Mobile Doppler Radar

After VORTEX-94, it was apparent that a serious problem existed that could prevent an adequate evaluation of any VORTEX tornadogenesis hypotheses. It was not possible to sufficiently resolve and document the motion of air within a small region of the storm that potentially could give rise to a tornado: the mesocyclone. It was unlikely that a WSR-88D would ever be near enough to one of the target mesocyclones to provide the needed data. The airborne Doppler radars on the NOAA P-3 and NCAR Electra research aircraft only provided data approximately every 300 meters and failed to resolve the vitally important variations in wind immediately adjacent to the ground. Data from these aircraft will provide important new knowledge about the structure and evolution of airflow features ranging in size from the mesocyclone up to the entire storm. However, information was needed about wind variations in features ranging in size from tornadoes up to mesocyclones (100 meters up to about 10,000 meters). Solving this problem was the motivating factor behind the development of a research Doppler radar that was fully mobile, a system that could be driven right up to the storm or mesocyclone, parked, and set up to obtain volume scans of high-resolution Doppler velocity data.

Joshua Wurman had spent several years at NCAR developing innovative Doppler radar technology. In the fall of 1994 he joined the faculty at the OU School of Meteorology as an Assistant Professor. Teaming with him, the groundwork was laid for the development of the "Doppler-On-Wheels." With the support of NSSL, development funds were provided to VORTEX. This funding paved the way for the collaborative support of the National Science Foundation and the University of Oklahoma. In addition, an NSSL vehicle was modified to transport the radar. The mobile Doppler radar system employs a rugged antenna pedestal and dish that were used for military missile-tracking applications for a number of decades. The transmitter was provided by NCAR and is a spare X-band 3-centimeter transmitter formerly used with the NCAR CP-2 research radar. Mitch Randell and Eric Loew at NCAR ATD developed the receiver and signal processor for this application, while Paul Griffin and Dennis Nealson of NSSL largely built the system. This complicated equipment was built in a very short amount of time. Parts were ordered in November and December, and development, construction, and testing were carried out primarily in March and April of 1995.

The radar was first deployed in VORTEX on 12 May. A few days later, on 16 May, a tornadic supercell moved from Garden City through Kalvesta, Jetmore, and Hanston, KS. As the sun set, the mobile Doppler began scanning from a ridge west of Hanston. A tornado formed quickly and then intensified and remained on the ground for at least 45 minutes as it moved toward the east-northeast through open country. The mobile Doppler radar provided the first-ever reflectivity and velocity data near a tornado viewed with such tremendous resolution.