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In this Issue

Antarctic Data Center at NSIDC
Arctic System Science (ARCSS)
Products and Services
Publications
News From Other Centers

NSIDC Notes

Issue 21, Spring 1997

ANTARCTIC DATA CENTER AT NSIDC

Significant progress has been made on the Antarctic Data Center at NSIDC in the last few months. This activity provides the U.S. focus for assembling metadata (in the form of Directory Interchange Format (DIF) data descriptions) for all U.S.-funded Antarctic research. These data will become part of the International Antarctic Master Directory (AMD).

The DIF is a set of basic information (including data set title, relevant dates, archive center and contact information, a list of searchable key words, bibliographic references, a text summary, etc.) that describes the data set. DIFs are the standard descriptive information that is available in current electronic data directories such as the Global Change Master Directory (GCMD).

DIFs for Antarctic data sets held at NSIDC, and DIFs for U.S.-funded Antarctic data sets that are in the GCMD have been compiled and are ready to be submitted to the AMD. A inventory of data centers with Antarctic data holdings and points of contact is also being developed. This work-in-progress forms the structure by which all data holdings eventually will be described.

The kick-off meeting for the AMD effort was held in Christchurch, New Zealand, on May 20-23, when representatives from 13 of the 26 Antarctic Treaty nations met. G. Scharfen and C. Hanson from NSIDC represented the NSF/Office of Polar Programs-funded U.S. component of the AMD. This was the first meeting of the SCAR-COMNAP Joint Committee on Antarctic Data Management. Each nation is invited by SCAR (Scientific Committee on Antarctic Research) and COMNAP (Council of Managers of National Antarctic Programs) to designate a center whose responsibility it will be to identify and describe all Antarctic data held by that nation, and to provide these descriptions to the online AMD, a cooperating node of the CEOS (Committee on Earth Observing Satellites) International Directory Network.

NSIDC's Antarctic Data Center project will continue its discussions with National Data Centers and other agency contacts, and with universities and other centers of data, to ensure all historical, current and future U.S.-funded Antarctic data sets are described in the AMD. G. Scharfen and R. Bauer comprise the staff of the U.S. Antarctic Data Center project at NSIDC. R.G. Barry, C. Hanson, R. Armstrong, A. Brennan, and F. Fetterer are the project's internal advisory group.

ARCTIC SYSTEM SCIENCE (ARCSS)

Change of Management at the ADCC

On June 1, 1997, Matthew Cross, formerly the ARCSS Data Coordinator at the ARCSS Data Coordination Center (ADCC), was appointed the ADCC Manager. He replaces Dr. David McGinnis who has accepted a tenure track position at the University of Iowa. We wish Dr. McGinnis the best in this important career move. Any management questions may now be directed to NSIDC User Services.

Greenland Ice Core CD-ROM

The Greenland Ice Core CD-ROM is in its final planning stages and should be ready for concurrent release with the Journal of Geophysical Research special issue on Ice Cores, due out at the end of the summer. Until then, interested investigators can access the ice core data through ARCSS. Data are placed there after appropriate quality checks. All of the data are expected to be available by July 1, 1997.

Arctic Circumpolar Data Sets

We will soon be making available a series of Arctic Circumpolar Data Sets through ARCSS. We have been working with D.A. Walker, an LAII investigator at the Institute of Arctic and Alpine Research, University of Colorado, on transferring these data sets to the ADCC. The gridded data sets provide information on hydrology, topography, and vegetation for the Arctic above 40°N latitude. The vegetation product is a Normalized Difference Vegetation Index (NDVI) derived from a composite 1km AVHRR image of the region. A false color composite AVHRR image of the same region will also be available. We are expecting all data sets to be downloaded by July 1, 1997. A description of the data sets will be added to the "New" section of ARCSS site when the data are released.

PRODUCTS AND SERVICES

Passive Microwave Derived Polar Sea Ice Concentration Time Series

NSIDC is distributing a combined Nimbus-7 SMMR, DMSP SSM/I F8 and F11 sea ice concentration data set. Data will be available via ftp by the end of June. The data span over 19 years, from October 1978 through September 1997. The data set includes gridded daily (every-other-day for the SMMR data) and monthly sea ice concentrations for both the north and south polar regions.

The data set is designed to provide a consistent time series of sea ice concentrations spanning the coverage of several passive microwave instruments. The ice concentrations were generated from SMMR and SSM/I brightness temperatures by the Oceans and Ice Branch, Laboratory for Hydrospheric Processes at NASA Goddard Space Flight Center (GSFC), using SMMR brightness temperatures that were processed at NASA GSFC and the NSIDC SSM/I brightness temperatures.

The basic characteristics of the SMMR and SSM/I platforms are described in the data set documentation. Also summarized are problems encountered when deriving sea ice concentrations from brightness temperatures using sensors with varied frequencies, footprint sizes, visit times, and calibrations. The techniques employed to reduce the effects of these problems are presented.

In addition to ftp access, the data will soon be distributed on three CD-ROMs. Current subscribers to the F13 Tbs and sea ice concentration will be notified. GIF images for the North and South Pole regions are distributed on Volume 1, with daily and monthly data available on Volumes 2 and 3 for the northern and southern polar regions, respectively.

For further information, contact NSIDC User Services.

Central Asian Snow Cover

NSIDC is pleased to announce the availability of a new data set of snow measurements from Central Asia. The Central Asian Snow Cover from Hydrometeorological Transects data are based upon observations made by personnel throughout three river basins within Central Asia. The river basins included are the Amu Darya, Syr Darya, and Naryn. These observations include end of month snow depth, snow density and snow water equivalent for snow points measured from the ground. Only snow depth is included for snow points measured from the air. Temporal coverage varies for each snow point, with the longest station record extending from 1932-1990. Data were provided to NSIDC by the State Hydrometeorological Service (Russian acronym SANIGMI) in Tashkent, Uzbekistan.

Figure 1. Areas circled indicate river sub-basins containing snow measurements within Central Asia.

Figure 1. Areas circled indicate river sub-basins containing snow measurements within Central Asia.

These data are described in NSIDC's Data Catalog. A subsetting interface has been provided to allow users to download data from a particular drainage basin or to download the entire data set.

For further information, contact NSIDC User Services.

HSDSD: Number of Days of Snow Cover

The Historical Soviet Daily Snow Depth (HSDSD) CD-ROM contains daily snow depth measurements at 284 sites throughout the Former Soviet Union. Ross Brown of the Canadian Atmospheric Environment Service has noted a difference between the number of days of snow cover within the monthly summaries on the HSDSD CD-ROM and the number of days of snow cover calculated based upon climate data. Using temperature and precipitation data obtained from the Carbon Dioxide Information Analysis Center, Dr. Brown calculated the variability of snow cover using a simple water balance approach (see Brown, 1996, Johnstone and Louie, 1983).

The number of days of snow cover within the monthly summaries for HSDSD was calculated by counting the number of days with a valid snow depth measurement which was equal to or greater than 1 cm. Dr. Brown notes that using a 2 cm threshold yields results closer to the values calculated from climate data.

Figure 2. Solid line is the number of days of snow using a 1 cm threshold. Broken line is the number of days of snow using a 2 cm threshold.

Figure 2. Solid line is the number of days of snow using a 1 cm threshold. Broken line is the number of days of snow using a 2 cm threshold.

During the quality control process at NSIDC, errors were detected where a 1 cm snow depth was reported during the summer months. This error was corrected for the months of June through August. However, the presence of this error within the snow season would account for the differences found by Dr. Brown. Also note that this anomaly is most prevalent at stations with greater snow variability which often have zero snow on the ground during the winter months. Thus, users should be cautious when using the calculated number of days of snow within the monthly summaries on the HSDSD CD-ROM.

The HSDSD CD-ROM is available for $50. For more information, please contact NSIDC User Services.

References:

Brown, R. D. 1996. Evaluation of methods for climatological reconstruction of snow depth and snow cover duration at Canadian meteorological stations. Eastern Snow Conference, 53rd Annual Meeting, 1-3 May 1996, Williamsburg, Virginia, p. 55-65

Johnstone, K. and P.Y.T. Louie. 1983. Water Balance for Canadian Climate Stations. Downsview, Ontario, Atmospheric Environment Service. (Report DS#8-83.)

DMSP F13 SSM/I Daily Polar Gridded Brightness Temperatures CD-ROM

DMSP F13 SSM/I Daily Polar Gridded Brightness Temperatures CD-ROM volumes 1 through 7 have been distributed to subscribers. The seven volumes contain gridded brightness temperatures for the period 3 May 1995 through 31 December 1996. Subsequent volumes will be distributed as the source data become available to NSIDC for processing.

Sea ice concentrations are available via ftp. The data are derived from the brightness temperature grids produced and distributed by NSIDC. Data may be accessed by ftp.

PUBLICATIONS

SHEBA Region Atlas

The Surface Heat Budget of the Arctic Ocean (SHEBA) program is designed to improve our understanding of the thermodynamic coupling between the Arctic atmosphere, the sea ice and ocean. SHEBA Phase I includes the analysis of existing data sets, modeling, satellite studies and experiment planning for the follow-on phase. Phase II, a field experiment in the Beaufort Sea, is designed to collect a suite of data sets leading to better understanding of the Arctic surface heat budget, in particular, the sea ice albedo feedback mechanism.

As a contribution to SHEBA Phase I, we have assembled existing data sets, data sets generated in-house and previously published results to provide an atlas of the mean state and variability of Arctic atmospheric and sea ice conditions. Monthly maps are provided of atmospheric circulation, water vapor characteristics, cloud cover and cloud properties, precipitation and precipitation characteristics, surface temperatures, surface winds, surface radiation fluxes and albedo, as well as, sea ice extent, concentration, motion and the timing of ice melt onset. Comparative analyses, summarized primarily as monthly histograms, are also conducted for the vicinity of the SHEBA manned camp. Each section of the atlas contains an overview of the data sets used, data analysis and brief interpretation of results. More detailed discussions are provided for new data sets or for those not widely examined previously.

This volume, Atmospheric and Sea Ice Characteristics of the Arctic Ocean and the SHEBA Field Region of the Beaufort Sea, NSIDC Special Report-4, is available without charge.

For further information, contact NSIDC User Services.

M. C. Serreze, J. A. Maslanik (NSIDC) and J. Key (Boston University)

An Intercomparison of DMSP F11- and F13-Derived Sea Ice Products

NSIDC has recently published Special Report-5, An Intercomparison of DMSP F11- and F13-Derived Sea Ice Products, by Julienne Stroeve, Xiaoming Li, and Jim Maslanik.

Passive microwave satellite data provide an extended time series for monitoring of polar processes, such as variability in sea ice extent. To ensure consistent data sets for time series analysis of sea ice cover, differences between ice concentration estimates from similar sensors on successive spacecraft must be understood. The effects of changing from the SSM/I F11 to the F13 satellite have been examined for a 5-month overlap period. In terms of hemispheric averages of mean ice concentration, the biases introduced by the switch from F11 to F13 are slight and are not statistically significant in most areas, although relatively large and significant differences are seen in some regions. Furthermore, differences in sea ice extent and total ice-covered area between the two platforms were found to be statistically significant.

Previous efforts to reduce such differences in geophysical parameters between earlier SSM/Is have focused on establishing relationships between brightness temperatures. However, we find the relations between the F11 and F13 brightness temperatures to be highly sensitive to the region chosen for the analysis. Consequently, the choice of sample has a substantial effect on the sensor-to-sensor adjustment and on the resulting sea ice concentrations. Analyses of ice concentrations between F8 and F11 and between F11 and F13 show that current attempts at a relative calibration using regressions of brightness temperatures for the two instruments do not offer a significant improvement in corresponding ice fractions.

This report is available without charge. A printed copy is available on request by contacting NSIDC User Services.

NEWS FROM OTHER CENTERS

Bering Sea Ecosystem Metadatabase: Call For Data

NOAA seeks entries for a metadatabase of biophysical data pertaining to the Bering Sea. This inventory of data will help researchers, managers, students, fishermen, and the general public investigate and understand the functioning of the complex ecosystem of the Bering Sea. Unrestricted access to the metadatabase will be provided through the World Wide Web.

If you have knowledge of data from the Bering Sea and surrounding regions that would enhance the database, please register through the Bering Sea and North Pacific or bering@pmel.noaa.gov or contact
Dr. Bern Megrey
NOAA/AFSC
7600 Sand Point Way N.E.
Seattle, WA 98115, USA
macklin@pmel.noaa.gov
(206) 526-4147 (phone).