Simulations of Cloud-Aerosol-Precipitation Interactions for Convective Clouds in ASR/ARM case studies

 

Author

Andrew Gettelman — National Center for Atmospheric Research (NCAR)

Category

Warm Low Clouds and Interactions with Aerosol

Description

We investigate aerosol invigoration effects on convection using a physically based two-moment bulk convective microphysics scheme in the Community Earth System Model (CESM) General Circulation Model (GCM) and it's single column atmosphere model (SCAM). SCAM simulations are forced by ARM/ASR and other large-scale forcing data for tropical and mid-latitude convective cases, using order of magnitude perturbations to activated aerosol number. The aerosol perturbations result in noticeable changes of convective characteristics. Liquid and ice water path, cloud top heights, and high cloud fraction increase with increased aerosol loadings. Increased aerosols results in updraft mass flux increases below freezing the level, but decreasing nass fluxes above the freezing level. The result appears due to more stable atmosphere layers formed by enhanced latent heat releasing below the freezing level. Increasing aerosol also decreases the incident solar radiation into the atmosphere through more reflection on the increased ice mass (up to -100 W/m2), and more longwave radiative heating is trapped by the ice mass and liquid condensates (up to 40 W/m2). There are noticeable decreases in light to moderate rain and increases in heavy rain with increased aerosol loadings. The global impacts of convective microphysics are also assessed.

Lead PI

Andrew Gettelman — National Center for Atmospheric Research (NCAR)