Spectrum width Patterns

Doppler velocity spectrum width is one of three base products generated by the WSR-88D weather radar. Compared to the other products the spectrum width is rarely used in the interpretation of weather phenomena. One of the difficulties in relating spectrum width features to weather phenomena is that the spectral width is a sum of contribution from different mechanisms (e.g., wind shears, turbulence, drop fall speed, antenna rotational speed, etc.). Furthermore, spectrum width fields are more susceptible to errors due to in proper radar set up. Nevertheless, in properly adjusted radars, these different contributors to spectrum width can be seen as characteristic features in RHI and PPI displays without additional data processing. The characteristic features of wind shears, turbulence, and drop fall speed exhibit signatures in the radar displays and will be shown in this paper. The data extracted from the spectrum width features can be used to estimate wind shears and turbulent dissipation rates in clouds and precipitation, and to identify the hazardous weather phenomena such as regions of strong shears and downdrafts.

Since large spectrum width values are often related to errors in the radar set up, departures of the spectrum width field from that expected based upon observations of the Doppler velocity and reflectivity fields could be used as a sensitive measure of the radar's deteriorating performance (e.g., improper AGC setting, the presence of overlaid echoes, etc.). The possibility to use the characteristic spectrum width patterns in the WSR-88D calibration procedures is also discussed.