Planned addition of a tail Doppler radar to the NOAA Gulfstream G-IV: Potential future opportunities for new flight profiles

In a separate oral presentation (see that abstract for more details), some new developments at the NOAA Aircraft Operations Center are to be discussed. Among the most exciting of these is the planned introduction of a Tail Doppler Radar (TDR) onto the Gulfstream G-IV-SP high altitude research and surveillance aircraft. Since its first operational flights in 1996, this aircraft has become a vital part of the highly successful effort to improve hurricane track forecast accuracy.

Flying at altitudes of 41,000 through 45,000 feet (near 150 millibars), the G-IV is able to release a pattern of dropsondes at prescribed locations over the sea in otherwise data sparse regions to more fully capture the synoptic environment that influences tropical cyclone and winter storm development and movement. The ingestion of these data into global models, as well as higher resolution nested models such as the GFDL and HWRF, has dramatically improved the ability of these models to initialize the location and intensity of deep tropospheric features surrounding a storm. This TC or winter storm surveillance mission can sometimes demand near round-the-clock flights as a major hurricane approaches the Eastern Seaboard or Gulf of Mexico (or in winter, if there are a series of cyclones moving across the North Pacific ).

Many early pioneers in describing the structure of hurricanes using aircraft reconnaissance data (such as William Gray and the late Noel LaSeur) stressed the importance of the high altitude flights conducted in the 1950s and 1960s that penetrated the upper portions of some intense systems near the tropopause. These early flights laid much of the groundwork for understanding the nature and magnitude of the warm anomaly that exists in the core region of TCs at high altitude as well as how cyclonic winds rotate at close proximity to the center then convert at greater radii to anticyclonic outflow. The mechanics of that transition in flow regimes are key to understanding mass divergence at the top of the storm and many aspects of hurricane intensification occurring below.

What is still lacking is high density three dimensional near in-situ depictions of air parcel motions within core convection in the upper tropospheric levels of an intensifying hurricane. While the WP-3 TDR flights have provided a wealth of such data in the lower layers of storms for many years, the highest resolution data is limited above the melting layer. The dilemma has been how to devise a methodology to collect TDR data using the G-IV but still avoiding high altitude direct eyewall penetrations (where, at such high altitides, turbulence and icing would potentially be prohibitively dangerous) and without performing such collection efforts at the expense of the critical synoptic surveillance mission described earlier.