NRL researchers use unmanned aircraft to probe hurricane outflow jets

Sep 10, 2012
This shows the COAMPS-TC analysis of the wind speed, meters per second (m s-1), and direction, at 40,000 feet (200hPa), during Hurricane Earl taken at 1200 Universal Coordinated Time Sept. 1, 2010. The center of Earl is shown by the black dot. The outflow at this time is spiraling outward from the storm, eventually directed towards the east. Credit: US Naval Research Laboratory – Marine Meteorology Division

Researchers at the U.S. Naval Research Laboratory (NRL) Marine Meteorology Division (MMD), Monterey, Calif., will take part in a new three-year NASA field campaign aimed at observing hurricanes from a unique vantage point 65,000 feet above the Atlantic, an altitude not previously attainable by hurricane research aircraft.

The NRL team comprised of research meteorologists specialized in tropical cyclone observations and prediction will focus on characterizing the upper-level portion of tropical cyclones (TCs), particularly hurricane outflow jets that spiral away from the storm center in organized channels.

"Outflow jets in hurricanes have never been systematically observed in previous experiments because they are at higher altitudes than routine hurricane research and reconnaissance aircraft can reach," said Dr. James Doyle, head, NRL Mesoscale Modeling Section, Marine Meteorology Division. "We hypothesize that the evolving outflow jet structure and location during the TC life cycle may play a key role in the processes that influence TC intensity changes."

Stationed at NASA's Wallops Island Flight Facility on Virginia's Eastern Shore, the NRL team will take part in the Hurricane and Severe Storm Sentinel (HS3) mission, led by Dr. Scott Braun of the NASA's Goddard Space Flight Center, Greenbelt, Md., to analyze meteorological data gathered by a pair of NASA unmanned aircraft equipped with an unparalleled suite of meteorological instrumentation.

Although the predictions of the paths or tracks of hurricanes have steadily improved over the last few decades, improvements in the prediction of hurricane strength or intensity have proven much more challenging. This is in part due to a fundamental lack of understanding of the key atmospheric and oceanic processes that take place during changes and partly due to lack of adequate observations. The Global Hawk is an ideal platform to probe the storm from the surface to the outflow layer, and will provide an unprecedented opportunity to unravel some of the mysteries underlying TC intensity change.

One Global Hawk will be focused on measuring the environmental conditions, especially the hurricane outflow layer, and is equipped with onboard remote sensors developed and deployed by NASA scientists to measure temperature and aerosol characteristics. The environmental Global Hawk also includes a system to deploy dropsondes—small tube-shaped devices, equipped with parachutes that gather and transmit data as they gently fall to the ocean surface—that will observe vertical profiles of temperature, wind, barometric pressure and humidity through the outflow layer and the environmental structures below.

A second Global Hawk will probe the inner-core of the storm using instruments developed by NASA such as a multi-frequency radiometer system to map ocean surface winds and rainfall rate, especially in the hurricane eyewall where the strongest winds and heaviest rainfall occur. In addition, other NASA instruments on the Global Hawk include a conically scanning Doppler radar that will observe the hurricane's wind and rainfall structure along with another radiometer system that will map precipitation features and measure the large thermal anomaly in the hurricane eye.

The NRL team will also employ the Coupled Ocean/Atmosphere Mesoscale Prediction System Tropical Cyclone (COAMPS-TC™) model in real time, currently under development at MMD, to help guide the Global Hawks in order to observe the key parts of the storm. Over the past two years the COAMPS-TC model has been shown to be a leading dynamical model for predicting TC intensity.

"The unique aspect about NRL's participation in NASA's Hurricane and Severe Storms Sentinel program is that it will provide an entirely new approach to atmospheric observation and a means for new data input to NRL's recently developed TC prediction model," said Dr. Peter Black, scientist, Science Applications International Corporation. "Flying at high altitudes, NASA's Global Hawk will be able to obtain high-resolution, in-situ observations of the vast unobserved outflow layer of extending into Earth's stratosphere, an approach that contrasts previous observational projects designed to improve understanding of the tropical cyclone air-sea boundary layer."

COAMPS-TC was first tested in real-time in support of two field campaigns sponsored by the Office of Naval Research (ONR): The Tropical Cyclone Structure-08 (TCS-08) conducted as part of The Observing System Research and Predictability Experiment (THORPEX) Pacific Asian Regional Campaign (T-PARC) in 2008 and the Impact of Typhoons on the Ocean in the Pacific (ITOP) in 2010, both of which took place in the Western Pacific. Additionally, COAMPS-TC advancements and real-time demonstrations in the Eastern Pacific and Western Atlantic have taken place through collaboration with the National Oceanic and Atmospheric Administration (NOAA) as part of the Hurricane Forecast Improvement Project (HFIP), a community-wide effort focused on improving intensity prediction.

The NRL research team anticipates that the observations gathered during HS3 will allow the COAMPS-TC predictions to be thoroughly evaluated and will lead to further improvements in the forecast system. NASA and the Office of Naval Research (ONR) sponsor NRL participation and research in the HS3 program.

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