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通过时空匹配2002-2010年逐年3月1日至9月30日中国海拔3km以下地区671个国家站逐时冰雹观测资料和NCEP(National Centers for Environmental Prediction) FNL(Final Analysis)资料,以海拔1km作为分界线划分为两个阶梯区域(简称两级阶梯,并把两个区域分别简称为一级阶梯和二级阶梯),对表征中国两级阶梯冰雹天气的水汽、热力和动力环境条件进行了统计分析.考虑气温0℃层高度对形成冰雹天气的影响,首先用0℃层高度对样本进行过滤,然后对两级阶梯冰雹天气的环境物理量特征进行统计和对比分析.结果表明,两级阶梯冰雹环境的水汽、热力和不稳定能量差异显著,一级阶梯冰雹往往出现在具有更不稳定的层结结构、更多不稳定能量、更多水汽含量以及更强的垂直风切变环境中.一级阶梯冰雹的整层可降水量集中在15～41 mm,二级阶梯则集中在6～ 30 mm,无冰雹出现在整层可降水量超过56 mm的环境中.两级阶梯超过50％的冰雹均出现在最有利抬升指数为负值的不稳定环境中,最优对流有效位能分布则表明,超过75％的冰雹均出现在具有一定不稳定能量的环境中;但当最有利抬升指数大于2.8℃时,两级阶梯均不会出现冰雹天气;两级阶梯超过50％的冰雹均出现在强的垂直温度递减率环境中.多物理量的高概率密度区更显著地揭示了两级阶梯冰雹天气所需的物理量分布差异.这些结果为两级阶梯冰雹天气的主客观潜势预报提供了客观的统计基础和依据.“,”Based on the hourly hail observations of 671 stations and National Centers for Environmental Prediction (NCEP) Final Analysis (FNL) data from March 1 to September 30 during 2002-2010,the atmospheric environmental conditions for hail over the two-step terrain (shortly for first-step and second-step respectively) areas of China with altitude above sea level of 1 km as the dividing line were analyzed.The hourly hail data and NCEP FNL data were matched by employing a temporal-spatial matching method.Due to the close relationship between hail forming and the height of characteristic temperature layers,the samples were filtered by using height of 0 ℃ layer above the ground,and then the environmental parameters representing moisture content,instability,and triggers were carefully analyzed,and the scatter plots also were studied.The results show that the environmental moisture conditions,the instability and best convective available potential energy (CAPE) conditions favorable for hails over the two-steps were much different.The hails over the first-step always had stronger instability,more CAPE,more moisture,and stronger vertical wind shear.The main scopes of total precipitable water (PWAT) for hails over the first-step terrain was 15～41 mm,but for the second-step,it was 6～30 mm.Almost no hails reported as PWAT were greater than 56 nun over the two-steps.More than 50％ hails over the two-steps occurred under negative best lifted index (BLI) environment.If characterized by best CAPE,the percentage was greater than 75％.No hail was expected when BLI is above 2.8 ℃ over the two-steps.If measured by the vertical temperature lapse rate (TLR),more than 50％ hails happened under high TLR environments.The differences on environmental conditions favorable for hails over the two steps were revealed dramatically by the scatter plots and probability density of parameters.The results provide an objective basis for the subjective and objective hail potential forecasting over the two-step terrains in China.