The Impact of Mountain-Plains Solenoids on the Diurnal Variations of Warm-season Precipitation over China

This study first explores the diurnal variations of the warm-season precipitation to the east of the Tibetan Plateau over China using the high-resolution CMORPH precipitation data and the GFS gridded analyses during mid-May to mid-August of 2003-2009. Complementary to the past studies using satellite or surface observations, it is found that there are strong diurnal variations in the summertime precipitation over the focus domain to the east of the Tibetan Plateau. These diurnal precipitation cycles are strongly associated with several thermally driven regional mountain-plains solenoids due to the differential heating between the Tibetan Plateau, the highlands, the plains, and the ocean. The diurnal cycles differ substantially from region to region and during the three different month-long periods, namely, the pre-Meiyu period (May 15-June 15), the Meiyu period (June 15-July 15), and the post-Meiyu period (July 15-August 15). In particular, there is substantial difference in the propagation speed and eastward extent of the peak phase of the dominant diurnal precipitation cycle that is originated from the Tibetan Plateau. This diurnal peak has a faster (slower) eastward propagation speed, the more (less) coherent propagation duration, and thus covers the longest (shortest) distance to the east during the pre-Meiyu (post-Meiyu) period than that during the Meiyu period. The differences in the mean midlatitude westerly flow and in the positioning and strength of the Western Pacific Subtropical High (WPSH) during different periods are the key factors in explaining the difference in the propagation speed and the eastward extent of this dominant diurnal precipitation cycle.

High-resolution convection-permitting experiments are further conducted to simulates a few consecutive episodes of warm-season precipitation that features clear diurnal variations to the lee of a few mountain ranges. These numerical simulations further elucidate the role of thermally driven regional mountain-plains solenoids being instrumental in the diurnal variation of the warm-season precipitation over China.