| More and more attention has been paid to the different types of ENSO events. By following Kao’s (2009), we have defined the EP-type ENSO index (Eastern Pacific-type ENSO index, EPI) for boreal summer in the present paper, with which we have investigated the simultaneous relationships between EP-type ENSO and Maritime Continent (MC) precipitation using the monthly mean data from NECP-NCAR reanalysis, global Seas Surface Temperature (SST) from Hadley center, and CAMP precipitation data for period from 1979 to 2013. On this basis, We construct SSTA index in the key area of SPCZ to analyse the correlation between the index and climate in MC, by using partial correlation analysis method. At the same time, We analyze the correlation between EPI index and the East Asian summer monsoon in South Asia for different periods with 11 years moving correlation. Results are summeried as follows:(1) The regional mean precipitation anomaly over Maritime Continent region is negatively but weakly correlated with the EPI, which is not well in agreement with the strong negative correlations between canonical ENSO and rainfall anomalies in Indonesia as we expected. It is found that this weak correlation is due to some co-occurrences of the EP-type El Nino (La Nina) with more (less) than normal rainfall in Indonesian region in some years. By removing the Nino4 signal from SST anomalies, the co-occurrences of positive EPI with positive anomalous rainfall in MC can still be found in some years. By performing some composite analysis, we found that there are two mechanisms that connecting the SST anomalies in eastern equatorial Pacific to precipitation anomalies in MC region. The one is what we usually expected; the anomalous Walker circulation with the ascending (descending) branch over east equatorial Pacific and the descending (ascending) branch over MC region in years when the EP-type EL Nino (La Nina) events occur. We can refer to this as a direction connection mechanism. The other is quite different from the direction connection mechanism. When the EP-type El Nino events occur in some years, there observe significant anomalous heating in the east of Philippines along with significant anomalous cooling in the South Pacific Convergence Zone (SPCZ). These two diabatic heating centers force the atmosphere to response, inducing a northwest-southeast vertical circulation bridging these two centers, which weakens the descent of atmosphere in MC and intensities the descent of air in SPCZ, consequently modifying the anomalous Walker circulation along equator. This slanted anomalous vertical circulation induced connection between east equatorial Pacific and MC region can be referred to as the indirect connection mechanism. In other words, the anomalous cooling in SPCZ plays a very important role in weakening the anti-phase relationship of the rainfall variations in MC region with EP-type ENSO events. These results are very meaningful for us better understanding the mechanisms behind the relationships of ENSO with climate variations in MC region and even in East Asia.(2) By defining an SSTA index in East Australia(ISP), We analyze the correlation between sea surface anomalies in east of Australia and the anomalies rainfall in MC region. When the ISP index is small (larger), SST anomalies will be in favor of strengthening the impact of Nino4 area SSTA positive anomalies (negative anomalies) on climate in Maritime continent. The reason for this phenomenon is attributed to the same number between the ISP and MC region SST. At the same time, Abnormal heating generated by SST anomalies leads to Gill-type response in atmospheric circulation, Which may play an important role in this relationship.(3) By defining summer EP type ENSO index EPI and using the Asian monsoon index, We analyze the interannual variability relationship between EP type ENSO and summer monsoon in Asia. Results are summeried as follows. There is an obivious decadal change between the EP type ENSO and Asia summer monsoon.In the 1979-2000 period, there is a significant negative correlation between EPI and Wester-Yang index, but a weak positive correlation between Shineng index.However,there is an opposite situation in the 2002-2013 period, EPI index and Shineng index are at a significant positive correlation,but a weak negative correlation between EPI index and Webster-Yang index. The reason for this correlation having a decadal change is that in the 1979-2000 period. When the EP type ENSO occures, Walker circulation anomalies will rise in the eastern equatorial pacific ocean and sink in the Indian monsoon region. In addition, Lower divergence south west airflow will weaken equatorial flow. What’s more, south China sea-west pacific ocean carrying southeast wind anomaly in acertain extent, strengthening East Asian summer monsoon region. In the second period, In the equatorial pacific region, There has been no agreement as the first time that low-level westerly wind anomalies and abnormal rise.But the emergence of low-level and and high level westerly wind anomalies to the west of decadal.This suggests that after 2000, EP type ENSO has a new change, Which may cause a significant positive correlation between EPI index and SHINENG index, While a weak negative correlation between EPI index and Wester-Yang index. |
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