• subgrid variability;
  • microphysics;
  • drizzle;
  • parametrization


Part I of this two-part series presents a method to account for the effects of subgrid variability on average microphysical process rates. The method involves upscaling a local microphysics scheme, that is, computing a grid-box average by integrating over an assumed probability density function (PDF). In this paper (Part II), the method is tested. The test case is based on research flight two (RF02) of the second Dynamics and Chemistry of Marine Stratocumulus (DYCOMS-II) field experiment. The upscaled microphysics scheme is incorporated into a single-column model (SCM). Then two SCM simulations of the RF02 test case are performed. They are identical except that one upscales the local microphysics scheme and one does not. Both SCM simulations are compared with a benchmark large-eddy simulation (LES) of the same test case using the same local microphysics scheme.

Compared to the local microphysics, the representation of variability inherent in the upscaled microphysics increases autoconversion of cloud droplets to raindrops and accretion (i.e. collection) of cloud droplets onto raindrops. The combined effect is that upscaling the microphysics in the RF02 case leads to significantly more rainwater at the ocean surface, in closer agreement to the LES. Copyright © 2012 Royal Meteorological Society