Diurnal variation of deep convection over the tropical western Pacific

An integration of observational and modeling studies of the diurnal variation of deep convection is presented in this thesis. The thesis consists of three parts: (1) an observational study on the diurnal variation of deep convection, (2) Adequacy of the National Center for Atmospheric Research (NCAR) Community Climate Model version 2 (CCM2) radiation scheme used in the modeling study and the sensitivity of outgoing longwave radiation (OLR) to atmospheric variables, (3) a modeling study on the mechanisms of the diurnal variation of deep convection.; The observational study concentrates on the tropical western Pacific (TWP) during the Tropical Ocean Global Atmosphere-Coupled Ocean Atmosphere Response Experiment (TOGA-COARE) intensive observation period (IOP). Four months of Geostationary Meterorological Satellite (GMS) infrared (IR) temperature data are analyzed using IR temperature threshold and cloud cluster techniques. Both techniques reveal the same results, that deep convective cloudiness reaches a maximum in the early morning (03–06 local standard time (LST)). The feature is very different from lower level cloudiness that reaches a maximum in the late afternoon. A cross-plot of IR temperature versus time shows that the phase of the diurnal variation has an abrupt change around 220K and propagates downward. Spectral analysis is used to establish the robustness of the diurnal signal of deep convection.; Unlike previous studies using idealized simulations, this study employs a three-dimensional regional model, the NCAR Mesoscale Model Version 5 (MM5), to realistically simulate the diurnal variation. Before this, however, the study focuses on the radiation code of MM5, since radiation is particularly important in the modeling study. Comparisons between CCM2 radiation code used in MM5 and its updated CCM3 version are to show the adequacy of CCM2 radiation code in the current study. The comparisons show that both solar and longwave radiation produced by the CCM2 code are close to the later CCM3 version under the clear sky condition. (Abstract shortened by UMI.)...