The buffering of Arctic mixed-phase stratocumulus to mean state perturbations

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Description

A recent study by Solomon et al. (2014) demonstrated that Arctic mixed-phase stratocumulus (AMPS) have remarkable insensitivity to changes in moisture source. This study used a suite of idealized large eddy simulations, based on AMPS observed during the Department of Energy Atmospheric Radiation Measurement Program’s Indirect and Semi-Direct Aerosol Campaign (ISDAC) (McFarquhar et al. 2011) near Barrow, Alaska, that varied water vapor above and below the cloud-driven mixed layer. It was found that when the overlying air is dried initially, radiative cooling and turbulent entrainment increase moisture import from the surface layer. When the surface layer is dried initially, the system evolves to a state with reduced mixed-layer water vapor and increased surface layer moisture, reducing the loss of water through precipitation and entrainment of near-surface air. Only when moisture is reduced both above and below the mixed layer does the AMPS decay without reaching a quasi-equilibrium state. In this follow-up study we investigate the sensitivity of the persistent equilibrated state found in Solomon et al. (2014) to perturbations in subsidence, surface fluxes, and radiation. Buffered feedbacks are identified and discussed that prevent the cloud system from collapsing when perturbed. Alternatively, thresholds in perturbations are identified where the equilibrated state cannot be maintained.