ATMOSPHERIC CONVECTIVE PLUMES EMANATING FROM LEADS .2. MICROPHYSICAL AND RADIATIVE PROCESSES

A one-dimensional, second-order turbulence model with bulk cloud micro physics and detailed radiative transfer is used to simulate the evolut ion of a thermal internal boundary layer (TIBL) which develops above a wide, open lead. A mixed-phase cloud, originally based at the surface , is produced within the TIBL. The cloud initially fills the entire TI BL but is later elevated above the surface with its top coincident wit h the top of the TIBL. Model-derived cloud ice and cloud liquid water mixing ratios exceed 0.06 g kg(-1) directly above the open lead, with a secondary maximum near the top of the TIBL. In addition, precipitati ng ice particles or snow fills the TIBL with a maximum snow mixing rat io of about 0.05 g kg(-1). Radiative flux divergence results in strong cooling at cloud top (which contributes to the local maxima in cloud water mixing ratio at this level) and warming near the surface. The le ad-induced cloud increases the downwelling long-wave irradiance receiv ed at the surface by up to 70 W m(-2) (reducing the surface radiative cooling by over 40%) during the baseline case. This value is quite sen sitive to the assumed particle size and cloud particle concentration. The vertical structure and composition of the lead-induced cloud is sh own to strongly depend on the rate of snow production and the cloud wa ter partitioning.