受地形影响的广西沿海前汛期降水日变化特征及成因OA

This study investigates the characteristics of diurnal variations of precipitation during pre-flood season(April-June)over the Guangxi coastal region,using hourly precipitation data from national surface meteorological observatory stations and regional automatic weather stations,as well as ERA5 hourly reanalysis data from 2010 to 2022.Based on the K-means clustering algorithm applied to diurnal precipitation patterns,the study area was divided into three sub-regions:Region 1 in the Shiwan Mountains and their northern regions,Region 2 along the coastline and in the adjacent flat terrain,and Region 3 in the Liuwan Mountains.After analyzing the physical mechanisms driving these peak characteristics,the key findings are as follows.(1)Diurnal variations in precipitation amount,frequency,and intensity are strongly influenced by topography.The diurnal precipitation exhibits three distinct patterns:a bimodal pattern with morning and afternoon peaks,a single morning peak,and a single afternoon peak.Both daily precipitation amount and intensity decrease from the coastal to the inland areas.The peak phases of precipitation amount and frequency are delayed by 3-4 hours propagating from the southwest to the northeast.(2)Region 1,located near the coast at a relatively high elevation,is jointly influenced by land-sea breezes,mountain thermal circulation,and nocturnal low-level jets.Although this region features lower overall precipitation amounts and weaker intensity,it exhibits the highest frequency of nighttime precipitation.Strong nocturnal southward moisture transport interacts with orographic uplift,generating frequent but weak precipitation at night.Conversely,afternoon heating of the terrain triggers local convective activity,forming a double-peak pattern.(3)Region 2 shows a single morning peak driven by intensified low-level moisture convergence and land breezes during nighttime to early morning.The western part of this region is significantly influenced by the blocking effect of the Shiwan Mountains,with enhanced orographic lifting leading to higher precipitation amounts and stronger intensity.(4)Region 3 is characterized by a pronounced afternoon peak of convective precipitation.The inland penetration of the afternoon sea breeze and terrain-induced thermal updrafts generate a robust local vertical thermal circulation.This mechanism destabilizes the atmospheric stratification,leading to intense and frequent afternoon convective rainfall,with the maximum precipitation intensity primarily occurring at noon.