The role of radiation in organizing convection in weak temperature gradient simulations

• Published in: Journal of advances in modeling earth systems 2016-03, Vol.8 (1), p.244-271
• Main Authors: Sessions, Sharon L., Sentić, Stipo, Herman, Michael J.
• Format: Article
• Language: English
• Subjects: Aggregation; Approximation; Boundary layers; Climate change; Cloud systems; Convection; convective organization; Cooling; Economic models; Entropy; Experiments; Gravitational waves; interactive radiation; Moist stability; Moist static energy; Moisture profiles; multiple equilibria; Organizations; Precipitation; Profiles; Radiation; Radiative cooling; Temperature gradients; weak temperature gradient
• ISSN: 1942-2466; 1942-2466
• DOI: 10.1002/2015MS000587

Using a cloud system resolving model with the large scale parameterized by the weak temperature gradient approximation, we investigated the influence of interactive versus noninteractive radiation on the characteristics of convection and convective organization. The characteristics of convecting environments are insensitive to whether radiation is interactive compared to when it is not. This is not the case for nonconvecting environments; interactive radiative cooling profiles show strong cooling at the top of the boundary layer which induces a boundary layer circulation that ultimately exports moist entropy (or analogously moist static energy) from dry domains. This upgradient transport is associated with a negative gross moist stability, and it is analogous to boundary layer circulations in radiative convective equilibrium simulations of convective self‐aggregation. This only occurs when radiation cools interactively. Whether radiation is static or interactive also affects the existence of multiple equilibria‐steady states which either support precipitating convection or which remain completely dry depending on the initial moisture profile. Interactive radiation drastically increases the range of parameters which permit multiple equilibria compared to static radiation; this is consistent with the observation that self‐aggregation in radiative‐convective equilibrium simulations is more readily attained with interactive radiation. However, the existence of multiple equilibria in absence of interactive radiation suggests that other mechanisms may result in organization. Key Points: Interactive radiation permits upgradient transport of moist entropy in dry steady states Characteristics of precipitating convection are insensitive to interactive versus static radiation Multiple equilibria exist over larger range of parameters with interactive radiation