Abstract:

Based on the daily observation data of 10 weather stations in the Yili valley from 1961 to 2016 and cold air process monitoring standards, the frequency and intensity change characteristics of cold air processes with different grades from September to next May were analyzed by using linear trend, Morlet wavelet and correlation analysis method, etc. The results are as follows: (1) In the past 56 years, the annual average frequency of cold air processes in the Yili valley was 18.5 times. The frequency of cold air processes in middle and western parts of the valley was relatively more, and it decreased significantly in westward and eastward areas. The frequencies of cold wave and moderate cold air were more in the middle of the valley, while the frequency of strong cold air gradually decreased from west to east. (2) The frequency of cold air processes in the Yili valley was the highest in January and the lowest in May, and the cold wave and strong cold air processes concentrated in winter, while the moderate cold air processes tended to occur in September to October. (3) The minimum air temperature during cold air processes with different levels was the lowest in January and the highest in May. The cooling rate of cold wave and strong cold air processes was the strongest in December, while for moderated cold air process it was the strongest in October. (4) The frequency and cumulative days of cold wave process in the Yili valley presented an obvious decreasing trend, while the cumulative cooling rate of cold air processes decreased significantly as a whole during 1961-2016. The mutation of cold wave frequency from many to a few occurred in 2004, and the frequency of cold wave and strong cold air processes existed the interdecadal change periods of 26-year and 31-year, respectively. (5) The frequency of cold air processes with different levels in the Yili valley was negative related to the average minimum temperature in the corresponding period during 1961-2016, and the correlation between cold wave frequency and minimum temperature was the highest, while for precipitation and mean wind speed the correlation was weak.

Key words: cold air process, frequency, intensity, variation characteristics, the Yili valley

摘要：

利用1961—2016年伊犁河谷10个气象站逐日观测资料，依据冷空气过程监测标准，采用线性趋势、Morlet小波和相关分析等方法，对河谷各站9月至次年5月期间不同等级冷空气过程的频数与强度气候变化特征进行分析。结果表明：（1）近56 a来，伊犁河谷年平均冷空气过程频数为18.5次，河谷中、西部的冷空气过程频数较多，向东、西两侧明显减少。其中，寒潮和中等强度冷空气过程频数在河谷中部较多，向东、西两侧逐渐减少；强冷空气过程频数自西向东逐渐减少。（2）伊犁河谷冷空气过程频数1月最多，5月最少。其中，寒潮和强冷空气过程高发期在冬季，中等强度冷空气过程高发期在秋季9—10月。（3）各级冷空气过程平均最低气温均1月最低、5月最高，且寒潮和强冷空气过程降温幅度均以12月最强，而中等强度冷空气过程降温幅度最强在10月。（4）1961—2016年，伊犁河谷寒潮过程频数、累积日数均呈显著减少趋势，而冷空气累积降温幅度整体呈显著减小趋势；寒潮频数于2004年发生由多到少的突变，且寒潮与强冷空气过程频数分别存在26 a和31 a的年代际变化周期。（5）伊犁河谷各级冷空气过程频数与同期平均最低气温呈反相关关系，其中寒潮频数与最低气温的相关程度最高，而与降水、平均风速相关程度较弱。

关键词: 冷空气过程, 频数, 强度, 变化, 伊犁河谷