89th American Meteorological Society Annual Meeting

Monday, 12 January 2009: 11:30 AM
The leading edge: using CASA radars to detect lower troposphere winds in quasi-linear convective systems
Room 130 (Phoenix Convention Center)
B. Philips, University of Massachusetts, Amherst, MA; and R. Przybylinski, J. Brotzge, D. J. Rude, W. Diaz, B. Dolan, and E. Bass
Identifying the genesis and growth of low-level mesovortices and straight line damaging winds along the leading edge of bow echoes and larger squall lines presents a challenge to warning forecasters. Several recent studies have shown that both tornadic and non-tornadic mesovortices often form below 3 km, in the lower troposphere, and therefore may not be well resolved by current WSR-88D scanning strategies at more distant ranges from the radar (greater than 150 km) due to the radar horizon. For example, some studies show that mesovortices may remain below 3 km during the first ten to fifteen minutes of their lifetime and the strongest rotation may often be observed between 1 and 2 km AGL.

This paper will discuss how CASA radar networks provide critical and timely data to facilitate the identification of these rotational and other low-level wind features and the potential impacts on severe weather warning and emergency manager operations. CASA, the center for Collaborative Adaptive sensing of the Atmosphere is a National Science Foundation Engineering Research Center developing systems of densely spaced, low power, X-band radar networks. CASA radar systems offer i) the ability to observe the lower troposphere (as low as 200m AGL) where these phenomena occur; ii) rapid (1 minute) volume scans at high spatial (100's m) resolution focusing on important areas of storm development; iii) dense spacing, with radars located approximately 25 km apart enabling a better viewing angle for observing the radial component of the wind than current long range radars; iv) overlapping radar coverage, providing multi-Doppler views of the velocity structures of the advancing line; and v) geographically specific data that matches the street-level scale of emergency management decisions. Two squall line events from May 30, 2007 and June 20, 2007 observed both by CASA and NEXRAD radars will be analyzed, along with NEXRAD only events. Comparisons of the reflectivity and velocity features from the CASA and WSR-88D radars will be shown in both cases.

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