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GEWEX Cloud System Study: Working Group 3


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Revision: Jan 10, 1996 - Main New Additions/p>

The utilization of cloud-resolving model (CRM) outputs to parameterize cloud effects in GCMs is one of the main components in the GCSS strategy for GCM cloud parameterization development. A list of CRM large-scale diagnostics have been suggested by GCM and CRM modellers for this purpose. This list of large-scale impact diagnostics and details of their calculations are given in the following.

A section on the definition and calculation of precipitation efficiency will be contributed by Brian Ryan. Please send additional suggestions or comments to Kit Szeto.

A. CRM Large-scale impact diagnostics:

Over subregions of the CRM with dimensions similar to those of a typical GCM grid box (~300x300 kmē x 500 m) and over a time interval representative of the typical time step used in a GCM integration, the following statistics (as functions of height and time) can be generated from the CRM outputs:

  1. Mean and variance of temperature
  2. Mean and variance of mixing ratios of various water substance, layer liquid water content, layer liquid water path, layer optical depth and surface precipitation rate
  3. Cloud coverage statistics
  4. Mean long (short) wave fluxes
  5. Fluctuations in the velocity fields and associated eddy fluxes of heat, moisture and momentum
  6. Apparent heat, moisture and momentum sources/sinks
  7. Precipitation efficiency

Calculations over subdomains with and without embedded convection (and/or CSI) would be useful. It is also understood that (2) and (3) will be calculated for the cloud types resolved by the model only.

B. Definitions and calculations:

C. Other useful CRM outputs

The development of a physically-based cloud scheme requires the knowledge of the relationships between the large-scale effects and the physical features occurring on the mesoscale (e.g. frontal features). As such, archives of all the CRM variables within selected vertical columns will be useful.

D. CRM diagnostic results

Several CRM groups (e.g. Katzfey and Ryan; Rasmussen et al.; Szeto et al.) have presented preliminary CRM large-scale diagnostic results at the WG3 workshop in New York City (Nov, 1995). Further studies such as inter-comparisons of the large-scale effects for different types of cloud systems will be needed. If you have any large-scale diagnostic results that you want to pose on this home page, please contact Kit Szeto.

D. Archives of large-scale computations

Archival format for the large-scale diagnostic calculations will be finalized during Spring of 1996. We are soliciting suggestions on the archive format, archive site, model and case-specific informations that should accompany the diagnostic results. Please send you suggestions to Kit Szeto and he will summarize the ideas and pose the guidelines for the archival format here.

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