A New Stochastic Model for the Boundary Layer Clouds and Stratocumulus Phase Transition Regimes: Open Cells, Closed Cells, and Convective Rolls. Issue 1 (15th January 2019)

• Record Type: Journal Article
• Authors: Khouider, Boualem; Bihlo, Alexander
• Is Part Of: Journal of geophysical research. Volume 124:Issue 1(2019)
• Page Start: 367
• Page End: 386
• Publication Date: 2019-01-15
• Subjects: shallow clouds -- stratocumulus -- fog -- stochastic models -- open cells -- parametrization; Atmospheric physics -- Periodicals; Geophysics -- Periodicals; 551.5
• DOI: 10.1029/2018JD029518
• Languages: English
• ISSNs: 2169-897X

Abstract

Abstract: Adequate forecasting, nowcasting, and parameterization of fog and low clouds is still challenging despite being the focus of intensive research for a long time. Stratocumulus clouds have the ability to self‐organize into a variety of topological structures, including closed and open convection cells, convection rolls, and scattered cumulus. A lot is known about the large‐scale conditions in which shallow clouds and fog develop and decay. However, because of the various complex interactions with the environment, transitions between these various cloud regimes are hard to capture in numerical models. Recent work viewed these cloud regimes as the equilibrium states of phase transition in a stochastic model. Here we build on this idea to propose a new stochastic model based on the lattice particles‐Ising model of statistical mechanics, bringing in important improvements by allowing, for example, multiple equilibria and for direct feedback onto the large‐scale dynamics. Idealized numerical simulations demonstrate that the new model reproduces qualitatively the observed regimes of stratocumulus when the external forcing is varied. The new model forms a metastable dynamical system where transitions between extreme regimes occur dynamically, that is, within the same numerical simulation, for a large range of fixed parameter values, and sometimes lead to the co‐occurrence of mixed states with pockets of closed cells and open cells intercepted by regions of scattered cloudiness, resembling the emergence of convection rolls in nature. This is believed to be a step forward in improving the parameterization of shallow clouds in climate models. Key Points: A stochastic lattice model qualitatively reproduces the evolving distribution of the cloud area fraction (CAF) of stratocumulus The CAF model depicts the regimes of stratocumulus, including open cells, closed cells, and convection rolls as multiple equilibria Cloud regime transitions occur naturally for a large range of fixed external parameters during the time integration of the CAF model