Impact of Global Hawk Observing Strategies on Vortex-Scale Tropical Cyclone Forecasts in an OSSE Framework

One aspect of NOAA’s Sensing Hazards with Operational Unmanned Technology (SHOUT) program is to provide targeted observations of tropical cyclones (TCs) using the Global Hawk unmanned aircraft system (UAS) in an effort to improve weather model forecasts and mitigate gaps in satellite observations.  Given limitations on how much of the atmosphere can be sampled at one time, it is important to strategize the placement of the observing system in order to maximize the utility of the data that are collected.  The possible presence of observations from other reconnaissance aircraft and/or satellites also needs to be taken into account in this decision-making process.  This study will examine how variations in the Global Hawk observing strategies, including the flight path and spatial distribution of observations along that path, affect TC analyses and forecasts in a vortex-scale data assimilation and forecasting system.

The potential impact of the flight patterns will be assessed through an observing system simulation experiment (OSSE), wherein observations from Global Hawk platforms (e.g., dropsondes) are simulated, in conjunction with observing platforms from other reconnaissance aircraft and/or satellites, by sampling the Nolan et al. (2013) hurricane nature run.  These data are then assimilated using NOAA/AOML/HRD’s Hurricane Ensemble Data Assimilation System (HEDAS), which includes a square-root ensemble Kalman filter and storm-relative observation processing, prior to running a forecast with NOAA’s HWRF model.  Discussion will include comparisons of the final analyses and HWRF forecasts to the nature run for all stages of the TC life cycle, as well as considerations for designing optimal Global Hawk flight tracks in the future.