Abstract:

:By using daily mean air temperature data of 22 meteorological observation stations located in the eastern Hetao area from A-
pril to October，the temporal and spatial evolution of ≥10 ℃ accumulated temperature and its beginning and ending date were statisti-
cally analyzed． Then，the cycle and abrupt change of ≥10 ℃ accumulated temperature were revealed by Morlet wavelet analysis and
Mann － Kendall test，respectively． Combined the atmospheric circulation fields before and after climate shift，the reasons leading to the
changes were also primarily discussed via contrastive analysis． The results show that the ≥10 ℃accumulated temperature in the eastern
Hetao area gradually reduced from north to south． The ≥10 ℃accumulated temperature of the whole area had been increasing during
the past 50 years，especially in recent 10 years the increasing rate with 76． 2 ℃ /10 a was faster and the rate of increase of irrigation
district in northern was the highest，while the mountain area in southern was the lowest． With climate warming，the beginning date of
≥10 ℃ accumulated temperature was earlier，yet the ending date was later，so its interval has obviously prolonged，especially in the
latest 10 years there was 7 days prolonging averaged in Ningxia． The ≥10 ℃ accumulated temperature of three regions of Ningxia hap-
pened abrupt change，the whole area and that in the irrigation district of the north and the mountain area of the south appeared in 1997
while the arid region of the middle in 1994． There were about 3 a，8 －9 a and 13 a cycles during 1961 －1990，among which the 3 a
period was relatively stronger and became the strongest in the 1990s． After the 1990s，there was a period of 9 a with its signal becom-
ing more and more strong especially in the 2000s．
The main reasons causing increasing trend and prolonging duration of the ≥10 ℃accumulated temperature were the significant ad-
justment of atmospheric circulation before and after climate warming． Before climate warming，the low trough was easily formed in the
high － mid latitude region on 500 hPa height，especially nearby the Balkhash Lake，which was beneficial for the cold air moving south-
ward from the polar for cooling． While after climate warming，the atmospheric circulation on 500 hPa changed significantly，and the in-
tensity of the two negative anomaly centres increased compared with before． Therefore，the meridional circulation weakened obviously，
while the zonal circulation strengthened，which wasn＇t helpful for the forming and developing of low trough，thus the activity of cold air
moving southward from the polar reduced and the temperature rised in the large － scale area of downstream．

Key words: eastern Hetao, ≥10 ℃accumulated temperature, the spatial and temporal evolution, causes analysis  

摘要：

利用河套地区东部宁夏 22 个气象台站 4 ～10 月逐日平均气温资料，统计分析了该区域≥10℃积温的时空演变及初日、终日的变化特征，采用复 Morlet 小波分析方法和 Mann － Kendall 突变检测方法，揭示了河套地区东部不同区域≥10 ℃积温的周期及突变特征，并初步探讨了演变成因。结果表明:近 50 a 河套地区东部≥10 ℃的积温均呈增加趋势，初终日间隔明显延长;≥10 ℃积温在 1997年出现由少到多的突变，在周期上存在 3 a 和 9 a 左右的长周期，主要原因是气候变暖前后大气环流在 1997 年前后出现了明显的长周期调整。1997 年前，500 hPa 高度场上中高纬度地区，特别是巴尔喀什湖附近易形成低槽，有利于极地冷空气南下影响河套地区东部，造成气温偏低，≥10 ℃的积温偏小;1997 年后，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少，下游大范围区域内的气温升高，≥10 ℃ 积温增加。

关键词: 河套地区东部, 10 ℃积温, 演变特征, 成因分析