Planetary boundary layer heights over a sharp vegetation-contrast area during the DECODE field campaign

During the DEsert–Oasis COnvergence line and Deep convection Experiment (DECODE) field campaign, conducted from 5 July to 9 August 2022, an unprecedented number of daytime balloon-borne soundings were collected over the Hetao region in North China. Using these high-resolution observations, this study investigates the observational characteristics of planetary boundary layer heights (PBLHs) over this sharp vegetation-contrast area, where daytime PBLH measurements have been rarely available. A total of 386 soundings ranging from 1100 to 1800 LST (local solar time) were selected to derive PBLHs at multiple sites across irrigated croplands and deserts. During this period, the PBLHs across all sites average around 2000 m above ground, with a diurnal peak reaching approximately 2500 m. These sites occasionally experience exceptionally deep PBLs, reaching up to about 6000 m above mean sea level, when the lower troposphere exhibits weak stability associated with an upper-level cold low. The PBLHs over irrigated croplands are generally lower than those over desert areas, although the difference shows considerable variability, ranging from several hundred to more than a thousand meters. 在2022年7–8月开展的“沙漠–绿洲辐合线与深对流观测试验(DECODE)”中, 试验团队在华北河套地区白天密集开展了数百次小球探空观测.基于这些稀有的高时空分辨率资料, 系统分析了沙漠与灌溉农田等植被反差显著区域的大气边界层高度(PBLH)特征.结果显示, 白天边界层平均高度约为2000米, 午后可发展至约2500米;在高空冷涡影响,低层大气稳定度较弱的条件下, 边界层有时可显著加深, 最高接近海拔6000米.总体而言, 灌溉农田上空的边界层高度低于沙漠区域, 但两者差异具有明显的变率, 幅度从数百米到上千米不等.