TROPICAL GRAVITY-WAVES AND SUPERCLUSTERS SIMULATED BY HIGH-HORIZONTAL-RESOLUTION SKYHI GENERAL-CIRCULATION MODELS

Tropical gravity waves and superclusters simulated by 40-level GFDL SK YHI general circulation model experiments with higher horizontal resol utions (0.6 degrees longitude x 0.72 degrees latitude) and (1.0 degree s x 1.2 degrees) are compared with those simulated by a lower-resoluti on (3.0 degrees x 3.6 degrees) experiment. Results indicated that simu lated precipitational heating appears to excite tropical gravity waves . At higher resolutions, precipitation is more confined in space and t ime, resulting in a broader wavenumber-frequency spectral distribution . Grid-scale precipitation, which is thought to mimic the precipitatio n associated with cloud clusters, is organized into larger-scale super clusters. The westward propagation of cloud clusters and eastward prop agation of superclusters can be more clearly seen in the high-resoluti on experiments. The high-resolution (0.6 degrees x 0.72 degrees) model indicates that the lower-stratospheric gravity-wave momentum flux is dominated by high-frequency components having periods shorter than one day. This flux doubles as the resolution is increased from (3.0 degre es x 3.6 degrees) to (0.6 degrees x 0.72 degrees). It is speculated th at a further increase in both the horizontal and vertical resolutions could substantially enhance the gravity-wave momentum flux convergence , thus forcing a stronger quasi-biennial oscillation.