Evaluating the effective stability and springtime clouds simulated in the CAM at the SGP

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Description

Atmospheric moist processes act to reduce the resistance of air to vertical displacement. We define the effective vertical stability of the moist atmosphere as the sum of dry stability and the compensation due to diabatic heating, which is parameterized in climate models. The effective stability is a controlling factor of the potential vorticity of the atmosphere, and it affects the propagation speed of synoptic systems. The ARM variational analyses of vertical velocity and diabatic heating at the SGP are used to evaluate the effective stability simulated in the Community Climate Model CAM4. We show that during the March 2000 ARM IOP, the model simulated smaller effective stability due to large compensation of the adiabatic cooling and diabatic heating, and thus faster cyclone propagation than in observations. The cyclone propagation error can largely explain the biases of cloud amount in the CAM simulation that was initialized using operational analysis.