Abstract: 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 (I_Z).The strongest cold wave in spring occured on April 15-16,2003.According to I_Z,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 1950s 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 1980s,and intensity of cold wave process in recent five years (from 2011 to 2015) is the strongest among the seven decades.

Key words: Cold wave, Evaluation index, Integrative intensity index, Occurrence frequency