Discrepancy Of Precipitation Diurnal Cycles Between The Tibetan Plateau And Its Neighboring Sichuan Basin In Warm Season

Satellite precipitation data has larger superiority than rain-gauge observation in the datasparse complex terrain area. However, satellite precipitation data need to be evaluated sincethey are indirectly achieved. The Tibetan Plateau (TP) and the Sichuan Basin (SB) aregeographically close but entirely different in physiognomy and elevation. Both the spatialpattern and the diurnal cycle of precipitation are distinct between the two regions. This studyaims to link diurnal cycles over the TP and SB together, and to further explain the mechanismof precipitation diurnal cycles. This research conducts the following studies:Firstly, COMORPH and TRMM3B42data for applicability in hourly-scale precipitationanalysis over the TP and its eastern neighboring regions of the SB are evaluated by using thehourly rain-gauge data in warm season (May to September) during2003-2008.Secondary, TRMM3B42is recognized as better data to reveal the climatologicallycharacteristics and interannual variability of the diurnal cycles of precipitation over the TP andthe SB.Finally, the mechanisms and their possibility association of the diurnal cycles ofprecipitation over the TP and the SB are explored based on the NECP/FNL reanalysis data.The main conclusions are as follows:(1) Compared with hourly rain-gauge data, the two satellite data perform better over the SBthan the TP and TRMM3B42performs better than CMORPH. This might be becauseTRMM3B42has already been combined with rain-gauge precipitation data. TRMM3B42is more consistent with the rain-gauge data over the TP and its neighboring SB bycomparison of mean hourly precipitation amount and frequency. More obviousdiscrepancy is found between CMORPH and the rain-gauge data. It is possibly due toincreased occurrences of light precipitation (0.1-1mm/hr), which may be a systematic biasof CMORPH. The diurnal cycles of precipitation reflected by in situ rain-gaugeobservation and the satellite products exhibit larger differences over the Tibetan Plateauthan over the SB. The discrepancy can be attributed to the fact that most rain-gaugestations over the Tibetan Plateau are located in valleys. Satellite data, especially TRMM3B42may complement the rain-gauge observations over the Tibetan Plateau, though more in-situ observations are valuable in reflecting meso-scale terrain influences.(2) The peak time of precipitation is found mostly in the afternoon in the area of the westlongitude area of90°and late afternoon to evening in the area of the east longitude area of90°over the TP by analysis of the TRMM3B42. Over the Sichuan Basin, TRMM3B42capture the late night to early morning rainfall peaks. A distinct propagation process ofprecipitation along the latitude belt exist form the TP to the SB.(3) Generally, the variability of the diurnal cycles of precipitation is fairly stable over the TPand the SB in warm season. The diurnal cycles of precipitation amount are more variablethan the precipitation frequency. The variability of diurnal cycles of precipitation existsover some local area of the TP and the East longitude area of105°over the SB.(4) The diurnal cycle of precipitation is close to the diurnal cycle of static instability andcirculation over the TP, while the diurnal cycle of precipitation is close to the diurnal cycleof southwest wind and relative humidity over the SB. The characteristics of the eastwardtransition of the upward motion coincide well with that of precipitation along the latitudebelt from the TP to the SB.