---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.