P3 Aircraft

In VORTEX-94 and 95, the National Oceanic and Atmospheric Administration's WP-3D aircraft, operated by the Air Craft Operations Center, was used to document the evolution of storm structure. The P-3 is equipped with two radars that utilize several techniques for scanning. The lower-fuselage radar is a 5.6 centimeter C-band radar. It scans horizontally, giving the scientist the 'big picture' while also monitoring the evolution of the targeted storm in its lowest layers. The tail radar is a 3.2 centimeter X-band Doppler radar that scans vertically. To obtain pseudo dual-Doppler measurements, the radar antenna can be alternately slewed fore and aft of the direction perpendicular to the fuselage by as much as 25 degrees. To maximize the spatial resolution, the tail radar antenna can be sectorized to one side of the aircraft. To further increase the spatial, along-track resolution, the "Alternate Fore-Aft Scanning Technique" (AFAST) is employed. Using AFAST, only fore scans are executed as the aircraft approaches the target storm, and only aft scans as the aircraft passes and moves away from the target.

During VORTEX, back-and-forth aircraft patterns were flown on the inflow side of the storm targeted by the field coordinator, Erik Rasmussen. The aircraft was flown in the lowest 300-2000 meters above ground level to optimize radar data collection in the region most likely to experience tornadogenesis. The turbulent ride along the boundary between warm moist inflow winds riding up over strong rain-cooled outflow was called "surfing the outflow" by the P-3 pilots. Usually this region was as close as the pilot could fly since the cloud boundary was just several hundred meters from the aircraft. The plane was as close as 7 km to the F3 tornado that occurred in open country between Newcastle and Olney TX on 29 May 1994. Normally the pilot maintained a distance within 10 to 15 km of the storm center.

The unique set of data that were obtained from the air has provided a new set of challenges. With the tail radar's Nyquist velocity of +/- 13m/s, and expected radial velocities of 50 to 80 m/s, extensive clean-up of the radar data is required. NSSL scientists are working to analyze these data from the aircraft, hoping to find clues to the evolution of storms and the tornadoes that they produce.

Irv Watson