Historical Soviet Daily Snow Depth (HSDSD) Version 2

Summary

The Historical Soviet Daily Snow Depth Version 2 (HSDSD) product on CD-ROM updates and replaces HSDSD Version 1. The new version contains an additional ten years of data, improved data quality control, an HTML interface, and a Java tool for data browsing and extraction. Data now span from 1881 (for the earliest operational stations) through 1995. Other parameters include snow cover percent, snow characteristics, site characterization, and quality flags. Data are in ASCII format.

The HSDSD product is based on observations from 284 World Meteorological Organization (WMO) stations throughout Russia and the former Soviet Union. The area covered is 35 to 75 degrees north latitude and 20 to 180 degrees east longitude. The State Hydrometeorological Service in Obninsk, Russia, sent the data to NSIDC through the bilateral US-USSR Working Group Eight data exchange program.

The development of this data product was funded through NOAA's Environmental Services Data and Information Management (ESDIM) program, and through the support of the NOAA/NESDIS National Geophysical Data Center. Data are available on one CD-ROM available for download via FTP.

Citing These Data

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.

Armstrong, R. 2001. Historical Soviet daily snow depth version 2 (HSDSD). Boulder, CO: National Snow and Ice Data Center. CD-ROM. http://dx.doi.org/10.7265/N5JW8BS3

Overview Table
 

Category Description
Data format ASCII
Spatial coverage and resolution 35oN to 75oN, 20oE to 180oE
Resolution varies; irregular sampling locations
Temporal coverage and resolution 1881 through 1995, daily measurements
Tools for accessing data HTML and Java browse and extraction tools on CD-ROM
Parameter(s) Snow depth
Metadata access View metadata
Data access The CD-ROM is available for download via FTP: soviet_snow_depth.zip (76.2 MB).

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

Richard Armstrong
National Snow and Ice Data Center
CIRES, 449 UCB, University of Colorado, Boulder, CO, USA 80309-0449

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

Data are stored in ASCII text files. See individual data sections below for descriptions of formats.

Daily Data

File names for daily data contain the letters "dat" and the WMO station number (for example, "dat22887.dat"). Data fields are fixed length and comma-delimited with a total record length of 26 characters. Each day appears as a separate record with the following parameters:

Sample Data Records for dat22887.dat:

1966, 1, 1,0,1,0,20, 23, 0
1966, 1, 2,0,1,0,20, 23, 0
1966, 1, 3,0,1,0,20, 28, 0

For the first record:

1966 : Year
1 : Month
1 : Day
0 : Snow cover percentage (SCP)
These data were not subject to additional quality control at NSIDC; suspect values may exist.
1 : Snow cover characteristic (SCC)
0 : Snow cover quality (SCQ)
20 : 2 = Location characteristic (LC)
0 = Location quality (LQ for the quality of the site characterization)
23 : Snow depth in cm (SD)
_0 : _= Snow depth characteristic (SDC)  In this case, the field is blank.
0 = Snow depth quality (SDQ)
If only one zero exists in this field, the user should read it as zero for both fields.

Codes for sample data records:

Year  Mon  Day  SCP  SCC  SCQ  LC/
 LQ
 SD SDC/
SDQ
1966   1   1   0,   1,   0,  20,  23,  0
1966   1   2   0,   1,   0,  20,  23,  0
1966   1   3   0,   1,   0,  20,  28,  0

Detailed Field Description:

Table 1. Examples for fields SCP, SCC, and SCQ.
("N" is any number between 0 and 9.)

Situation SCP  SCC  SCQ 
Value is reliable      
  Snow cover is from 0 to 9 
         (0% to 90%)
N 0 0
  Snow cover is 100%  0 1 0
  Temporary snow melting 0 2 0
Value is suspect  N 0 2
Value is rejected 9 9 3
Observation was not made 9 9 4

Table 2. Meaning of values found in field LC.

Code - LC Site Characteristic 
Site is protected from strong wind
2 Site is open to wind 
Observations are made at two sites
There is no information about the site's characteristic
Site is not protected and not always open 
Type of site is not specified and therefore snow depth is not measured 
Site characteristic value was rejected or observations were not made. 

Table 3. Examples of values found in fields LC and LQ, and field LC values for given values of LQ.
("N" is any site characteristic code; any number between 1 and 9. See Table 2).

Situation  LC  LQ 
Value is correct  0
Type of the site is not specified; therefore, snow depth is not measured
Continuous snow melting (summer) 0
Value is suspect
Value is rejected
Observations were not made

Table 4. Example snow depth values (column SD) for given values of SDC and SDQ, and snow depth and SDC values for given values of SDQ.
("NNN" indicates any snow depth measurement in cm.)

Situation SD  SDC  SDQ
Value is correct (C3 = 0 or blank) NNN 
Snow cover is less than 0.5 cm  000 
Snow cover absent at site; however, snow is in the vicinity and a coverage is specified. 000 
Value suspected to be humidity - set to 000 or 999 000 5 0
Snow depth was identified as high by a factor of ten and was rescaled by 0.1 NNN 6 0
Snow depth was identified as low by a factor of ten and was rescaled by 10 NNN 7 0
Continuous snow melting (summer) 000 
Temporary snow melting 000  0
Value is suspect NNN  2
Value is rejected 999  3
No observations 999  4

Seasonal Summary Data

NSIDC computed the first and last dates of existing snow. All years (1881 through 1995) are included even if no data were reported. File names for seasonal summary data contain the letters "sea" and the WMO station number (for example, "sea22887.dat"). Data fields are fixed length and comma-delimited with a total record length of 34 characters. All data files are in the "seasonal_summary" directory and contain the following fields:

Sample Data Records:

1965,29,10,1964,303, 3, 5,1965,123
1966,13,10,1965,286,30, 4,1966,120
1967,15,10,1966,288,20, 4,1967,110
1968,23,10,1967,296,30, 4,1968,121

A hydrological year runs from October through the following September. For example, the hydrological year 1978 runs from October 1977 through September 1978. All other years in the seasonal summary data refer to the standard calendar year.

Monthly Climatology Data

NSIDC generated monthly climatological data for a 30-year time series (1966-1995). The data are stored in fixed length, comma-delimited fields with a total record length of 46 characters. The first record contains the station number for the file. Records 2 through 11 contain the data fields. The monthly climatology file names contain the letters "clm" and the WMO station number (for example, "clm22887.dat"). The files are stored in the "climatology" directory. The following fields are included:

First record:

Second and continuing records:

Sample Data Records for clm22887.dat

38987 
 1  8.457,  7.758,  269, 16.538,  11.079, 26,  1.130,  0.344,  23

The first record indicates data for station 38987. The second record contains the following fields:

Data Manipulation:

The monthly climatological data are calculated using all observations from 1966 to 1995 for each individual month. The mean depth and standard deviation are generated with data from all valid days in a given month.

The mean maximum and minimum depth are calculated based on the number of months of valid data between 1966 and 1995. Because each month has only one maximum and minimum, a maximum of 30 values are averaged for these fields.

The number of valid and missing days inform the user of the number of days of data. Large numbers of missing days indicate that the station closed or that its data records were not included in the latest update (1985 through 1995).

In October 2001, NSIDC discovered errors in these snow depth climatology files. The data have been correted and are included in the CD-ROM zip file on the FTP site. Note: There is one file missing from the corrected climatologies: clm37171.dat.

Monthly Summary Data

These data include the number of days where snow depth was greater than 5 cm, 10 cm, or 50 cm. File names for monthly summary data contain the letters "sum" and the WMO station number (for example, "sum22887.dat"). All data fields are fixed length and comma-delimited. The total record length is 16 characters. The data files are in the "monthly" directory. A value of "-2" indicates missing data.

The data fields are as follows:

Sample Data Record:

1966, 1,31,31, 0
1966, 2,28,28,10
1966, 3,31,31,28

Synoptic Data

The synoptic data product includes data for single days from every station from 1966 through 1995. These data are intended for validation of remote sensing or other projects that require data for a single day over a large spatial extent. All data files are in the "synoptic" directory. The file name contains the year, month, and day of the data contained in each file (for example, "19831226.dat"). Each field is fixed length and comma-delimited with a total record length of 37 characters. The data in each record include:

Sample Data Records for 19891221.dat:

20674 73.5  80.4 0047 0,1,0,20, 12, 0
20891 72.0 102.5 0033 0,1,0,20, 19, 0
21946 70.6 147.9 0048 0,1,0,20, 18, 0

For the first record:

20674 : WMO station number
73.5 : Station latitude
80.4 : Station longitude
0047 : Station elevation
0 : Snow cover percentage (SCP)
1 : Snow cover characteristic (SCC)
0 : Snow cover quality (SCQ)
20 : 2 = Location characteristic (LC)
0 = Location quality (LQ for the quality of the site characterization)
12 : Snow depth in cm (SD)
_0 : _ = Snow depth characteristic (SDC). In this case the field is blank.
0 = Snow depth quality (SDQ).
If only one zero exists in this field, the user should read it as zero for both fields.

Example codes for sample data records:

WMO
#
Lat Lon Alt SCP SCC SCQ LC/
LQ
SD SDC/
SDQ
20674 73.5 80.4 0047 0, 1, 0, 20, 12, 0
20891 72.0 102.5 0033 0, 1, 0, 20, 19, 0
21946 70.6 147.9 0048 0, 1, 0, 20, 18, 0

Detailed Field Description:

Spatial Coverage

WMO stations are primarily located in inhabited areas within the middle latitudes of Eurasia: 35 to 75 degrees north latitude and and 20 to 180 degrees east longitude.

Spatial Resolution

Resolution varies; data were collected from irregular sampling locations. See a list of weather stations.

Temporal Coverage

Data span from 1881 (for the earliest operational stations) through 1995.

Temporal Resolution

Data were collected daily.

Quality Assessment

Systematic data gaps (caused by breaks in station function or punch card deterioration) are set to default values. To estimate the quality of the data, each snow depth value in the archive is followed by characteristic (C) and quality (Q) flags set to one of the following values:

CQ
00: valid value
02: suspect value
93: rejected value
94: observation was not made

Field positions are filled with "9" for quality flag values of "3" or "4". NSIDC added additional flags in the characteristic field to indicate data with errors that were fixed during processing. Data flagged in this manner have a quality value of "0", indicating valid data. The numeric flags are as follows:

50 - Humidity data
60 - Snow depth high by a factor of ten
70 - Snow depth low by a factor of ten

The quality flag is set to "99" for invalid dates such as 30 February.

NSIDC checked the locations of the meteorological stations against the WMO station directory for close correlation.

NSIDC developed a quality control routine to correct gross errors within the data. This routine differs from that used in Version 1 of the Historical Soviet Daily Snow Depth; therefore, Version 2 data supersede all Version 1 data.

NSIDC developed an improved quality control routine for HSDSD Version 2, based on input from several users of HSDSD Version 1. Results were compared to manually-corrected Version 1 raw data independently developed by Dr. David Robinson at Rutgers University.

The new algorithm checks for data entries outside of two standard deviations from the monthly mean and examines these entries for the following known errors:

Corrections to Factor of Ten Errors

NSIDC noted anomalously large snow depth fluctuations -- often more than a normal snowfall -- and determined that the data changed by a factor of ten, for example, from 11 cm one day to 110 cm the next.

The Russian and USSR data collection instructions required snow depth in cm and precipitation in mm. NSIDC discovered errors in transcribing or reporting the snow depth, for example, confusing the units of snow depth and precipitation in the original data; therefore, if a change in snow depth was greater than or equal to two standard deviations from the mean, a factor of ten error was investigated. If the value had changed by approximately a factor of ten, NSIDC rescaled the data by 0.10.

Other data appeared to be a factor of ten lower than data from the surrounding days. If the value had changed to a single digit and could be explained by a factor of ten decrease, NSIDC rescaled the value by ten.

For both types of factor of ten errors, NSIDC checked the corrected value for plausibility by evaluating the difference between the mean daily change for the previous day and that of the corrected current day.

Humidity Flag Corrections

The completed HSDSD data product contains no humidity values; however, the raw data uses the same field for both snow depth and humidity data, depending on the season. A data quality flag of "50" indicates that humidity data were recorded. This flag was occasionally missed during digitization, resulting in an invalid snow value. If a value deviated more than ten times from the mean for a given month, the value was assumed to represent humidity data and was flagged accordingly. NSIDC set the value of these data records to 000. Any record with a characteristic and quality code combination of 50 is suspect and should be ignored.

Misplaced Summer Melt Flag

A characteristic and quality flag combination of "10" indicates summer melting. The value "00010" represents a valid snow measurement during the summer months; however, errors in the digitization process might yield an entry of "00100" that would indicate a valid 1 cm snow depth measurement. NSIDC fixed this problem by taking the indication of summer as truth; therefore, if a day indicated summer melting ("10") then all values less than 1 cm were corrected to 0 cm depth with a characteristic and quality flag combination of 02 to indicate a suspect value.

Monthly Products Quality Control

Valid snow depths with a characteristic and quality flag combination of 50 were used for the development of the monthly products. These flags indicate a non-zero and valid snow depth measurement.

Errors in Snow Depth Climatology

In October 2001 NSIDC discovered errors in mean and standard deviation depth values for climatology data files. Mean snow depth values were computed using erroneous data. Mean maximum and minimum depth were calculated correctly.

NSIDC computed a corrected mean snow depth climatology. The statistics in the reprocessed files were calculated without using zero snow depth values; therefore, they represent mean snow depth only when snow was present. The correted climatlogies are included in the CD-ROM zip file on the FTP site. Note: There is one file missing from the corrected climatologies: clm37171.dat.

3. Data Access and Tools

Data Access

To request a copy of the CD-ROM, complete the Data Order Form. Corrected mean snow depth climatology data are available via FTP.

Volume

File sizes vary by data type:

Software and Tools

The Historical Soviet Daily Snow Depth Version 2 CD-ROM contains an HTML interface and Java tool for extracting and browsing data.

Related Data Collections

4. Data Acquisition and Processing

Data Acquisition Methods

Observers took daily measurements of snow depth from three snow measuring rods placed in a meteorological enclosure. In individual cases when the enclosure was not representative of the surroundings with respect to snow cover formation, they placed the snow measuring rods near the station on a specially selected plot.

Observations were made on each rod to 1 cm precision. The observers remained 2 m to 3 m away from the rod while making measurements. The measured snow depth was indicated by the line on the rod that was level with the snow surface. The observers also read the layer of ice or water on the rod that often formed after snow melted near the rod.

If the reading was less than 0.5 cm, they recorded it as 0 cm. If the depth was greater than 0.5 cm but less than 1.0 cm, they recorded it as 1 cm.

The observers calculated the daily mean by averaging the readings on the three rods, rounded to the nearest whole cm. If the mean was less than 0.5 cm, they recorded it as 0 cm; if the mean was greater than 0.5 cm but less than 1 cm, they recorded it as 1 cm.

Data Source

NSIDC derived the HSDSD product from the Soviet meteorological archive, Sytochny Temperatur, Osadki, Sneg (STOS), which contains daily temperature, precipitation, and snow depth data from Russian World Meteorological Organization (WMO) stations. The State Hydrometeorological Service in Obninsk, Russia, sent the data to NSIDC through the bilateral US-USSR Working Group Eight data exchange program.

The original data set was a compilation of the following three meteorological archives:

The latest update from 1985 through 1995 comes from the Day-76 meteorological archives and includes 222 stations.

NSIDC checked the WMO station latitude and longitude of the original data with those listed in the WMO Handbook to determine the station name and elevation. The WMO station position was used where slight differences between the two existed. Six stations had WMO numbers that did not match any station within the WMO directory. The original data may have contained typographic errors such as 24759 for station 24959. NSIDC corrected these station numbers to match the WMO station listing based on the station name, latitude, longitude, and elevation. Corrected station numbers are identified by an asterisk (*). The list of stations summarizes station locations in the data set, ordered by WMO number.

5. References and Related Publications

World Meteorological Organization. 1984. Handbook No. 9 Weather Reporting Vol. A.

Robinson, D.A. 1993. Historical daily climatic data for the United states. Preprints of the Eighth Conference on Applied Climatology, Anaheim, CA, American Meteorological Society, 264-269.

6. Document Information

Acronyms and Abbreviations

The following acronyms and abbreviations are used in this document.

ASCII American Standard Code for Information Interchange
ESDIM Environmental Services Data and Information Management
ftp File Transfer Protocol
HSDSD Historical Soviet Daily Snow Depth
HTML Hypertext Markup Language
NESDIS National Environmental Satellite, Data, and Information Service
NOAA National Oceanic and Atmospheric Administration
NSIDC National Snow and Ice Data Center
WMO World Meteorological Organization

Document Creation Date

October 1999

Document Revision Date

January 2006

Document Review Date

October 1999

Document URL

http://nsidc.org/data/docs/daac/g01092_hsdsd.gd.html