Low-level mesocyclonic concentration by nonaxisymmetric transport, Part II

J. Atmos. Sci., 63, 1113-113

Parameterization of convective clouds, mesoscale convective systems, and convective-generated cirrus

A level 2.5w deep convection updraft/downdraft parameterization scheme has been refined and tested against 3D simulations of sea-breeze generated convection over S. Florida. Cases for explicit simulation of MCSs in mid-latitudes and tropics have been encouraging. After a few refinements in those cases, fine resolution explicit simualtions of deep convection and mesoscale, stratiform clouds will be begun

Explicit simulation and parameterization of mesoscale convective systems. Final report, November 1, 1993--April 30, 1997

This research has focused on the development of a parameterization scheme for mesoscale convective systems (MCSs), to be used in numerical weather prediction models with grid spacing too coarse to explicitly simulate such systems. This is an extension to cumulus parameterization schemes, which have long been used to account for the unresolved effects of convection in numerical models. Although MCSs generally require an extended sequence of numerous deep convective cells in order to develop into their characteristic sizes and to persist for their typical durations, their effects on the large scale environment are significantly different than that due to the collective effects of numerous ordinary deep convective cells. These differences are largely due to a large stratiform cloud that develops fairly early in the MCS life-cycle, where mesoscale circulations and dynamics interact with the environment in ways that call for a distinct MCS parameterization. Comparing an MCS and a collection of deep convection that ingests the same amount of boundary layer air and moisture over an extended several hour period, the MCS will generally generates more stratiform rainfall, produce longer-lasting and optically thicker cirrus, and result in different vertical distributions of large-scale tendencies due to latent heating and moistening, momentum transfers, and radiational heating

A cumulus parameterization scheme designed for nested grid meso-. beta. scale models

A generalized cumulus parameterization based upon higher order turbulence closure has been incorporated into one dimensional simulations. The scheme consists of a level 2.5w turbulence closure scheme mated with a convective adjustment scheme. The convective adjustment scheme includes a gradient term which can be interpreted as either a subsidence term when the scheme is used in large scale models or a mesoscale compensation term when the scheme is used in mesoscale models. The scheme also includes a convective adjustment term which is interpreted as a detrainment term in large scale models. In mesoscale models, the mesoscale compensation term and the advection by the mean vertical motions combine to yield no net advection which is desirable since the convective moistening and heating is now wholly accomplished by the convective adjustment term; double counting is then explicitly eliminated. One dimensional simulations indicate satisfactory performance of the cumulus parameterization scheme for a non-entraining updraft

Development and testing of an aerosol/stratus cloud parameterization scheme for middle and high latitudes. Year 3 technical progress report, November 1, 1996--August 31, 1997

At the present time, general circulation models (GCMs) poorly represent clouds, to the extent that they cannot be relied upon to simulate the climatic effects of increasing concentrations of greenhouse gases, or of anthropogenic perturbations to concentrations of cloud condensation nuclei (CCN) or ice nuclei (IN). The net radiative forcing of clouds varies strongly with latitude. Poleward of 30 degrees in both hemispheres, low-level clouds create a net cooling effect corresponding to radiative divergences of {minus}50 to {minus}100 W/m{sup 2}. It is likely that a combination of fogs, boundary-layer stratocumulus, and stratus clouds are the main contributors to this forcing. Models of the response of the microphysical and radiative properties of clouds to changes in aerosol abundance, for a variety of large-scale meteorological forcings, are important additions to GCMs used for the study of the role of Arctic systems in global climate. The overall objective of this research is the development of an aerosol/cloud microphysics parameterization of mixed-phase stratus and boundary-layer clouds which responds to variations in CCN and IN. The parameterization is to be designed for ultimate use in GCM simulations as a tool in understanding the role of CCN, IN, and Arctic clouds in radiation budgets. Several versions of the CSU RAMS (Regional Atmospheric Modeling System) will be used during the course of this work. The parameterizations developed in this research are intended for application in a single-column cloud model, designed as an adaptive grid model which can interface into a GCM vertical grid through distinct layers of the troposphere where the presence of layer clouds is expected