5月中国土壤湿度异常对7月华南-青藏高原东部偶极子型降水年际变化的影响
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国家自然科学基金资助项目(42230603);南方海洋科学与工程广东省实验室(珠海)创新团队建设项目(311021001)


Impact of May soil moisture anomalies in China on the interannual variation of July precipitation dipole over South China and the eastern Tibetan Plateau
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    摘要:

    利用1979—2019年ERA5再分析资料和站点降水资料,研究了5月中国土壤湿度异常对7月华南和青藏高原东部偶极子型降水年际变化的影响及其可能的物理过程。结果表明,当5月青藏高原土壤湿度偏湿,华中地区土壤湿度偏干时,对应7月华南(高原东部)降水偏多(偏少),两地降水呈偶极子型分布。通过进一步的诊断分析发现,青藏高原(华中地区)土壤湿度正(负)异常可从5月持续至7月,使得7月中国北方地区地表湍流热通量正异常,进而使得对流层中低层大气增暖,中国北方与贝加尔湖之间经向温度梯度和大气斜压性增强,天气尺度的瞬变波活动增强。通过瞬变的涡度强迫有利于中国北方及蒙古地区准正压异常高压和Rossby波波源的形成,相关的Rossby波向东南方向传播至我国南方,使得华南地区出现准正压结构的异常低压,有利于西北太平洋副热带高压东移,南亚高压西移。对应中国北方及蒙古-华南地区对流层中低层为反气旋-气旋式环流异常,进而导致华南地区(高原东部)降水增多(减少)。此外,中国北方-蒙古地区的异常高压与局地偏干的土壤湿度之间的正反馈过程,有利于上述物理过程的维持和增强,进而有利于7月偶极子降水的异常,反之亦然。

    Abstract:

    During the period of 1979—2019,there was a significant negative correlation between the interannual variation in precipitation anomalies over South China (SC) and those in the eastern Tibetan Plateau (ETP) in July,with a correlation coefficient of -0.60 between the area-averaged precipitation over the two regions.It is statistically significant at the 99% confidence level.Therefore,a precipitation dipole index (PDI) is defined as the difference in the standardized area-averaged precipitation between SC (20°—26°N,108°—123°E) and the ETP (28°—35°N,90°—108°E) in July.The positive phase of the July precipitation dipole is characterized by increased (decreased) precipitation over SC (the ETP),and vice versa.Based on this,we utilize ERA5 reanalysis data and station precipitation data from the period of 1979—2019 to investigate the influence of soil moisture anomalies in May on the interannual variation of the July precipitation dipole,along with its underlying physical processes.The study results show that higher soil moisture in the TP and lower soil moisture in Central China (CC) in May tend to lead to increased (decreased) precipitation over SC (the ETP) in July,displaying a dipole pattern of precipitation over the two regions.Further analysis reveals that the positive (negative) soil moisture anomalies in the TP (CC) may persist from May to July,resulting in positive surface turbulent heat flux anomalies in the Northern China (NC) region in July.This in turn causes local middle to lower troposphere warming,thus intensifying the meridional temperature gradient and atmospheric baroclinicity between NC and Lake Baikal.Correspondingly,enhanced synoptic-scale transient wave activity is observed,which creates an anomalous high pressure with an equivalent barotropic structure and Rossby wave sources over NC-Mongolia by transient vorticity forcing.The associated Rossby waves propagate southeastward to SC.Subsequently,an anomalous low pressure appears over SC with an equivalent barotropic structure,which facilitates the eastward shift of the western Pacific subtropical high and westward shift of the South Asian high.This anomalous circulation respectively corresponds to anticyclone and cyclone anomalies in the middle and lower troposphere over Mongolia and SC,and consequently enhanced (suppressed) precipitation occurs in SC (the ETP).In addition,the positive feedback process between the anomalous high over Mongolia and local low soil moisture is favorable to the formation of the July precipitation dipole by intensifying and maintaining the above physical process,and vice versa.

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王娟,范可,徐志清,2024.5月中国土壤湿度异常对7月华南-青藏高原东部偶极子型降水年际变化的影响[J].大气科学学报,47(1):108-123. WANG Juan, FAN Ke, XU Zhiqing,2024. Impact of May soil moisture anomalies in China on the interannual variation of July precipitation dipole over South China and the eastern Tibetan Plateau[J]. Trans Atmos Sci,47(1):108-123. DOI:10.13878/j. cnki. dqkxxb.20230616001

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  • 收稿日期:2023-06-16
  • 最后修改日期:2023-09-15
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  • 在线发布日期: 2024-03-19
  • 出版日期: 2024-01-28

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