Storm divergence from the Aggie Doppler Radar (ADRAD): Synoptic forcing and convective/stratiform variations
Cameron R. Homeyer, Texas A&M University, College Station, TX; and A. J. Wiley
Horizontal divergence was calculated from over 60 hours of data collected from the Aggie Doppler Radar (ADRAD) from June 2006 - September 2007. ADRAD is an S-band radar located on the campus of Texas A&M University in College Station, TX. The divergence was calculated using radial velocities within a 100 km range of the radar based on the technique of Mapes and Lin (2005). Each storm hour was classified by its synoptic forcing (frontal or non-frontal) and rain type (convective or stratiform). Frontal forcing includes cold fronts, warm fronts, and stationary fronts. Non-frontal forcing includes upper-level disturbances, low- to mid-level cyclones, shortwaves, and seabreezes. Dynamical forcing of each storm was determined by observing surface maps, upper air maps, and satellite images. The separation of rain into convective and stratiform categories was determined using reflectivity cross-sections and contoured frequency altitude diagrams (CFADs). When surface reflectivity was weaker and reflectivity maxima predominantly occurred at mid-levels (i.e., resembling a bright band signature), the hour was classified as stratiform. When surface reflectivity was more intense and reflectivity maxima predominantly extended from the surface upward, the hour was classified as convective.
Initial results suggest that storm divergence is larger at upper levels when the dynamical forcing is frontal in nature. In addition, convection has a low-level convergence closer to the surface and divergence extending to higher heights in frontal situations. The midlevel convergence in the stratiform region appears to be elevated with a more narrow vertical extent when forcing is frontal. Other features of the storm systems, such as region of origin and environmental wind shear, will be discussed. These variations in storm divergence can potentially provide a better understanding of mesoscale-synoptic interactions in southeast Texas and the larger subtropics.
Poster Session 1, Student Conference General Poster Session
Sunday, 20 January 2008, 5:30 PM-7:00 PM, Exhibit Hall B
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