Ww. Grabowski, Coupling cloud processes with the large-scale dynamics using the Cloud-Resolving Convection Parameterization (CRCP), J ATMOS SCI, 58(9), 2001, pp. 978-997
A formal approach is presented to couple small-scale processes associated w
ith atmospheric moist convection with the large-scale dynamics. The approac
h involves applying a two-dimensional cloud-resolving model in each column
of a three-dimensional large-scale model. In the spirit of classical convec
tion parameterization, which assumes scale separation between convection an
d the large-scale flow, the cloud-resolving models from neighboring columns
interact only through the large-scale dynamics. This approach is referred
to as Cloud-Resolving Convection Parameterization (CRCP). In short, CRCP in
volves many two-dimensional cloud-resolving models interacting in a manner
consistent with the large-scale dynamics.
The approach is first applied to the idealized problem of a convective-radi
ative equilibrium of a two-dimensional nonrotating atmosphere in the presen
ce of SST gradients. This simple dynamical setup allows comparison of CRCP
simulations with the cloud-resolving model results. In these tests, the lar
ge-scale model has various horizontal grid spacings, from 20 to 500 km, and
the CRCP domains change correspondingly. Comparison between CRCP and cloud
-resolving simulations shows that the large-scale features, such as the mea
n temperature and moisture profiles and the large-scale flow, are reasonabl
y well represented in CRCP simulations. However, the interaction between as
cending and descending branches through the gravity wave mechanism, as well
as organization of convection into mesoscale convective systems, are poorl
y captured. These results illustrate the limitations of not only CRCP, but
also convection parameterization in general.
The CRCP approach is also applied to the idealized problem of a rotating co
nstant-SST aquaplanet in convective-radiative equilibrium. The global CRCP
simulation features pronounced large-scale organization of convection withi
n the equatorial waveguide. A prominent solitary equatorial "super cloud cl
uster'' develops toward the end of the 80-day long simulation, which bears
a strong resemblance to the Madden-Julian oscillation observed in the terre
strial Tropics.