Results on this page show the effect of different gridding techniques on the resulting dual Doppler kinematic and reflectivity structure for the 990223 event (21 UTC). In order to capture the convection sampled by the aircraft at the time of the TRMM satellite overpass, radar data were placed onto a cartesian grid extending out to 150 km from the S-pol radar. The beam-crossing angle criteria for dual Doppler synthesis was reduced from 22 to 20 deg in order to retrieve the 3-D wind field as far as possible north of the S-pol radar site.
In order to perform the cartesian gridding, the NCAR software program REORDER was utilized using two different methods to interpolate the radar data in polar coordinates to a cartesian system (i.e., the radius of influence). In the first method, a fixed radius of influence was selected with x=y=1.5 km and z=1.0 km. In this method, the program uses a selected weighting scheme (Cressman) to map data points within the radius of influence zone, independent of range. In the second method, a variable radius of influence was selected with the azimuth and elevation criteria equal to 1.65 deg (beamwidth of the TOGA radar). In this method, the radius of influence distance varies as a function of range (like a cone) so that the search for data points extends farther out at long range compared to short range.
As shown in the CAPPI's below, the effect of the variable radius of influence is to smooth the reflectivity field and fill in gaps compared to the fixed radius of influence (the smoothing and gap filling effect becomes more pronounced with height).
To better compare the different radius of influence techniques on the vertical structure of convection, the plots below show a comparison of volume averaged vertical air motion and reflectivity. In these plots, the red profile represents the results using the variable radius of influence while the blue profile represents the fixed radius of influence.