This study investigates the spatiotemporal characteristics of convective available potential energy (CAPE) in the Yangtze-Huaihe region during summer(2018—2022) using IGRA sounding data and ERA5 reanalysis data.A linear regression method was applied to develop a correction formula for ERA5 CAPE based on IGRA sounding observations,yielding a corrected dataset (CAPE_COR) for 08:00 BST and 20:00 BST on a daily scale.Correlation analysis shows that CAPE_ERA5 and CAPE_IGRA exhibit relatively strong agreement,with correlation coefficients of 0.58 at 08:00 BST and 0.59 at 20:00 BST.The scatter plot indicates that data points are densely clustered along the diagonal,confirming the accuracy of the correction.After applying the adjustment,the correlation coefficients between CAPE_COR and CAPE_IGRA slightly decrease to 0.57 and 0.58,respectively,demonstrating the reliability of the correction formula and its improved representation of the actual convective environment.
Spatially,summer CAPE_COR in the Yangtze-Huaihe region exhibits a distinct geographical pattern,increasing from southeast to northwest and from river valleys to mountain peaks.High CAPE_COR values are primarily concentrated in the Yangtze River valley,particularly in areas enclosed by three major mountain ranges,while lower values are observed over higher elevations.This distribution highlights a strong correlation between CAPE and topographic features,with higher CAPE_COR values more frequently occurring in the Yangtze River valley and weaker values over elevated terrains.Further analysis reveals that CAPE_COR at both 08:00 BST and 20:00 BST is negatively correlated with terrain height and positively correlated with the terrain index,suggesting that areas with lower elevations and steeper slopes exhibit stronger convective energy.These findings emphasize the influence of topography on local convective conditions,where low-altitude valleys with pronounced terrain gradients are more conducive to the accumulation of convective energy.Temporally,CAPE_COR in the Yangtze-Huaihe region exhibits significant intra-seasonal and diurnal variations.The seasonal fluctuation exceeds 1 400 J/kg,peaking at approximately 1 800 J/kg in late July.The diurnal cycle follows a distinct pattern:CAPE_COR decreases in the early morning (00:00 BST—05:00 BST),rises sharply from morning to mid-afternoon (05:00 BST—15:00 BST),and then declines again in the evening and night (15:00 BST—24:00 BST).During the daytime (08:00 BST—20:00 BST),CAPE_COR consistently exceeds 1 000 J/kg,while at night (20:00 BST—08:00 BST),it remains below 1 000 J/kg.The daily minimum occurs around 05:00 BST (approximately 850 J/kg),while the maximum appears at 15:00 BST (around 1 200 J/kg).This diurnal cycle indicates that convective activity peaks in the afternoon,coinciding with maximum solar heating,and weakens during the early morning hours.
Overall,this study underscores the critical role of geographic and topographic features in shaping the spatial and temporal distribution of convective energy in the Yangtze-Huaihe region.These findings enhance the understanding of CAPE characteristics and provide a valuable scientific basis for improving severe weather forecasting and advancing knowledge of convective processes in complex terrain.