Hurricane and Severe Storm Sentinel (HS3): Results from the 2012 and 2013 deployments

The HS3 objectives are: (1) To obtain critical measurements in the hurricane environment in order to identify the role of key factors such as large-scale wind systems (troughs, jet streams), Saharan air masses, African Easterly Waves and their embedded critical layers (that help to isolate tropical disturbances from hostile environments). (2) To observe and understand the three-dimensional mesoscale and convective-scale internal structures of tropical disturbances and cyclones and their role in intensity change.

The mission uses two Global Hawk (GH) Unmanned Airborne Systems (UASs) with separate comprehensive environmental and over-storm payloads. The GH flight altitudes (>16.8 km) allow overflights of most convection and sampling of upper-tropospheric winds. Deployments from Goddard's Wallops Flight Facility and ~24-26-hour flight durations provide coverage of most of the Atlantic Ocean basin and on-station times of 8-20 h depending on storm location. Deployments have been held during September 6-October 4, 2012, and August 20-September 23, 2013, with a final deployment planned in the late August through September time frame in 2014.

Measurements from the Environmental GH Payload include: (1) Continuous sampling of temperature and relative humidity in the clear-air environment from the scanning High-resolution Interferometer Sounder (S-HIS). (2) Full tropospheric wind, temperature, and humidity profiles from the Advanced Vertical Atmospheric Profiling System (AVAPS) dropsonde system, which is capable of releasing up to 88 dropsondes in a single flight. (3) Aerosol and cloud layer vertical structure from the Cloud Physics Lidar (CPL).

Measurements from the Over-Storm GH Payload include: (1) Three-dimensional wind and precipitation fields from the High-altitude Wind and Rain Airborne Profiler (HIWRAP) conically scanning Doppler radar. (2) Surface winds and rainfall from the Hurricane Imaging Radiometer (HIRAD) multi-frequency interferometric radiometer. (3) Temperature, water vapor, and liquid water profiles, rain rates, and vertical precipitation profiles from the High-Altitude MMIC Sounding Radiometer (HAMSR).

Results from the 2012 and 2013 deployments will be discussed. The 2012 campaign used only the environmental GH and consisted of one flight over the outflow layer of Hurricane Leslie and five flights covering the life cycle of Hurricane Nadine. The 2013 campaign consisted of two Saharan Air Layer flights, four flights into Tropical Storm Gabrielle and its precursor disturbance, and one flight each into Hurricane Ingrid, Tropical Storm Humberto, and the non-developer Invest 95L.