In the tropics our attention is drawn automatically to regions of disturbed weather even though the majority of the region is suppressed. We argue that these extended periods are critical of suppression are extremely important in the “preconditioning” of the atmosphere in intraseasonal variability. We use serial data from the Joint Air-Sea Monsoon Interaction Experiment (JASMINE) and TOGA COARE (conducted, respectively, in the Indian Ocean and the western Pacific) to determine the dominant physical processes that occur near the surface of the ocean during suppressed conditions. Cloud fields develop below the inversion with mid-afternoon maxima accompanying the diurnal variability of the SST which during these periods of light winds can be as high as 3?C. Distinct plumes of enhanced moisture are observed to penetrate through the boundary layer sequentially enhancing the moisture content of the boundary layer over periods of days.

It is shown that many numerical weather models of stand-alone atmospheric climate models do not have diurnally varying SST. Also, the majority of these models fail to contain reasonable simulations of tropical intraseasonal variability, if they simulate them at all. Coupled models fair slightly better but it is noted that these models possess suppressed period diurnal variability that is much smaller than observed. We argue that there are two reasons why models fail to simulate these oscillations. First, preconditioning within the suppressed boundary layer does not occur because of the lack of realistic diurnal variability and second, convective schemes allow penetrative convection through the troposphere during the suppressed phase. However, before convective parameterization can be corrected, it is necessary to account for the preconditioning. Some simple solutions are suggested.