The relationship between the atmospheric subseasonal variability and interannual variation of SST over the tropical Indian Ocean is studied using winds from 54 yr of the NCEP reanalysis and the monthly SST analysis. The primary focus is on whether and how the subseasonal variability is related to the zonal dipole structure of SST which peaks in boreal fall. The level of subseasonal activity is measured based on the band pass filtered zonal wind field on the 5-30 day and 30-90 day timescales.

During boreal fall (September-November), interannual variations in the level of 5-30 day wind (1000mb) activity in the central Indian Ocean is highly correlated with large scale zonal SST gradient, while no significant correlation is found with the local SST. The intensity of subseasonal (5d-30d) variability is largely reduced during positive dipole years including ENSO-independent dipole events (e.g., 1961). The subseasonal wind activity in this period range is also well correlated with the mean vertical shear. A significant reduction of intraseasonal (30d-90d) wind activity is also evident during large dipole events. However, the correlation with the zonal SST gradient is much lower than that of the 5-30 day timescale variability. It is suggested that the Indian Ocean SST dipole has a significant impact on the atmospheric subseasonal variability, and that the impact strongly depends on the timescale of the variability.