Beginning this summer, and over the next several years, NASA will be sending unmanned aircraft dubbed "severe storm sentinels" above stormy skies to help researchers and forecasters uncover information about hurricane formation and intensity changes. The Hurricane and Severe Storm Sentinel (HS3) airborne mission will investigate the processes that underlie hurricane formation and intensity change in the Atlantic Ocean basin.

The NASA Global Hawk is well-suited for hurricane investigations because it can over-fly hurricanes at altitudes greater than 60,000 feet with flight durations of up to 28 hours — something piloted aircraft would find nearly impossible to do. HS3 will use two Global Hawk aircraft and six different instruments this summer, flying from a base of operations at Wallops Flight Facility in Virginia. The HS3 mission will operate during portions of the Atlantic hurricane seasons, which run from June 1 to November 30. The 2012 mission will run from late August through early October.

HS3 will address the controversial role of the hot, dry, and dusty Saharan Air Layer in tropical storm formation and intensification. Past studies have suggested that the Saharan Air Layer can both favor or suppress intensification. In addition, HS3 will examine the extent to which deep convection in the inner-core region of storms is a key driver of intensity change or just a response to storms finding favorable sources of energy.

The instruments to be mounted in the Global Hawk aircraft that will examine the environment of the storms include the scanning High-resolution Interferometer Sounder (S-HIS), the Advanced Vertical Atmospheric Profiling System (AVAPS) — also known as dropsondes — and the Cloud Physics Lidar (CPL).

Another set of instruments will fly on the Global Hawk focusing on the inner region of the storms. Those instruments include the High-Altitude Imaging Wind and Rain Airborne Profiler (HIWRAP) conically scanning Doppler radar, the Hurricane Imaging Radiometer (HIRAD) multi-frequency interferometric radiometer, and the High-Altitude Monolithic Microwave Integrated Circuit Sounding Radiometer (HAMSR) microwave sounder. Most of these instruments represent advanced technology developed by NASA, that in some cases are precursors to future satellite sensors.

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