A First Look at the Impact of Coyote UAS Observations from Hurricane Edouard (2014) on Tropical Cyclone Data Assimilation and Prediction

The hurricane boundary layer is the lowest layer of the atmosphere where momentum is exchanged with the surface and where heat and moisture are extracted from the ocean. As such, this region of the storm is critical as it relates to tropical cyclone formation, maintenance, intensification and weakening. Despite the inherent importance of this environment, flight safety risks currently limit the routine collection of wind, pressure, temperature and moisture observations near the ocean-atmosphere interface. In-situ measurements below 500 m in high-wind hurricane conditions are typically from point-source, instantaneous, GPS dropsonde observations. The lack of continuous data coverage at low levels is a primary reason why hurricane boundary layer structure and associated physical processes within this critical region of the storm remain poorly understood and inadequately represented in today's numerical models. In turn, inadequate representation of physical processes often leads to errors in model initialization and data assimilation, which can adversely impact the accuracy of subsequent hurricane forecasts. It is believed that an improved understanding of boundary layer processes, through targeted, enhanced and continuous observations using low altitude unmanned aircraft systems (UAS) will be essential in order to significantly improve scientific understanding and future predictions of hurricane structure and intensity.

During recent reconnaissance missions into Hurricane Edouard (2014), NOAA conducted the first-ever air-deployed UAS experiments into a tropical cyclone environment. On September 16th 2014, Sensintel's 13-lb, 5-ft-wingspan Coyote UAS was released into Major Hurricane Edouard's eye. NOAA's P-3 crewed aircraft launched the UAS and provided in-flight command, control and data delivery support for the Coyote. At an approximate altitude of 2900 ft, the UAS penetrated Edouard's western eyewall and recorded platform record-breaking winds of 100 kt as it proceeded to ‘orbit' this high-wind region during its historic 28-minute inaugural mission.

On September 17th, a second successful P-3/Coyote UAS flight was conducted. Here, the experimental design was to send the UAS along an inflow channel similar to what an air parcel might experience as it spirals towards the storm's center of circulation. This event set endurance records for the Coyote platform as it remained airborne within the hurricane boundary layer for 68 minutes (at controlled altitudes ranging from 1200-2500 ft).

Using NOAA's HWRF and HEDAS modeling and data assimilation systems, Coyote UAS flight data collected in Hurricane Edouard will be incorporated into an Observing System Experiment framework in order to assess the potential impact these unique observations may have had on subsequent track and intensity forecasts. In addition, using NOAA/AOML's Observing System Simulation Experiment capability for regional and vortex-scale tropical cyclone (TC) initialization and prediction, experiments will be conducted to identify the optimal sampling strategies for the Coyote UAS to maximize the impact of its data on regional and vortex-scale data assimilation and prediction. Initial results from these experiments will be presented and some ideas for future missions will be discussed.