Research on the Key Method of Radar Derived Precipitation Estimation over the Tibet Plateau

Radar-derived quantitative precipitation estimation (QPE) product has become the basic references for the research on weather and climate. However, it is great challenge for the radar-derived QPE over the Tibet Plateau because the radar in this area can be seriously blocked by terrain, such estimation can also be significantly affected by the brightband, and the rain gauges are so scarce. In this paper, a new hybrid scan algorithm based on the reflectivity climatology has been proposed. Being independent on the terrain data, the climatology-based hybrid scan method provides a more accurate the lowest unblocked elevation, thus, the effects of terrain blockage on QPE has been reduced. The climatology-based hybrid scans are then used to examine the spatial coverage provided by the six operational weather radars over the Tibetan Plateau. By calculating the mean vertical profile of reflectivity from radar observations, the areas impacted by brightband can be identified and corrected. VPR correction was found to be effective in reducing the root mean square error and increasing the correlation coefficient in radar-derived QPE, and the errors of QPE due to brightband effects has been decreased. Based on the height of Brightband top and brightband bottom by brightband identification, the precipitation areas of stratiform cloud is divided into three areas: the solid precipitation area above the height of brightband top, the liquid precipitation area below the height of brightband bottom, the area effected by bright band between the height of brightband top and the height of brightband bottom. Meanwhile, the climate Z-R relationship of these three areas has been worked out respectively: (above the brightband), (below the bright band) and (the brightband correction area), thus decreasing the errors of QPE caused by inappropriate Z-R relationship. It is further improved that the accuracy of radar-derived QPE in areas with rare rain gauges through the racalibration by average calibration method.