1960—2020年内蒙古荒漠草原连续无降水日变化特征分析

Variation characteristics of dry spell in desert steppe of Inner Mongolia during 1960-2020

基于内蒙古荒漠草原9个气象站逐日降水和美国国家环境预报中心(National Centers for Environmental Prediction,NCEP)/美国国家大气研究中心(National Center for Atmospheric Research,NCAR)再分析资料,利用统计方法分析了该地区1960—2020年连续无降水事件变化特点及异常年份环流特征。结果表明:(1)连续无降水事件最多出现在夏季,但平均持续日数和最大持续日数在夏季最短,短期连续无降水事件和较长期降水事件相间出现是夏季降水分配格局,而其他季节则相反。(2)研究区年均无降水日数为304.1 d·a^(−1),年均连续无降水事件次数为39.6次·a^(−1),年均连续无降水事件平均持续日数为8.0 d·a^(−1),年均最大持续日数为43.7 d·a^(−1)。(3)近61 a连续无降水事件3个参数变化不显著,但2005—2020年连续无降水事件次数显著增加而平均持续日数则显著减小。(4)年平均持续日数和最大持续日数均与连续无降水事件次数呈显著负相关关系,而平均持续日数和最大持续日数呈显著的正相关。(5)异常连续无降水事件期间对流层中高层有明显的温度、湿度和高度异常。

The long-term changing characteristics of dry spells during 1960-2020 are analyzed based on the daily precipitation data from nine meteorological stations and National Centers for Environmental Prediction(NCEP)/National Center for Atmospheric Research reanalysis data in the Inner Mongolia desert steppe of China in this paper.Additionally,the atmospheric circulation characteristics of extreme events(August 7th-14th,1979 for extreme precipitation event and August 9th-31st,2007 for an extreme dry spell event)are analyzed by the composite analysis method.The results show that:(1)dry spells mostly occur in summer,with the shortest mean and maximum length.Short dry spells and long precipitation events alternate in summer,whereas,long dry spells and short precipitation events appear alternatively in other seasons.(2)The annual mean non-precipitation day number is 304.1 d·a^(−1),with no significant trend in the last 61 a.The long-term annual mean is 39.6 times·a^(−1) for dry spell frequency,8.0 d·a^(−1) for the mean length of dry spells,and 43.7 d·a^(−1) for the maximum length of dry spells.(3)All the factors show no decreasing or increasing trend during 1960-2020,whereas,during 2005-2020 the number of dry spells apparently increased and the mean length of dry spells decreased(all passed the 90%significant test).The scatter density analysis shows that the most commonly seen number of dry spells per year is 40,while the mean length of dry spells is mostly concentrated around 6-8 d.The maximum length of dry spells is mostly seen between 30-50 d.(4)The mean length of dry spells shows a strong negative correlation(-0.91)with the number of dry spells and a positive correlation(0.61)with the maximum length of dry spells,while the number of dry spells shows a negative correlation(-0.51)with the maximum length of dry spells.All the spells passed 99%significant level test.(5)The extreme long-lasting dry spell year saw significant anomalies in temperature,humidity,and geopotential height mid and high altitude.During abnormal long-lasting dry spell event,warm anomaly and anticyclonic circulation were seen over 500 hPa level.At the 850 hPa pressure level,the west Pacific high extended westwardly and northwardly.The relative humidity shows a negative anomaly.All the above conditions are to the disadvantage of precipitation development.