| Impact of the Anomalous Thawing in the Tibetan Plateau on Summer Precipitation in China and Its Mechanism |
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| 作者姓名： | GAO Rong WEI Zhigang DONG Wenjie ZHONG Hailing |
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| 作者单位： | [1]KeyLaboratoryofRegionalClimate-EnvironmentforEastAsia,InstituteofAtmosphericPhysics,ChineseAcademyofSciences,STARTRegionalCenterforTemperateEastAsia,Beijing100029 [2]ColdandAridRegionsEnvironmentalandEngineeringResearchInstitute,ChineseAcademyofSciences,Lanzhou730000 [3]NationalClimateCenter,ChinaMeteorologicalAdministration,Beijing100081 |
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| 基金项目： | 中国科学院资助项目，国家自然科学基金，国家自然科学基金 |
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| 摘 要： | The impact of the anomalous thawing of frozen soil in the late spring on the summer precipitation in China and its possible mechanism are analyzed in the context of the frozen soil thawing date data of the 50 meteorological stations in the Tibetan Plateau, and the NCEP/NCAR monthly average reanalysis data.Results show that the thawing dates of the Tibetan Plateau gradually become earlier from 1980 to 1999,which is consistent with the trend of global warming in the 20th century. Because differences in the thermal capacity and conductivity between frozen and unfrozen soils are larger, changes in the freezing/thawing process of soil may change the physical properties of the underlying surface, thus affecting exchanges of sensible and latent heat between the ground surface and air. The thermal state change of the plateau ground surface must lead to the thermal anomalies of the atmosphere over and around the plateau, and then further to the anomalies of the general atmospheric circulation. A possible mechanism for the impact of the thawing of the plateau on summer (July) precipitation may be as follows. When the frozen soil thaws early (late) in the plateau, the thermal capacity of the ground surface is large (small), and the thermal conductivity is small (large)， therefore, the thermal exchanges between the ground surface and the air are weak (strong). The small (large) ground surface sensible and latent heat fluxes lead to a weak (strong) South Asian high, a weak (strong) West Pacific subtropical high and a little to south (north) of its normal position. Correspondingly, the ascending motion is strengthened (weakened) and precipitationin creases (decreases) in South China, while in the middle and lower reaches of the Changjiang River, the ascending motion and precipitation show the opposite trend.
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| 关 键 词： | 青藏高原 冻土融化 夏季降水量 气候变暖 |
Impact of the anomalous thawing in the Tibetan Plateau on summer precipitation in China and its mechanism |
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| GAO Rong,WEI Zhigang,DONG Wenjie,ZHONG Hailing.Impact of the Anomalous Thawing in the Tibetan Plateau on Summer Precipitation in China and Its Mechanism[J].Advances in Atmospheric Sciences,2005,22(2):238-245. |
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| Authors: | Gao Rong Wei Zhigang Dong Wenjie Zhong Hailing |
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| Institution: | Key Laboratory of Regional Climate-Environment for East Asia, Institute of Atmospheric Physics, Chinese Academy of Sciences, START Regional Center for Temperate East Asia, Beijing 100029;Cold and Arid Regions Environmental and Engineering Research Institu,Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou 730000,Key Laboratory of Regional Climate-Environment for East Asia, Institute of Atmospheric Physics, Chinese Academy of Sciences, START Regional Center for Temperate East Asia, Beijing 100029;National Climate Center,China Meteorological Administration,Beijing,,Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou 730000 |
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| Abstract: | The impact of the anomalous thawing of frozen soil in the late spring on the summer precipitation in China and its possible mechanism are analyzed in the context of the frozen soil thawing date data of the 50meteorological stations in the Tibetan Plateau, and the NCEP/NCAR monthly average reanalysis data.Results show that the thawing dates of the Tibetan Plateau gradually become earlier from 1980 to 1999,which is consistent with the trend of global warming in the 20th century. Because differences in the thermal capacity and conductivity between frozen and unfrozen soils are larger, changes in the freezing/thawing process of soil may change the physical properties of the underlying surface, thus affecting exchanges of sensible and latent heat between the ground surface and air. The thermal state change of the plateau ground surface must lead to the thermal anomalies of the atmosphere over and around the plateau, and then further to the anomalies of the general atmospheric circulation. A possible mechanism for the impact of the thawing of the plateau on summer (July) precipitation may be as follows. When the frozen soil thaws early (late) in the plateau, the thermal capacity of the ground surface is large (small), and the thermal conductivity is small (large), therefore, the thermal exchanges between the ground surface and the air are weak (strong). The small (large) ground surface sensible and latent heat fluxes lead to a weak (strong) South Asian high, a weak (strong) West Pacific subtropical high and a little to south (north) of its normal position. Correspondingly, the ascending motion is strengthened (weakened) and precipitation increases (decreases) in South China, while in the middle and lower reaches of the Changjiang River, the ascending motion and precipitation show the opposite trend. |
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| Keywords: | Tibetan Plateau thawing of frozen soil summer precipitation |
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