Weather Center

Rapid-scan Radar Observations of the Time-height Evolution of Rotation During Tornadogenesis


Rapid-scan Radar Observations of the Time-height Evolution of Rotation During Tornadogenesis
Presented by Jana Houser, Ph.D.

10:25 a.m. – 10:50 a.m.

 

 

Over the last decade, high-resolution numerical weather models and rapid-scan radar platforms have shed new light on the spatio-temporal evolution of rotation associated with nascent tornadoes, particularly on fine spatial scales. The results from these recent studies have concluded that tornadogenesis, which historically used to be thought of as a top-down process, commonly follows a sequence of events more congruent with a non-descending process. While numerical models have become substantially more sophisticated and capable of resolving near-ground processes, to date, there has been a paucity of high-quality observations having sufficient spatio-temporal resolution to truly resolve real-world tornadogenesis events. Only a handful of such studies have analyzed tornadogenesis through this lens, and most of these document the evolution of significant tornadoes. Furthermore, near-ground observations (z<100 m AGL) are missing in most of these studies, owing to the inherent limitations of working with mobile radar data.

This presentation describes rapid-scan, mobile radar observations acquired over multiple recent spring field campaigns in the Central Plains of the US from the rapid-scan, X-band, polarimetric (RaXPol) radar. It analyzes high spatio-temporal resolution [volume updates occurring on O (20 s)] observations of severe new tornadogenesis cases for weaker tornadoes varying in intensity from EF0-EF2 by tracking 1) the evolution of the tornadic vortex signature (TVS), 2) the maximum velocity differential across the TVS, and 3) the pseudovorticity for five minutes prior to tornadogenesis through the first 2 minutes of the tornado. Six out of the eight cases collected near-ground data (within the lowest 100 m AGL). Results for seven out of the eight cases clearly indicate a non-descending evolution of the TVS. The interpretation of one case was dependent upon the radial velocity threshold used to define a TVS. In addition, it was discovered that many of these tornadoes were very shallow, being confined to heights < 1.5 km AGL.