| 摘要: |
| 利用1979—2018年CRU和ERA5再分析资料，通过经验正交函数（empirical orthogonal function，EOF）分析方法，研究亚洲西风急流经向位置的变化特征及其与华北、中亚地区夏季降水的关系，并结合水汽收支诊断分析方法探究降水变化的物理机制。结果表明：亚洲西风急流EOF分解的前两个主要模态分别代表东亚和中亚西风急流的经向位移特征。在东亚西风急流北移年，华北夏季降水相对于气候平均态增加12.32%，华北地区的南风异常利于附近海域水汽输送至华北，水平动力项主导降水的变化；而在南移年，华北夏季降水减少9.47%，由于华北上空大气显著的下沉运动，垂直动力项对降水减少的贡献较大。在中亚西风急流南移年，中亚夏季降水相对于气候平均态增加25.31%，由于中亚上空大气上升运动显著加强，垂直动力项主导降水增多；而在北移年，中亚夏季降水减少17.47%，中亚中部地区存在北风异常，阻碍水汽输送，降水减少由水平动力项主导。因此，环流变化主导了急流经向位置异常年华北和中亚夏季降水的变化。 |
| 关键词: 亚洲西风急流 中纬度地区 夏季降水 水汽收支诊断分析方法 |
| DOI：10.7515/JEE222089 |
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| 基金项目:中国科学院战略性先导科技专项（B类）（XDB40030100）；国家自然科学基金项目（41991254，42175059）；中国科学院“西部之光”人才培养计划（XAB2019A02） |
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| A comparative study on the relationship between Asian westerly jet position and summer precipitation in mid-latitude regions of East Asia and Central Asia |
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GUO Jianing1, 2, XIE Xiaoning1, 3*, WANG Anqi4, 1
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1. State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710061, China
2. University of Chinese Academy of Sciences, Beijing 100049, China
3. CAS Center for Excellence in Quaternary Science and Global Change, Xi’an 710061, China
4. School of Geography and Tourism, Shaanxi Normal University, Xi’an 710119, China
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| Abstract: |
| Background, aim, and scope The Asian westerly jet is one of the significant atmospheric circulations affecting the weather and climate system in the mid-latitude regions of the Northern Hemisphere. Meridional displacement of the westerly jet is the most remarkable feature and plays an essential role in summer precipitation over mid-latitude regions. However, it remains unclear whether changes in atmospheric circulation (dynamic factors) or specific humidity (thermodynamic factors) are the primary drivers of precipitation variability. The moisture budget analysis is widely used to quantify the dynamic and thermodynamic contributions to precipitation change. Therefore, we employed this analysis method to quantify the relative contributions from different factors of precipitation change in the Asian westerly jet anomaly shift years and provide the main physical mechanisms of precipitation change. Materials and methods The Climatic Research Unit (CRU) provides 0.5°×0.5° monthly observation-based precipitation data. The evaporation data and circulation data including horizontal wind component, vertical velocity, surface pressure, and specific humidity are derived from ERA-5 0.25°×0.25° monthly mean reanalysis data published by the European Centre for Medium-Range Weather Forecasts (ECMWF). The EOF analysis, composite analysis, and moisture budget analysis are used in this study. Results The first two leading EOF modes of the Asian westerly jet represent the characteristics of the meridional displacement of the westerly jet in East Asia and Central Asia, respectively. In the East Asian westerly jet northward shift years, summer precipitation increased by 12.32%. In the southward shift years, summer precipitation in North China decreased by 9.47%. In the Central Asian westerly jet southward shift years, Central Asia summer precipitation increased by 25.31%. In the northward shift years, summer precipitation increased by 17.47%. Discussion This study reveals the mechanism of summer precipitation changes in mid-latitude regions when the westerly jet shifts southward and northward. In the East Asian westerly jet northward shift years, the anticyclone over the Korean Peninsula led to the abnormal southerly wind appearing in North China, which brought a large amount of moisture from the nearby sea and increased the summer precipitation in North China. Thus, the horizontal dynamic term dominated the increase in summer precipitation. In the southward shift years, the significant descending movement suppressed the summer precipitation in North China, with the vertical dynamic term dominating the decrease in precipitation. In the Central Asian westerly jet southward shift years, the Central Asian anomalous cyclone enhanced moisture transport from the Indian Ocean and strengthened ascending movement, leading to a vertical dynamic term-dominated increase in summer precipitation. In the northward shift years, the cyclone over Central Asia induced abnormal northerly winds, blocking tropical moisture transport and reducing summer precipitation, with the horizontal dynamic term dominating the decrease. Recent trends indicate a wetter climate in Central Asia, particularly during summer, coinciding with a southward shift of the westerly jet. However, it remains unclear whether these trends align with interannual precipitation mechanisms. Besides, the southward movement of the westerly jet relative to the Qinghai-Xizang Plateau during the last deglaciation and the northward movement during the early-middle Holocene led to summer precipitation changes in East Asia. The similarities and differences between the mechanism of precipitation changes caused by jet meridional movement in geological time and modern times are the focus of future research. Conclusions The first two leading EOF modes for the Asian westerly jet represented the meridional movement of the East and Central Asian westerly jet, respectively. The dynamic terms dominated the precipitation changes owing to the atmospheric circulation change in the Asian westerly jet anomaly shift years. In the southward shift years, due to the significantly ascending motion in Central Asia and the descending motion in North China, the vertical dynamic term mainly contributed to precipitation changes in these regions. In the northward shift years, because of the abnormal southerly wind in North China and abnormal northerly wind in Central Asia, the horizontal dynamic term dominated precipitation changes. Recommendations and perspectives We expect that the mechanism of interannual precipitation change can provide a reference to study the mid-latitude regions’ precipitation change mechanisms in the decadal time scales and different geological periods. |
| Key words: Asian westerly jet mid-latitude regions summer precipitation moisture budget analysis |
