Observations of 2017 Atlantic Tropical Cyclones Using the New Solid State Tail-Doppler Radar Aboard the NOAA WP-3D Aircraft.

Since 1982, tropical cyclones have been observed by the NOAA (National Ocean and Atmospheric Administration) WP-3D aircraft using the tail Doppler radar (TDR) system. The antenna(s) scan around an axis that is along the fuselage of the aircraft, permitting the mapping of a three-dimensional volume as the aircraft flies. The present configuration uses two flat-plate antenna(s) designed to scan in cones either 20 degrees fore or aft of the plane normal to the fuselage. In 2016, the TDR used magnetron amplification, and transmitted at X-band alternately out of the fore and aft antennas. The radar operating system was Vaisala RVP-8. Before the VORTEX-SE (The Verification of the Origins of Rotation in Tornadoes EXperiment-Southeast ) experiment in spring 2017, the TDR system was upgraded to use solid-state amplification, and to transmit simultaneously from both fore and aft antennas. The rotation rate was also increased from 10 to 15 rpm. The result was a 3-fold improvement in the along-track resolution, going from 1.5 km to 0.5 km. Pulse compression was used to improve the sensitivity of the system (improving to approximately -10 dBZ at 10 km). The radar still operates at X-band, and the newer RVP-900 system permits more flexibility in signal processing. The results of the changes in the system were an improvement in the sensitivity and along-track resolution of the system, but a loss of data within 3 km of the radar. It is expected that this 3-km-radius tube following the flight track will eventually be eliminated using a short pulse.

The new radar was operated in Tropical Storm Franklin, and Hurricanes Harvey, Irma, Jose, Maria, and Nate. At the conference we will present examples showing the improvement in sensitivity of the radar, particularly in showing much more of the upper-level outflow of the tropical systems. Of particular interest were cases where systems were intensifying and the outflow was particularly prominent. We will also discuss challenges with the 2017 data, so those interested in the data will be properly informed. Using the new system to produce high-resolution analyses of convection has only just begun. We plan to present examples during the conference.