Global Snow-Water-Equivalent Depth Coefficient-of-Variation Classification

Summary

This data set provides a global distribution of nine subgrid snow-depth-variability categories and a coefficient of variation applicable to each category, as the result of the Subgrid SNOW Distribution (SSNOWD) submodel that defines subgrid snow-depth and snow-cover variability. This data set provides the distribution of those nine categories and their coefficient-of-variation values on a global, 2.5 arc-min latitude-longitude (approximately 5-km) grid. The time period covered is 1 January 1994 through 1 January 2004.

The SSNOWD submodel was formulated to improve the depiction of autumn through spring land-atmosphere interactions and feedbacks within global weather, climate, and hydrologic models. From both atmospheric and hydrologic perspectives, the subgrid snow-depth distribution is an important quantity to account for within large-scale models. In the natural system, these subgrid snow-depth distributions are largely responsible for the mosaic of snow-covered and snow-free areas that develop as the snow melts, and the impacts of these fractional areas must be quantified in order to realistically simulate grid-averaged surface fluxes. SSNOWD's formulation incorporates observational studies showing that snow distributions can be described by a lognormal distribution and the snow-depth coefficient-of-variation (CV). Using an understanding of the physical processes that lead to these observed snow-depth variations, a global distribution of nine subgrid snow-depth-variability categories was developed, and coefficient-of-variation values were assigned to each category based on published measurements.

Data are in binary format, and are available via NCAR.

Citing These Data

Liston, Glen E. 2005. Global Snow-Water Equivalent Depth Coefficient-of-Variation Classification. Boulder, CO: National Center for Atmospheric Research, ARCSS Data Archive.

Overview Table

Category Description
Data format 2-byte binary integers
Spatial coverage and resolution Global; 2.5 arc-min latitude-longitude (approximately 5 km).
Temporal coverage and resolution Winter, from 01 January 1994 through 01 January 2004
File size Files range in size from 1 KB to 214 KB.
Parameter(s) Snow cover, snow melt, snow-water equivalent
Procedures for obtaining data Data are available for ordering through NCAR.

Table of Contents

1. Contacts and Acknowledgments
2. Detailed Data Description
3. Data Access and Tools
4. Data Acquisition and Processing
5. References and Related Publications
6. Document Information

1. Contacts and Acknowledgments

Investigator(s) Name and Title

Glen E. Liston
Department of Atmospheric Sciences
Colorado State University
Fort Collins, CO 50523-1371 USA

Technical Contact

Acknowledgements

The National Science Foundation (NSF) Geography and Regional Sciences and Arctic System Science (ARCSS) programs funded the data project. The following grants apply:

National Science Foundation Grant OPP 9415386: The Role of Snow Cover and its Distribution in Governing Heat and Mass Exchange in the Arctic.

National Science Foundation Grant OPP 0229973: Winter Precipitation, Sublimation, and Snow-Depth in the Pan-Arctic: Critical Processes and a Half Century of Change.

National Science Foundation Grant OPP 9732077: Snow, Shrubs and Weather: Winter Pathways of Change in the Arctic..

2. Detailed Data Description

This data set provides a global distribution of nine subgrid snow-depth-variability categories, as the result of the Subgrid SNOW Distribution (SSNOWD) submodel that defines subgrid snow-depth and snow-cover variability. These categories apply to land areas; water and sea ice areas are excluded from the category system.

Format

The data consist of two-byte binary integers. This data set is a single, global, two-dimensional array on a latitude-longitude grid, with a 2.5 arc-minute (approximately 5-km) grid increment.

The data indicate the nine snow-depth-variability categories. These categories have values of 1 through 9 over all land. All water grid cells have been given an undefined value of -9999.

The snow cover categories, the integer value assigned to each category, and the coefficient of variation (CV) assigned to each category are as follows:

Category
General description
CV value
1
Ephemeral snow
0.06
2
Mid-latitude, non-mountainous forest
0.09
3
High-latitude, non-mountainous forest
0.12
4
High-latitude, mountainous forest
0.17
5
Arctic tundra
0.40
6
Mid-latitude, prairie
0.50
7
Mid-latitude, mountainous forest
0.60
8
High-latitude, mountains
0.70
9
Mid-latitude, treeless mountains
0.85

File and Directory Structure

The data set consists of four files. The files include a FORTRAN routine ("ssnowd_cv_classes.f") that when compiled, will extract the data. When compiled, a text file is output that includes a text header with additional descriptive information about the data structure.

File Size

File sizes range from 1 KB to 214 MB.

Spatial Coverage

The spatial coverage of the classification system is global, but applies to only land. All water grid cells have been given an undefined value of -9999.

Southernmost Latitude: 90.00 S
Northernmost Latitude: 90.00 N
Westernmost Longitude: 180.00 W
Easternmost Longitude: 180.00 E

Spatial Resolution

Data are on a 2.5 arc-min latitude-longitude grid (0.041666667 degree; approximately 5-km).

Grid Description

The grid defines 8640 grid points in the W-E (x) direction, with the first grid point starting at -179.97916666666667 degree and incrementing by 0.041666667 degree. There are 4320 grid points in the S-N (y) direction, with the first grid point starting at -89.97916666666667 degree and incrementing by 0.041666667 degree. In other words, the center of the lower left grid cell is located at -179.97916666666667 degrees longitude, and -89.97916666666667 degrees latitude, and the grid increment is 2.5 arc-minute (0.041666667 degree; approximately 5-km).

Temporal Coverage

Data reflect conditions during winter, from 01 January 1994 through 01 January 2004.

Parameter or Variable

Parameter Description

Snow cover, snow melt, snow-water equivalent

3. Data Access and Tools

Data Access

Data are available for ordering through NCAR.

Software and Tools

The data set includes a FORTRAN routine ("ssnowd_cv_classes.f") for extracting the data.

Related Data Collections

4. Data Acquisition and Processing

Theory of Measurements

The classification categories and the corresponding coefficient-of-variation values are based on the Subgrid SNOW Distribution (SSNOWD) submodel that defines subgrid snow-depth and snow-cover variability. Snow depths vary greatly at subgrid scales; the SSNOWD model was formulated to account for subgrid snow distributions by defining nine snow-distribution categories. The nine categories are based on factors that influence snow-depth variability: air temperature, topographic variability, and wind speed. The coefficient of variation (CV, equal to the ratio of the standard deviation to the mean of the snow variation) defines the variability of snow distribution for each category. The theory of measurements and CV values are described in detail in the following published article about this data set:

Liston, G. E. 2004. Representing subgrid snow cover heterogeneities in regional and global models. Journal of Climate 17(6): 1381-97.

Data Acquisition Methods

Categories were mapped to the grid using global distributions of air temperature, topographic variability, and wind speed from several data sets. Specific coefficient-of-variation values were assigned to each of the SSNOWD categories based on published snow-distribution measurements; see Liston (2004) for a discussion of the CV values.

5. References and Related Publications

Liston, G. E. 2004. Representing subgrid snow cover heterogeneities in regional and global models. Journal of Climate 17(6): 1381-97.

See also Global Seasonal Snow Classification System

6. Document Information

Document Creation Date

20 January 2005

Document URL

http://data.eol.ucar.edu/codiac/dss/id=106.ARCSS138