西南雨季降水不同年代水汽输送对比分析

为了研究西南地区雨季降水不同年代水汽输送的对比,选取了云南和四川的全部地区,以及贵州和重庆的部分地区共81个气象台站资料,从1960年伊始,到2022年的每年雨季的观测资料,还采用了ERA5从1940年至今的压力水平和单一水平的月平均数据,数据的分辨率是0.25˚ × 0.25˚。凭借天气学诊断分析、multiquadric插值算法、相关系数的显著性检验等方法,对西南地区的雨季不同年代水输送进行了详尽的对比分析,其研究结论表明:1) 西南地区整体水汽输送与全球气候变化紧密相关,水汽输送的基本形势是地形上西北方位弱,正东和正南方位强。拥有的若干传统高值区在近30年来均呈减弱趋势,其中云贵交界减弱最为明显,而传统低值区的水汽输送趋势与整体保持一致。2) 对于传统的高值区,水汽输送情况并不一致。对于传统高值区,近30年来减弱程度从高到低分别为云贵交界,雅安周边,云南南部,雅安周边和以及云南南部还将维持稳定的高值降水。3) 存在一个异常带,约位于104˚E附近,这些区域常与西南地区整体呈相反趋势,拥有独立的水汽输送通道,是异常水汽输送的高发区。异常带有向周围扩散的趋势,表现为沿104˚E线向外扩散,这一异常带更多受到来自孟湾向北方向的水汽输送,并引导产生异常降水,伴随西南整体周期性的水汽输送增强和异常降水增多,104˚E周边地区将易发异常低值。To study the contrast of water transport during the rainy season across different decades in Southwest China, data from 81 meteorological stations in Yunnan and Sichuan provinces, as well as parts of Guizhou and Chongqing, were selected. The observation data span from the rainy seasons of 1960 to 2022, and ERA5 monthly average data from pressure levels and single levels, with a resolution of 0.25˚ × 0.25˚, were used from 1940 to the present. Using synoptic diagnostic analysis, multiquadric interpolation algorithm, and significance tests of correlation coefficients, a detailed comparative analysis of water transport during the rainy seasons in different decades in Southwest China was conducted. The study concluded that: 1) The overall moisture transport in Southwest China is closely related to global climate change, with a basic pattern of weak transport in the northwest and strong transport in the east and south directions due to topography. Traditional high-value areas have shown a weakening trend in the past 30 years, with the Yunnan-Guizhou border weakening the most significantly, while the trend in traditional low-value areas remains consistent with the overall pattern. 2) For traditional high-value areas, the moisture transport situation is not uniform. In the past 30 years, the degree of weakening from highest to lowest is as follows: Yunnan-Guizhou border, around Ya’an, and southern Yunnan. Both around Ya’an and southern Yunnan will maintain stable high-value precipitation. 3) There is an anomalous belt approximately located near 104˚E, where these regions often show a trend opposite to the overall trend in Southwest China, having independent moisture transport channels and being high-incidence areas of anomalous moisture transport. This anomalous belt shows a tendency to spread outward along the 104˚E line, more influenced by moisture transport from the north of the Bay of Bengal, leading to anomalous precipitation. Accompanied by the periodic enhancement of moisture transport and increased anomalous precipitation in Southwest China, the areas around 104˚E are prone to anomalously low values.

西南雨季降水异常大气环流特征

为了研究造成西南雨季降水异常的大气环流特征,利用西南地区81个气象站1960~2022年的逐日气象降水量观测数据和同期NCEP/NCAR逐月再分析数据集,水平分辨率为2.5˚ × 2.5˚,运用合成分析和显著性检验等现代气候统计诊断分析方法对西南地区63年来雨季降水异常的高低层大气环流场、其他物理量场以及水汽输送场进行了研究,结果表明:1) 西南雨季降水空间分布不均,雨季降水三个大值区,分别位于四川省中部雅安、峨眉山和乐山一带,云南南部地区以及云南西部地区,且多雨区和少雨区呈交替分布。西南雨季降水长期变化趋势呈微弱递减的趋势,且存在明显的年际变化特征,总的来说降水偏多年主要集中在70年代以前,偏少年集中在2005年以后,西南地区降水有一定的年代际变化特征。2) 多雨年南亚高压较常年偏弱,南支槽活跃,贝加尔湖高压增强,整体为经向环流,西南地区产生显著的西南风异常,有利于对西南地区的水汽输送,有利于降水。少雨年南亚高压较往年偏强,高压中心偏东,整体为纬向环流,中南半岛西北风异常风场形势不利于孟加拉湾水汽向西南地区的输送,会导致降水偏少。西南雨季的垂直运动具有区域性,多雨年在云南西南部和四川东部垂直运动较强。少雨年在四川东部垂直运动较强。3) 多雨年孟加拉湾中部存在一气旋性距平水汽输送,其南侧有显著的西南向水汽通量输送带,说明孟加拉湾南部对西南地区的水汽输送加强。在两广和湖南一带有反气旋性距平水汽输送,南侧存在东南向水汽通量距平,表明来自南海的水汽向贵州、重庆及四川东部输送加强。西南地区多雨年的水汽通量散度距平从南向北表现为“辐合–辐散–辐合”的空间分布,水汽汇集的大值区位于四川东部和云南的南部。少雨年云南存在气旋性水汽通量距平,印度半岛东部有反气旋性水汽通量距平,前者后部和后者前部的北向水汽通量距平在中南半岛汇合,减弱了孟加拉湾北部对西南地区的输送。从孟加拉湾南部来的西南向水汽通量距平在中南半岛转为自西向东的水汽通量距平,不利于水汽向西南地区输送。少雨年西南地区水汽汇集的主要地带分别位于四川东部、重庆一带和云南的东部和南部。在云南西部和贵州的水汽通量散度距平很小,虽有水汽的汇集和辐散,但造成当地水汽变化不是很明显。多、少雨年的水汽辐合区均在云南中部和南部、四川东部,但多雨年在这两地水汽辐合强度远远大于少雨年。In order to study the characteristics of atmospheric circulation that cause precipitation anomalies in the rainy season in Southwest China, daily meteorological precipitation observation data from 81 meteorological stations in Southwest China during 1960⁓2022 and monthly NCEP/NCAR reanalysis data set of the same period were used, with a horizontal resolution of 2.5˚ × 2.5˚. By using the modern climate statistical diagnostic analysis methods such as synthesis analysis and significance test, the high and low layer atmospheric circulation field, other physical quantity field and water vapor transport field of the rainy season precipitation anomaly in Southwest China in the past 63 years are studied. The results show that: 1) The spatial distribution of rainy season precipitation is uneven in southwest China. The three regions with high rainfall value are located in Ya’an, Mount Emei and Leshan in central Sichuan Province, southern Yunnan and western Yunnan respectively, and the regions with heavy rainfall and low rainfall are alternately distributed. The long-term variation trend of rainy season precipitation in southwest China showed a weak decreasing trend, and there were obvious inter-annual variation characteristics. In general, the precipitation was mainly concentrated before 1970s, and the precipitation was mainly concentrated after 2005. The precipitation in Southwest China had certain inter-decadal variation characteristics. 2) In rainy years, the South Asian high is weaker than the usual, the south branch trough is active, the Baikal high is strengthened, and the overall meridonal circulation, the southwest region produces a significant southwest wind anomaly, which is conducive to water vapor transport to the southwest region and conducive to precipitation. In the year of low rainfall, the South Asian high pressure is stronger than in previous years, the high pressure center is eastward, and the overall zonal circulation is present. The abnormal wind field situation of northwest wind over Indochina Peninsula is not conducive to the transport of water vapor from the Bay of Bengal to the southwest, resulting in less precipitation. The vertical movement of rainy season in southwest China is regional, and the vertical movement is stronger in southwest Yunnan and eastern Sichuan in rainy years. The vertical movement is stronger in the eastern part of Sichuan in the year of low rainfall. 3) There is a cyclonic anomaly water vapor transport in the middle of the Bay of Bengal in rainy years, and there is a significant southwest water vapor flux conveyor belt In the south side, indicating that the water vapor transport from the south of the Bay of Bengal to the southwest is strengthened. There is an anticyclonic anomaly of water vapor transport in Guangxi, Guangdong and Hunan, and a southeastward anomaly of water vapor flux in the south, indicating that water vapor from the South China Sea is transported to Guizhou, Chongqing and eastern Sichuan. The divergence anomaly of water vapor flux in rainy years in southwest China shows the spatial distribution of “convergence-divergence-convergence” from south to north, and the large value area of water vapor convergence is located in eastern Sichuan and southern Yunnan. There are cyclonic water vapor flux anomalies in Yunnan and anticyclonic water vapor flux anomalies in the eastern part of the Indian Peninsula. The northward water vapor flux anomalies in the rear part of the former and the front part of the latter converge, which weakens the transport of water vapor from the northern part of the Bay of Bengal to the southwest. The southwesterly water vapor flux anomaly from the south of the Bay of Bengal turns to the west-east water vapor flux anomaly in Indochina Peninsula, which is not conducive to the transport of water vapor to the southwest. The main areas of water vapor accumulation in southwest China are located in eastern Sichuan, Chongqing and eastern and southern Yunnan respectively. In western Yunnan and Guizhou, the divergence anomaly of water vapor flux is very small, although there is water vapor convergence and divergence, but the local water vapor change is not obvious. The convergence areas of water vapor in both rainy and rainy years are in central and southern Yunnan and eastern Sichuan, but the convergence intensity of water vapor in rainy years is much greater than that in rainy years.

西南雨季降水时空变化特征

为研究西南雨季降水的时空变化特征,利用1960~2022年西南地区81个气象站点的逐日气象降水量观测资料,通过EOF分解、Morlet小波分析和EEMD分析等方法,对西南地区雨季降水量的多尺度变化特征进行了详细研究。结果表明:1) 西南地区63年来雨季降水量空间分布不均匀,大体有由东向西逐渐递减,以及由南向北逐渐递减的变化趋势。川西高原为降水量低值区,雅安、峨眉以及云南南部为降水量高值区。西南地区趋势系数正值区和负值区交错分布,正值区主要在川西高原以及川东和贵州,负值区在云南地区。2) EOF分析表明:西南地区雨季降水量第1模态为全区一致型,大值中心位于云南地区以及四川中南部。西南地区雨季降水量第2模态显示为北负南正型,正值大值中心位于云南地区,负值大值区位于川西和川东。西南地区雨季降水量第3模态显示为东北到西南正负交错的分布类型。西南地区雨季降水量第4模态为西负东正的分布类型。西南地区雨季降水量第5模态显示为东北到西南呈正负交错的分布类型。3) 小波分析表明西南地区雨季降水量主要有3~4年、7~8年、10~14年、15~23年的变化周期;EEMD分解表明西南地区雨季降水量主要有2.66年、5.33年、10年、21.3年的变化周期。由此可知,西南地区主要存在4年、8年和20年左右的周期。In order to study the spatio-temporal variation of rainy season precipitation in Southwest China, the multi-scale variation of rainy season precipitation in Southwest China was studied in detail by means of EOF decomposition, Morlet wavelet analysis and EEMD analysis, based on the daily meteorological precipitation observation data of 81 meteorological stations in Southwest China during 1960~2022. The results show that: 1) The spatial distribution of rainy season precipitation in Southwest China in the past 63 years is uneven, with a gradual decline from east to west and from south to north. The West Sichuan Plateau has a low precipitation value, while Ya’an, E’mei and southern Yunnan have a high precipitation value. The positive and negative regions of the trend coefficient in Southwest China are interleaved, the positive regions are mainly in the west Sichuan Plateau, the east Sichuan and Guizhou, and the negative regions are in Yunnan. 2) The EOF analysis shows that the first mode of precipitation in the rainy season in southwest China is the uniform type in the whole region, and the large value center is located in Yunnan and central and southern Sichuan. The second mode of rainy season precipitation in Southwest China shows that the north is negative and the south is positive. The positive value center is located in Yunnan, and the negative value area is located in west and east Sichuan. The third mode of precipitation in the rainy season in Southwest China shows the distribution type of positive and negative interleaving from northeast to southwest. The fourth mode of precipitation in the rainy season in Southwest China is the distribution type of west negative and east positive. The fifth mode of precipitation of rainy season in Southwest China shows the distribution type of positive and negative from northeast to southwest. 3) Wavelet analysis shows that the rainy season precipitation in Southwest China mainly has a change cycle of 3~4 years, 7~8 years, 10-14 years and 15~23 years. The EEMD decomposition shows that the rainy season precipitation in Southwest China mainly has a change cycle of 2.66 years, 5.33 years, 10 years and 21.3 years. It can be seen that there are cycles of about 4 years, 8 years and 20 years in Southwest China.