Northern Hemisphere Seasonal and Intermittent Frozen Ground Areas, 1901-2001

Summary

This data set contains monthly values of the total exposed land area of seasonally frozen ground and annual values for intermittently frozen ground in the Northern Hemisphere. Seasonally frozen ground is defined as the near-surface soil that experiences freeze for more than 15 days per year, while intermittently frozen ground experiences fewer than 15 days of freeze per year. The values were calculated based upon the monthly mean air temperature from the 1901-2002, 0.5 deg. global land temperatures from the University of East Anglia Climate Research Unit (Mitchell and Jones, 2005) using the technique described by Zhang, et al. (2003).

Two ASCII files are available. One file contains monthly values of seasonally frozen ground area in square kilometers for 1901-2001. The other file contains annual values of intermittently frozen ground area. Data are available via FTP.

Citing These Data

Zhang, T. and J. Smith. 2005. Northern Hemisphere seasonal and intermittent frozen ground areas, 1901-2001. Boulder, CO: National Snow and Ice Data Center. Digital media.

Overview Table

Category	Description
Data format	ASCII text files
Spatial coverage and resolution	Southernmost Latitude: 0°N Northernmost Latitude: 90°N Westernmost Longitude: 180°W Easternmost Longitude: 180°E
Temporal coverage and resolution	Monthly values of seasonally frozen ground and annual values of intermittently frozen ground for 1901 - 2002
File naming convention	"seasonal_frozen_area.txt" and "intermittent_frozen_area.txt"
File size	16 KB and 4 KB
Parameter(s)	Area (km2) of seasonally or intermittently frozen ground
Procedures for obtaining data	Data are available via FTP.

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

Investigators

Tingjun Zhang
National Snow and Ice Data Center
CIRES, 449 UCB
University of Colorado
Boulder, CO 80309-0449

Technical Contact

Acknowledgments

This study was supported by the U. S. National Science Foundation (NSF) Office of Polar Programs through grant OPP-9907541 and the National Oceanic and Atmospheric Administration (NOAA) through grant NA06GP0582.

The EASE-Grid land-ocean-coastline-ice (LOCI) mask was derived from the Boston University version of global 1 km land cover from MODIS 2001, version 4, courtesy of K. Knowles, National Snow and Ice Data Center, Boulder, CO.

2. Detailed Data Description

Format

ASCII text tables with fixed width columns. Each file has a four line header with column headers and a brief description of the data values.

File Naming Convention

"seasonal_frozen_area.txt" and "intermittent_frozen_area.txt"

File Size

"seasonal_frozen_area.txt" is 16 KB
"intermittent_frozen_area.txt" is 4 KB

Spatial Coverage

Northern Hemisphere

Southernmost Latitude: 0°N
Northernmost Latitude: 90°N
Westernmost Longitude: 180°W
Easternmost Longitude: 180°E

Spatial Resolution

Values were derived from 0.5° gridded data (Mitchell and Jones 2005).

Temporal Coverage

1901 - 2001

Temporal Resolution

Monthly for seasonally frozen ground and annual for intermittently frozen ground.

Parameter or Variable

Parameter Description

Monthly values of the total area of seasonally frozen ground in km² and annual values of the total area of intermittently frozen ground in km². Seasonally frozen ground is defined as the near-surface soil that experiences freeze for more than 15 days per year, while intermittently frozen ground experiences fewer than 15 days of freeze per year.The specifics of calculating these values from monthly mean air temperatures is described in section 4.

Sample Data Record

The following values come from "seasonal_frozen_area.txt":

Year   January  February    March     April      May      June      July     August  September   October  November  December
----  --------  --------  --------  --------  --------  --------  --------  --------  --------  --------  --------  --------
1901                                                               1212145   2208127  14535686  34029291  48517220  53636003
1902  54199660  53681875  47683360  37908909  22461443   7558155   1109719   2111357  14388017  35094395  48522247  53745341
1903  54653979  53460057  48665517  35513524  21643921   7225742   1245449   2728426  15270891  35041611  48755376  54975709
1904  55138460  52695318  49236715  37847327  19809680   6206509   1223456   2573216  16884571  33879736  47848623  53801267

Errors and Uncertainty

Missing values in the source data were replaced with the 1961-1990 climatological values as described in Mitchell and Jones (2005).

3. Data Access and Tools

Data Access

Data are available via FTP

Volume

"seasonal_frozen_area.txt" is 16 KB
"intermittent_frozen_area.txt" is 4 KB

Related Data Collections

• See Northern Hemisphere EASE-Grid Annual Freezing and Thawing Indices, 1901 - 2002

4. Data Acquisition and Processing

Theory of Measurements and Processing Steps

Seasonally frozen ground is defined as the near-surface soil that experiences freeze for more than 15 days per year, while intermittently frozen ground experiences fewer than 15 days of freeze per year. Zhang, et al. (2003) established a relationship between near-surface soil freeze/thaw status and mean monthly air temperatures. They compared daily 5 cm soil temperature data from several Russian hydrometeorological stations with mean monthly air temperature. The station measurements indicate that soils experience freezing at 5 cm for several weeks when the mean monthly air temperature is at or near 0°C. This relationship led to the algorithm where seasonally frozen ground areas are defined as the areas that experience annually at least one month with a mean monthly air temperature of 0°C or less, or two months with mean monthly air temperatures of 5°C or less. Intermittently frozen ground areas experience only one month of mean monthly air temperatures less than or equal to 5°C. The values were calculated based upon the monthly mean air temperature from the 1901-2002, 0.5 deg. global land temperatures from the University of East Anglia Climate Research Unit (Mitchell and Jones, 2005) regridded to the NSIDC Equal Area Scalable Earth Grid (EASE-Grid). Zhang et al. (2003) provide more information on the methodology.

Data Source

These data were derived from the 1901-2002 0.5° gridded monthly global land temperatures from the University of East Anglia Climatic Research Unit (Mitchell and Jones, 2005).

Land areas are derived from the EASE-Grid land-ocean-coastline-ice (LOCI) mask was derived from the Boston University version of global 1 km land cover from MODIS 2001, version 4, courtesy of K. Knowles, National Snow and Ice Data Center, Boulder, CO.

5. References and Related Publications

Zhang, T., R. G. Barry, K. Knowles, F. Ling, and R. L. Armstrong. 2003. Distribution of seasonally and perennially frozen ground in the Northern Hemisphere. in Phillips, M., S. M. Springman, and L. U. Arenson (editors). Permafrost: Proceedings of the Eighth International Conference on Permafrost, 21-25 July 2003, Zurich, Switzerland. Lisse, The Netherlands: A.A. Balkema.

Mitchell T. D. and P. D. Jones. 2005. An improved method of constructing a database of monthly climate observations and associated high-resolution grids. International Journal of Climatology 25, 693-712.

6. Document Information

List of Acronyms

The following acronyms are used in this document:

ASCII: American Standard Code for Information Interchange
EASE-Grid: Equal-Area Scalable Earth Grid
FTP: File Transfer Protocol
NSF: National Science Foundation
NSIDC: National Snow and Ice Data Center
URL: Uniform Resource Locator

Document Creation Date

31 January 2006

Document Review Date

Document URL

http://nsidc.org/data/docs/fgdc/ggd650_froz_ground_area/index.html