Wavelet Analysis of Simulated Tropical Convective Cloud Systems. Part I: Basic Analysis

Abstract

A wavelet analysis of a three-dimensional 7-day explicit simulation of the tropical cloud systems in the Global Atmosphere Research Programme (GARP) Atlantic Tropical Experiment Phase III is performed. Three physically distinct regimes (squall line, nonsquall cloud cluster, and scattered convection) in a doubly periodic domain are analyzed using discrete Meyer wavelets. These wavelets are complete and facilitate the inversion of the decomposed modes. The full wavelet spectra well characterize the spatial localization of each physical variable, in particular, the vertical velocity and the condensate fields. The probability distribution of the wavelet coefficients is non-Gaussian despite the horizontal winds, the temperature, and humidity being closely Gaussian in physical space. This demonstrates the effectiveness of the wavelet basis for analyzing cloud system organization. The full wavelet spectrum also selects a preferred spatial orientation of the convective organization in physical space. A pseudospectrum is defined by taking the maximum absolute value of the wavelet coefficients for a given horizontal wavenumber vector as the spectrum coefficient. Unlike the conventional spectrum, this pseudospectrum objectively selects the observed convective-scale and mesoscale structure characteristic of observed mesoscale convective systems. The results demonstrate the broad utility of discrete Meyer wavelet analysis for objectively characterizing the structure and organization of multiscale convective cloud systems in an objective way.