Goal:

Performing Cloud Resolving Model (CRM) simulations with horizontal grid spacings of about 1 km to explicitly simulate convection over the continental U.S.

Simulations verified against observations from the IHOP field program and also used to develop improved convective parameterizations for weather and climate prediction models.

Key scientific aspect: understand how convection, radiation, cloud-microphysics, boundary layer and surface processes interact and collectively affect large scales.

First, we will incorporate a surface scheme (e.g. LSM) into the CRM to realize an interactively atmosphere-land coupled modeling system (i.e., the counterpart of our atmosphere-ocean explicitly coupled system developed in CCP).

Second, we will conduct multi-day simulations using a mesoscale-domain CRM driven by the above large-scale forcing. This major task has many facets:

a) orogenic convection and the subsequent multiscale propagating convective systems responsible for the sequences of precipitation;

b) sensitivity of the simulated cloud systems to parameterizations of cloud microphysics and cloud-radiation interaction (i.e., on the nocturnal evolution of convection);

c) the importance of large-scale forcing compared to surface forcing by the land-surface processes;

d) the dynamical effects of wind shear on longevity, propagation and its analytic approximation;

e) the multiscale organization and propagation of convection over land compared to the corresponding properties over the tropical oceans, the motivation being to investigate universal mechanisms involving the role of wind shear; and

f) develop microphysical parameterization schemes, in the first instance for the CRM, and eventually for weather prediction models and climate models.

Key points concerning atmospheric convection:

Convective cloud systems and attendant interactions among the physical processes at cloud-to-meso scales play a key role in the atmospheric processing of water (vapor, liquid and solid phases).

Precipitating convection tends to get organized into mesoscale systems, which strongly affect the atmosphere and its boundary conditions.

The mesoscale organization of convection is an intrinsically upscale process whose large-scale implications are not understood.

Convection initiation (therefore the diurnal cycle of precipitation) depends on the concept of metastability, which is a function of highly nonlinear interactions between the planetary boundary layer and the free atmosphere.

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