EXPLORATORY CLOUD-RESOLVING SIMULATIONS OF BOUNDARY-LAYER ARCTIC STRATUS CLOUDS PART-I - WARM-SEASON CLOUDS

Two-dimensional simulations of arctic stratus clouds (ASC) were conduc ted using a sophisticated cloud-resolving model with explicit microphy sics and a two-stream radiative transfer model. The effects of varying cloud condensation nuclei (CCN) concentrations upon the subsequent cl oud and its microphysical, radiative and dynamical structure were stud ied. In this study CCN concentrations were varied within the ranges fo und in warm-season arctic boundary layers (ABLs) to produce non-drizzl ing and weakly drizzling stratus decks. Experiments that included all model physics, no-drizzle, and no shortwave radiation were conducted t o elucidate the effects of microphysics and radiation on the simulated stratus. Both simulations that did and that did not include the effec ts of drizzle showed that the higher CCN concentrations produced a clo ud with larger reflectivity and absorptivity, but also produced eddies that were weaker than with lower CCN concentrations. Simulations that included the effects of drizzle showed a similar response to changes in CCN concentrations. Simulations with no drizzle produced more vigor ous eddies than their drizzling counterparts because cooling due to ev aporation below cloud tends to stabilize the ABL. The simulations with out the effects of short-wave radiation produced very vigorous eddies that penetrated more deeply into the ABL. In this case, the simulation with higher CCN concentrations produced the most vigorous eddies. Thi s resulted from a subtle interplay of microphysics, radiation, and dyn amics. (C) 1998 Elsevier Science B.V. All rights reserved.