Quantitative Assessment of Diurnal Variation of Tropical Convection Simulated by a Global Nonhydrostatic Model without Cumulus Parameterization

Abstract

his study investigated the resolution dependence of diurnal variation in tropical convective systems represented by a global nonhydrostatic model without cumulus parameterization. This paper describes the detailed characteristics of diurnal variation in surface precipitation based on three-dimensional data, with the aim of explicitly clarifying the mechanism that underlies the variation. The study particularly focused on the evolution in the size of the precipitation area for deep convective systems with an analysis of the vertical structure of thermodynamic fields. This analysis compares the results of simulations with horizontal grid sizes of 14 and 7 km (R14 and R7, respectively). Over land, the phase delay of diurnal variations in R7 is about 3 h less than that in R14. R7 produces a pronounced diurnal variation in the size distributions of precipitating area(s), especially for areas with a radius of 0?100 km; this characteristic is not found for R14. Such areas actively evolve between noon and evening, leading to the smooth development of larger-scale precipitating areas having a radius of 100?150 km. The maximum surface precipitation in R7 over land occurs at around 2000 local time throughout the tropics, approximately 2 h prior to the development of nighttime deep convection. Deep convective regimes are important as agents of vertical heat transport in the tropics. The present results suggest that precipitating areas with a radius <100 km make a strong contribution to the total amount of precipitation and to mass transport.