Analysis of Echo Characteristics of Doppler Velocity in a Rainstorm Event

摘要

Doppler radar, when used in detecting large-scale intense precipitation, has its echo features differing than those from warm or cold advection alone (as an S- or anti-S- form) and than those just from large-scale convergence or divergence (as a bow-like shape) but the features of Doppler velocity resulting from the combination of warm or cold advection with convergence or divergence are called the complex windfield. Analysis of Doppler weather radar data from an extensive, persistent strong rainfall event over the Hai river basin on August 16, 2005 reveals that 1) in the presence of a low-level complex windfield related to the combination of warm advection and convergence, i.e., the Doppler velocity products show that, starting from the radar center, clockwise curvature of a zero-speed line on one side toward the positive velocity zone is more remarkable than the counterpart on the other side towards the negative velocity zone, implying that when the negative speed zone is bigger compared to the maximum positive area, rainfall is reinforced or maintained; 2) in the presence of a low-level complex windfield resulting from warm advection combined with divergence, the precipitation would be weakened or ceased. Therefore, the study on the convergence and divergence in the radar velocity field gives a good indicator of nowcasting prediction of the formation, development, maintenance and decay phases of a large-scale rainfall event.