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Data Set ID:
GGD651

Arctic EASE-Grid Freeze and Thaw Depths, 1901 - 2002, Version 1

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
deg. 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.

Geographic Coverage

Parameter(s):
  • Frozen Ground > Active Layer
  • Frozen Ground > Active Layer > Freeze/Thaw Depth
Spatial Coverage:
  • N: 90, S: 50, E: 180, W: -180

Spatial Resolution: Not Specified
Temporal Coverage:
  • 1 January 1901 to 31 December 2002
Temporal Resolution: Not specified
Data Format(s):
  • ASCII Text
Platform(s) Not specified
Sensor(s): Not specified
Version: V1
Data Contributor(s): Tingjun Zhang, R. Barry
Data Citation

As a condition of using these data, you must cite the use of this data set using the following citation. For more information, see our Use and Copyright Web page.

Zhang, T., J. McCreight, and R.G. Barry 2006. Arctic EASE-Grid Freeze and Thaw Depths, 1901 - 2002, Version 1. [Indicate subset used]. Boulder, Colorado USA. NSIDC: National Snow and Ice Data Center. [Date Accessed].

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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.

Detailed Data Description

Format

ASCII text files

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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.

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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.

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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.

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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)

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Temporal Coverage

1901 - 2002

Temporal Resolution

Annual

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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.

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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.

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Software and Tools

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Data Acquisition and Processing

Theory of Measurements and Processing Steps

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

full Stefan solution equation(1)

where:

Z = thaw depth (m)
kt = the thermal conductivity of the thawed soil (Wm-1 °C-1)
nt = the n-factor for the thaw season
DDTa = the annual thawing index (°C-day), defined as the cumulative number of degree-days above 0°C over a year
Pb = 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):

Simplified Stefan solution equation (2)

where

edaphic factor equationn(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:

Simplified Stefan Solution equation to calculate freeze depth.

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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.

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References and Related Publications

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

No technical references available for this data set.
No FAQs or How Tos available for this data set.

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