A study on the mechanism of the tropical cyclone remote precipitation

Based on CMA 24 h precipitation data, JTWC’s best track data set of tropical cyclones and the NCEP reanalysis data, the mechanism of the Tropical Cyclone Remote Precipitation (TRP) has been discussed. The statistical analysis shows that 14.7% tropical cyclones could produce the TRP events (TRPs) in 1971-2006. Majority of the events would last more than two days. A number of TRPs have the feature of wide distribution and high rainfall rate. High frequency of TRPs occurs in July and August. The statistical analysis also shows that there are two areas with the high frequency of TRPs, i.e, the area of encircling Bo Hai Sea (region Ⅰ) and the juncture area between Sichuan and Shaanxi provinces (region Ⅱ). The diagnostic study with inter-comparison between the two group data of TRPs and Non-TRPs indicates that the prominent differences in lower levels either in region Ⅰ or Ⅱ lay in that there exists the typhoon interaction with a westerly trough in TRP group and without a westerly trough in Non-TRP group but with the dry northwesterly flow instead. More over, it is found that tropical cyclones with TRP have strong southeast wet flow channel connected and Non-TRP cyclones without such channel. Obvious differences are also appeared in the upper level. In region Ⅰ, the jet stream is located to the north of the remote rainfall region, and it incurs the divergence and ascending motion for TRP. However, the upper level jet stream covers the region and induces the descending motion in the same region for Non-TRP. Similar results are showed in the region Ⅱ. The composite data analysis of the moisture fluxes budget in region Ⅰ and Ⅱ shows that tropical cyclones with TRP can transport moisture to reach the region Ⅰ and Ⅱ and moisture transport form the cyclones without TRP is restricted only in a local area. The moisture increases remarkably form the area of TRP. On the contrary, moisture decreases obviously in the same area without TRP. Moisture transport of a tropical cyclone plays an important role in TRP.