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#            Gridded Monthly Northern Hemisphere Snow Cover Extent           #
#          at 1/4, 1/2 and 1 Degree Spatial Resolutions (1986-1995)          #
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File Name Convention
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The following files are included in this data set:

snow_cover_data_XX_YYYY.csv: Original files submitted by the Principal 
Investigator in tabular format. These original data contain gridded Northern 
Hemisphere monthly snow cover extent, in percent, arranged within 10 yearly 
files. XX is qd, hd, or 1d indicating a spatial resolution of one quarter, one 
half, or 1 degree, respectively, in both latitude and longitude. YYYY is the 
year from 1986 to 1995. These files are in the "snow_cover_data" directories. 
See below for complete file descriptions.

snow_cover_map_1d_YYYYMM00.asc: 120 files with the 1 degree gridded snow cover 
extent arranged on a global grid. YYYY is the year from 1986 to 1995 and MM is 
the month from 01 to 12. The 00 means this is a monthly average. These files are 
in the "snow_cover_map_1deg" directory. NOTE***: At this revision, these files 
are only available at a 1 degree spatial resolution. 

snow_cover_mask_diffs_1d.asc: Gridded file with values describing the 
differences between the 1 degree ISLSCP II land/water mask and the 1 degree 
original land/water mask. The values here can be 0, 1, or 2 (see below for 
description).


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ASCII File Format
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1) Original Files (snow_cover_data_XX_YYYY.csv)
All of the files in the ISLSCP Initiative II data collection are in the ASCII, 
or text format. The original data files snow_cover_data_XX_YYYY.csv all have a 
total of 15 columns separated by a single comma and a number of rows that ranges 
from 8585 (File "snow_cover_data_1d_1994.csv") to 140621 (File 
"snow_cover_data_qd_1987.csv"). No data are written to the tables for cells which 
had 0% snow cover for the entire year. Only numerical fields are included as 
described below. The contents for each column are given below:

LON: Longitude for the center of a cell in decimal degrees

LAT: Latitude for the center of a cell in decimal degrees

JAN: Percentage of time in the month of January of the year YYYY that a 
particular cell was snow covered.

FEB: Percentage of time in the month of February of the year YYYY that a 
particular cell was snow covered.

...

DEC: Percentage of time in the month of December of the year YYYY that a 
particular cell was snow covered.

LAND_MASK: Value of the 1 degree ISLSCP II land/water mask (0 = Water; 1 = Land)


2) "Mapped" Files
The file format for the "mapped" monthly snow cover extent files 
"snow_cover_map_1d_YYYYMM00.asc" and the snow_cover_mask_diffs_1d.asc files 
consists of numerical fields of varying length, which are delimited by a single 
space and arranged in columns and rows. The files each contain 360 columns by 
180 rows. All values in these files are written as real numbers. Water cells in 
the "snow_cover_map_1d_YYYYMM00.asc" files are given the value -99. There are 3 
cells over land that have no data (value=-88).

For the "snow_cover_mask_diffs_1d.asc" file the values range from 0 to 2 and mean 
the following:
  0 = Data sets agree over land or water
  1 = ISLSCP II 1 degree mask is water and original 1 degree data show land (439 
      points)
  2 = ISLSCP II 1 degree mask is land and original 1 degree data show water (76 
      points)

These files are all gridded to a common equal-angle lat/long grid, where the 
coordinates of the upper left corner of the files are located at 180 degrees W, 
90 degrees N and the lower right corner coordinates are located at 180 degrees E, 
90 degrees S. Data in the files are ordered from North to South and from West
to East beginning at 180 degrees West and 90 degrees North.