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云南夏季旱涝与前期冬季环流变化的关系
The Relationship Between Rainfall in Yunnan Summer and the Circulation in Preceding Winter
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摘要: 夏季气候异常的前期信号特征分析一直是短期气候预测工作的重点。利用1948—2004年NCEP/NCAR月平均再分析资料、1961—2004年云南124个站的月平均降水和1948—2003年英国Hadley中心的月平均海温资料, 分析了云南夏季旱涝的时空特征, 探讨了云南夏季旱涝与前期大气环流和大气热力状态变化的关系, 发现云南夏季旱涝前冬12月—1月, 特别是1月东亚中高纬度地区的大气环流变化和赤道附近高低层大气的热力状态对云南夏季旱涝有重要的指示意义, 当前冬东亚大槽强 (弱), 冬季风强 (弱), 赤道附近高低层大气温度偏低 (高) 时, 后期云南夏季降水偏多 (少)。同时, 初步探讨了东亚冬夏季风环流变化的相互联系及热带海温变化的可能影响, 指出冬季到夏季印度洋和赤道西太平洋地区持续的海温异常有可能通过改变夏季海陆的热力对比, 进而影响夏季风活动和云南夏季降水的变化。Abstract: At present, in view of the limitation of the understanding of the atmospheric movement, the climate change projection depending completely on general circulation model (GCM) is in an immature period, and relying on the anomalous characteristic of early general circulation is still one of the main methods, particularly in provincial and regional meteorological observatory. So investigating on the prediction clue from early circulation anomalies is very important work, which may provides some scientific evidences to accurately predict the following climate anomalies. A lot of previous researches show the close inter-season linkage between early wintertime circulation and the following summer climate anomalies, the precipitation variations in different regions are not only the significant difference, but also the relationships between them, and early circulation anomalies are distinctly different which needs to be further investigated. Yunnan Province is located in Asian monsoon region and is commonly affected by East Asian monsoon and South Asian monsoon. Its climate anomaly is very complicated and different from those in other regions. Further study on the relationship between early circulation anomalies and Yunnan summer precipitation will be beneficial to improving the forecast accuracy and providing the accurate weather information for government's decision-making to prevent and mitigate the damages resulting from disastrous weather. Based on the monthly NCEP/NCAR reanalysis dataset from 1948 to 2004, 124 stations rainfall from 1961 to 2004 and sea surface temperature of the UK Hadley Center from 1948 to 2003, the temporal and spatial variation features of Yunnan summer (JJA) precipitation are firstly analyzed by using EOF and Morlet wavelet analysis method. Secondly, the relationship between the rainfall and preceding general circulation, air temperature is further investigated by using correlation and composite analysis methods. Yunnan summer precipitation in different regions trends to have the similar variation, and has a significant inter-annual variability and period circle feature with 2 and 4 years. The circulation anomalies in mid-high latitude region of Eastern Asia and atmospheric thermal situation from low-high layer in tropical India Ocean and Pacific Ocean in preceding December and January, particularly in January are significant signals indicating the following climate variation of Yunnan. The rainfall increases when East Asian trough deepens and East Asian winter monsoon (EAWM) strengthens, air temperature from low-high layer is cold. The opposite situation occurs when early East Asian trough weakens, EAWM weakens, and air temperature from low-high layer is warm. Furthermore, the anomalous characteristics of SST in tropical Ocean and its possible effect on the linkage relationship between East Asian winter monsoon and summer monsoon are also investigated. The results show that SSTA in tropical Indian Ocean and western Pacific Ocean keep unchanged from winter to summer, which will impact possibly EASM and rainfall in Yunnan summer by changing land-sea thermal contrast.
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图 1 1961—2004年6—8月云南124站降水量EOF分析的第一模态 (a) 和第二模态 (b)
Fig. 1 The first (a) and second (b) empirical orthogonal function (EOF) modes of 124 stations precipitation of Yunnan in JJA during 1961—2004
图 2 1961—2004年6—8月云南124站降水的第一时间系数距平 (a) 和相应的Morlet小波分析 (b)
(粗等值线区域表示云南夏季降水周期变化通过95%信度检验的区域)
Fig. 2 The first principal component time coefficient anomaly of 124 stations precipitation of Yunnan in JJA during 1961—2004 (a) with its Morlet wavelet analysis (b)
(the area encircled by thick solid line denotes that the period is over 95% level)
图 3 云南夏季正负降水异常年前期前一年10月—当年5月逐月500 hPa高度距平差 (等值线, 单位:gpm) 及t检验 (阴影区)
Fig. 3 Difference of anomalous monthly 500 hPa geopotential height from preceding October to succedent May in anomalous Yunnan summer rainfall years (isolines, unit: gpm) with t-test (shaded areas)
图 4 1961—2001年云南夏季降水与前冬1月850 hPa经向风 (a) 和纬向风 (b) 相关分析
(阴影区表示通过95%信度检验的区域)
Fig. 4 Correlations between Yunnan summer rainfall and meridional wind (a), zonal wind (b) in preceding January for 1961—2001
(shaded areas indicate changes at the 95% confindence level)
图 5 正、负降水异常年前冬1月沿135°~145°E的经向距平流场 (a, b) 和沿10°~25°N的纬向距平流场 (c, d) 剖面
(实线和虚线分别为经、纬向风的等值线, 浅色影阴区表示垂直速度大于0.005 Pa·s-1的上升区, 深色表示垂直速度小于-0.005 Pa·s-1的下沉区, 矢量箭头分别表示经向和纬向距平风矢)
Fig. 5 Meridional section along 135°—145°E average (a, b) and zonal section along 10°—25°N average (c, d) stream anomaly in preceding January in anomalous Yunnan summer rainfall years
(solid and dashed lines denote meridional and zonal wind; light shaded areas denote ascending flow with velocity above 0.005 Pa·s-1 and dark shaded areas denote descending flow with velocity below-0.005 Pa·s-1; arrow heads denote meridional and zonal wind anomaly)
图 6 正负降水异常年前期12月 (a) 和1月 (b) 地面温度距平差 (单位:℃) 和t检验 (阴影区), 以及云南夏季降水与12月 (c) 和1月 (d) 地面温度的相关分布
(阴影区为通过95%信度检验的区域)
Fig. 6 Difference of surface temperature anomalies and its t-test (shaded areas) in preceding December (a) and January (b), correlation between Yunnan summer rainfall and surface temperature in preceding December (c) and January (d)
(shaded areas denote exceeding the test of 95% level)
图 7 正 (a)、负 (b) 降水异常年前期冬季1月气温距平沿20°S~20°N的纬向剖面图
Fig. 7 Zonal section of 20°S—20°N temperature average in January of positive rainfall anomaly (a) and negative rainfall anomaly (b)
图 8 正 (a)、负 (b) 降水异常年夏季850 hPa的距平风合成 (单位:m/s; 阴影区分别表示通过95%, 98%和99%信度检验的区域)
Fig. 8 Composites of anomalous wind (unit: m/s) at 850 hPa (a) positive rainfall anomaly, (b) negative rainfall anomaly (shaded areas are exceeding 95%, 98% and 99% level, respectively)
图 9 1—8月正、负降水异常年赤道东印度洋 (10°S~10°N, 80°~110°E)(a)、赤道西印度洋 (10°S~10°N, 40°~80°E)(b)、西北太平洋 (10°~30°N, 120°~150°E)(c) 和赤道东太平洋 (5°S~5°N, 90°~150°W)(d) 海温距平的区域平均 (单位:℃)
Fig. 9 Regional averaged SSTA from January to August in equatorial east India ocean (10°S—10°N, 80°—110°E)(a), equatorial west India ocean (10°S—10°N, 40°—80°E)(b), northwest Pacific ocean (10°—30°N, 120°—150°E)(c), and equatorial east Pacific ocean (5°S—5°N, 90°—150°W)(d)
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