Influences Of The Indian Ocean Dipole On The Atmospheric Intraseasonal Oscillations In The Tropical And Extratropical Regions During Boreal Summer

Influences of the Indian Ocean Dipole (IOD) on the intensity of MJO in the atmosphere in boreal summer and the related possible mechanisms have been studied in the present article, using the daily NECP/NCAR Reanalysis and monthly GISST SST data from 1979 through to 1998. The results are summarized as follows:(1) Influences of the IOD on the MJO intensity are noticeable in the East-South Indian Ocean. The negative correlations between DMI and the MJO intensity of zonal winds and those between DMI and the MJO intensity of meridional winds are found significant The influences of IOD on wind fields may be modulated by tropical convective activities as detected from mean OLR and OLR MJO. The further analysis indicates that the convective activity is driven by large-scale SST gradients associated with IOD.(2) In 1989, a typical negative IOD year, features of the wind fields show that the positive anomalies of the MJO intensity of zonal and meridional winds have been found in East-South Indian Ocean. The intraseasonal components dominate the variations of the wind fields. The MJOs in zonal and meridional winds propagate eastward in the east of 70°E and poleward from equatorial region.(3) The IOD has significant influences on the MJO intensity in boreal summer. The influences of IOD on SLP MJO intensity are observed in the central, western and southern parts in Africa. The variations of the zonal winds, meridional winds and geopotential heights on intraseasonal timescales at 200hPa have been modulated by the IOD.(4) The impacts of IOD and ENSO on MJO intensity are different;oppositely signed differences are found in some regions.(5) The distinct differences between 1994 and 1992 are observed in the intensity and the propagations of MJO of the zonal and meridional winds on 850hPa and 200hPa. Clear 30-60d oscillations are found in the areas where the precipitation is large. The intraseasonal circulations and water vapor conditions appear to facilitate the precipitation on intraseasonal timescales.