受地形影响的广西沿海前汛期降水日变化特征及成因

Characteristics and Mechanisms of Diurnal Variations of Precipitation During Pre-flood Season over Guangxi Coastal Region Influenced by Topography

关键词:  广西沿海  前汛期降水  日变化  K均值聚类算法

Key words:  Guangxi coastal region  pre-flood season precipitation  diurnal variations  K-mean clustering algorithm

摘要:

基于2010—2022年前汛期（4—6月）广西国家气象观测站、区域自动气象站逐小时降水数据及ERA5再分析资料，利用K均值聚类算法，依据前汛期降水日变化特征将广西沿海划分为3个研究区域。其中，区域1位于十万大山及其以北地区，区域2位于沿岸及离岸平缓地带，区域3位于六万大山一带。深入分析各区域降水日变化峰值特征及成因，结果表明：（1）广西沿海降水量、降水频率及降水强度日变化受地形分布影响显著。日降水量存在明显的清晨与午后双峰型、清晨单峰型和午后单峰型3种日变化特征；日降水量、日降水强度沿海岸线前沿向内陆递减；日内降水量与降水频率峰值自西南向东北延后约3~4小时。（2）区域1离岸近，海拔高，受海陆风、山地热力环流及夜间低空急流共同调制，日降水量偏少、日降水强度偏弱，但夜间降水最频繁。区域1夜间南支水汽输送强，携水汽翻越高山，配合局地上升气流，导致弱降水频繁；午后地形加热触发局地热力对流，形成日降水量双峰特征。（3）区域2夜间至清晨低层水汽辐合强，配合陆风促进沿岸降水发展，呈清晨单峰特征；其西部受十万大山地形阻挡作用，气流爬升显著，导致降水量多，清晨小时降水强度最强。（4）区域3午后海风叠加高地抬升气流，形成强盛的局地热力垂直环流，热对流降水频繁且强度较大，呈午后单峰特征，降水强度日峰值主要出现在正午12时。

Abstract:

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.