Low frequency oscillations in assimilated global datasets using TRMM rainfall observations

By using GEOS data assimilation system, we investigate the influence of TRMM precipitation products on the structure and underlying physics of ISO in a GCM assimilation system. We get the following conclusion: 1) In 1998 summer, the strong ISO is apparently in Asia monsoon region off equator and and east equatorial Pacific region .2) 20- 30-day eastward propagation is the dominant mode of ISO near equator. 30-60-day northeastward propagation is the dominant mode of ISO north of equator averaged over 10°N-25°N. 3) For 20-30-day eastward propagation near equator, the wavenumver 1 intensity of control run is usually weaker than that of assimilation run and observation. For 30-60-day northward propagation averaged over 60°E-140°E, the wavenumber 1 intensity of control run is usually stronger than that of assimilation run and observation. 4)By comparing the correlation coefficients and RMS of Kelvin wave structure for geopotential height and wind vector at 150hPa between control run and observation with assimilation run with observation, we can conclude that the assimilation run are more resemble observation, especially near equator. 5) For assimilation run, the convection, which occurred between high and low geopotential height at 150hPa or between easterly and westerly and the two anticyclone at 150hPa off equator, are more organized than that for control run compared with observation. The better Kelvin wave features for the eastward-propagating MJO in the tropic from the assimilation with TRMM precipitation imply that latent heating is very important in exciting equatorial MJO.