Variations Of The Equatorial Indian Ocean Zonal Vertical Circulation And Its Correlation With The Walker Circulation

Based on the 20CR reanalysis dataset, and sea surface temperature (SST) dataset provided by NOAA, the variations of the equatorial Indian Ocean zonal vertical circulation (EIOZVC) and its correlation with the Walker circulation are investigated. Firstly, structures of the EIOZVC in four seasons and annual mean state are analyzed. Then, the intensity index of EIOZVC and the zonal mass flux stream function over equatorial zone are calculated to examine the variation characteristics of the EIOZVC in spring, autumn and annual mean state. The correlation between the EIOZVC and Walker circulation, and the correlation between the EIOZVC and SSTs in different periods are also investigated.The results reveal the EIOZVC in a strict zonal direction only appears in spring, autumn and annual mean state. During the period of 1901～2010, the intensity of the spring EIOZVC increased, while the autumn EIOZVC exhibited interdecadal variations with strong, weak and strong pattern. The intensity variability of the spring, autumn and annual mean EIOZVC varies with time obviously, while the position of the EIOZVC center showed a westward shift.There is a noticeable interdecadal variation in the correlation between the EIOZVC and Walker circulation, and the relationship between the EIOZVC and the SSTs over the Indian and Pacific Oceans also exhibits different patterns during each period. No high correlation is found between the spring EIOZVC and Walker circulation during the period of 1951～1980, when the EIOZVC was mainly influenced by the equatorial eastern Indian Ocean SSTs. During the period of 1981～2010, however, the spring EIOZVC and Walker circulation was highly correlated, and the EIOZVC is influenced primarily by the Pacific ENSO-like SST signal in the previous winter and simultaneous spring.The autumn EIOZVC was influenced primarily by the SST anomalies in the tropical western Indian Ocean and the central Pacific Ocean in the previous summer and simultaneous autumn during 1930～1964, when no high correlation is found between the autumn EIOZVC and Walker circulation. During 1965～2010, however, the autumn EIOZVC and Walker circulation was highly correlated, when both the Indian Ocean Dipole (IOD) and the ENSO-like signal in the tropical Pacific Ocean had an effect on the intensity of EIOZVC. In annual mean state, a significant correlation between the intensity of EIOZVC and the ENSO-like SST signal also appears when the annual mean EIOZVC and Walker circulation was highly correlated.