Improving Cloud Microphysics in the IPRC Regional Climate Model

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Improving Cloud Microphysics in the IPRC Regional
Climate Model
A. Lauer (IPRC), V. Phillips (UH), and Y. Wang
(IPRC)
(b) New cloud scheme
(c) MODIS, July 2002-2007
(a) Old cloud scheme
Important cloud properties, such as precipitation
formation efficiency and cloud optical
properties, depend strongly on the number and
size of cloud droplets. Cloud droplet number
concentrations of low maritime clouds retrieved
from NASA MODIS satellite observations (c) reveal
that droplet density is high near the coastlines
and then falls off dramatically toward remote
ocean regions, reflecting the dominant
continental sources of the aerosols that serve as
cloud condensation nuclei. Until recently,
computational limitations only allowed the use of
a bulk treatment for cloud microphysics (a),
which assumed a constant number of cloud droplets
(100/cm3 over oceans and 300/cm3 over land) and
could not reproduce the observed fine structure
of cloud droplet density. In contrast, a new
cloud scheme (b) implemented into the IPRC
Regional Climate Model calculates cloud droplet
density explicitly by taking into account
numerous physical and cloud microphysical
processes. This version will now allow IPRC
scientists to study the impact of anthropogenic
aerosol emissions on cloud properties including
cloud climate forcing.
Courtesy of Ralf Bennartz, University of
Wisconsin - Madison