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ISLSCP II Northern Hemisphere Monthly Snow Cover Extent
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Revision date: April 26, 2010


This ISLSCP data set is derived from the National Snow and Ice Data Center (NSIDC) Northern Hemisphere EASE-Grid Weekly Snow Cover and Sea Ice Extent product which combines snow cover and sea ice extent at weekly intervals for October 1978 through June 2001, and snow cover alone from 1966 through June 2001. The original data set was the first representation of combined snow and sea ice measurements derived from satellite observations for the period of record. Designed to facilitate study of Northern Hemisphere seasonal fluctuations of snow cover and sea ice extent, the original NSIDC data set also includes monthly climatologies describing average extent, probability of occurrence, and variance.

This data set shows the extent of snow on the land at a variety of scales (1.0 degree, 0.5 degree, 0.25 degree). The values represent the percentage of days in each month where snow was present -- 100 means 100% of the month, 80 means 80% of the month, etc. There are 4 .zip files provided. Missing data is represented by -99 for water and -88 for land. The data were originally in a yearly tabular format. The file was converted to multi-scale maps by plotting each point in the tabular data onto a map of -99 (water) and -88 (land) created from the standard ISLSCP II Land/Sea Mask.

Additional Documentation:

This data set is one of the products of the International Satellite Land-Surface Climatology Project, Initiative II (ISLSCP II) data collection which contains 50 global time series data sets for the ten-year period 1986 to 1995. A complete description of the data, it's derivation, acknowledgements, and references provided by the ISLSCP II Data Management Staff is included with this data set as a companion file named 1_snow_cover_doc.pdf .

ISLSCP II is a consistent collection of data sets that were compiled from existing data sources and algorithms, and were designed to satisfy the needs of modelers and investigators of the global carbon, water and energy cycle. The data were acquired from a number of U.S. and international agencies, universities, and institutions. The data and documentation have undergone two peer reviews.

ISLSCP is one of several projects of Global Energy and Water Cycle Experiment (GEWEX) [] and has the lead role in addressing land-atmosphere interactions -- process modeling, data retrieval algorithms, field experiment design and execution, and the development of global data sets.

Related Data Sets

ISLSCP II Global Sea Ice Concentration

ISLSCP II Sea Surface Temperature

Data Citation:

Cite this data set as follows:

Armstrong, R. L., and M. J. Brodzik. 2010. ISLSCP II Northern Hemisphere Monthly Snow Cover Extent. In Hall, Forrest G., G. Collatz, B. Meeson, S. Los, E. Brown de Colstoun, and D. Landis (eds.). ISLSCP Initiative II Collection.  Data set. Available on-line [] from Oak Ridge National Laboratory Distributed Active Archive Center, Oak Ridge, Tennessee, U.S.A. doi:10.3334/ORNLDAAC/982

File Information:

The archived data sets for ISLSCP II have been organized by categories. This data set is in the Snow, Sea Ice, and Oceans -- a collection of snow, oceans, and sea ice data sets.

Data Set Spatial Extent: Global gridded

Westernmost Longitude: -180 W

Easternmost Longitude: 180 E

Northernmost Latitude: 90 N

Southernmost Latitude: -90 S

Projection: Geographic

Data Set Spatial Resolution: one, half, and quarter degree in both latitude and longitude

Data Set Temporal Extent: January 1986-December 1995

Data File Format

All of the data files in each data set within the ISLSCP Initiative II data collection are in standard ASCII grid format. The file format consists of numerical fields of varying length, which are delimited by a single space and arranged in columns and rows.

There are three data files (.zip files) in this data set at one degree (1deg), half degree (hdeg), and quarter degree (qdeg) spatial resolution. Each file contains ten .csv files of original data for the years 1986-1995: when extrapolated  contains 10 files: snow_cover_data_1deg_1986.csv through snow_cover_data_1deg_1995.csv  when extrapolated contains 10 files: snow_cover_data_hdeg_1986.csv through snow_cover_data_hdeg_1995.csv : when extrapolated contains 10 files: snow_cover_data_qdeg_1986 .csv through snow_cover_data_qdeg_1995.csv

There is also the file which when extrapolated contains 120 files ( a file for each month of each of the ten years) with the one degree gridded snow cover extent data arranged on a global grid. This zip file also includes snow_cover_mask_diffs_1d.asc: a gridded ASCII map showing the difference between the ISLSCP II land/water mask and the original data set. These files are in standard ESRI ArcGIS ASCII grid format.


Data file naming conventions are further described in the 1_snow_cover_doc.pdf and  0_snow_cover_readme.txt .

Data Access:

These data are available through the Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC) [].

Data Archive Contact Information:

Telephone: +1 (865) 241-3952