THE THUNDERSTORM PREDICTABILITY EXPERIMENT

 

Ominous clouds signal a thunderstorm brewing on the U.S. Great Plains. Credit: NOAA

FROM: NATIONAL SCIENCE FOUNDATION
Where, When Will Thunderstorms Strike Colorado's Front Range, Adjacent Great Plains?

To better predict where and when spring thunderstorms rip across Colorado's Front Range and the adjacent Great Plains, researchers launched a major field project with high-flying aircraft and fine-grained computer simulations.

The month-long study could point the way to major improvements in lead times for weather forecasts during what has been called a crucial six- to 24-hour window.

"People want to know whether there will be thunderstorms and when," says National Center for Atmospheric Research (NCAR) scientist Morris Weisman, one of four principal investigators on the project.

"We're hoping to find out where you need to collect observations in order to get the most improvement in short-term forecasts. Better prediction with a few hours of lead time could make a big difference in helping people prepare."

MPEX (pronounced "em-pex"), the Mesoscale Predictability Experiment, runs from May 15 to June 15 and is funded by the National Science Foundation (NSF).

The project includes participants from NCAR; Colorado State University; the University at Albany, State University of New York; Purdue University; the University of Wisconsin-Milwaukee; and the National Oceanic and Atmospheric Administration's National Severe Storms Laboratory.

"MPEX will lead to a better understanding of the initiation and development of severe storms in an area of the country that's particularly affected by them," says Chungu Lu, program director in NSF's Division of Atmospheric and Geospace Sciences.

"If we can move 'early warnings' even sooner through the results of MPEX, it will lead to safer skies for air travelers and safer situations on the ground as well."

The project will include early morning flights with the NSF/NCAR Gulfstream V aircraft to sample the pre-storm atmosphere across Colorado and nearby states.

The Gulfstream V can cruise at 40,000 feet for up to six hours, which will enable researchers to thoroughly canvass the entire region where triggers for severe weather might be lurking.

MPEX will also include afternoon launches of weather balloons carrying instrument packages called radiosondes, which will profile conditions around thunderstorms as they develop and move east across the Great Plains.

Filling the same-day gap

Severe weather warnings from the National Weather Service give people up to an hour's notice for tornadoes and other threats on a county-by-county basis. A key goal of MPEX is to help improve the forecasts that fall between two types of longer-range alerts:
convective outlooks, which highlight the risk of severe weather up to eight days in advance across large parts of the country;
tornado and severe thunderstorm watches, which are issued up to eight hours in advance for state-sized areas.
Same-day forecasts often note the likelihood of severe storms, but they do not usually specify where and when the storms will develop.

MPEX will help determine whether more detailed observations and simulations could lead to more specific forecasts of storm location and behavior as much as a day in advance.

Advanced forecast models can now simulate the weather using data at points packed as closely as about a half-mile from each other. This allows showers and thunderstorms (known as "convection") to be explicitly depicted. But the newer models still struggle to reliably map out storm behavior beyond about six hours in advance.

Scientists believe this may be largely because the models need more detail on upper-level features, such as pockets of strong wind or dry air, located several miles above ground level.

As these features move into the Great Plains, they can be critical for triggering or suppressing severe storms. However, weather satellites may not see these features, and they often go undetected by limited surface and upper-air networks across the Rocky Mountain states.

"The structure of the atmosphere two to six miles above sea level is incredibly important," Weisman says. "This appears to be where the biggest forecast errors develop, so we need to collect more data at these heights."

In the sky and on the ground

To get around the data roadblock, MPEX will send the Gulfstream V from its base at the Rocky Mountain Metropolitan Airport in Broomfield on missions that will start as early as 3 a.m.

The Gulfstream V will sample jet-stream winds, upper-level temperatures, and other features across Colorado and nearby states.

The aircraft will use a microwave-based temperature sensor to profile horizontal temperature contrasts miles above the region.

At pre-specified locations, the Gulfstream V will also use parachute-borne minisondes--compact instrument packages, similar to the 200-plus radiosondes used every day across the nation--to gather extra detail between flight level and ground level.

The minisondes will provide information on temperature, moisture, and winds four times each second.

"The Gulfstream V is perfect for this kind of study," says NCAR project manager Pavel Romashkin, who will oversee MPEX aircraft operations. "The G-V is one of very few aircraft in weather research that can sample the atmosphere near the top of important features for a number of hours."

MPEX will also gather data with three radiosonde launch units operated by Purdue and NSSL in vehicles that will maneuver around late-day thunderstorms.

The goal is to find out how well the extra data can help predict local and regional weather conditions into the next day, as well as to assess how the thunderstorms interact with the atmosphere that surrounds and supports them.

"We know that even isolated, short-lived thunderstorms influence their environment," says Robert "Jeff" Trapp of Purdue, an MPEX principal investigator.

"The MPEX data will allow us to quantify these influences and examine how well they are represented in computer forecast models. This information can then be used to help improve weather forecasts."

Testing the value of enhanced observations

With the help of improvements in computing power and scientific understanding, forecast models can depict weather in far more detail than just a few years ago.

On each day of operations (about 15 in all during the project), MPEX will produce an ensemble of up to 30 forecasts using the NCAR-based research version of the multiagency Weather Research and Forecasting model (WRF-ARW).

Along with data from the Gulfstream V flights, each WRF-ARW ensemble member will use a slightly different characterization of early-morning weather conditions in order to allow for the uncertainty inherent in those measurements.

Forecasters can then issue forecasts with greater or lesser confidence based on how the ensemble forecasts agree or disagree.

The MPEX team will also evaluate how much the Gulfstream V data improve forecasts in two other modeling systems, both of which are updated each hour.

The complex process of incorporating observed data into the MPEX simulations will be handled by NCAR's Data Assimilation Research Testbed.

Studies have shown that major forecast improvements are possible when the right kinds of data are collected and assimilated into forecast models.

Scientists hope the results from MPEX will help advance this process, which could improve predictions of severe thunderstorms as well as other types of high-impact weather where better forecasts in the six- to 24-hour period could help people and communities better prepare.

-NSF-

HURRICANE HUNTERS

 FROM: NATIONAL SCIENCE FOUNDATION
September 24, 2012

The Deep Convective Clouds & Chemistry (DC3) Experiment, which began in mid-May, explores the influence of thunderstorms on air just beneath the stratosphere, a region that influences Earth's climate and weather patterns. Scientists used three research aircraft, mobile radars, lightning mapping arrays and other tools to pull together a comprehensive picture. Credit: NOAA

Dropsondes--Work Horses in Hurricane Forecasting
Small cylinders dropped from airplanes gather atmospheric data on their way down

Inside a cylinder that is about the size of a roll of paper towels lives a circuit board filled with sensors. It's called a dropsonde, or "sonde" for short. It's a work horse of hurricane forecasting, dropping out of "Hurricane Hunter" airplanes right into raging storms. As the sonde falls through the air, its sensors gather data about the atmosphere to help us better understand climate and other atmospheric conditions.

"Dropsondes have a huge impact on our understanding of hurricanes and our ability to predict hurricanes," explains electrical engineer Terry Hock at the Earth Observing Laboratory in the National Center for Atmospheric Research (NCAR), located in Boulder, Colo.

With support from the National Science Foundation (NSF), Hock and his colleagues at NCAR have been designing, building and improving dropsonde technology for more than 30 years. "Our most current development is a fully automated dropsonde system for NASA's unmanned Global Hawk aircraft," says Hock.

Compared to earlier models, today's sondes are lighter weight, relatively inexpensive and loaded with sensors.

"We have a lot of electronics and, on the back side, a battery pack to operate the sonde. We have a temperature and two humidity sensors, and we have a GPS receiver," explains Hock, as he points out the different circuit board components. "As the sonde moves, we're using that GPS receiver to track the sonde's movements very precisely, which is then telling us the wind speed and wind direction. At the top of the sonde is a parachute which slows down the descent."

Electrical engineer Dean Lauritsen, a member of Hock's team, developed the system software on the aircraft, which controls the aircraft data system and process, and also displays dropsonde data during the sondes free fall to earth. There's such a system on the HIAPER, the NSF/NCAR Gulfstream V Research Aircraft, which uses sondes for scientific research, and a similar system used by the U.S. Air Force Reserve Hurricane Hunters in Biloxi, Miss., and the NOAA Hurricane Hunters in Tampa, Fla. On board each aircraft are a computer and a rack of electronic equipment to monitor and receive information from sondes. "The system is capable of tracking as many as eight dropsondes in the air at the same time. Each one of them is transmitting data on a separate frequency as it falls." says Lauritsen.

From the time the sonde leaves the aircraft, it is checking surroundings two times a second and sending information back to the aircraft, including pressure, temperature, humidity, wind speed, and wind direction. Future developments are expected to include sensors for chemicals such as ozone.

"We're taking vertical slices of the atmosphere constantly as the sonde falls," says Hock. "We're seeing very precise single measurements show up immediately on the computer screen."

Researchers process the information using NCAR-developed custom software, and then send it to weather forecasters and researchers around the world. In the case of the Hurricane Hunters, the information goes to the National Hurricane Center in Miami.

NCAR software engineer Charlie Martin develops custom software called ASPEN, which stands for Atmospheric Sounding Processing Environment. ASPEN helps make sense of all the dropsonde data. "Once the dropsonde has fallen through the atmosphere and the data has come back to the aircraft, that raw data needs a little more treatment before we send it to weather services around the world," explains Martin.

Martin points to a map showing a compilation of dropsonde wind data collected in August 2011, as Hurricane Irene was churning its way toward the Florida coast. "The winds are in a circular pattern," says Martin, as he identifies small triangles on the map that represent the wind and wind direction. "The center of the hurricane is clearly depicted in the center of the circular pattern. The National Hurricane Center uses this data along with other data to classify the hurricane and assign a category to it."

Hock and his team also custom fit aircraft with launchers to deploy the sondes, including one system for helium-filled balloons. In 2010, American and French researchers deployed balloons over Antarctica that dropped 600 sondes over a four-month period to study atmospheric conditions and the shifting ozone layer. "There is now a very dense set of measurements that came out of this project that has mapped the Antarctic atmosphere like it has never been done before," notes Martin.

"Atmospheric conditions above the Antarctic continent are hard to study since only a handful of sounding stations are regularly maintained there," says Peter Milne, program manager for ocean and atmospheric sciences within NSF's Office of Polar Programs. "Fortunately, the Antarctic polar vortex, a huge cyclone that sets up above the entire continent, is like the NASCAR of long distance ballooning, with balloons sweeping around the continent for as long as they stay aloft. Using these drifting platforms provided a unique data set."

Such "inside information" is helping scientists learn more about climate and hurricanes. Data from dropsondes is also giving scientists a better understanding about atmospheric conditions that spawn any number of weather conditions. Hock expects this will help forecasters make earlier and more precise hurricane predictions, giving people in the path of a killer storm more time to get out of harm's way.