Contrast of tropical cyclone frequency in the western North Pacific between two types of La Nia events  

作　　者：HA Yao ZHONG Zhong 

机构地区：[1]Institute of Meteorology and Oceanography,PLA University of Science and Technology

出　　处：《Science China Earth Sciences》2013年第3期397-407,共11页中国科学（地球科学英文版）

基　　金：supported by National Natural Science Foundation of China(Grant No.41175090);National Basic Research Program of China(Grant No.2010CB428505)

摘　　要：According to the different pattern of sea surface temperature anomaly （SSTA） in the previous year of La Nifia events, we cat- egorized La Nifia events into two types to investigate the different characteristics of tropical cyclone （TC） activity over the western North Pacific （WNP） in TC peak season of two types La Nifia events. One type is following the previous El Nifio event （La Nifia I）; the other is following the previous neutral phase or developing La Nifia event （La Nifia II）. Results show that TC genesis frequency in the WNP during TC peak season of La Nifia I is less than normal year, whereas it has no differ- ences from normal year during La Nifia II. The main reason is attributed to the different amplitude SSTA in the East Indian Ocean （EIO） and the western Pacific Ocean （WPO）. Similar to the capacitor effect, strongly positive SSTA in the EIO-WPO during La Nifia I triggers an equatorial baroclinic Kelvin wave, which intensifies the easterly in the lower troposphere and weakens the East Asian summer monsoon, and thus the TC frequency decreased during La Nifia I. However, the easterly anomaly shows a weak response to the SSTA in the EIO-WPO during La Nifia II, and there is no significant change in the en- vironmental pattern over the WNP; so is TC frequency. The modulation of strong EIO-WPO SSTA on large-scale circulation over the WNP reduces the environmental barotropic energy conversion into synoptic-scale disturbances during La Nifia I, and also suppresses TC disturbances. The understanding of two different types of La Nifia events could help improve the seasonal prediction of TC activity in the WNP during La Nifia.According to the different pattern of sea surface temperature anomaly(SSTA) in the previous year of La Nia events,we categorized La Nia events into two types to investigate the different characteristics of tropical cyclone(TC) activity over the western North Pacific(WNP) in TC peak season of two types La Nia events.One type is following the previous El Nio event(La Nia I);the other is following the previous neutral phase or developing La Nia event(La Nia II).Results show that TC genesis frequency in the WNP during TC peak season of La Nia I is less than normal year,whereas it has no differences from normal year during La Nia II.The main reason is attributed to the different amplitude SSTA in the East Indian Ocean(EIO) and the western Pacific Ocean(WPO).Similar to the capacitor effect,strongly positive SSTA in the EIO-WPO during La Nia I triggers an equatorial baroclinic Kelvin wave,which intensifies the easterly in the lower troposphere and weakens the East Asian summer monsoon,and thus the TC frequency decreased during La Nia I.However,the easterly anomaly shows a weak response to the SSTA in the EIO-WPO during La Nia II,and there is no significant change in the environmental pattern over the WNP;so is TC frequency.The modulation of strong EIO-WPO SSTA on large-scale circulation over the WNP reduces the environmental barotropic energy conversion into synoptic-scale disturbances during La Nia I,and also suppresses TC disturbances.The understanding of two different types of La Nia events could help improve the seasonal prediction of TC activity in the WNP during La Nia.

关 键 词：La Nifia event western North Pacific tropical cyclone FREQUENCY SSTA energy conversion 

分 类 号：P444[天文地球—大气科学及气象学] P426.6