Abstract:
Doppler radar, when used in detecting largescale intense precipitation, has it
s echo features differing from the warm or cold advection alone (as an S or an
tiS shape) and also differing from the largescale convergence or divergenc
e (as a bowlike shape). The features of
Doppler velocity resulting from the combination of warm or cold advection with c
onvergence or divergence are called the complex windfield.
Based on the Doppler weather radar data in Tanggu, AWS data and EVAD technique,
analysis of Doppler weather radar data from an extensive, persistent strong rain
fall event over the Hai river basin on August 16, 2005 was conducted and gave th
e following results: (1) In the presence of a lowlevel complex windfield rel
ated to the combination of warm advection and convergence, it can be seen from t
he Doppler velocity products that, starting from the radar center, the clockwise
curvature of a zerospeed line on one side toward the positive velocity zone i
s more remarkable than the counterpart on the other side towards the negative ve
locity zone, implying that when the negative speed zone is bigger compared to th
e maximum positive area, rainfall is reinforced or maintained; (2) In the presen
ce of a lowlevel complex windfield resulting from warm advection combined wit
h divergence, the precipitation would be weakened or ceased. Therefore, the stud
y on the convergence and divergence in the radar velocity field gives a good ind
icator of nowcasting for the formation, development, maintenance and
decay phases of a largescale rainfall event.