Observational Determination of Cloud Mass Flux Distributions

Abstract

Using Arakawa's spectral representation of cumulus convection, the cloud mass flux distributions and other cloud properties are diagnostically determined from large-scale observations. Observational data over the tropical Atlantic Ocean during the BOMEX Phase 3 (22?30 June 1969) are used. The analyzed period is subdivided into three parts according to different synoptic situations. The cloud properties and the manner of interaction between large-scale fields and cumulus convection under the different situations are examined. During the period in which a strong trade inversion lies near 800 mb, most clouds detrain below the trade inversion and cloud mass flux is confined below this level. The large apparent heat sink and apparent moisture source found near the inversion base are mainly due to the cooling and moistening effects of the detrainment from clouds. During the period affected by an upper-level extended trough, the trade inversion is weakened and some clouds penetrate through the 800-mb level but the cloud mass flux is still confined below 500 mb. During the period disturbed by an organized cloud cluster, not only small, shallow clouds but large, deep clouds make large contributions to the vertical mass flux. The total cloud mass flux extends into the upper troposphere. Approximate distributions of cloud area ratio are also estimated from the budget of cloud liquid water using a simple pararmeterization of the rainfall rate. Computed results of cloud mass flux distributions are qualitatively verified by aircraft cloud photographs and radar echo analyses.