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Issue no. 39, March 2002


Snow Melt Onset over Arctic Sea Ice

The National Snow and Ice Data Center (NSIDC) recently released a compilation of yearly snow melt onset dates over arctic sea ice, derived from Scanning Multichannel Microwave Radiometer (SMMR) and Special Sensor Microwave/Imager (SSM/I) brightness temperatures. Sheldon Drobot (University of Colorado) and Mark Anderson (University of Nebraska) developed the data set, which provides a new proxy for climate in arctic sea ice zones.

Microwave emissivity of snow increases dramatically as snow melts and liquid water appears. With the presence of liquid water in the snow pack, surface scattering dominates over volume scattering, resulting in a sharp increase in the brightness temperature (Tb) signature. Thus, snow melt onset is defined as the point in time when microwave brightness temperatures of the snowpack increase sharply.

Initial locations of sea ice melt vary both spatially and temporally. Melt signatures appear first in lower latitudes and advance northward with time. Along the Asian Arctic coast, snow melt begins in the far eastern (Chukchi Sea) and western (Barents and Kara Seas) regions. Over several weeks, melt progresses zonally toward the Laptev Sea.

The snow melt onset data currently span the years 1979 through 1998, and are in a polar stereographic grid at 25 km resolution. Tab-delimited ASCII files and GIF images are available from NSIDC's data catalog via ftp.

Several value-added products derived from these data are also available. Value-added data sets include the following for each pixel: mean melt onset date, latest (maximum) melt onset date, earliest (minimum) melt onset date, range of melt onset dates (the difference between maximum and minimum -- an index of variability), standard deviation of melt onset date (another index of variability), and a trend analysis. Graphical representations of value-added data are also available.

Arctic mean melt onset

Mean melt onset over sea ice in the Arctic from 1979 through 1998. Darker shades of gray correspond to earlier melt onset and lighter shades to later melt onset dates. Initial occurences of snow melt over sea ice happen in the lower latitudes (represented by darker shades of gray) and advance northward with time. Along the Asian arctic coast, snow melt first starts in the far eastern (Chukchi Sea) and western (Barents and Kara Seas) regions. Over several weeks, the melt progresses zonally toward the Laptev Sea.

Oceanographic Data Collection Released

The Arctic System Science (ARCSS) Data Coordination Center announced the initial release of "Physical and Chemical Properties from Selected Expeditions in the Arctic Ocean," a pan-Arctic collection of oceanographic data formerly referred to as the "Western Oceanographic Data Set" (WODS).

The purpose of this growing data collection is to preserve and distribute physical and chemical data from the Arctic Ocean that have been compiled through a cooperative international effort involving the United States, Canada, Germany, Sweden, and Russia. Data were collected over several decades during icebreaker and conventional research vessel cruises and from ice camps using traditional wire casts, CTD (conductivity, temperature, depth) casts, and CTD/rosette casts. In addition to conductivity and temperature data, derived measurements of oxygen, nutrients, and alkalinity are also included for some expeditions. Data are available in National Oceanographic Data Center standard formats from NSIDC's data catalog.

New Data Sets from AGDC

NSIDC's Antarctic Glaciological Data Center (AGDC) recently released two new data sets, including ice velocity and snow temperature and permeability measurements from Antarctica. The data were provided to AGDC by investigators funded by NSF's Antarctic Glaciology program.

Dr. Mary R. Albert of the U.S. Army Cold Regions Research and Engineering Laboratory contributed "Snow and Firn Temperature and Permeability Measurements from Siple Dome, Antarctica." This data set includes measurements of snow and firn temperature and permeability collected between November 1998 and June 1999 at Siple Dome. A better understanding of snow's physical properties will help scientists more accurately interpret ice core records of atmospheric composition and paleoclimate. Data are available from NSIDC's data catalog.

Dr. Sridhar Anandakrishnan of the University of Alabama provided "Ice Velocity Data from Ice Stream C, West Antarctica." Ice velocity data from ice stream C, including the body of the ice stream and its area of onset, are included. Dr. Anandakrishnan calculated velocities from precise ice displacement measurements made with a geodetic-quality Global Positioning System (GPS). These ice displacement measurements accompanied seismic experiments aimed at understanding controls on the flow of ice streams in West Antarctica. An understanding of ice stream flow is essential to predicting the response of the West Antarctic Ice Sheet to future climate change. Data are available from NSIDC's data catalog in both ASCII and Excel formats.

2000/2001 NASA DAAC Yearbook Available

NSIDC released the 6th edition of the NASA DAAC Yearbook, titled "Research Uses of Earth observing data from NASA's Earth Science Enterprise." The DAAC Yearbook is an annual, multidisciplinary publication designed to highlight research conducted using NASA DAAC data, DAAC tools development, and data management issues.

Topics in this year's issue include African dust transport, early detection of hurricanes, monitoring amphibian health, and population analysis studies.

Articles from the DAAC Yearbook are also available electronically on NASA's Earth Observatory and DAAC Alliance Web sites. Researchers working with NASA DAAC data are invited to contact Laurie Schmidt, Editor, to explore possibilities for developing a future DAAC Yearbook article.

For a free copy of the DAAC Yearbook, contact NSIDC User Services.

Antarctic Sea Ice Thickness Data Set Available

Moored upward-looking sonar data from the Weddell Sea, covering the period 1990 through 1998, are now available from the National Snow and Ice Data Center. The data were contributed by Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany, and represent one of few Antarctic ice draft measurements available to the public. Data may be accessed via NSIDC's data catalog.

Product Update

On 01 January 2002, the Global Hydrology Resource Center (GHRC) began using the latest processing software from Frank Wentz in the automated processing of SSM/I brightness temperatures. This new code contains inter-calibration coefficients (calibrated to F8) for the F11 and F13 sensors.

Near Real-Time DMSP SSM/I Daily Polar Gridded Brightness Temperatures and Near Real-Time DMSP SSM/I Daily Polar Gridded Sea Ice Concentrations are affected by the software change, which will result in different brightness temperature values for the low resolution channels (e.g. 19, 22 and 37 GHz) and slightly different sea ice concentrations. For a summary of the effects of inter-calibration on brightness temperatures and sea ice concentrations, please see NSIDC Special Publications.


European Space Agency Announces Opportunity for CryoSat Mission

ESA is pleased to release the 1st Announcement of Opportunity for the CryoSat mission. The European Space Agency (ESA) developed the CryoSat mission to determine fluctuations in mass of the Earth's land and marine ice fields. As the world's first satellite mission aimed directly at quantifying variations in Arctic sea ice thickness, CryoSat will also provide high-resolution radar altimeter measurements over the margins of the Antarctic and Greenland ice sheets and smaller ice bodies throughout the world. The mission will also continue the time-series of Antarctic and Greenland elevation change provided by the ESA's Earth Remote Sensing (ERS) and ENVISAT satellite altimeters. Detailed information about the CryoSat mission objectives, satellite system and data products, calibration and validation concept, and approach to ice thickness retrievals may be found on the ESA Earth Explorer Web site.

The ESA is now inviting interested groups to participate in activities related to the CryoSat mission. Specific areas in which contributions are sought include (1) validation ground experiments providing independent measurements of sea ice thickness and land ice elevation change, (2) calibration and validation ground experiments to further understanding of radar echo interactions with sea ice and land ice, and (3) validation of ice thickness and ice elevation retrieval algorithms (Level 1b and 2 data products).

For more information on the objectives of this AO and instructions on how to respond, please visit the ESA Web site. The deadline for submission of proposals is 15 April 2002.

For additional information about the ESA's Earth Observation Programme contributions to cryospheric remote sensing, contact Mark Drinkwater ( or Helge Rebhan (


Frozen Ground Workshop at NSIDC

The World Data Center (WDC) for Glaciology in Boulder, Colorado, hosted a workshop for the International Permafrost Association's Standing Committee on Data, Information, and Communication. The primary purpose of the workshop was to plan the production and content of the Circumpolar Active-Layer Permafrost System, Version 2 (CAPS v.2) CD ROM. The WDC for Glaciology published the first CAPS CD in 1998. This follow-on version will be released at the 2003 International Conference on Permafrost in Zurich.

The CD will publish data from four major IPA programs: the Global Terrestrial Network for Permafrost (GTN-P), the Circumpolar Active-Layer Monitoring (CALM) Program, the Arctic Coastal Dynamics (ACD) Project, and the Cryosols database project, all of which are part of the World Meteorological Organization's Global Climate Observatory System (GCOS). The WDC for Glaciology also plans to publish a variety of other frozen gound related data and information, in addition to data from these major projects.

For more information or to contribute data, please visit the Frozen Ground Data Center.


NSIDC welcomes Kate Daniels (User Services Representative), Todd Edmands (Raytheon Security Administrator), Marilyn Kaminksi (MODIS Product Team Lead), Tatiana Khromova (Fulbright Visiting Scholar), Matt Savoie (Scientific Programmer), and Evelyn Yohe (Science/Technical Writer).

NSIDC bids farewell to Martyn Clark (Research Scientist II), Paul Farley (Business Manager), and Annette Varani (DAAC Outreach Coordinator). After serving nearly 10 years as NSIDC's Business Manager, Paul relocated to the Pacific Northwest to assume a position at the University of Washington in Seattle. Martyn and Annette both joined the Cooperative Institute for Research in Environmental Sciences (CIRES) at the University of Colorado. We wish them all the best of luck in their new positions.