Radiative Impacts on the Growth of Drops within Simulated Marine Stratocumulus. Part I: Maximum Solar Heating

Christopher M. Hartman, Jerry Y. Harrington
2005 Journal of the Atmospheric Sciences  
The effects of solar heating and infrared cooling on the vapor depositional growth of cloud drops, and hence the potential for collection enhancement, is investigated. Large eddy simulation (LES) of marine stratocumulus is used to generate 600 parcel trajectories that follow the mean motions of the cloud. Thermodynamic, dynamic, and radiative cloud properties are stored for each trajectory. An offline trajectory ensemble model (TEM) coupled to a bin microphysical model that includes the
more » ... ncludes the influences of radiation on drop growth is driven by the 600-parcel dataset. In line with previous results, including infrared cooling causes a reduction in the time for collection onset. This collection enhancement increases with drop concentration. Larger concentrations (400 cm Ϫ3 ) show a reduction in collection onset time of as much as 45 min. Including infrared cooling as well as solar heating in the LES and microphysical bin models has a number of effects on the growth of cloud drops. First, shortwave (SW) heating partially offsets cloud-top longwave (LW) cooling, which naturally reduces the influence of LW cooling on drop growth. Second, SW heating dominates over LW cooling at larger drop radii (տ200 m), which causes moderately sized drops to evaporate. Third, unlike LW cooling, SW heating occurs throughout the cloud deck, which suppresses drop growth. All three of these effects tend to narrow the drop size spectrum. For intermediate drop concentrations (100-200 cm Ϫ3 ), it is shown that SW heating primarily suppresses collection initiation whereas at larger drop concentrations (տ250 cm Ϫ3 ) LW cooling dominates causing enhancements in collection.
doi:10.1175/jas3477.1 fatcat:pqc4aldrvzacxoupsmrhcjim2e