary evacuation. Some MIT researchers think there may be a better, cheaper way of getting that crucial information.

So far, there's only one surefire way of measuring the strength of a hurricane: Sending airplanes to fly right through the most intense winds and into the eye of the storm, carrying out wind-speed measurements as they go.

That's an expensive approach-the specialized planes used for hurricane monitoring cost about $100 million each, and a single flight costs about $50,000. Monitoring one approaching hurricane can easily require a dozen such flights, and so only storms that are approaching U.S. shores get such monitoring, even though the strongest storms occur in the Pacific basin (where they are known as tropical cyclones).

Nicholas Makris, associate professor of mechanical and ocean engineering and director of MIT's Laboratory for Undersea Remote Sensing, thinks there may be a better way. By placing hydrophones (underwater microphones) deep below the surface in the path of an oncoming hurricane, it's possible to measure wind power as a function of the intensity of the sound. The roiling action of the wind, churning up waves and turning the water into a bubble-filled froth, causes a rushing sound whose volume is a direct indicator of the storm's destructive power.

Makris has been doing theoretical work analyzing this potential method for years, triggered by a conversation he had with MIT professor and hurricane expert Kerry Emanuel. But now he has found the first piece of direct data that confirms his calculations. In a paper accepted for publication in Geophysical Research Letters, Makris and his former graduate student Joshua Wilson show that Hurricane Gert, in 1999, happened to pass nearly over a hydrophone anchored at 800 meters depth above the mid-Atlantic Ridge at about the latitude of Puerto Rico, and the same storm was monitored by airplanes within the next 24 hours.

The case produced exactly the results that had been predicted, providing the first experimental validation of the method, Makris says. “There was almost a perfect relationship between the power of the wind and the power of the wind-generated noise,” he says. There was less than 5 percent error-about the same as the errors you get from aircraft measurements.

Satellite monitoring is good at showing the track of a hurricane, Makris says, but not as reliable as aircraft in determining destructive power.

The current warning systems are estimated to save $2.5 billion a year in the United States, and improved systems could save even more, he says. And since many parts of the world that are subject to devastating cyclones cannot afford the cost of hurricane-monitoring aircraft, the potential for saving lives and preventing devastating damage is even greater elsewhere.

“You need to know, do you evacuate or not?” Makris explains. “Both ways, if you get it wrong, there can be big problems.”

To that end, Makris has been collaborating with the Mexican Navy's Directorate of Oceanography, Hydrography and Meteorology, using a meteorological station on the island of Socorro, off Mexico's west coast. The island lies in one of the world's most hurricane-prone areas-an average of three cyclones pass over or near the island every year. The team installed a hydrophone in waters close to the island and are waiting for a storm to come by and provide further validation of the technique.

Makris and Wilson estimate that when there's a hurricane on its way toward shore, a line of acoustic sensors could be dropped from a small plane into the ocean ahead of the storm's path, while conditions are still safe, and could then provide detailed information on the storm's strength to aid in planning and decision-making about possible evacuations. The total cost for such a deployment would be a small fraction of the cost of even a single flight into the storm, they figure.

In addition, permanent lines of such sensors could be deployed offshore in storm-prone areas, such as the Sea of Bengal off India and Bangladesh. And such undersea monitors could have additional benefits besides warning of coming storms.

The hydrophones could be a very effective way of monitoring the amount of sea salt entering the atmosphere as a result of the churning of ocean waves. This sea salt, it turns out, has a major impact on global climate because it scatters solar radiation that regulates the formation of clouds. Direct measurements of this process could help climate modelers to make more accurate estimates of its effects.

Source: Massachusetts Institute of Technology


www.physorg.com/news127045166.html

Forecasters Implement New Hurricane-Tracking Technique

A new technique that helps forecasters continuously monitor landfalling hurricanes, giving them frequent and detailed images of a storm's location, will be implemented this summer.

The new system, developed by National Science Foundation (NSF)-funded researchers at the National Center for Atmospheric Research (NCAR) in Boulder, Colo., and the Naval Research Laboratory (NRL) in Washington, D.C., will be implemented at the National Hurricane Center (NHC).

The technique, known as VORTRAC (Vortex Objective Radar Tracking and Circulation), was successfully tested by the hurricane center last year.

"VORTRAC is an excellent example of the application of basic research to help improve short-term hurricane warnings," says Steve Nelson, program director in NSF's Division of Atmospheric Sciences.

The system, which relies on existing Doppler radars along the U.S. coast, provides details on hurricane winds and central pressure every six minutes, indicating whether the storm is gathering strength in the final hours before reaching shore.

"We are very gratified by the decision of the National Hurricane Center to adopt this new now-casting tool," says NCAR scientist Wen-Chau Lee. "VORTRAC will enable hurricane specialists, for the first time, to continuously monitor the trend in central pressure as a dangerous storm nears land. With the help of VORTRAC, vulnerable communities can be better informed of sudden changes in hurricane intensity."

Lee, NRL's Paul Harasti, and NCAR's Michael Bell led the technique's development. Funding came from NSF and the National Oceanic and Atmospheric Administration (NOAA).

One of VORTRAC's strengths is that it can use radar data to calculate the barometric pressure at the center of a hurricane, a key measure of its intensity.

"VORTRAC allows us to take the wind measurements from the radar, turn the crank, and have a central pressure drop out of a calculation," says Colin McAdie, a meteorologist at NHC. "This will be a valuable addition to the tools available to the forecaster."

Rapidly intensifying storms can catch vulnerable coastal areas by surprise. Last year, Hurricane Humberto struck near Port Arthur, Texas, after unexpectedly strengthening from a tropical depression to a hurricane in less than 19 hours. In 2004, parts of Florida's southwest coast were caught unprepared when Hurricane Charley's top winds increased from 110 to 145 miles per hour in just six hours as the storm neared land.

Lee and his collaborators applied VORTRAC retroactively to the two hurricanes and found that the technique would have accurately tracked their quick bursts in intensity.

"VORTRAC has demonstrated that it can capture sudden intensity changes in potentially dangerous hurricanes in the critical time period when these storms are nearing land," Bell says.

VORTRAC uses the Doppler radar network established by NOAA in the 1990s.

About 20 of these radars are scattered along the Gulf and Atlantic coastlines from Texas to Maine. Each radar can measure winds blowing toward or away from it, but no single radar could provide an estimate of a hurricane's rotational winds and central pressure until now.

The VORTRAC team developed a series of mathematical formulas that combine data from a single radar near the center of a landfalling storm with general knowledge of Atlantic hurricane structure in order to map the approaching system's rotational winds. VORTRAC also infers the barometric pressure in the eye of the hurricane, a very reliable index of its strength.

"By merging several techniques, we can now provide a missing link in short-term hurricane prediction," Harasti says.

Forecasters using VORTRAC can update information about a hurricane each time a Doppler radar scans the storm, which can be as often as about every six minutes. Without such a technique, forecasters would need at least two coastal radars in close proximity to each other in order to obtain the same information. But most of the network's radars are too far apart to qualify.

Each radar can sample conditions out to about 120 miles. This means VORTRAC can track an incoming hurricane for at least several hours, and possibly even as long as a day or more, depending on the storm's speed, trajectory, and size.

To monitor the winds of a landfalling hurricane, forecasters now rely on aircraft to drop instrument packages into the storm that gather data on winds and pressure. But due to flight logistics, the aircraft can take readings no more than every few hours, which means that coastal communities may not be swiftly alerted to changes in approaching hurricanes.

VORTRAC may also help improve long-range hurricane forecasts by using data from airborne Doppler radars or spaceborne radars to produce detailed information about a hurricane that is far out to sea.

Forecasters could input the data to computer models to improve three- and five-day forecasts.

Source: National Science Foundation



www.physorg.com/news127052446.html

New study validates hurricane prediction

Hurricanes in some areas, including the North Atlantic, are likely to become more intense as a result of global warming even though the number of such storms worldwide may decline, according to a new study by MIT researchers.

Kerry Emanuel, the lead author of the new study, wrote a paper in 2005 reporting an apparent link between a warming climate and an increase in hurricane intensity. That paper attracted worldwide attention because it was published in Nature just three weeks before Hurricane Katrina slammed into New Orleans.

Emanuel, a professor of atmospheric science in MIT's Department of Earth, Atmospheric and Planetary Sciences, says the new research provides an independent validation of the earlier results, using a completely different approach. The paper was co-authored by postdoctoral fellow Ragoth Sundararajan and graduate student John Williams and appeared last week in the Bulletin of the American Meteorological Society.

While the earlier study was based entirely on historical records of past hurricanes, showing nearly a doubling in the intensity of Atlantic storms over the last 30 years, the new work is purely theoretical. It made use of a new technique to add finer-scale detail to computer simulations called Global Circulation Models, which are the basis for most projections of future climate change.

“It strongly confirms, independently, the results in the Nature paper,” Emanuel said. “This is a completely independent analysis and comes up with very consistent results.”

Worldwide, both methods show an increase in the intensity and duration of tropical cyclones, the generic name for what are known as hurricanes in the North Atlantic. But the new work shows no clear change in the overall numbers of such storms when run on future climates predicted using global climate models.

However, Emanuel says, the new work also raises some questions that remain to be understood. When projected into the future, the model shows a continuing increase in power, “but a lot less than the factor of two that we've already seen” he says. “So we have a paradox that remains to be explained.”

There are several possibilities, Emanuel says. “The last 25 years' increase may have little to do with global warming, or the models may have missed something about how nature responds to the increase in carbon dioxide.”

Another possibility is that the recent hurricane increase is related to the fast pace of increase in temperature. The computer models in this study, he explains, show what happens after the atmosphere has stabilized at new, much higher CO2 concentrations. “That's very different from the process now, when it's rapidly changing,” he says.

In the many different computer runs with different models and different conditions, “the fact is, the results are all over the place,” Emanuel says. But that doesn't mean that one can't learn from them. And there is one conclusion that's clearly not consistent with these results, he said: “The idea that there is no connection between hurricanes and global warming, that's not supported,” he says.

Source: MIT


www.physorg.com/news127668580.html

Mysterious Weather Pulses Help Predict Hurricanes
Michael Reilly, Discovery News


Aug. 31, 2009 -- Every month or so, a wave of mysterious weather pops up over the Indian Ocean and begins marching eastward through the tropics.

Scientists are unsure what causes it, but a new study has shown that tracking these pulses -- known as the Madden Julian Oscillation -- could allow weather forecasters to predict hurricane and tropical storm formation up to three weeks ahead of time.

Forecasters know enough about the conditions that produce these vicious storms to make annual guesses about how active each hurricane season might be, and to forecast their behavior about five days into the future once they form.

But in between is a vast chasm of uncertainty.

Frederic Vitart of the European Center for Medium-Range Weather Forecasts in the United Kingdom is beginning to bridge that gap, by shedding light on the way the Oscillation influences tropical storm formation, intensity and movement.

Alternating between a vast province of moist, stormy air or an unusually dry patch, the Oscillation slowly blows through the tropics, often circling the globe several times. In a computer simulation of the last 20 years of hurricane seasons, Vitart showed it could increase or decrease risk that a storm would make landfall by as much as 50 percent.

The results were published earlier this month in the journal Geophysical Research Letters.

"The Madden Julian Oscillation creates large-scale conditions which are known to favor tropical storm genesis," he said, bringing with it increased moisture and weakening wind shear.

Vitart's model reliably predicts storm formation out to about 20 days. But the Oscillation is a diffuse, widespread weather pattern; using it to forecast hurricanes can dramatically improve forecasts, but it does not turn weather models into crystal balls.

Even armed with knowledge of the Oscillation's influence on Hurricane Katrina, for instance, no one could have foreseen the storm's devastating strike on New Orleans.

"We may not be able to predict the strike of a storm at a given time and given location, but we can predict if the probability of a tropical storm strike will increase or decrease in the next few weeks over a large area," Vitart said.

"I think that the forecasting that would arise from the Madden Julian Oscillation would be different in nature from the three- and five-day operational track forecasts that currently come out of the National Hurricane Center, which predict the track (and cone of uncertainty) of a storm that already exists," Gabriel Vecchi of the National Oceanic and Atmospheric Administration in Princeton, New Jersey said in an email to Discovery News.

"The Madden Julian Oscillation would help us to predict the genesis of a storm that doesn't exist yet, and the likely character of its track, landfall, etc."

Vitart added that he is working on developing a way to use this type of forecasting to construct maps that display advanced warning of increased risk of hurricane strikes for a given stretch of islands or coastline.



dsc.discovery.com/news/2009...ction.html