1974-2013年甘肃冰雹日数的变化特征  

Variation Characteristics of Hail Days in Gansu Province During 1974-2013

作　　者：黄玉霞[1] 王宝鉴[1] 王研峰[2] 黄武斌[1] 孔祥伟[1] 谭丹[1] 李文莉[1] 

机构地区：[1]兰州中心气象台,兰州730020 [2]甘肃省人工影响天气办公室,兰州730020

出　　处：《气象》2017年第4期450-459,共10页Meteorological Monthly

基　　金：中国气象局预报预测核心业务发展专项(CMAHX20160214);国家科技支撑计划项目(2015BAC03B06)共同资助

摘　　要：利用甘肃省1974—2013年80个观测站的冰雹观测资料和NCEP/NCAR 1°×1°再分析资料,通过统计分析和物理量诊断等方法,对1974—2013年甘肃冰雹日数的变化特征进行了分析,结果表明:冰雹总的分布特征是高原和高山多,河谷、盆地、沙漠戈壁少,多年平均降雹日数在0.05~9 d之间,有三个高发中心,主要位于高原和高山地区,说明海拔高度对甘肃冰雹的形成具有重要影响。降雹最早始于3月,最晚结束于11月,主要发生在5—8月。近40年年冰雹日数呈明显的下降趋势,20世纪70一80年代是冰雹的高发期,进入21世纪以后迅速减少,全省而言每10年减少0.5 d。5—8月冰雹日数总体上也呈下降趋势,但各月的年际和年代际变化又具有显著的差异性。除河西地区外,甘肃其他四个区的年冰雹日数均发生了显著减少突变。对5月甘肃降雹偏多年和偏少年的对比分析表明,作为一种强烈的对流运动,降雹偏多年首先表现出对流不稳定能量的异常偏高,能够达到常年的两倍以上,其次发现环境温、湿层结在偏多年份朝着冰雹在积雨云中形成、增长及其落地前融化等一系列物理过程的有利条件方向发展,例如500 hPa有一明显的温度槽且较常年偏低2℃左右,低层水汽增多、中层减少,形成了"上干下湿"的不稳定层结配置,有适宜生长和降落的0℃层(3900~4500 m)和-20℃高度(6400~7000 m)。此外,200 hPa涡旋特征的出现保证了一支强上升气流支撑空中冰雹的增长。According to hail observation data based on 80 weather stations in Gansu Province and the NCEP/NCAR data with resolution of1°×1°, spatio-temporal characteristics of hail events during 1974--2013 in Gansu are analyzed by the methods of statistical analysis and physical diagnosis. The results show that hail occurs frequently in plateau and mountain regions but rarely in valley, basin, and Gobi desert. Annual mean of hail days is 0.05-9 days with three largest values in plateau and mountains, which indicates that the altitude plays an important role in the formation of hail in Gansu. The seasonal cycle shows that hail fails earliest in March, latest in November, and mainly from May to August. The hail days pres- ent an evident decreasing trend during the recent 40 years. Hail days decrease rapidly by 0.5 d/10 yr on average in the whole province since 21st century after a high incidence during the seventh--eighth decades of last century. The decreasing trend can also be found in hail days from May to August. However, its interannual and interdecadal variations are greatly different. Except in Hexi area, the annual means of hail days in the other four regions undergoes an abrupt change of decline. Comparison analysis of years with more and less hail days in May over Gansu reveals that： As hail is a product of severe convection, the most significant character in more hail years is the positive abnormal convective energy, which can be more than two times of the normal value. After that, environmental temperature and humidity level in the more hail years develop into favorable conditions for a series of physical processes of hail formation in cumulonim- bus, growing and melting before the hail falls to the ground. For example, there is an evident temperature trough at 500 hPa with temperature of 2℃ below normal value, and meanwhile, humidity increases in low level and decreases in middle level. Such condition is beneficial to form the unstable ＂upper dry and lower wet layer＂. The 0℃ layer （3900-4500 km）

关 键 词：甘肃 冰雹日数 年际和年代际变化 中尺度对流环境条件 

分 类 号：P467[天文地球—大气科学及气象学]