The Application Of Doppler Weather Radar In The Quantitative Measurement Of Precipitation And Short-time Heavy Rainfall Forecast

This article is completed under the patronizing of Sichuan MeteorologicalAdministration, landslide and debris flow specific (Project number: GYHY201006039).It is not uncommon that flash floods, urban waterlogging and geological disasters arecaused by short-time heavy rainfall, but so far, the forecast level is far from meeting thedemand of National Disaster Prevention and Mitigation. In addition, because of thetimely and accurate remote sensing capability, Doppler Weather Radar plays animportant role in monitoring and early warning of small scale severe weather. As aconsequence, it has very important practical significance for governments to organizedisaster prevention and mitigation, develop economy by carry out the research aboutDoppler weather radar in the warning and forecast of heavy rainfall.By use of radar, lightning and gauge data form June-September,2009-2011, thepaper has researched the Z-I relationship around effective detection range of Chengduradar though optimization technique first, for establishing the suitable algorithm aboutChengdu radar quantitative measurement of precipitation and highlighting the role ofradar in precipitation estimation. Secondly, it has analyzed the characteristics of radarand lightning in short-time heavy rainfall, much reference value were obtained forimproving the nowcasting of short-time heavy rainfall. The main conclusions of thestudy are as follows:1. The study has established the different Z-I formula in experimental region basedon the precipitation type, location and altitude, and the Z-I relationship of convectiveprecipitation in Chengdu is Z=255I1.43. After calculation, the error of estimated rainfallby these Z-I formula was under15%, which was better than Z=300I1.4, and theaccuracy of radar precipitation estimation has improved.2. When using the Z-I relationships for rainfall and its distribution retrieval, itfound that Z=255I1.4is better than Z=300I1.4, The precipitation intensity and area havecoincided with the real value, and the inversion of convective region is better than thestratiform precipitation region.3. It has required many important parameters for the forecast about precipitation area and its intensity. These regions of strong echo, heavy convergence, headwind,strong VIL, substantially correspond with heavy rainfall area.(1)In short-time heavyrainfall, the echo intensity is35-55dBz, echo top is8-12km, echo more than35dBzconcentrate in3-8km, and the strong echo more than45dBz is about5-6km, thecentroid of echo is a bit low.(2)On the other hand, there always been headwind area,convergence of wind direction and speed, small-scale systems, bull’s-eye (LLJ) invelocity field. The presence and persistent of headwind area showed that convectiveactivity was very strong, and the heavy rainfall would be sustained, which provide awarning in the short-time heavy rainfall nowcasting.(3)Finally, the VIL was alwaysmore than35kg·m-2, and it even more than45kg·m-2in the heavy precipitation center.4. In the short-time heavy rainfall, there are many very active negative CGlightning, which accounted for more than90%. Lightning activity is closely related tothe convective precipitation, only few lightning occurred in stratiform precipitationregion. The negative CG lightning intensive areas substantially correspond to the strongecho region (more than35dBz), and the direction of them is basically consistent.5. The negative CG lightning appear and its frequency increase can warn the heavyrainfall. Negative CG flash rate suddenly increase can indicate the beginning ofpersistent heavy rainfall, and its peak has a good indicating significance for rainfallintensity peak. From the statistical analysis of100short-time heavy rainfall, the studyshowed that the negative CG lightning rate suddenly increase and continuously growth6-30min later,83%of the events appear persistent heavy rainfall (6min accumulatedrainfall≥2mm). After the peak value of negative CG lightning6-30min, there isprecipitation peak in67%of the events. The rate of negative CG flash and intensity ofprecipitation has a same trend change over time, there are singlet, multi-peak.