---TITLE: CASPR-ARCMIP EASE GRID data set ---AUTHORS: Prof. Judith Curry School of Earth and Atmospheric Sciences Georgia Institute of Technology Atlanta, GA 30332-0340 office: 404 894-3955 fax: 404 894-5638 e-mail: curryja@eas.gatech.edu Contact for data questions : Randolph A. Reeder Aerospace Engineering Dept. University of Colorado Boulder, CO 80309 office: 303 492-4266 e-mail: rreeder@cloud.colorado.edu ---DATA SET OVERVIEW: The CASPR-ARCMIP EASE GRID data set consists of SHEBA AVHRR Arctic satellite retrievals corresponding to the ARCMIP domain location in EASE grid coordinates for the years 1997 and 1998. The original data is the ' SHEBA AVHRR Arctic 25 km Retrievals ( version 1.0 ) ' data set produced using the Cloud and Surface Parameter Retrieval ( CASPR ) algorithms. The original data set covered the entire Arctic twice daily for all of 1997 and 1998 at 25 km resolution. It is available from the web site at http://stratus.ssec.wisc.edu/products/ This CASPR-ARCMIP EASE GRID data is a subset of the original data corresponding to a 50 km resolution grid using EASE coordinates for the ARCMIP region. The ARCMIP region is defined to be the region bounded by columns numbers 100 through 260 and rows numbers 100 through 260 of the 50 km resolution Northern Hemisphere EASE grid. Information about the EASE grid is available at http://www-nsidc.colorado.edu/data/ease/ . The program ezlhconv.f available at this site was used to convert column and row numbers into latitudes and longitudes for a 50 km resolution grid. The time period for the CASPR-ARCMIP EASE GRID data set is 01 January 1997 through 31 December 1998. Twice daily data is given for 04:00 and 14:00 hours local time. The data set consists of a total of 1459 gzipped files, one for each day ( 2 years ) and each time ( 2 per day ). There is no data for 14:00 hours on 10 March 1998 ( file caspr_1998069_1400.easegrid.nc.gz is missing. ) ---DATA FORMAT: The CASPR-ARCMIP EASE GRID data set is contained in gzipped tar files. These files contain a set of monthly data and are called caspr_yyyymm.easegrid.tar.gz where yyyy = 1997 or 1998 and mm specifies the month. Each monthly tar.gz file contains individual data files named caspr_yyyyddd_hhhh.easegrid.nc.gz . Here xxx = 001 thru 365 is the day of year and hhhh is either 0400 for 04:00 hours local time or 1400 for 14:00 hours local time. One file is missing ( 1998069_1400 ). All the files are gzipped NetCDF files containing 20 variables. Each variable is a two dimensional array indexed by row and column numbers related to the EASE grid coordinates. Most of the variables are stored as integer*2 and must be multiplied by a scale factor. The names of the variables are : 1. LAT = the latitude in degrees 2. LON = the longitude in degrees 3. LANDMASK = the surface type mask 4. TSKIN = the surface skin temperature in K 5. ALBEDO = the surface broadband albedo 6. RADIUS = the cloud droplet effective radius in micrometers 7. TAU = the cloud optical depth 8. PHASE = the cloud particle phase 9. CLDTEMP = the cloud top temperature in K 10. CLDPRES = the cloud top pressure in hPa 11. WATER = the precipitable water in cm 12. SWDSFC = downwelling shortwave radiation at surface in W/m^2 13. LWDSFC = downwelling longwave radiation at surface in W/m^2 14. SWUSFC = upwelling shortwave radiation at surface in W/m^2 15. LWUSFC = upwelling longwave radiation at surface in W/m^2 16. SWDTOA = downwelling shortwave radiation at TOA in W/m^2 17. SWUTOA = upwelling shortwave radiation at TOA in W/m^2 18. LWUTOA = upwelling longwave radiation at TOA in W/m^2 19. SWCLDF = shortwave cloud forcing at surface in W/m^2 20. LWCLDF = longwave cloud forcing at surface in W/m^2 Each file contains 25921 ( 161 * 161 ) data values for every variable. The latitude and longitude given in the files are the positions of the nearest AVHRR data to the EASE grid position specified by the row and column number. The column index nx and row index ny both run from 1 thru 161. To obtain the EASE column and row index for the Northern Hemisphere 50 km grid just add 99 to these indexes.