GCM simulator-oriented ISCCP cloud product

 

Description:

This document describes the GCM simulator-oriented ISCCP cloud product prepared to facilitate the evaluation of the model simulated clouds. This product is derived from the ISCCP D1 data (http://isccp.giss.nasa.gov ) which are quasi-instantaneous spatial averages of pixel-level retrievals over equal-area grid cells. Our GCM product represents monthly averages of a small subset of these observations. It is analogous to the ISCCP D2 monthly averages with the following differences:

  • We include a small subset of the observations: cloud top pressure, cloud top temperature, cloud albedo, and the full-resolution (6x7 categories) in the cloud top pressure/cloud optical thickness joint histogram.
  • Averages include only daytime observations, consistent with the ISCCP simulator being applied only to daylight points in GCMs.
  • Averages are done over the entire month at once. In contrast, D2 data are first averaged at each of the eight observation times, and the monthly mean derived from these eight hourly averages.
  • We provide two sets of averages for some variables. The default is weighted by the cloud fraction at each time, consistent with weighting by the number of cloud pixels observed and with the CFMIP data request. The alternative (variable names with suffix “_unweighted”) is a straightforward average in time.
  • These files were produced by Dr. Yuying Zhang at LLNL from equal-area data provided by Dr. Robert Pincus from University of Colorado. If you publish work that uses these data please contact us (zhang24@llnl.gov and Robert.Pincus@colorado.edu) for current citation information.

    The simulator-oriented ISCCP cloud product is provided in CF-compliant netcdf format on a latitude-longitude grid. The current data cover the period July 1983 to June 2008. Each file includes the complete time series for a single variable.

    The data files are:

    1. clisccp_198307-200806.nc: monthly mean 6x7 cloud top pressure/optical thickness (pc-tau) joint histogram.

    The following variables are weighted by cloud fraction at each time:

    1. pctisccp_198307-200806.nc: monthly mean cloud top pressure.
    2. cttisccp_198307-200806.nc: monthly mean cloud top temperature.
    3. albisccp_198307-200806.nc: monthly mean cloud albedo

    The following files contain linear averages over time:

    1. pctisccp_unweighted_198307-200806.nc: monthly mean cloud top.
    2. cttisccp_unweighted_198307-200806.nc: monthly mean cloud top temperature.
    3. albisccp_unweighted_198307-200806.nc: monthly mean cloud albedo.

    Grid-mean cloud albedo is determined from the grid-mean optical thickness (byte 92) in the ISCCP D1 using the analytic formula:

    isccp_formula.png



    This is the approximation to the ISCCP lookup tables used in the ISCCP and is used by the ISCCP simulator to compute grid-box mean cloud albedo.

     

    References:

    - Rossow, W.B., and Schiffer, R.A., 1999: Advances in Understanding Clouds from ISCCP. Bull. Amer. Meteor. Soc., 80. [PDF], 27 pp.

    - Rossow, W.B., A.W. Walker, D.E. Beuschel, and M.D. Roiter, 1996: International Satellite Cloud Climatology Project (ISCCP) Documentation of New Cloud Datasets*. WMO/TD-No. 737, World Meteorological Organization, 115 pp.

     

    Exemple of plot:

    isccp.png

     

    Ftp CMOR data access: ISCCP

     

    Matlab routine: isccp.m

     

    Contact:

    Please contact Dr. Yuying Zhang if you have any question or comments about GCM simulator Oriented ISCCP cloud product dataset.