Comparison of the diurnal variations of precipitation east of the Tibetan Plateau among sub-periods of Meiyu season

Abstract

This study divides the Meiyu period (15 June–15 July) into three sub-periods according to the consecutive Meiyu precipitation days: TMY (typical Meiyu days; TMY), pre-TMY and post-TMY. It is shown that the eastward propagation and diurnal variations of precipitation during the three sub-periods are obviously different. The similar phase delay of precipitation from the eastern part of the Tibetan Plateau (TP) to the “second step” terrain during the three sub-periods is possibly caused by the propagation of precipitation systems originating from the eastern part of the TP, but the phase speed during the pre-TMY period is fastest due to the prevailing zonal wind speed. The precipitation continues to propagate eastward from the east of the “second step” terrain to the central Yangtze River valley during the pre-TMY and TMY periods, but the phase speed during the pre-TMY period is faster. During the post-TMY period, precipitation east of the “second step” terrain mainly appears in the afternoon. The diurnal variation of the horizontal wind anomaly and mountain–plain solenoid (MPS) circulations east of 110°E during the TMY period is more obvious than in the other two sub-periods. MPS circulations due to different terrain distributions are mainly responsible for forcing the diurnal cycles of precipitation over the TP and Sichuan Basin (SCB), but for the diurnal variation of precipitation over the Yangtze-Huai River Valley, MPS circulations coupled with the favorable synoptic patterns (Meiyu front) could intensify the precipitation and its diurnal cycles.