Circular flight tracks for deducing tropical cyclone inner-core structure using airborne Doppler radar

Airborne Doppler radars such as the NCAR ELDORA and NOAA P3 X-band tail radars have been used to sample the kinematic and precipitation fields from a variety of meteorological phenomena, including tropical cyclones (TCs). Multi-Doppler synthesis from these platforms can provide high-resolution, three-dimensional structure of a TC's inner core for research, nowcasting, and data assimilation. Typical flight tracks with a single aircraft involve straight-line segments in which multiple radial velocity measurements separated by ~30 degrees are synthesized to produce a three-dimensional wind field. Long straight-line segments penetrating the TC eyewall form the basis of the ‘figure-4' flight pattern typically used by the NOAA P3's during operational reconnaissance. This paper will present an alternative flight pattern in which the aircraft circumnavigates the inner core, maximizing the orthogonality of the Doppler geometry in the eyewall region and increasing the temporal resolution of the observations. Circular tracks have previously been performed by NOAA P3's inside the hurricane eye, and were recently performed outside the eyewall by the NRL P3 with ELDORA during the Hurricane Rainband and Intensity Change Experiment (RAINEX). These flight patterns have yielded encouraging results. The structure derived from different Doppler geometries will be explored using observing system simulation experiments with idealized flight tracks into simulated TCs, and observations from RAINEX will also be presented.