MODULATION OF INTRASEASONAL OSCILLATIONS ON RAINFALL INDUCED BY TROPICAL CYCLONES OVER SOUTHEAST CHINA
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摘要: 利用1985—2015年6—8月登陆中国东南部(福建和浙江)的35个西北行热带气旋(TC)和站点观测的日降水量，根据区域TC过程降水量，分为强降水、适量降水和弱降水TC，分析影响各级TC降水的环境场异常特征及其季节内振荡(ISO)的调制作用。(1)对流层低层850 hPa表现为中心位于福建东部强的气旋异常，来自孟加拉湾和南海强水汽输送在中国东南部产生强的水汽辐合促使TC强降水的发生，其中10~20天和30~60天ISO的环流和水汽输送都有贡献，但东南部的水汽辐合主要受10~20天ISO的影响；与TC强降水相比，TC弱降水对应的异常气旋和水汽辐合明显减弱。(2)影响TC强降水的10~20天ISO环流异常在TC登陆过程，自菲律宾群岛附近向西北方向传播至中国东南部，30~60天ISO环流异常自南海向东北偏北方向传播至台湾西南部，且环流异常强度不断加强。(3)影响TC弱降水的10~20天ISO环流异常自菲律宾西部向北传播，30~60天ISO环流异常自南海南部向东北方向传播。Abstract: Using 35 tropical cyclones (TCs) which moved northwestward and made landfall at the southeast of China and observational daily rainfall data at stations during June-August in 1985—2015, this study analyzes the rainfall induced by the 35 TCs, focusing on the modulation processes of intraseasonal oscillation (ISO) in environmental anomalies. The 35 TCs are separated into three types of strong, moderate, and weak rainfall. The results show that for the strong rainfall type, a cyclonic anomaly center appeared in eastern Fujian and strong moisture was supplied from the Bay of Bengal and the South China Sea (SCS), and strong moisture convergence resulted in heavy rainfall in the southeast coast of China. Both the 30~60 day and 10~20 day ISOs of the circulation and water vapor transport contributed to it, but moisture convergence in the southeast coast of China was mainly influenced by 10~20 day ISO. Compared to strong rainfall, cyclonic anomaly and moisture convergence for weak rainfall weakened significantly. For strong rainfall, both the 10~20 day and 30~60 day ISOs persistently enhanced cyclonic anomaly propagating northwestward from the Philippines to the southeast coast of China and northeastward /northward from the SCS to the southwest of Taiwan in the process of TC landfall. For weak rainfall, both 10~20 day and 30~60 day ISOs of cyclonic anomaly propagated northward from the western Philippines and northeastward from the SCS.
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图 3 产生强(a~c)、适量(d~f)、弱(g~i)降水的TC登陆当天流函数(a，d，g，105 m2/s)、水汽通量(b，e，h，kg/m)及水汽通量散度(c，f，i，10-7 kg/s)低频合成异常场
阴影区域表示通过0.10的显著性水平检验。
实心五角星为TC平均登陆位置，红框表示TC平均登陆位置的内核区。
图 4 产生强(a~c)、适量(d~f)、弱(g~i)降水的TC登陆当天10~20天流函数(a，d，g，105 m2/s)、水汽通量(b，e，h，kg/m)及水汽通量散度(c，f，i，10-7 kg/s)低频合成异常场
说明同图 3。
图 5 产生强(a~c)、适量(d~f)、弱(g~i)降水的TC登陆当天30~60天流函数(a，d，g，105 m2/s)、水汽通量(b，e，h，kg/m)及水汽通量散度(c，f，i，10-7 kg/s)低频合成异常场
说明同图 3。
表 1 1985—2015年6—8月在福建、浙江登陆的35个TC
降水强度 名称 登陆日期 降水强度/mm 登陆时TC强度/(m/s) 强 Saola 2012.8.3 183 18 Yancy 1990.8.21 148 15 Morakot 2009.8.9 123 8 Soudelor 2015.8.8 118 23 Fung-wong 2008.7.28 113 23 Omar 1992.8.31 106 13 Haikui 2012.8.8 104 30 Herb 2006.7.14 102 23 Bilis 1996.8.1 92 15 Bilis 2000.8.23 90 45 Matmo 2014.7.23 89 25 Sepat 2007.8.19 79 23 Rananim 2004.8.12 70 35 适量 Soulik 2013.7.13 63 30 Toraji 2001.7.31 61 18 Bing 1997.8.29 58 18 Cass 1997.8.30 58 17 Chaba 2004.8.25 54 33 Kalmaegi 2008.7.19 53 15 Tim 1994.7.11 51 33 Winnie 1997.8.18 49 33 Otto 1998.8.5 48 25 Fred 1994.8.21 48 40 Matsa 2005.8.6 47 28 Krovanh 2003.8.20 46 13 Janis 1995.8.25 43 25 Kaemi 2006.7.25 42 23 弱 Kirk 1996.8.7 41 15 Abe 1990.8.31 39 40 Linfa 2009.6.21 37 25 Etau 2003.8.4 33 28 Maria 2006.8.10 31 38 Gloria 1996.7.27 30 35 Jelawat 2000.8.10 24 23 Nichole 1998.7.12 11 10 
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表 2 ISO区域格点平均水汽通量散度(10-7 kg/s)及其占低频的比例(%)
降水强度 低频散度 10~20天散度 30~60天散度 10~20天占低频比例 30~60天占低频比例 强 -10.25 -4.5 -1.79 44 17 适量 -2.89 -2.15 -0.21 74 7 弱 -0.06 -0.006 -0.03 10 50
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