西北干旱区和黄土高原大气边界层特征对比及其对气候干湿变化的响应

利用西北干旱区民勤、 黄土高原平凉和榆中3站2006-2009年1、 4、 7月和10月逐日08:00时和20:00时探空资料、 降水和日最高气温, 计算和对比分析了最大混合层厚度(ML)、 逆温层特征和垂直温湿场及其对干湿气候变化形成的影响. 结果表明: 最大混合层厚度与最高地气温差关系较为密切, 呈显著正相关, 干旱区民勤较密切其相关系数达0.92. 最大混合层厚度4月最深厚, 干旱区民勤高达2 871 m, 明显高于黄土区两站200~400 m左右, 平凉最为浅薄, 1月不足1 000 m; 但日降水量≥5 mm的降水发生时榆中较深厚, 高于其他两站300~400 m. 强降水发生前后干旱区湿度变化大, 发生时高低空湿度迅速增大, 而黄土高原变化湿度小, 榆中中低层增湿较明显. 干旱区近地层较干, 但有降水时中高层增湿较黄土高原显著. 干湿气候变化与最大混合层厚度、 逆温层的频数和强度、 近地面层的干湿程度关系密切, 混合层越深厚, 逆温层多而强, 近地层越干, 干旱加剧.

Atmosphere Boundary Layer Characteristics and Their Responses to Wetness Change over Arid Regions and Loess Plateau in Northwest China

Utilizing the daily sounding data observed at 08: 00 and 20:00, precipitations and maximum temperatures of Minqin in arid region, Yuzhong and Pingliang in Loess Plateau in January, April, July and October during 2006-2009, the maximum atmospheric mixed layer depth (hereafter ML), inversion layer characteristics, vertical T-Td field and their impacts on the wetness are calculated and analyzed. It is found that the maximum ML depth has a positive correlation with the difference value between the maximum ground temperature and the maximum air temperature, with a correlation coefficient up to 0.92 in Minqin. The maximum ML depth is deepest in April, reaching 2 871 m in Minqin, 200~400 m higher than that in the two stations in Loess Plateau; the maximum ML depth in Pingliang is the thinnest, less than 1 000 m in January; However, the maximum ML depth in Yuzhong is 300~400 m higher than that in the other two stations when daily precipitation ≥5 mm. Humidity changes greatly in the arid regions before and after a heavy precipitation. When daily precipitation ≥5 mm, humidity rapidly increases from high level to low level over arid regions, but it is less increases over Loess Plateau, with an obvious increase in Yuzhong from middle level to low level. Arid regions in Northwest China are drier near surface, but humidity from high level to middle level obviously increases as precipitation going on. Wetness change has a positive correlation with maximum ML depth, inversion's frequencies and strength, wetness characteristics near surface. The deeper maximum ML depth, more and stronger inversion and drier near surface are, the worse the drought is.