Extended Abstract (124K)9.3
The P-3 Era of Airborne Hurricane Research
Hugh E. Willoughby, Florida International University, Maimi, FL
In 1976 and 1977 NOAA commissioned two WP-3D research aircraft, N42RF and N43RF. The original motivation for this procurement was confirmatory replications of the apparently successful STORMFURY hurricane amelioration experiments during the 1960s. With their large fuselage volume, shirtsleeve cabin environment, substantial electrical generation capacity, relatively slow true airspeed, and long range and endurance, these aircraft have proved to be nearly ideal platforms for hurricane research. The initial instrumentation suite included flight level measurements of thermodynamic and kinematic variables, horizontally and vertically scanning digital reflectivity radar, dropsondes based upon the Omega navigation system, hyrdometeor imaging and replication systems, and air expendable bathythermographs. The P-3s were operated by NOAA’s Research Flight Facility, now the Aircraft Operations Center (AOC). The primary users for the hurricane mission were scientists from the National Hurricane and Experimental Meteorology Laboratory, now the Hurricane Research Division (HRD) of NOAA’s Atlantic Oceanographic and Meteorological Laboratory. Their first hurricane flights were on 1-2 September 1977 in Anita as it made landfall on the Mexican coast south of Brownsville, Texas. Throughout the late 1970s, institutional difficulties prevented more cloud seeding, and the STORMFURY investigators turned their attention to unmodified hurricanes as controls for the modification experiments. The new observing platforms quickly revealed that hurricanes contained too little supercooled water for glaciogenic seeding to work. Moreover, unmodified hurricanes---particularly intense ones with small eyes that fit the STORMFURY experimental design---frequently formed a second eyewall that encircled the preexistent eye and supplanted it. This natural process, which exactly mimicked the expected result of cloud seeding, called into question the apparent success of STORMFURY and led NOAA to abandon hurricane modification. Studies of unmodified hurricanes revealed new paradigms for the vortex and convective scale structure of the eyewall and for the time evolution of the primary vortex. At the same time the new platforms supported pioneering of both airborne Doppler radar and passive and active microwave sensing of surface winds. The need to replace the STORMFURY mission led R. W. Burpee to initiate synoptic surveillance to improve track forecasts through more detailed observation of the flow around the hurricane vortex, see Sim Aberson’s talk in this session. Observations from the WP-3Ds played a key role in analysis of surface winds in landfalling hurricanes. Composites of airborne radar observations revealed the convective and mesoscale structure of hurricane vertical motions and hydrometeor distributions. Operational highlights of the late 1980s were extrapolation of the lowest western-hemisphere sea-level pressure ever reported in Hurricane Gilbert (888 hPa) on 13 September 1988 and the near loss of N42RF when it was damaged by an eyewall mesovortex during a low-level penetration to the center of Hurricane Hugo on 15 September 1989. Hugo subsequently passed onshore near Charleston South Carolina, causing $7B in damage, the largest toll in a hurricane to that date. Perhaps the greatest disappointment of the P-3’s operational life was the decision by AOC management not to fly any research missions when Hurricane Andrew struck southern Miami-Dade County, causing $25-30B in damage, the most expensive natural disaster in United States history. In the wake of Andrew, AOC and the P-3s moved from Miami International Airport to McDill Air Force Base near Tampa, Florida. Although the move greatly complicated the logistics of hurricane research missions, it also resulted in much better aircraft maintenance and reliability through availability of hangers and generally improved facilities generally. A second positive outcome of Andrew was Congress’ appropriation of funds to commission a Gulfstream IV jet airplane dedicated to the synoptic surveillance mission, along with new dropsosndes based upon the Global Positioning System (GPS). The new dropsondes revealed hurricanes low-level wind structure in unprecedented detail. As a result, forecasters at the National Hurricane Center adopted much improved techniques for estimation of hurricane surface winds, and incidentally reclassified Andrew from Saffir-Simpson category 4 to category 5. Although synoptic surveillance, improved assimilation of remotely sensed observations, and new generations of numerical models accelerated the improvement of track forecast errors, intensity forecasting remained a significant challenge---highlighted by the rapid intensifications of Andrew before landfall and of Hurricane Opal in 1995, which weakened even more rapidly than it had intensified in the last hours before landfall on the Gulf coast. Extensive, regrettably sparsely published, observations dating from the 1970s and results of a simple numerical model pointed to the importance of a warm ocean that stays warm and low vertical shear of the horizontal wind to rapid deepening. Additionally, sea-air interactions in the high wind regime are poorly understood. The dynamics of convection and Rossby waves in the highly rotational hurricane core are of great theoretical and practical interest. They are also ideal objects for observation by airborne dual-Doppler radar. Despite its addressing world–class scientific problems, HRD lost a substantial fraction of its best scientists as a result of austere funding during the 1990s, and was unable to recruit replacements. The now venerable aircraft are expensive to maintain and operate. It is by no means clear that the United States is willing to invest enough to sustain and enhance the unique resource for airborne hurricane research embodied in NOAA’s WP-3Ds into the 21st Century.
Session 9, Advances in hurricane forecasting and research during the past 50 years
Wednesday, 5 May 2004, 8:00 AM-9:30 AM, Le Jardin Room
Previous paper Next paper
Recorded presentation