Eastward-Propagating Intraseasonal Oscillation Represented by Chikira-Sugiyama Cumulus Parameterization. Part I: Comparison with Observation and Reanalysis

The eastward-propagating intraseasonal oscillation represented by the Chikira-Sugiyama cumulus parameterization in an atmospheric general circulation model is compared with observations and reanalyses. The scheme is characterized by state-dependent entrainment rates that vertically vary affected by the environment. The zonal wavenumber-frequency power spectrum shows a strong signal corresponding to the Madden-Julian oscillation. The eastward-propagating feature of the convective region and accompanying anomalous zonal wind structure is well extracted by the first and second modes of the combined empirical orthogonal function (CEOF) with a reasonable explained variance for the first mode, though the second mode is not sufficiently reproduced. The basic features of the composited anomalous fields including moisture, temperature, and vertical and zonal winds resemble those of the reanalysis in both the free troposphere and surface air. The anomalous free-tropospheric moisture exhibits its westward tilt and the peak moist static energy of the surface air is shifted eastward as in the reanalysis. The anomalous low-level zonal wind changes its direction to the east of the convective center. The model's outstanding deficiencies include the weak convective activity over the Indian Ocean, weaker westward tilt, and seemingly underestimated shallow convection.