Global Hawk Dropsonde Observations of the Arctic Atmosphere

In February and March of 2011, the Global Hawk (GH) unmanned aircraft system (UAS) was deployed over the Pacific Ocean and the Arctic in science missions designed to: (1) improve our understanding of Pacific weather systems and the polar atmosphere; (2) evaluate the operational use of unmanned aircraft for investigating them; and (3) demonstrate the operational and research applications of a UAS dropsonde system at high latitudes. The dropsondes successfully obtained high-resolution profiles of temperature, pressure, relative humidity, wind speed and direction from the stratosphere to the surface. The 116-foot wingspan Global Hawk, which can soar for 28 hours up to 65,000 feet, was remotely operated from NASA Dryden Flight Research Center in southern California. During the 25-hour polar flight on 9-10 March 2011, the GH released 35 sondes in the Arctic from just off the North Slope of Alaska to 85° N latitude marking the first UAS Arctic dropsonde mission of its kind. The polar flight transected an unusually cold polar vortex, notable for record Arctic ozone loss, and documented variations in the polar boundary layer over a sizable lead feature. Comparison of the dropsonde observations with reanalyses data reveal that while large-scale structures, such as the polar vortex and air masses, are captured, smaller-scale features, including low-level jets and inversion depths, are mis-characterized. The successful dropsonde deployment in the Arctic demonstrates the capability of the GH to conduct operations in harsh, remote regions and the value of observations in the Arctic atmosphere where in situ measurements are practically non-existent.