A Simple Framework for the Dynamic Response of Cirrus Clouds to Local Diabatic Radiative Heating

TL;DR

This paper introduces a simple analytical framework describing how cirrus clouds dynamically respond to local radiative heating, identifying three main adjustment modes and validating them with numerical simulations.

Contribution

It presents a novel, simplified analytical model for cirrus cloud response to radiative heating, capturing three distinct adjustment modes and demonstrating potential for climate model parameterization.

Findings

Three cloud adjustment modes identified: isentropic ascent, turbulent spreading, and evaporation.

Model predictions align well with high-resolution numerical simulations.

Framework offers a computationally efficient way to incorporate cloud-radiation interactions in climate models.

Abstract

This paper presents a simple analytical framework for the dynamic response of cirrus to a local radiative flux convergence, expressible in terms of three independent modes of cloud evolution. Horizontally narrow and tenuous clouds within a stable environment adjust to radiative heating by ascending gradually across isentropes while spreading sufficiently fast so as to keep isentropic surfaces nearly flat. More optically dense clouds experience very concentrated heating, and if they are also very broad, they develop a convecting mixed layer. Along isentropic spreading still occurs, but in the form of turbulent density currents rather than laminar flows. A third adjustment mode relates to evaporation, which erodes cloudy air as it lofts. The dominant mode is determined from two dimensionless numbers, whose predictive power is shown in comparisons with high resolution numerical cloud simulations. The power and simplicity of the approach hints that fast, sub-grid scale radiative-dynamic atmospheric interactions might be efficiently parameterized within slower, coarse-grid climate models.