Variations of the Spring Equatorial Indian Ocean Zonal-Vertical Circulation and Its Correlation with the Walker Circulation

Based on the 20CR reanalysis dataset and the sea surface temperature (SST) dataset provided by NOAA, seasonal differences and variations of the equatorial Indian Ocean zonal-vertical circulation (EIOZVC) and its correlation with the Walker circulation are investigated. First, structures of the EIOZVC in the four seasons are analyzed, and the results suggest that the EIOZVC in a strictly zonal direction only appears in the spring and autumn. Further studies on variations of the EIOZVC in the spring show that the intensity of the EIOZVC and its variability increased during the period of 1951-2010, while the position of the EIOZVC center experienced a remarkable interdecadal variation:prior to 1981, the EIOZVC center shifted westward; however, it shifted eastward after 1981. There is also a noticeable interdecadal variation in the correlation between the EIOZVC and the Walker circulation in the spring. No high correlation is found between them prior to 1981, whereas the two circulations are found to be highly correlated after 1981. The relationship between the spring EIOZVC and seasonal mean SSTs over the Indian and Pacific Oceans also exhibits different patterns between the two periods, indicating that the EIOZVC is influenced primarily by the Pacific ENSO-like SST signals in the previous winter and the subsequent spring after the year of 1981. Before 1981, however, the EIOZVC was mainly influenced by the equatorial eastern Indian Ocean SSTs.