The Characteristics of Frontal Precipitation in South China During the Pre-Rainy Season and Its Response to Indian Ocean Sea Surface Temperature Anomalies
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摘要: 使用1991—2020年逐日降水观测资料、ERA5再分析资料、NOAA逐月海表面温度资料,采用经验正交函数(EOF)分析和水汽收支方程诊断等方法,研究了华南前汛期锋面降水特征及其对印度洋海温的响应。结果表明,华南前汛期锋面降水主模态为全区一致型。锋面降水涝年,西太平洋副热带高压位置偏西,低层存在异常气旋,受正涡度中心控制,气流辐合,上升运动加强,水汽通量异常辐合,有利于降水发生。锋面降水旱年与之相反。华南前汛期锋面降水异常主要受动力学导致的水汽平流变化项和风场辐合辐散的动力学贡献项影响,其中以风场辐合辐散的动力学贡献项为主。对流层低层经向水汽收入在华南前汛期锋面降水中起重要作用。印度洋关键区(80~108 °E,12 °S~14 °N)海温正异常,通过凝结潜热加热大气,形成东传的大气Kelvin波,导致南海-西太平洋对流层低层产生异常反气旋,向华南地区的低层经向水汽输送增多,降水增多。Abstract: Using daily precipitation data, ERA5 reanalysis data and NOAA monthly sea surface temperature (SST) data from 1991 to 2020, we employed Empirical Orthogonal Function (EOF) analysis and water vapor budget diagnostics to investigate the characteristics of frontal precipitation in South China during the pre-rainy season (FRSCPS) and its response to Indian Ocean SST anomalies. The results indicate that the leading spatial mode of FRSCPS is characterized by a regionally coherent pattern across South China. During flood years, the Western Pacific Subtropical High shifts westward, accompanied by an anomalous cyclone in the lower troposphere. This configuration induces air mass convergence, enhances upward motion, and promotes anomalous moisture flux convergence, which increases precipitation. The circulation during drought years exhibits opposite patterns. The abnormal FRSCPS is primarily influenced by two dynamic factors: changes in moisture advection and the dynamic contribution from wind field convergence and divergence, with the latter playing a dominant role. Meridional moisture transport in the lower troposphere is crucial for FRSCPS. Positive SST anomalies in the Indian Ocean key regions (80-108 °E, 12 °S-14 °N) excite eastward propagation Kelvin waves by triggering atmosphere heating via latent heat release from condensation, leading to an anomalous anticyclonic in the lower troposphere over the South China Sea-Western Pacific region, thereby enhancing the meridional moisture transport to South China and increasing precipitation.
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表 1 华南前汛期1991—2020年锋面降水日期(月.日)
年开始—结束 年开始—结束 年开始—结束 年开始—结束 年开始—结束 年开始—结束 1991 05.01—06.10 1992 03.23—06.12 1993 04.16—06.09 1994 04.21—05.10 1995 04.18—05.17 1996 03.28—05.29 1997 03.29—06.06 1998 04.09—05.31 1999 04.17—05.26 2000 04.01—05.25 2001 04.02—05.21 2002 03.22—05.20 2003 04.12—05.06 2004 04.04—05.23 2005 04.22—06.02 2006 04.06—05.22 2007 04.13—05.24 2008 04.18—05.03 2009 03.05—05.08 2010 04.05—06.08 2011 05.01—05.22 2012 04.05—05.14 2013 03.27—05.23 2014 03.29—05.11 2015 05.03—05.20 2016 03.19—05.23 2017 04.20—06.01 2018 04.21—06.13 2019 04.20—05.26 2020 03.28—06.04 表 2 海温与降水的相关系数及排除其他海域条件下的偏相关系数
系数 IO EP WP 相关系数 0.47** 0.43* -0.35* 偏相关系数 0.34* 0.17 -0.2 注:**表示通过0.01显著性检验,*表示通过0.05显著性检验。 -
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