Greenland Climate Network (GC-Net) Radiation for Arctic System Reanalysis

Summary

This data set provides incoming shortwave radiation measurements from fourteen stations of the Greenland Climate Network (GC-Net) distributed over the Greenland Ice Sheet. The original data were obtained from the GC-Net and subsequently quality controlled. The data extend from 01 January 1995 through 09 May 2008. The data set is approximately 15 megabytes comprised of fourteen Network Common Data Form (netCDF) files. The data 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. For more information, see our Use and Copyright Web page.

The following example shows how to cite the use of this data set in a publication. List the principal investigators, year of data set release, data set title and version number, dates of the data you used (for example, March to June 2004), publisher: NSIDC, and digital media.

Kindig, David. 2009. Greenland Climate Network (GC-Net) Radiation for Arctic System Reanalysis. Boulder, Colorado USA: National Snow and Ice Data Center. Digital media.

Use the following reference to give credit to the Greenland Climate Network (GC-Net) authors when citing this data set:

Steffen, Koni, Jason E. Box, and Waleed Abdalati. 1996. “Greenland Climate Network: GC-Net”, in Colbeck, S. C. Ed. CRREL 96-27 Special Report on Glaciers, Ice Sheets and Volcanoes, trib. to M. Meier, pp. 98-103.

Overview Table

Category Description
Data format netCDF
Spatial coverage and resolution Southernmost Latitude: 63.15° N
Northernmost Latitude: 80.75° N
Westernmost Longitude: 61.09° W
Easternmost Longitude: 42.50° W
Temporal coverage and resolution Temporal coverage: 01 January 1995 to 09 May 2008
Temporal resolution: hourly average data
Tools for accessing data ncdump, and other netCDF readers
File naming convention gcnet_CP1.nc
File size 508 KB to 1.3 MB
Parameter(s) Incoming Short Wave Radiation (Solar Radiation) in W/m2
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

Investigator(s)

David Kindig
National Snow and Ice Data Center
University of Colorado
Boulder, Colorado
USA

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

Acknowledgements

This research was supported by the National Science Foundation Collaborative Research: IPY: Arctic System Reanalysis grant ARC 0732986.

Original data obtained for this data set were provided by the Greenland Climate Network (GC-Net) Project from Konrad Steffen, Cooperative Institute for Research in Environmental Sciences, University of Colorado; Jason E. Box, Atmospheric Sciences Program, Byrd Polar Research Center, The Ohio State University; and Waleed Abdalati, Cooperative Institute for Research in Environmental Sciences, University of Colorado.

2. Detailed Data Description

Format

The data are in Network Common Data Form (netCDF) format. NetCDF is a set of software libraries and self-describing machine-independent data formats that support the creation, access, and sharing of array-oriented scientific data. The netCDF project homepage is hosted by the Unidata program at the University Corporation for Atmospheric Research (UCAR). The format is an open standard.

File and Directory Structure

Data are available on the FTP site in the following directory:
ftp://sidads.colorado.edu/pub/DATASETS/GCNet/

File Naming Convention

Files are named according to the following convention and as described in Table 1:

gcnet_XXX.nc

Where:

Table 1. File Naming Convention
Variable Description
gcnet Greenland Climate Network incoming short wave radiation measurements
XXX GC-Net station names:
CP1
DYE_2
GITS
HUMBOLDT_GLACIER
JAR1
JAR2
NASA_SE
NASA_U
NGRIP
PETERMANN_GLACIER
SADDLE
SOUTH_DOME
SUMMIT
SWISS_CAMP
nc indicates data are netCDF format

Example: gcnet_HUMBOLDT_GLACIER.nc (GC-Net incoming short wave radiation readings recorded at the Humboldt Glacier station, in netCDF file format).

File Size

The files range in size from 508 KB to 1.3 MB, and total about 15 MB.

Spatial Coverage

Southernmost Latitude: 63.15° N
Northernmost Latitude: 80.75° N
Westernmost Longitude: 61.04° W
Easternmost Longitude: 42.50° W

Temporal Coverage

The data in this data set span from 01 January 1995 through 09 May 2008.

Temporal Resolution

Hourly average data are transmitted via satellite link using Geostationary Operational Environmental Satellite (GOES) or Argos data collection relay system (ARGOS) throughout the year.

Parameter or Variable

Solar Radiation (incoming short wave radiation).

Parameter Description

Solar radiation is Surface Downwelling Shortwave Radiation (RSDS) measured in W/m2.

Error Sources

This section lists potential problems which may occur in GC-Net solar radiation measurements, as described in Box and Steffen 2000.

Quality Assessment

Because up to 20 percent of GC-Net data are not transmitted via the satellite uplink, interpolation techniques are used to optimize the data record. When AWS station maintenance is performed in the field, the continuous data stream, including data not transmitted, can be retrieved (Box and Steffen 2000).

Statistical procedures are applied to the GC-Net data in effort to check data quality. First, impossible values are rejected. Second, a gradient threshold compares a measurement with the next sequential hourly measurement. If the change is greater than a threshold, the later point is rejected. Third, a moving statistics window scans the time series to identify and reject data beyond a variance threshold for a given window size. In some cases, a spectrum of window sizes is employed to reject outliers due to occasional transmission errors. In general, the data that are identified as bad by these filters represent less than a few percent of the total data volume. Missing data are interpolated linearly if there are data available within an autocorrelation threshold of the flagged value. If there is a gap of greater than the autocorrelation threshold, then no interpolation is performed (Box and Steffen 2000).

Quality Control

After obtaining the incoming short wave radiation data from the GC-Net, the data were quality controlled. The following steps describe the quality control method.

  1. A uniform time vector was created from the beginning (T=0) and ending (T=t_last) times in the data set. The time vector uses a uniform time step, such as three minutes.
  2. Measurements that failed the following criteria were flagged:
    1. Missing data: missing data were given the missing value by the original data provider.
    2. Negative values: though incoming Short Wave radiation (SW) may go slightly negative in certain instances over ice sheets due to issues with the pyranometers, this was not allowed, and all negative values were set to zero.
    3. Duplicate time steps: some of the data contained duplicate time steps. Whenever a duplicate time step was found, all data for that time were flagged as bad.
    4. Persistent values: Two separate tests were conducted to search for regions in the data where persistent values exist. Persistent values were indicators of stuck sensors or other flaws in data collection. The first test looked for a flat line in the data where greater than two consecutive data values were unchanged. The second test looked for occurrences where the slope in the data was constant for greater than five consecutive data values. Data that did not pass these two tests were flagged as bad.
  3. Flagged data were removed. This step prepared the data for running spline to fill in the missing and removed time steps.
  4. A spline was run on the remaining data comparing the time steps to the actual time remaining. This comparison put the data on a uniform time step. The IDL function, SPLINE, was used to perform a cubic spline interpolation with sigma set to the default value of 1.0.
  5. The splined data were compared to a model of shortwave radiation appropriate for the latitude of the station. Data were removed if they exceeded Top of Atmospheric (TOA) radiation levels. Using the model involved choosing the value for atmospheric transmissivity, as described below.
    1. Data that exceed a modeled value with atmospheric transmissivity set to 1 were removed.
    2. A minimum value of atmospheric transmissivity was set at 0.6, but values for the GC-Net were on the order of 0.86. Each year of data were compared to find the highest value for which atmospheric transmissivity works.
    3. Data were compared to an ideal (such as the optimum for the location) atmospheric transmissivity plus 2 standard deviations of the atmospheric transmissivity value for each year.
    4. A smooth array of hourly values was created using the maximum from each day.
    5. A diffuse radiation adjustment was applied to the modeled value. The default is 50 W/m2. This value may be too high.
    6. Data that exceed the modeled value were removed.

3. Data Access and Tools

Data Access

Data are available via FTP.

Volume

The entire data set is approximately 15 MB.

The total distribution volume for the data set is listed in Table 2.


Table 2. GC-Net Radiation for Arctic System Reanalysis File Volume
File Name Volume
gcnet_CP1.nc 1.30 MB
gcnet_DYE_2.nc 1.20 MB
gcnet_GITS.nc 1.20 MB
gcnet_HUMBOLDT_GLACIER.nc 1.29 MB
gcnet_JAR1.nc 1.19 MB
gcnet_JAR2.nc 0.90 MB
gcnet_NASA_SE.nc 0.89 MB
gcnet_NASA_U.nc 1.30 MB
gcnet_NGRIP.nc 0.85 MB
gcnet_PETERMANN_GLACIER.nc 0.50 MB
gcnet_SADDLE.nc 1.10 MB
gcnet_SOUTH_DOME.nc 1.01 MB
gcnet_SUMMIT.nc 1.20 MB
gcnet_SWISS_CAMP.nc 1.17 MB

Software and Tools

The files in this data set are netCDF format. The netCDF files can be viewed using ncdump or any other tool capable of reading netCDF files. The ncdump tool generates an ASCII representation of a netCDF file. For more on ncdump, see the ncdump manual on the UCAR Web site.

Related Data Collections

4. Data Acquisition and Processing

Theory of Measurements

The GC-Net AWS capture a range of weather data important to ice sheet conditions, including air temperature, wind speed, relative humidity, pressure, wind direction, solar radiation, net radiation, snow temperature, and surface height change. The GC-Net Radiation for Arctic System Reanalysis data set consists of only one of these data types: solar radiation. The data, which were quality assessed during GC-Net processing, were further quality controlled subsequent to acquisition from GC-Net. Refer to Quality Control.

Sensor or Instrument Description

The pyranometer contains a thermopile sensor with a black coating that absorbs solar radiation. The thermopile sensor generates a voltage output signal that is proportional to the solar radiation, measured in watts per square meter (W/m2). Refer to Table 3.

Table 3. Shortwave Radiation Parameter and Instrument
Parameter
Instrument
Instrument Accuracy
Sample Interval
No. per station
Shortwave radiation flux (W/m2) Li Cor Photodiode
5 - 15%
15 sec
1

Data Acquisition Methods

Solar radiation data were acquired via the GC-Net stations distributed over the Greenland ice sheet. Solar radiation was recorded with a pyranometer. The GC-Net AWS are equipped with communication satellite transmitters that enable near-real time monitoring of weather conditions on the Greenland ice sheet. Transmission latency is as short as four minutes, typically one to two hours, and occasionally as long as 48 hours (Box and Steffen 2000). Table 4 provides a listing of Station Identification (ID) Numbers, station names, station latitude and longitude coordinates, the date when the station became operational, and the station's Site ID. Note: This data set does not include measurements from stations shaded in gray in Table 4.

Table 4. GC-Net Stations (from GC-Net Web site version: June 03, 2002)
ID #
Name
Latitude
Longitude
Elev.[m]
Start Date
Site ID
1 Swiss Camp 69.5732° N 49.2952° W 1149 1995.00 fn_dkswcamp
2 CP1 69.8819° N 46.9736° W 2022 1995.39 fn_dkandcp1
3 NASA-U 73.8333° N 49.4953° W 2368 1995.41 fn_dkdnasau
4 GITS 77.1433° N 61.0950° W 1887 1995.43 fn_dkndgits
5 Humboldt Gl. 78.5266° N 56.8305° W 1995 1995.47 fn_dkhumbdt
6 Summit 72.5794° N 38.5042° W 3208 1996.37 fn_dksummit
7 Tunu-N 78.0168° N 33.9939° W 2020 1996.38 fn_dkdtunun
8 DYE-2 66.4810° N 46.2800° W 2165 1996.40 fn_dkdye2
9 JAR1 69.4984° N 49.6816° W 962 1996.47 fn_dkjar1
10 Saddle 66.0006° N 44.5014° W 2559 1997.30 fn_dksaddle
11 South Dome 63.1489° N 44.8167° W 2922 1997.31 fn_dksdome
12 NASA-E 75.0000° N 29.9997° W 2631 1997.34 fn_dkdnasae
13 CP2 69.9133° N 46.8547° W 1990 1997.36 fn_dkandcp2
14 NGRIP 75.0998° N 42.3326° W 2950 1997.52 fn_dkdngrip
15 NASA-SE 66.4797° N 42.5002° W 2579 1998.30 fn_dknasase
16 KAR 69.6995° N 32.9998° W 2400 1999.38 fn_dkandkar
17 JAR2 69.4200° N 50.0575° W 568 1999.41 fn_dkjar2
18 KULU 65.7584° N 39.6018° W 878 1999.46 fn_dkndkulu
19 JAR3 69.3954° N 50.3104° W 323 2000.41 fn_dkndjar3
20 Aurora 67.1352° N 47.2911° W 1798 2000.48 fn_dkaurora
22 Petermann Gl. 80.7500° N 54.0000° W n/a n/a n/a


Data Source

The GC-Net data were obtained from the Steffen Research Group on Greenland Climate Network Data.

5. References and Related Publications

Box, Jason E., and Konrad Steffen. 2000. Greenland Climate Network (GC-NET) Data Reference Version: November 19, 2000. University of Colorado, Boulder, http://cires.colorado.edu/science/groups/steffen/gcnet/Gc-net_documentation_Nov_10_2000.pdf, 893 KB.

Steffen Research Group, Greenland Climate Network (GC-Net), Cooperative Institute for Research in Environmental Sciences (CIRES), http://cires.colorado.edu/science/groups/steffen/gcnet/.

Table 5 lists related documents that are available on the NSIDC Web site.

Table 5. Related Documents
Document Description URL
MODIS Interactive Subsetter Tool (MIST) Provides subsets of certain Version 5 (V005) MODIS products, over the Greenland Climate Network (GC-Net) http://nsidc.org/data/mist/index.html
NSIDC Education Center Arctic Climatology and Meteorology: Solar Radiation http://nsidc.org/arcticmet/factors/radiation.html
PARCA Data Program for Arctic Regional Climate Assessment (PARCA) http://nsidc.org/data/parca/

6. Document Information

Acronyms

The acronyms used in this document are listed in Table 6.

Table 6. Acronyms and Abbreviations
Acronym Description
ARGOS Argos data collection relay system
AWS Automatic Weather Stations
FTP File Transfer Protocol
GC-Net Greenland Climate Network
GOES Geostationary Operational Environmental Satellite
MIST MODIS Interactive Subsetter Tool
netCDF Network Common Data Form
NSIDC National Snow and Ice Data Center
PARCA Program for Arctic Regional Climate Assessment
TOA Top Of Atmospheric
UCAR University Corporation for Atmospheric Research
URL Uniform Resource Locator

Document Creation Date

December 2009

Document Revision Date

Document URL

http://nsidc.org/data/docs/daac/nsidc0437_gcnet_radiation/index.html