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Title: On the reversibility of transitions between closed and open cellular convection

The two-way transition between closed and open cellular convection is addressed in an idealized cloud resolving modeling framework. A series of cloud resolving simulations shows that the transition between closed and open cellular states is asymmetrical, and characterized by a rapid ("runaway") transition from the closed- to the open-cell state, but slower recovery to the closed-cell state. Given that precipitation initiates the closed-open cell transition, and that the recovery requires a suppression of the precipitation, we apply an ad hoc time-varying drop concentration to initiate and suppress precipitation. We show that the asymmetry in the two-way transition occurs even for very rapid drop concentration replenishment. The primary barrier to recovery is the loss in turbulence kinetic energy (TKE) associated with the loss in cloud water (and associated radiative cooling), and the stabilization of the boundary layer during the open-cell period. In transitioning from the open to the closed state, the system faces the Sisyphusian task of replenishing cloud water fast enough to counter precipitation losses, such that it can generate radiative cooling and TKE. Recovery to the closed cell state is slower when radiative cooling is inefficient such as in the presence of free tropospheric clouds, or after sunrise, whenmore » it is hampered by the absorption of shortwave radiation. Tests suggest that a faster return to the closed-cell state requires that the drop concentration recovery be accompanied by significant dynamical forcing, e.g., via an increase in surface latent and sensible heat fluxes. This is supported by simulations with a simple predator-prey dynamical system analogue. It is suggested that the observed closing of open cells by ship effluent likely occurs when aerosol intrusions are large, when contact comes prior to the heaviest drizzle in the early morning hours, and when the free troposphere is cloud-free.« less
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Atmospheric Chemistry and Physics Discussions (Online)
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Journal Name: Atmospheric Chemistry and Physics Discussions (Online); Journal Volume: 15; Journal Issue: 4; Journal ID: ISSN 1680-7375
European Geosciences Union
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