西南地区夏季降水变化与青藏高原大气热源的关系

为进一步研究青藏高原大气热源对西南地区夏季降水的影响,用NCEP/NCAR1961~2022年的月平均再分析资料,网格距2.5˚ × 2.5˚、采用点相关分析、SVD分解、合成分析法及热源计算倒算法对西南地区62年夏季降水的时空分布特征及其与青藏高原大气热源的关系进行了详细研究,结果表明:1) 62年来,整个西南地区的夏季降水有减小的趋势,且西南地区的夏季降水存在三个高值区,高值区分别位于云南的南部地区、四川东部地区和贵州东南部地区,并且在降水高值区附近降水量的梯度也更大。降水量自东向西,自南向北逐渐减少,可以明显看出海拔较高的地区降水量较少。这与西南季风、复杂的地形地貌以及影响西南地区的环流系统等因素有关。2) 在青藏高原在1961~2022年均为大气热源,可以看出大气热源在1961年开始时较弱,随着时间逐渐增强,在70年代中期和80年代末期分别达到强度的最大值,之后大气热源逐渐减弱呈下降趋势,在2020年达到最低值。总体来看,从1961到2022年,青藏高原的大气热源强度呈现由强到弱的变化趋势,且存在一定的年际变化特征。3) 青藏高原地区(26˚00'~39˚47'N,73˚19'~104˚47'E),除东北部的少部分地区为较强冷源外和北部地区为较弱冷源之外,其余大部分地区全年平均均为大气热源,中部地区为较强的大气热源。4) 在青藏高原范围内,与西南地区夏季降水存在显著正相关的地区是高原东部地区的大气热源和高原西部地区大气热源,与西南地区夏季降水存在显著负相关的地区是高原北部地区。总体来说西南地区夏季降水与青藏高原大气热源存在显著的相关性且西南地区夏季降水与青藏高原大气热源具有较高的年际线性相关性。5) 青藏高原大气热源的异常增加会影响西南地区夏季降水的不均变化,部分地区夏季降水量异常增多且存在大值区,部分地区夏季降水量异常减少且存在大值区;而青藏高原大气热源的异常减小时,西南地区夏季降水的增加较均匀。

西南雨季降水变化的区域特征

为了更好地对西南雨季降水的时空变化特征进行研究,利用中国西南地区1960~2022年81个气象站点共63年的逐日降水量气象观测资料,通过旋转经验正交函数分解(REOF)、Mann-Kendall突变检验和Morlet小波分析等研究方法,揭示西南地区降水的时空分布特征、长期变化趋势以及周期变化特征。分析结果表明:1) 西南地区1960~2022年来主要有3个降水大值区,分别为云南南部、贵州西南部以及四川中东部地区,降水量分布自东、南向西、北逐渐递减。2) 在EOF分析的基础上进行REOF分解,将西南地区分为5个区:1区为云南区,2区为川西高原区,3区为川中区,4区为贵州区,5区为川东区。3) 5个区域的雨季降水除2区呈现缓慢上升趋势外,其余区域均呈现程度不同的下降趋势,5个区域的雨季降水突变主要集中在21世纪初期,且突变后呈现不同的变化趋势。变化周期主要以5~10a、准5a周期为主。In order to better study the spatio-temporal variation characteristics of rainy season precipitation in Southwest China, the day-by-day precipitation meteorological observations of 81 meteorological stations in Southwest China for a total of 63 years from 1960 to 2022 are utilized to reveal the spatio-temporal precipitation in Southwest China through the Rotated Empirical Orthogonal Function Decomposition (REOF), the Mann-Kendall Mutation Test, and the Morlet wavelet analysis and other research methods to reveal the spatial and temporal distribution characteristics of precipitation, long-term trends and cycle change characteristics in Southwest China. The analysis results show that: 1) there are three major precipitation areas in Southwest China from 1960 to 2022, namely, southern Yunnan, southwestern Guizhou, and east-central Sichuan, and the distribution of precipitation gradually decreases from east and south to west and north. 2) REOF decomposition is carried out on the basis of EOF analysis, and the southwest region is divided into 5 zones: zone 1 is Yunnan, zone 2 is the western Sichuan plateau zone, zone 3 is the central Sichuan zone, zone 4 is the Guizhou zone, and zone 5 is the eastern Sichuan zone. 3) The rainy season precipitation in the five regions shows a decreasing trend in varying degrees, except for region 2, which shows a slowly increasing trend. The sudden changes in rainy season precipitation in the five regions are mainly concentrated at the beginning of the 21st century and show different trends after the sudden changes. The change cycles are mainly 5~10a and quasi 5a cycles.

西南雨季降水变化与海温的关系

为了研究中国西南雨季降水变化和海温的关系,利用西南地区1960~2022年81站共63年的逐日气象观测降水量资料、同期英国哈德莱中心月平均海表温度(SST)资料(格点分辨率为1˚ × 1˚)、欧洲气象资料中心(ERA-interim)的月平均降水再分析资料(格点分辨率为0.25˚ × 0.25˚)。通过相关分析、经验正交函数分解(EOF)和奇异值分解(SVD)等方法,对西南雨季降水变化与全球SST之间的关系进行了研究分析,结果表明:1) 西南地区63年的雨季降水空间分布不均,呈现东多西少,南多北少的态势,同时,其与前冬、春季澳大利亚东北部太平洋,夏、秋季北印度洋和同期5⁓10月份的北印度洋海温呈现显著负相关关系,即关键区海温异常偏暖(冷),西南雨季降水偏少(多)。2) EOF分析表明:在第1模态下,前一年冬季和当年春季关键区海域海温的分布形式多呈现出西高东低的形式,包括了东太平洋冷舌和西太平洋暖池形态,并且在千禧年之前大部分都是海温多为偏冷状态;而千禧年之后关键区海温由偏冷转为偏暖状态。而当年夏秋季和雨季同期关键区海域海温呈现出全区一致偏暖状态,并且在90年代之后海温从偏冷转变为偏暖状态,其第2空间模态为印度洋正偶极子分布形式。3) SVD分解表明:关键区海温与川西高原地区雨季降水存在正相关关系,而与川东、黔南和云南呈现出一个显著的负相关性,不同季节的海温关键区影响的降水大值区域可能略有不同,但总体来说,当关键区海温异常偏高(低),川西高原的雨季降水异常偏多(少),而其余大部分地区降水异常偏少(多);其分解结果与相关系数的分析结果基本一致并且近年来西南地区的雨季降水呈现出逐年减少的态势。In order to study the relationship between precipitation change and sea surface temperature in the rainy season in southwest China, the daily meteorological observations of 81 stations in Southwest China from 1960 to 2022 for a total of 63 years were used measured precipitation data, the monthly mean sea surface temperature (SST) data of the Hadley Center in the United Kingdom (grid resolution of 1˚ × 1˚) and the monthly mean precipitation reanalysis data of the European Meteorological Data Center (ERA-interim) (grid resolution of 0.25˚ × 0.25˚). The relationship between precipitation change in the rainy season in southwest China and global SST was analyzed by correlation analysis, empirical orthogonal function decomposition (EOF) and singular value decomposition (SVD). The results shows: 1) The spatial distribution of rainy season precipitation in southwest China in 63 years was uneven, showing a trend of more precipitation in the east and less in the west, and more in the south and less in the north, and at the same time, it was significantly negatively correlated with the sea surface temperature in the Pacific Ocean in northeast Australia in the early winter and spring, the northern Indian Ocean in summer and autumn, and the northern Indian Ocean in May and October in the same period, that is, the SST in the key areas was abnormally warm (cold), and the precipitation in the southwest rainy season was less (more). 2) EOF analysis shows that in the first mode, the distribution of sea surface temperature in the key areas in the winter and spring of the previous year mostly shows the form of high in the west and low in the east, including the cold tongue of the eastern Pacific and the warm pool of the western Pacific, and most of the SST is in a cold state before the millennium. After the turn of the millennium, the sea surface temperature in key areas changed from cold to warm. However, the SST in the key areas of the key area in the same period of summer, autumn and rainy season showed a uniform warming state in the whole region, and after the 90s, the SST changed from cold to warm, and the second spatial mode was the normal dipole distribution of the Indian Ocean. 3) SVD decomposition showed that the sea surface temperature in the key area and the rainy season in the western Sichuan Plateau. There is a positive correlation with precipitation, and there is a significant negative correlation with eastern Sichuan, southern Guizhou and Yunnan, and the influence of key areas of SST in different seasons is positive. The precipitation area may be slightly different, but in general, when the sea surface temperature in the key area is abnormally high (low), the rainy season precipitation in the western Sichuan Plateau is abnormally biased more (less), while most of the rest of the precipitation is abnormally low (more). The decomposition results are basically consistent with the analysis results of the correlation coefficient and in recent years. The rainy season precipitation in southwest China shows a decreasing trend year by year.