Two NASA scientists have for the first time taken simultaneous high-altitude radar, temperature, and wind measurements that reveal the anatomy of hurricanes and shed light on what makes them intensify. The results could lead to better forecasting in the future.
The activities were part of CAMEX-4 (The Convection And Moisture EXperiment), a joint effort between NASA, the National Oceanic and Atmospheric Administration (NOAA) and a number of universities, that ended on September 24.
"We had three flights over Hurricane Humberto in the last three days," NASA Goddard Space Flight Center researcher and a mission scientist for Camex-4, Gerry Heymsfield said. "These were the most comprehensive measurements of the structure of the hurricane ever recorded."
As Hurricane Humberto raged over the Atlantic Ocean, Heymsfield fitted NASA's high altitude ER-2 aircraft with a downward-looking radar, called an ER-2 Doppler Radar (EDOP). From the ER-2's vantage of 12 miles (20 km) up, the EDOP uses the Doppler shift of rain and ice particles within clouds to measure rain intensity, air speed and velocity within the storm. NASA's ER-2 aircraft provides a unique perspective over the top of the storm and flies so high the pilot needs to wear a spacesuit.
Earlier, on September 10, another Goddard scientist, Jeff Halverson, made use of ER-2 to drop temperature and wind sensors into the eye of Hurricane Erin. The sensors, called dropsondes, were automatically released from the plane by a computer-operated system.
As they fell, the dropsondes tallied air temperatures and winds through the storm's eye, from the top of the hurricane to the ocean surface. By taking these readings at eight different locations in the hurricane, "It's as though we obtained a topographical temperature map of the storm," says Halverson, who maintains a dual appointment between Goddard and the University of Maryland-Baltimore County's Joint Center for Earth Systems Technology. He adds that Erin had a classic hurricane structure with a well-defined eye, and the new data will provide excellent baselines for figuring out how these storms intensify.
When hurricanes occur, heat gets generated inside the center of thunderstorms that eventually make up a hurricane. The heat, created largely by condensation in clouds, causes the air to expand and rise and that lowers air pressure near surface of the water. When the surface pressure lowers, air accelerates from areas of higher pressure surrounding the storm toward the lower pressure area near the sea surface. As it flows, the air picks up some of the spin of the Earth and starts to move counterclockwise in a vortex. The winds begin blowing faster towards the center and the storm intensifies into a hurricane.
By using dropsonde measurements of winds, temperature, surface pressure and moisture, and then combining those readings with EDOP data of air motions and precipitation levels in those clouds, the researchers now have necessary data for assessing a hurricane's structure. That's because the EDOP provides information about the clouds that create heat and warm the hurricane's spinning vortex, and in turn, the dropsondes measure the high altitude temperatures that drive the vortex and in turn create more clouds.
"It is significant to understand the temperature inside the eye of the storm at high altitudes because that is something that is not very well known," Halverson said. "To understand whether the storm is intensifying or not you have to know whether the temperature is increasing."
Halverson's temperature readings and Heymsfield's results "work best together to answer fundamental questions about the physics that drive a hurricane," said Halverson.
Scott Braun, another NASA Goddard Space Flight Center researcher, will now use the new data to create detailed computer simulations of hurricanes. These models may help to better predict future hurricanes.
The dropsonde system was developed by the National Center for Atmospheric Research (NCAR), and installed onto NASA's ER-2 aircraft.
The Convection And Moisture EXperiment (CAMEX) was the fourth in a series of field research investigations sponsored by the Earth Science Enterprise at NASA Headquarters, Washington, DC. The mission united researchers from 10 universities, five NASA centers and the National Oceanic and Atmospheric Administration (NOAA). Based out of the Naval Air Station at Jacksonville, Fla., this year's mission ran from Aug. 16 through Sept. 24 - traditionally the most active part of the hurricane season.
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