宁夏0℃积温时空演变特征分析

Space-time evolution of ≥0℃ accumulated temperature in Ningxia and its cause analysis

利用宁夏全区25个气象台站日平均气温资料,统计分析≥0℃积温的时空演变及其开始、结束日期的变化特征;采用复Morlet小波分析方法和Mann-Kendall突变检测方法,揭示了宁夏不同区域≥0℃积温的周期及突变特征;并对其演变成因进行了初步探讨。结果表明:近50 a宁夏各区域≥0℃的积温均呈增大趋势,积温的持续时间明显延长;全区及引黄灌区0℃积温在1997年出现由少到多的突变,在周期上存在3～4 a和9 a左右的长周期;≥0℃积温期间引黄灌区极端最低气温<0℃的出现日数明显减少,由此而引起的冻害也相应减少。造成宁夏≥0℃积温增加、持续时间延长的主要原因是气候变暖前后大气环流出现了明显调整。变暖前,500 hPa高度场上中高纬度地区,特别是巴尔喀什湖附近易于形成低槽,有利于极地冷空气南下影响宁夏区域,造成气温偏低,≥0℃的积温偏小;气候变暖之后,500 hPa环流场发生了显著变化,中高纬度地区经向环流减弱,纬向环流增强,不利于槽区的形成和发展,极地南下冷空气活动次数减小,下游大范围区域内的气温升高,对应的0℃积温增加。

Using daily mean air temperature data of 25 evolution of ≥0℃ accumulated temperature and its meteorological observations in Ningxia, the space -time beginning and ending dates are statistically analyzed. The pe- riod and sudden change of ≥0℃ accumulated temperature are revealed by complex Morlet wavelet analysis and Mann - Kendall mutation detection methods, respectively. And the cause of its climatic evolution has been primari- ly discussed through comparable analysis of atmospheric circulation characters between before and after climate shift. The results show that： during the past 50 years, the ≥0℃ accumulated temperature in the whole area of Ningxia shows an increasing trend, especially in the background of climate warming the increasing speeds are the most, with averaged increase of 231.8 ℃. The beginning time of stably ≥0℃ accumulated temperature has been early and ending time late, so its duration has became significantly longer, especially in the latest 10 years, with 8 day longer averaged in all Ningxia. The ≥0℃ accumulated temperature in the whole Ningxia and in the area of Yellow River Irrigation Area of Ningxia changed suddenly in 1997 from less to more, and there were about 3 -4 a and 9 a periods since 1960s. Among these periods the 9 a period is relatively stronger, and with the strongest in the 1990s. The days of extreme minimum temperature of -≤0℃ in the area of Yellow River Irrigation Area has been significantly reduced during the period of ≥0℃ accumulated temperature. So correspondingly the frost damages al- so should be reduced. And the related departments should adjust agriculture structure distribution in time according to the indices proposed in this paper. It is atmospheric circulation significant adjustment before and after climate warming that caused increasing trend and duration time longer of ≥0℃ accumulated temperature. Before climate warming change, in the high-mid latitude region on 500 hPa height, especially in area near Balkhash Lake, it was easy to form low trough, so it was advantage of cold air in the polar going down southerly and affecting Ningxia, and causing temperature lower, and ≥0℃ accumulated temperature smaller. While after climate warming change, the atmospheric circulation on 500 hPa changed significantly. The meridional circulation has been weakened, and the latitudinal circulation strengthened. This was disadvantage of low trough forming and developing, the numbers of cold air going down southerly from polar reduced, the temperature raised in the large-scale area of downstream, and so corresponding to the ≥0℃ accumulated temperature increase.