单站寒潮降温过程强度评估指标及其在乌鲁木齐市的应用

Evaluation index of cold wave intensity at a single station and its application in Urumqi

利用1951年1月1日至2015年12月31日乌鲁木齐市日最低气温资料,基于《寒潮等级》标准细化了寒潮降温过程的6项单要素强度指标,基于不同指标对乌鲁木齐市寒潮过程的强度进行了评估,并分析了乌鲁木齐市寒潮降温过程强度的变化特征。结果表明:以过程降温幅度或过程最低气温指数为评估指标,乌鲁木齐市冬季寒潮过程强度最大;以过程最大24 h降温幅度指数为评估指标,春季寒潮过程强度最大;以过程最大48 h降温幅度或过程最强气温距平偏低幅度指数为评估指标,秋季寒潮过程强度最大。基于综合强度指数IZ,1951—2015年乌鲁木齐市最强的寒潮过程出现在1952年11月25日至12月1日,春季最强的寒潮过程出现在2003年4月15—16日。近65 a乌鲁木齐市冬季寒潮降温过程强度最大,秋季次之,春季寒潮强度较弱。乌鲁木齐市秋季和冬季最强的10次寒潮过程中,有6次寒潮过程均出现在20世纪50年代;但春季最强的10次寒潮过程中,有5次出现在2000年之后。1951—2015年乌鲁木齐市年寒潮过程发生频数呈显著减少的趋势,寒潮过程强度也呈显著减弱的趋势,秋季寒潮过程发生频数的减少幅度最大;春季寒潮过程强度自20世纪80年代后略增大,在7个时间段中,2011—2015年春季寒潮过程的平均强度最大。

Based on the minimum temperature data from January 1,1951 to December 31,2015 in Urumqi and six intensity indexes extracted from＂Grades of cold wave＂（ GB /T 21987-2008）, the intensity of cold wave processes in Urumqi was evaluated. The variation of intensity of cold wave processes was analyzed. The results show that the intensity of cold wave processes depends on the selection of index. If a cooling range or the minimum temperature during this process is taken as an evaluation indicator, then the intensity is the strongest in winter. If the maximum cooling range within 24 h is taken as an indicator, the intensity of cold wave processes in spring becomes the strongest.The intensity of cold wave processes in autumn is the strongest if the maximum cooling range within 48 h or a lower amplitude of temperature anomaly is taken as an evaluation indicator. During the past 65 years（ from 1951 to 2015）, the strongest cold wave in Urumqi happened on days from November 25 to December 1,1952,based on integrative intensity index（ IZ）. The strongest cold wave in spring occured on April 15-16,2003. According to IZ,the strongest cold wave appears in winter followed in autumn. The intensity of cold wave appeared in spring is relatively weak. There are six cold wave processes appearing in the 1950 s among the top 10 strongest cold wave processes happened in autumn and winter and five cold wave processes appearing after 2000 among the top 10 strongest cold wave processes happened in spring of Urumqi. Both the occurrence frequency and intensity of cold wave process decreased significantly from 1951 to 2015 in Urumqi. During the past 65 years, the occurrence frequency of cold wave process in autumn decreased significantly. The intensity of cold wave process in spring has increased since the 1980 s,and intensity of cold wave process in recent five years（ from 2011 to 2015） is the strongest among the seven decades.