Canadian Meteorological Centre (CMC) Daily Snow Depth Analysis Data

Summary

This data set consists of Northern Hemisphere daily snow depth analysis data processed by the Canadian Meteorological Centre (CMC). Snow depth data obtained from surface synoptic observations (synops), meteorological aviation reports (metars), and special aviation reports (SAs) were acquired from the World Meteorological Organization (WMO) information system for use in the CMC analyses. This CMC data set includes daily observations from 1998 through 2013 and will be updated annually. Monthly averages and monthly climatologies of snow depth and estimated Snow Water Equivalent (SWE) are provided, where SWE was estimated using a density look-up table. The volume of the data set is approximately four gigabytes. Data are provided in tab-delimited ASCII text files and are available via FTP.

Citing These Data

We kindly request that you cite the use of this data set in a publication using the following citation example. For more information, see our Use and Copyright Web page.

Brown, Ross D. and Bruce Brasnett. 2010, updated annually. Canadian Meteorological Centre (CMC) Daily Snow Depth Analysis Data. © Environment Canada, 2010. Boulder, Colorado USA: National Snow and Ice Data Center.

Important: These data are provided by Environment Canada for research purposes only. Refer to the Conditions of Data Use section before working with these data.

Overview Table

Category Description
Data format ASCII tab-delimited text
Audio-Visual Interleave (AVI animation)
Graphic Interchange Format (GIF image)
Spatial coverage and resolution Southernmost Latitude: 0° N
Northernmost Latitude: 90° N
Westernmost Longitude: 180° W
Easternmost Longitude: 180° E

Spatial resolution: 24 km
Temporal coverage and resolution 01 August 1998 - 31 December 2013
Daily data collection
Tools for accessing data Any text editor or Web browser
Any video/media player software
File naming convention File names vary; refer to Table 2 for details on file name variables.
File size 1 - 900 MB
Parameter(s) Snow Depth
Snow Water Equivalent (SWE)
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

Ross D. Brown
Environment Canada
Climate Processes and Earth Observation Division
Environment Canada @ Ouranos
550 Sherbrooke St. West, 19th Floor
Montréal QC H3A 1B9
Canada

Bruce Brasnett
Meteorological Service of Canada
2121 Trans Canada Highway
Dorval, QC H9P 1J3
Canada

Technical Contact

NSIDC User Services
National Snow and Ice Data Center
CIRES, 449 UCB
University of Colorado
Boulder, CO 80309-0449  USA
phone: +1 303.492.6199
fax: +1 303.492.2468
form: Contact NSIDC User Services
e-mail: nsidc@nsidc.org


2. Detailed Data Description

Format

The CMC data files are in ASCII tab-delimited format for the Northern Hemisphere and have been interpolated to a 24 km resolution (706 x 706 pixel) polar stereographic grid that closely approximates the grid used for the NOAA Interactive Multisensor Snow and Ice Mapping System (IMS) daily snow cover product.

Northern Hemisphere Daily Snow Depth Files

A Northern Hemisphere subset of the daily global analysis was created on a standard 24 km polar stereographic grid that closely approximates the grid used by NOAA for the 24 km daily IMS snow product. At 706 pixels, the grid covers a slightly smaller area than the full 1024-pixel IMS grid. The land/sea mask should be used to remove snow over sea ice and over Greenland.

Grid Specification:
North Polar Stereographic
NI = 706, NJ=706 (bottom left grid point = 1,1)
Grid rotation -10°
Pole position = 353, 353
Grid resolution at 60°N = 23812.5 m

Geocoordinates:
The latitude and longitude coordinates corresponding to the center of each grid point is provided in the file cmc_analysis_ps_lat_long.txt.

Data Format:
Each file contains one year of data with the following FORTRAN statements:

do 1001 iday=1,ndays ! 365 or 366 depending on # days in year
write(60,*) idate ! date in format YYYYMMDDHH where HH is always 00
do 1002 i=1,NI
write(60,100) (sdep(i,j),j=1,706) !cm
100 format(706(1x,f5.1)) !values exceeding 1000 set to 999.9
1002 continue
1001 continue

Note: In 1998, the data start at 01 August, listed as 1998080100 in the data file.

Land/Sea Mask

The CMC analysis includes snow on sea ice. A custom binary (0,1) land/sea mask is provided to mask out ocean areas and Greenland. Land (mask=1) was assigned for grid land cover fractions greater than or equal to fifty percent. The array should be read in as follows:

open(50,file='cmc_analysis_lsmask_binary_nogland.txt',status='old')
do 5 i=1,706
read(50,21) (lsmask(i,j),j=1,706)
21 format(706(i1))
5 continue

Monthly Average Snow Depth Files

Monthly average snow depth data are included with one year of data per file with naming convention: cmc_analysis_mly_avg_YYYY.txt. An upper snow depth limit of 600 cm was applied to the recent analyses to maintain continuity. The land/sea mask should be used to remove snow over sea ice and over Greenland where the analysis is unreliable.

Each file contains one year of data with the following FORTRAN statements:

do 1000 imon=1,12
write(60,*) iyear,imon
do 1001 i=1,ni
write(60,100) (sd_avg(i,j),j=1,706) !cm
100 format(706(1x,f5.1))
1001 continue
1000 continue

Note: In 1998, the data start in April.

File and Directory Structure

The directory structure on the FTP site is described in Table 1.


Table 1. Directories and Contents
Top Level Directory Description of Contents
nsidc0447_CMC_snow_depth_v01 Along with three subdirectories, the top-level directory contains the following files:

cmc_analysis_ps_lat_long.zip: Provides the position of grid points (latitude/longitude coordinates) for the Northern polar stereographic grid centered on the pole.

cmc_analysis_lsmask_binary_nogl.zip: Land/sea mask defining ocean points for the data set.

ps_cmc_sdepth_analyses_yyyy_ascii.zip: Snow depth analyses data files.

Subdirectories Description of Contents
Monthly_Climatologies This subdirectory contains the following files:

cmc_monthly_mean_sdep_animation_1999-2006.avi: Snow depth animation file.

cmc_sdep_legend.gif: Snow depth legend file.

cmc_sdep_mly_climatol_1998to2012.zip: Mean monthly snow depth climatology, snow seasons (Aug-July) beginning 1998-2012. Note: snow seasons span two calendar years, e.g. Aug. 1998 to July 1999.

cmc_swe_mly_climatol_1998to2012.zip: Mean monthly SWE climatology, snow seasons (Oct-Jun) beginning 1998-2012. Note: snow seasons span two calendar years, e.g. Oct. 1998 to Jun. 1999.

Monthly_Snow_Depth_Files Contains monthly average files for each calendar year from 1998-2013:
cmc_analysis_mly_avg_yyyy.zip
Monthly_SWE_Estimates Contains one file with monthly average SWE values for each calendar year from 1998-2013:
cmc_mly_swe_1998to2013.zip

For a description of file names, refer to Table 2.


File Naming Convention

The data files employ a variety of naming conventions. All file name variables are listed and described in Table 2.

Table 2. Description of File Name Variables
Variable Description
cmc Refers to the Canadian Meteorological Centre
ps Refers to the Polar Stereographic grid
long Longitude
lat Latitude
ims Refers to the Interactive Multisensor Snow and Ice Mapping System
lsmask Land/sea mask
nogl No Greenland (used in land/sea mask file that masks out Greenland)
sdep Snow depth
sdepth Snow depth
mly Monthly
climatol Climatology
swe Snow Water Equivalent
avg Average
yyyy 4-digit year¹
.zip Indicates this is a zipped file
.gz Indicates this is a zipped file
.txt Indicates this is an ASCII text file
.avi Indicates this is an animation file
.gif Indicates that this is a GIF image file
¹yyyy in climatology files refers to the start of the snow season.

File Size

The files included in this data set range from approximately 1 MB to 900 MB.

Spatial Coverage

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

Spatial Resolution

The analysis has a resolution of 1/3° Gaussian. The error correlations used by the analysis have an e-folding distance of approximately 120 km horizontally and 800 m vertically.

Temporal Coverage

Data include daily observations from 01 August 1998 to 31 December 2013.

Temporal Resolution

The analysis is updated every six hours, but only the 00 hour analysis is archived in this data set.. For more information, refer to the Processing Steps section of this document.

Parameter or Variable

This data set includes all available real-time snow depth observation measurements from synops, metars, and SAs.

Parameter Description

Snow Water Equivalent

Monthly average estimates of SWE (mm) are also included in this data set. Monthly average SWE for the October through June period of each year was estimated from monthly average snow depth files applying a look-up table (see Table 3) of mean monthly snow density values. Mean monthly snow density values were derived from Canadian snow course observations corresponding to snow climate classes in the Sturm et al. (1995) classification. The July through September time period was not processed due to a lack of observed snow density information during the time period.

Table 3 lists the mean monthly snow density look-up table used to estimate SWE based on Canadian snow course observations averaged over the snow-climate classes defined by Sturm et al. (1995) (Brown and Mote, 2009). This assumes the Canadian density observations are representative of snow-climate classes in other regions of the Northern Hemisphere.

Table 3. Parameter Range and Description
Month Tundra Taiga Maritime Ephemeral Prairie Alpine
Oct 200.0 160.0 160.0 250.0 140.0 160.0
Nov 210.7 176.9 183.5 300.0 161.6 172.0
Dec 218.1 179.8 197.7 335.1 185.1 181.6
Jan 230.3 193.1 216.5 316.8 213.7 207.2
Feb 242.7 205.9 248.5 337.3 241.6 241.5
Mar 254.4 221.8 283.3 364.3 261.0 263.5
Apr 273.6 263.2 332.0 404.6 308.0 312.0
May 311.7 319.0 396.3 458.6 398.1 399.6
Jun 369.3 393.4 501.0 509.8 464.5 488.9

The method used in Sturm et al. (1995) for snow climate classification interpolated from the 0.5° by 0.5° gridded version at the National Snow and Ice Data Center (NSIDC) (Liston and Sturm 1998) to the 24 km polar stereographic grid of the monthly averaged snow depth. This process resulted in land/sea confusion at a number of points which were excluded from the analysis. The number of points affected by this problem (nconf) is indicated in the header record for each month.

The SWE estimates are contained in a single file (cmc_mly_swe_1998to2013.txt) with -999.0 values at all grid points where SWE could not be calculated (such as ocean or Sturm snow-class undefined). Greenland was excluded from the analysis as the analysis is considered unreliable in this area. Values were written as tab-delimited with the following FORTRAN statements:

write(60,*)iyear,imonth,nconf
do 1002 i=1,ni
write(60,107) (swe(i,j),j=1,706) !mm
107 format(706(1x,f6.1))
1002 continue

Note: In 1998, values start on 01 August.


Snow Depth and Estimated SWE Climatologies

Monthly average snow depth and SWE climatologies for the 1998/99 to 2012/13 snow seasons are included along with an animation of monthly mean snow depth averaged over the 1999-2006 period (cmc_monthly_mean_sdep_animation_1999-2006.avi). The land/sea mask was applied to these outputs. A legend for the snow depth animation is included in a separate GIF image file; units are cm.

The monthly snow depth climatology includes values from January to December while the SWE climatology includes values from October to June. Both files are written in comma-delimited latitude-longitude tagged format with a single header record containing the variable names.

Sample Analysis Image

Figure 1 displays an example of the CMC analysis data used for evaluating Global Climate Model (GCM) output from Brown and Mote (2008).

 
Sample CMC Analysis Image
Figure 1. Sample of CMC Analysis Data Used for Evaluating Model Output
Comparison of thirteen GCM mean SWEmax (panel 2) with estimated SWEmax from CMC daily snow depth analyses (panel 1) for 2001-2006. The mean model bias (model-CMC) is shown in panel 3. From top to bottom, Figure 1 displays panels 1, 2, and 3. Sample analysis image courtesy of Ross Brown.

Quality Assessment

A complete description of the analysis methodology and validation is published in Brasnett (1999). The methodology was applied to carry out a reanalysis of snow depths over North America for the Atmospheric Model Intercomparison Project - 2 (AMIP-2) project from 1979-1997 using a more elaborate snow model for the first guess field (Brown, et al. 2003). The scheme makes use of an analysis of screen-level temperature produced with vertical correlations taken into account.

Over most of the Arctic region there are no observations, so the analysis is based on estimated snow depths from the first guess field. In addition, snow depth observations over northern Canada tend to be biased to coastal locations with observing sites at open areas near airports. The snow at these sites tends to be shallower and to melt out earlier than snow in surrounding terrain.

In cold, high precipitation environments, such as Greenland, the snow accumulation is capped at 600 cm to avoid excessive amounts of snow accumulating. The analysis is not considered reliable in these regions. This limit was changed to 1200 cm in October 2008 when a Limited Area Model (LAM) version of the analysis was implemented over British Columbia. Verification of that product showed it had insufficient residual snow during the summer months due to the 600 cm limit, so the limit was also changed in the global analysis. Mean annual snowfall in some locations in British Columbia exceeds 1000 cm, so this limit is not unreasonable. The following mean annual snowfall levels for the 1951 through 1980 normal climate period confirms this assertion:

Allison Pass: 1431.5 cm
Rogers Pass: 1106.7 cm
Pine Pass: 1075.5
Tahtsa Lake: 1041.2
Mt. Fidelity: 1974.8 cm

Values exceeding 1000 cm after 01 January 2007 were set to 999.9 to conform to the existing database format.

Error Sources

The analysis had been run essentially unchanged from 12 March 1998. An error was introduced into the operational implementation of the analysis in October 2006, but this has been corrected in offline runs and an offline version of the analysis is being run in parallel with the operational analysis to maintain data continuity.

Prior to 04 January 2010, the analyses from October 2006 were inadvertently run with the vertical correlation component of the optimal interpolation switched off which would have affected snow depths in mountainous areas. These files were corrected and replaced on 04 January 2010. The error resulted in slightly lower continental snow cover extent (less than 10 percent) from October to June, but 10 to 20 percent underestimates of snow cover extent from July to September.

Error Sources Update, 13 February 2012:
A change in the resolution of the GEM model generating the forecast precipitation fields in 31 October 2006 from 100 km to 33 km has likely resulted in increased SWE values. A preliminary evaluation over Arctic land areas suggests maximum SWE values are approximately 20 mm higher after the implementation of the higher resolution version of GEM.

Error Sources Update, 05 April 2013:

Data prior to 01 August 1998 have been removed from the data archive as the snowpack model used in the analysis was unable to be properly initialized for the 1997/98 snow season. The snow depths have been determined to be anomalously high in consequence.

3. Data Access and Tools

Data Access

Data are available via FTP.

Volume

The volume of this data set is approximately four gigabytes.

Software and Tools

Tools appropriate for viewing these data include any video or media software package and any text editor or Web browser.

Conditions of Data Use

  1. Grant of License:
    The Government of Canada (Environment Canada) is the owner of all intellectual property rights (including copyright) of this Data Product. You are granted a limited, non-exclusive, non-assignable and non-transferable license to use this data product for research purposes only subject to the terms below. This license is not a sale of any or all of the owner's rights. This product may only be used by you, and you may not rent, lease, lend, sell, sub-license or transfer the data product or any of your rights under this agreement to anyone else.

  2. Redistribution Restrictions:
    You are not authorized to further distribute the data, including any portion of it, contained in this product.

  3. No Warranties:
    Environment Canada does not warrant the quality, accuracy, or completeness of any information or data. Such information and data is provided "as is" without warranty or condition of any nature. Environment Canada disclaims all other warranties, expressed or implied, including but not limited to implied warranties of merchantability and fitness for a particular purpose, with respect to the software, the data retrieved from this product, and any accompanying materials.

  4. Restriction and Limitation of Liability:
    In no event shall Environment Canada be liable for any other damages whatsoever (including, without limitation, damages for loss of business profits, business interruption, loss of business information, or other pecuniary loss) arising out of the use of, or inability to use this Environment Canada product, even if Environment Canada has been advised of the possibility of such damages.

  5. Responsible Use:
    It is your responsibility to ensure that your use of this product complies with these terms and to seek prior written permission from Environment Canada and pay any additional fees or royalties, as may be required, for any uses not permitted or not specified in this agreement.

  6. Acceptance of this Agreement:
    Any use whatsoever of this Data Product shall constitute your acceptance of the terms of this agreement.

Related Data Collections

4. Data Acquisition and Processing

Data Acquisition Methods

Real-time snow depth data were originally acquired from the World Meteorological Organization (WMO) information system.

Processing Steps

The analysis is updated every six hours using the method of optimum interpolation with an initial guess field provided by a simple snow accumulation and melt model using analyzed temperatures and forecast (six hour) precipitation from the CMC Global Environmental Multiscale (GEM) forecast model. The precipitation is assumed to be snow if the analyzed screen-level temperature is less than 0 degrees. A degree-day melting algorithm removes mass from the snowpack at the rate of 0.15 mm-h-1-K-1.

In regions where there are no observations of snow depth, the snow depth shown in the analysis corresponds to the initial guess field simplified assumptions regarding snowfall, melt and aging.

Note: When there is an ice cover, the analysis will accumulate snow on it so the snow field can extend over water bodies. This can be masked out if desired.

Snowpack Density

The first-guess snow model assumes the density of new snow to be 100 kg/m3 and the snowpack gradually increases in density as it ages. The increase in density with aging stops when the density reaches 300kg/m3 (except 210 kg/m3 if the vegetation is needleleaf forest, since in these regions the canopy shelters the snowpack from wind and sunlight and densities are less). New snow causes the density to decrease by an amount related to the mass of the new snow and the mass of the existing snowpack. During melting, the density is allowed to increase up to a maximum of 550 kg/m3.

5. References and Related Publications

Brasnett, Bruce. 1999. A Global Analysis of Snow Depth for Numerical Weather Prediction. Journal of Applied Meteorology 38: 726-740.

Brown, Ross D. and Philip W. Mote. 2009. The Response of Northern Hemisphere Snow Cover to a Changing Climate. Journal of Climate 22: 2124–2145.

Brown, Ross D., Brasnett, Bruce, and David Robison. 2003. Gridded North American Monthly Snow Depth and Snow Water Equivalent for GCM Evaluation. Atmosphere-Ocean 41: 1-14.

Liston, G. E., and M. Sturm. 1998. A Snow-Transport Model for Complex Terrain. Journal of Glaciology 44: 498-516.

Sturm, M., J. Holmgren, and G. E. Liston. 1995. A Seasonal Snow Cover Classification System for Local to Global Applications. Journal of Climate 8: 1261-1283.

6. Document Information

Acronyms and Abbreviations

Table 4 lists the acronyms and abbreviations used in this document.

Table 4. Acronyms and Abbreviations
Acronym Description
AMSR-E Advanced Microwave Scanning Radiometer - Earth Observing System
AMIP-2 Atmospheric Model Intercomparison Project - 2
ASCII American Standard Code for Information Interchange
AVI Audio-Visual Interleave (video format)
CMC Canadian Meteorological Centre
DAAC Distributed Active Archive Center
FTP File Transfer Protocol
GCM Global Climate Model and/or General Circulation Model
GEM Global Environmental Multiscale
GIF Graphic Interchange Format
IMS Interactive Multisensor Snow and Ice Mapping System
LAM Limited Area Model
Metars Meteorological aviation reports
N/A Not Applicable
NASA National Aeronautics and Space Administration
NOAA National Oceanic and Atmospheric Administration
NSIDC National Snow and Ice Data Center
SA Special Aviation report
SWE Snow Water Equivalent
Synops Surface synoptic observations
TM Thematic Mapper
URL Uniform Resource Locator
WMO World Meteorological Organization

Document Creation Date

January 2010

Document Revision Date

February 2012

Document URL

http://nsidc.org/data/docs/daac/nsidc0447_CMC_snow_depth/index.html