Connection between Two Leading Modes of Autumn Rainfall Interannual Variability in Southeast China and Two Types of ENSO-Like SSTA

Kui Liu,Jilong Chen,Ruowen Yang

doi:10.1155/2019/1762505

Abstract

The interannual variability of autumn rainfall in Southeast China (SEC) is significant, with two major modes, namely, monopole and dipole modes. It is found that the monopole mode is closely related to EP ENSO-like sea surface temperature anomaly (SSTA), and the dipole mode is related to CP ENSO-like SSTA. During the warm phase of EP ENSO-like SSTA, an anomalous anti-Walker circulation emerges in the tropical Pacific, with an anomalous subsiding during 110°E–120°E and an anomalous ascending branch in SEC. These two branches of anomalous current are in the same longitude and form a closed meridional circulation. Besides, there also exists an anticyclone anomaly in the Northwest Pacific (NWP), transporting water vapor into SEC. These circulation configurations induced by the warm phase of EP ENSO-like SSTA are consistent with those of monopole mode positive anomaly year. The good correspondence between EP ENSO warm event and the positive monopole mode also helps to support the corresponding relationship between the EP ENSO-like SSTA and monopole mode of SEC autumn rainfall. After the diagnosis of the perturbation omega equation, the anomalous subsiding branch over SEC, as the key link of EP ENSO-like warm phase SSTA exerting impact on the monopole mode during positive anomaly year, is mainly related with the anomalous relative vorticity advection transported by basic zonal wind and temperature advection transported by meridional wind anomaly. As for the dipole mode, it is related to the CP ENSO-like SSTA, but the corresponding relationship is weaker than that of the monopole mode and EP ENSO-like SSTA. In special, during the warm phase of CP ENSO-like SSTA, an anomalous cyclone appears in the NWP and prevailing sinking motion over SEC, both of which favors the appearance of positive anomaly of the dipole mode. Specially, the local anomalous vertical motion mainly depends on anomalous relative vorticity transported by basic meridional wind. Generally speaking, the monopole (dipole) mode is closely associated with the EP (CP) ENSO-like SSTA, demonstrating some correspondence.

Highlights

Southeast China is economically prosperous and Chinese important tropical and subtropical crop production base, mainly including Fujian, Guangdong, East Guangxi, Jiangxi, Hunan, South Hubei, and South Zhejiang
The anomalous Walker circulation cannot be a bridge to convey corresponds to and EP (CP) ENSO-like sea surface temperature anomaly (SSTA)’s influence to the dipole mode, which is different to the monopole mode, As presented in the regression map of 850 hPa wind and vorticity on EMI index, when the tropical central Pacific warms up, an anomalous cyclone emerges over the Northwest Pacific (NWP) (Figures 9(a) and 9(b)), with an anti-Walker circulation in the tropical Pacific and the subsiding branch located in 110°E–120°E (Figure 9(c))
E significant area between interannual variation sequence of autumn rainfall in Southeast China (SEC) and tropical sea surface temperature (SST) is mainly located in the tropical Middle and East Pacific, where the difference of SST is most significant between the more rainfall year and less rainfall year of SEC. is illustrates that SEC autumn rainfall is closely related to the Middle and East tropical SSTA, and in special, the monopole mode of autumn rainfall interannual variability over SEC is closely related to EP ENSO-like SSTA and the dipole mode is associated with CP ENSO-like SSTA, with the correlation coefficients between PC1 and Nino 3 index, and PC2 and EMI index reach up to 0.46 and 0.3, respectively

Summary

Introduction

Southeast China is economically prosperous and Chinese important tropical and subtropical crop production base, mainly including Fujian, Guangdong, East Guangxi, Jiangxi, Hunan, South Hubei, and South Zhejiang. It has been recognized that ENSO is the strongest air-sea interaction phenomenon associated with Indo-Pacific SST at the annual scale, whose warm (cold) phase is named El Niño (La Niña) event, respectively It can be divided into two types (EP ENSO and CP ENSO) based on the difference of maximum SSTA locations. E tropical East Pacific SST, mainly in the Nino 3 region, is positively correlated with precipitation in SEC, but the “C” type region to its west is negatively correlated with rainfall over SEC. As shown in the correlation pattern between the EOF first mode temporal serial PC1 and SST, when the SST is warm (cold), the monopole mode exhibits more (less) rainfall (Figure 4(e)), which illustrates that EP ENSO-like SSTA is closely associated with the monopole mode of interannual variation of SEC autumn rainfall. The correlation coefficient of PC1 and Nino 3 index is up to 0.46, and the correlation coefficient between PC2 and EMI index is − 0.30, both through the significance test at the 90% confidence level, which further identifies that, to some extent, the monopole (dipole) mode corresponds to and EP (CP) ENSO-like SSTA

The Physical Process of EP ENSO-Like SSTA Influencing Monopole Mode over SEC

The Physical Process of CP ENSO-Like SSTA Influencing Dipole Mode over SEC

Findings

Conclusions and Discussion