Diurnal variation in short- and long-duration precipitation within the Dabie Mountain region in Central China

Diurnal variation in regional precipitation in Central and East China has been broadly identified in previous study. This study focused on clarifying not only the differences in the diurnal variation concerning the local precipitation occurred in the Dabie Mountain (DBM) region and the regional precipitation occurred through the middle-lower reaches of the Yangtze River Basin, but also the association mechanism between diurnal variation in local precipitation with differing duration and diurnal modulation of ambient circulations driven by large-scale background synoptic force or local-scale orographic force of the DBM. It was found that cases of short duration precipitation (SDP, duration <6 h) and cases of long duration precipitation (LDP, duration >= 6 h) exhibit vastly different patterns of diurnal variations. Further investigation revealed that the primary pattern of the ambient circulation responsible for SDP and LDP is the recycling transformation between a closed cyclonic circulation to a cyclonic wind shear, and the recycling movement of a closed cyclonic circulation in the lower troposphere respectively. Although the diurnal variation in LDP exhibited greater orographic regional differences between the west slope (WS) region and the east slope (ES) region in comparison with that of SDP, topographical sensitivity experiments of the DBM and detailed analysis of background synoptic systems associated with LDP indicated that this regional orographic difference shows closer association with eastward propagation of background synoptic systems than orographic effects of the DBM. Respective strengthening of upward vertical motion at different levels of the troposphere during diurnal variation in SDP and LDP cases provide substantial evidences to reconfirm the close association with orographic force in lower the troposphere for SDP cases and background synoptic force in middle troposphere for LDP cases. Further quantitative diagnosis also confirmed that the orographic effects of the DBM is conducive to cause marked differences in the diurnal variation in SDP cases between the WS region and the ES region via adjustment of the upslope wind over the former and the circumventing wind over the latter.