Abstract:Doppler radar, when used in detecting large scale intense precipitation, has it s echo features differing from the warm or cold advection alone (as an S or an ti S shape) and also differing from the large scale convergence or divergenc e (as a bow like shape). The features of Doppler velocity resulting from the combination of warm or cold advection with c onvergence or divergence are called the complex wind field. 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 low level complex wind field 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 zero speed 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 low level complex wind field 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 large scale rainfall event.