MESOSCALE NUMERICAL-SIMULATION OF CIRRUS CLOUDS - FIRE CASE-STUDY AND SENSITIVITY ANALYSIS

The 28 October 1986 First ISCCP (International Satellite Cloud Climatology Program) Regional Experiment (FIRE) case was simulated using the Regional Atmospheric Modeling System developed at Colorado State University. This three-dimensional mesoscale model was applied in nonhydrostatic and nested-grid mode using explicit, bulk microphysics and radiation. The simulation resulted in very good agreement between observed and model-predicted dynamic and cloud fields. Cloud height, thickness, areal extent, and microphysical composition were verified against GOES satellite imagery, lidar, and aircraft measurements taken during the FIRE cirrus intensive field observation. Cloud-top generation zones and layering were simulated. Sensitivity simulations were run to determine long- and shortwave radiative forcing. Also, a simulation was run with no condensate to examine cloud feedbacks on the environment. Longwave radiation appeared to be instrumental in developing weak convective-like activity, thereby increasing the cloud's optical depth.