Suppression of Arctic Air Formation by Cloud Radiative Effects in a Two-Dimensional Cloud Resolving Model

Abstract:

To better understand equable paleoclimates, Arctic amplification of winter warming, and the high-latitude lapse-rate feedback, we investigate the process of Arctic air formation, wherein a high latitude maritime air mass is advected over land during polar night and strongly cooled from the surface up. We extend previous work done using a single-column model (Cronin and Tziperman, PNAS, in press) by performing two-dimensional idealized cloud-resolving simulations with the Weather Research and Forecasting (WRF) model. Quantitatively consistent with previous results, we find that as the initial atmospheric state is warmed, increases in low cloud amount reduce the average surface cooling over a 14-day period by roughly a degree for each degree of warming of the initial atmospheric state, with the feedback strength increasing with warming. This is primarily attributed to a monotonic increase in surface cloud radiative forcing of approximately 2 W m^-2 for each degree that the initial atmospheric sounding is warmed. The use of a two-dimensional model as opposed to a single-column model shows that the lower-tropospheric cloud layer becomes more turbulent and dominated by cumulus clouds as the climate is warmed, yet the cloud fraction remains high owing to the continued prevalence of stratus and fog layers. These results are robust across a variety of cloud microphysics schemes and are not sensitive to the horizontal or vertical resolution of the model. We also explore the vertical structure and horizontal variability of the bulk horizontal flow, the sensitivity of the results to subsidence and atmospheric carbon dioxide concentration, and the contrasting roles of top-of-atmosphere and surface cloud radiative effects.