Open AccessA toy model of tropical convection with a moisture storage closure
Author(s) -
Masunaga Hirohiko,
Sumi Yukari
Publication year - 2017
Publication title -
journal of advances in modeling earth systems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.03
H-Index - 58
ISSN - 1942-2466
DOI - 10.1002/2016ms000855
Subject(s) - moisture , convection , precipitation , environmental science , advection , forcing (mathematics) , atmospheric sciences , diabatic , climatology , meteorology , geology , thermodynamics , physics , adiabatic process
A time‐dependent, zero‐dimensional toy model is constructed to study the large‐scale variability in association with tropical moist convection. Case studies from sounding‐array observations are analyzed as a benchmark to test the model performance. The model predicts the vertical integral of vertical moisture advection decomposed into the deep convective and congestus/stratiform modes. A closure representing the consumption efficiency of water vapor into precipitation is introduced using the moisture storage ratio, or the degree to which the vertical moisture advection associated with each vertical mode accounts for moisture storage. The observations suggest that this moisture consumption is highly inefficient for the convective/stratiform mode while efficient for the deep convective mode. The model solution is interpreted as a delayed response to the diabatic forcing, unless the sum of the moisture storage ratio and gross moist stability is negative, in which case the system is unstable. Baseline experiments with a fixed moisture storage closure overall reproduce the vertical moisture advection and precipitation as observed, but fail to simulate a sharp pickup of precipitation in the well‐known moisture‐rainfall curve. This deficiency is eliminated when the moisture storage ratio is allowed to vary as convection intensifies and dissipates.