Arctic EASE-Grid Freeze and Thaw Depths, 1901 - 2002

Summary

This data set contains mean, median, minimum and maximum freeze and thaw depths for each year from 1901 to 2002 on the 25 km resolution Equal-Area Scalable Earth Grid (EASE-Grid) for areas north of 50°. Freeze and thaw depths are estimated using a variant of the Stefan solution using an edaphic factor and freezing or thawing indices as inputs. The edaphic factor is estimated based on different land surface types; the freezing and thawing indices are from Northern Hemisphere EASE-Grid annual freezing and thawing indices, 1901 - 2002 (Zhang, et al. 2005).

Two ASCII files are available for each year for freeze depth and thaw depth, respectively. Each file is approximately 25.6 MB in size. In addition, there is one 10.5 MB ASCII file defining the latitude and longitude coordinates for each grid point. The data set is available via FTP as three compressed files.

Citing These Data

Zhang, T., J. McCreight, and R. G. Barry. 2006. Arctic EASE-Grid freeze and thaw depths, 1901 - 2002. 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: 50°N Northernmost Latitude: 90°N Westernmost Longitude: 180°W Easternmost Longitude: 180°E
Temporal coverage and resolution	Annual values for 1901 - 2002
File naming convention	"ease25_XXX_depth.yyyy.txt" where "XXX" is either "frz" for freeze depth or "thw" for thaw depth, and "yyyy" is the four digit year. "E25_lon_lat_nh.txt" contains the grid coordinates.
File size	Two compressed tar files (freeze depth = 173.8 MB, thaw depth = 305.6 MB) containing 102 25.6 MB text files plus one 2.6 MB compressed text file. The total uncompressed volume is approximately 5.1 GB.
Parameter(s)	median, mean, standard deviation, minimum, and maximum freeze and thaw depths
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
Roger G. Barry
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 grants OPP-0229766 and OPP-0352910 and the International Arctic Research Center, University of Alaska Fairbanks, under the auspices of the NSF cooperative agreement number OPP-0327664.

2. Detailed Data Description

Format

ASCII text files

File and Directory Structure

The data set consistes of two tarred and compressed files, "ease25_frz_depth.tgz" and "ease25_thw_depth.tgz", containing 101 freeze depth and 102 thaw depth files, respectively, plus and one compressed text file, "E25_lon_lat_nh.gz", defining the grid points.

File Naming Convention

"ease25_frz_depth.tgz" contains 101 files in the format "ease25_frz_depth.yyyy.txt", where "yyyy" is the four digit year. "ease25_thw_depth.tgz" contains 101 files in the format "ease25_thw_depth.yyyy.txt", where "yyyy" is the four digit year. In addition, "E25_lon_lat_nh.txt" contains the grid coordinates.

File Size

Data are in two compressed tar files (freeze depth = 173.8 MB, thaw depth = 305.6 MB) containing 102 text files, 25.6 MB each, plus one 2.6 MB compressed text file. The total uncompressed volume is approximately 5.1 GB.

Spatial Coverage

Northern Hemisphere

Southernmost Latitude: 50°N
Northernmost Latitude: 90°N
Westernmost Longitude: 180°W
Easternmost Longitude: 180°E

Spatial Resolution

25 km

Projection

Lambert-Azimuthal Equal Area projection on a spherical geoid (See All About EASE-Grid)

Grid Description

25-km Northern Hemisphere EASE-Grid (See All About EASE-Grid)

Temporal Coverage

1901 - 2002

Temporal Resolution

Annual

Parameter or Variable

Parameter Description

Values for each file are, in column order, median, mean, standard deviation in depth, minimum, and maximum freeze and thaw depths. Depths are calculated using median, mean, standard deviation, minimum, and maximum edaphic factors.

Sample Data Record

The following values come from "ease25_thw_depth.1981.txt":

      1.02822      1.28081      1.00488     0.359907      4.73452
      1.26628      1.18782     0.567485     0.584154      2.20349
      1.27872      1.19949     0.573059     0.589891      2.22513
      1.23724      1.16058     0.554470     0.570756      2.15295
     -999.000     -999.000     -999.000     -999.000     -999.000
     -999.000     -999.000     -999.000     -999.000     -999.000
     -999.000     -999.000     -999.000     -999.000     -999.000
     -9999.00     -9999.00     -9999.00     -9999.00     -9999.00

These values correspond to the latitudes and longitudes of the grid points listed in "E25_lon_lat_nh.txt":

      52.4834      137.231
      52.3213      136.975
      52.1583      136.721
      51.9945      136.469
      51.8299      136.219
      51.6645      135.971
      51.4982      135.725
      51.3311      135.481

-99.00 denotes urban/built up areas.
-999.00 denotes water.
-9999.00 denotes grid points off the earth.

Errors and Uncertainty

The relationship between freeze/thaw depth and freezing and thawing indices has been demonstrated in several places. For example, Brown et al. (2000) review the relationship between thaw depth and the annual thawing index. Romanovsky and Osterkamp (1995), Zhang et al. (1997), Nelson et al. (1998), Klene et al. (2001), and Hinkel and Nelson (2003) all demonstrate the general validity of the approach. Nelson et al. (1997) used the approach to map active layer depth for the Kuparuk River Basin in Alaska. Zhang et al. (2005b) also use the approach to map active layer depth in the Ob, Yenisey, and Lena River Basins of Russia.

The quality of the input freezing and thawing indices is described in Frauenfeld, et al. (submitted) and in the documentation for the data set, Northern Hemisphere EASE-Grid Annual Freezing and Thawing Indices, 1901 - 2002. The investigators conclude they are adequate for broad scale analysis. The difficulty lies in calculating the edaphic factors. There is some uncertainty in the estimation of the edaphic factors as discussed in Zhang et al. (2005b). Overall this approach is reasonable for broad scale calculations and for estimating the response of freeze and thaw depth to different climatological factors.

3. Data Access and Tools

Data Access

Data are available via FTP.

Volume

Data are in two compressed tar files (freeze depth = 173.8 MB, thaw depth = 305.6 MB) containing 102 text files, 25.6 MB each, plus one 2.6 MB compressed text file. The total uncompressed volume is approximately 5.1 GB.

Related Data Collections

• See All About EASE-Grid

4. Data Acquisition and Processing

Theory of Measurements and Processing Steps

Thaw depth can be estimated from a variant of the Stefan solution shown here.

(1)

where:

Z = thaw depth (m)
k_t = the thermal conductivity of the thawed soil (Wm^-1 °C^-1)
n_t = the n-factor for the thaw season
DDT_a = the annual thawing index (°C-day), defined as the cumulative number of degree-days above 0°C over a year
P_b = the soil bulk density (kg m^-3)
w = the soil water content by weight (dimensionless)
L = the latent heat of fusion (J kg^-1)

The relationship between thaw depth and the annual thawing index can be simplified using an catchall scaling parameter, the edaphic factor, E (Nelson and Outcalt, 1987):

(2)

where

(3)

By rearranging equation 2, the investigators were able to calculate mean, median, maximum, minimum, and standard deviation edaphic factors for 104 sites in the Circumpolar Active Layer Monitoring (CALM) Network (Nelson et al. 2005). The E values vary spatially due to changes in land cover type and soil type. To evaluate spatial variability of the edaphic factor, the investigators categorized E values based on land cover type using a 1-km resolution global land cover characteristics data set (Knowles 2004). Thawing indices were taken from Northern Hemisphere EASE-Grid Annual Freezing and Thawing Indices, 1901 - 2002 (Zhang et al. 2005a). Mean, median, maximum, minimum, and standard deviation (in depth) thaw depth values are calculated for the different E values. The approach is described in detail by Zhang et al. (2005b)

A similar approach can be used to calculate freeze depth in seasonally frozen ground areas:

Data Source

Circumpolar Active Layer Monitoring Network (CALM) (Nelson et al. 2005): Established in the 1990s, CALM observes the long-term response of the active layer and near-surface permafrost to changes and variations in climate at more than 125 sites in both hemispheres.

Northern Hemisphere EASE-Grid Annual Freezing and Thawing Indices, 1901 - 2002 (Zhang et al. 2005a): 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).

EASE-Grid Land Cover Data Resampled from AVHRR Global 1 km Land Cover, Version 2, March 1992 - April 1993 (Knowles 2004): This data set is derived primarily from 1-km Advanced Very High Resolution Radiometer (AVHRR) satellite images spanning a 12-month period from April 1992 to March 1993 from the Global Land Cover Characteristics Database.

5. References and Related Publications

Brown, J., K. M. Hinkel, and F. E. Nelson. 2000. The Circumpolar Active Layer Monitoring (CALM) program: Research designs and initial results. Polar Geogr. 24(3), 163-258.

Frauenfeld, O. W., T. Zhang, and J. L. McCreight. Submitted. Climatology and variability of the 20th century Northern Hemisphere freezing/thawing index. International Journal of Climatology.

Hinkel, K. M., and F. E. Nelson. 2003. Spatial and temporal patterns of active layer thickness at Circumpolar Active Layer Monitoring (CALM) sites in northern Alaska, 1995-2000. J. Geophys. Res., 108 (D2), 8168. doi:10.1029/2001JD000927.

Klene, A. E., F. E. Nelson, N. I. Shiklomanov, and K. M. Hinkel. 2001. The N-factor in natural landscapes: Variability of air and soil-surface temperatures, Kuparuk River Basin, Alaska. Arct. Antarct. Alp. Res., 33 (2), 140-148.

Knowles, K. 2004. EASE-Grid land cover data resampled from AVHRR Global 1 km land cover, Version 2, March 1992 - April 1993. Boulder CO, USA: National Snow and Ice Data Center. Digital media.

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.

Nelson, F. E., N. I. Shiklomanov, G. R. Mueller, K. M. Hinkel, D. A. Walker, and J. G. Bockheim. 1997. Estimating active-layer thickness over a large region: Kuparuk River basin, Alaska, U.S.A. Arct. Alp. Res. 29 (4), 367-378.

Nelson, F.E., N.I. Shiklomanov, K. M. Hinkel, and J. Brown (comp.). 2005. Circumpolar Active Layer Monitoring (CALM) Program Network. Newark, DE: University of Delaware, Department of Geography. Digital media.

Nelson, F. E., and S. I. Outcalt. 1987. A computational method for prediction and regionalization of permafrost. Arct. Alp. Res. 19, 279-288.

Nelson, F. E., S. I. Outcalt, J. Brown, N. I. Shiklomanov, and K. M. Hinkel. 1998. Spatial and temporal attributes of the active-layer thickness record, Barrow, Alaska, U.S.A. in Lewkowicz, A. and M. Allard (editors). Proceedings of 7th International Conference on Permafrost. Ste-Foy, Canada: Cent. d'Etudes Nordique, Univ. Laval, 797-802.

Romanovsky, V. E., and T. E. Osterkamp. 1995. Interannual variations of the thermal regime of the active layer and near-surface permafrost in Northern Alaska. Permafrost Periglacial Proc. 6, 313-335.

Zhang, T., O. W. Frauenfeld, J. McCreight, and R. G. Barry. 2005a. Northern Hemisphere EASE-Grid annual freezing and thawing indices, 1901 - 2002. Boulder, CO: National Snow and Ice Data Center. Digital media.

Zhang, T., O. W. Frauenfeld, M. C. Serreze, A. Etringer, C. Oelke, J. McCreight, R. G. Barry, D. Gilichinsky, D. Yang, H. Ye, F. Ling, and S. Chudinova. 2005b. Spatial and temporal variability in active layer thickness over the Russian Arctic drainage basin. J Geophysical Research 110, D16101. doi:10.1029/2004JD005642.

Zhang, T., T. E. Osterkamp, and K. Stamnes. 1997. Effects of climate on the active layer and permafrost on the north slope of Alaska, U.S.A. Permafrost Periglacial Proc. 8, 45-67.

6. Document Information

List of Acronyms

The following acronyms are used in this document:

ASCII: American Standard Code for Information Interchange
CALM: Circumpolar Active Layer Monitoring Network
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 URL

http://nsidc.org/data/docs/fgdc/ggd651_frzthw_depth_efac/index.html