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In this Issue
PRODUCTS AND SERVICES
ARCTIC SYSTEM SCIENCE (ARCSS)
NEWS FROM OTHER CENTERS
Recently NSIDC was notified by the Polar Science Center, University of Washington, of an error in the buoy data from the International Arctic Buoy Program. These data are archived at NSIDC, and we provide pointers to them in our online and printed data catalog. Users of these data are encouraged to evaluate whether or not the reported error may have affected the results of any previous work. As noted below, we expect corrected data to be available by late June 1996. Please contact Mr. Ignatius Rigor, IABP Data Manager (address below) or contact NSIDC User Services if you have questions or concerns.
Dear IABP User,
Ongoing quality control and research on the International Arctic Buoy Program (IABP) datasets have uncovered a systematic error in the computation of the second derivative of pressure, d2p/dxdy, reported in the AB datasets. The other pressure derivatives were also checked and found to be correct.
Though this error does not affect more commonly used quantities such as geostrophic wind and vorticity, it does affect some seldom used quantities such as the shear of the geostrophic wind.
The error occurs in the datasets processed after 1981, including the 1979 data which were reprocessed in 1994. The original 1979, 1980, and 1981 data do not contain the error.
In essence, the derivative was divided erroneously by4. We must caution users that simply multiplying the erroneous field by 4 does not correct the error, since the variable has been rounded off. For example, if the original calculation of d2p/dxdy is 1.51x10-6, this result is reported in the AB dataset as 2 after multiplication by 106 and truncation. If we simply multiply by 4, we get 8, whereas the correct truncated value is 6. Other quantities that we have checked such as the var(d2p/dx2)/var(d2p/dxdy), which should be approximately 3 (Thorndike and Colony, Journal of Geophysical Research, 87(C9), 5,845-5,852, 1982), give us values close to 5 after multiplying the erroneous d2p/dxdcalculating variances.
We have corrected the optimal interpolation code and are currently reprocessing the data as outlined in the 1982 data report. The erroneous datasets have been removed from the IABP FTP site and the new datasets will be available via FTP and HTTP from the server IABP.APL.WASHINGTON.EDU and through the National Snow and Ice Data Center/World Data Center-A for Glaciology (NSIDC/WDC-A) after quality control procedures are applied to the reprocessed data. We hope to have the reprocessed datasets available by the end of June.
We hope that this error has not had an adverse impact on your research. Please let us know how we can serve you better.
IABP Data Manager
Polar Science Center
University of Washington
1013 NE 40th Street
Seattle, WA 98105
The ARCSS Data Coordination Center at NSIDC recently launched a new home page on the World Wide Web. In an attempt to better serve the ARCSS community and other interests, our page provides a variety of new and improved services.
The ARCSS database has been reorganized into a subject-oriented structure. This design was implemented to serve a broader community with a logical, user- friendly interface to browse and retrieve data sets. Overviews of the formal ARCSS projects are also presented to educate users about the goals of ARCSS and each of its components. To facilitate communication among the ARCSS community, a comprehensive directory that includes an e-mail service is also maintained. A calendar of events keeps users informed of ARCSS and ARCSS- relevant conferences and deadlines. Finally, real-time data access to Arctic weather has been initiated with both Alaskan and Canadian surface data and forecasts.
We hope that our new web format will not only provide the ARCSS community with valuable services and an efficient database, but also be an inviting site for the interested public and educators wishing to learn more about Arctic System Science. We anticipate a proactive role in maintaining an evolving web page to best meet the needs of our users. Work is also underway to improve web visibility.
Please give the ARCSS site a try.
The U.S. International Trans Antarctic Scientific Expedition (ITASE) Workshop was held in Baltimore, MD, on May 22 and 23. The purpose of the workshop was to develop a science and implementation plan for the US ITASE program to be presented at the international ITASE meeting this summer in Cambridge, UK. NSIDC representatives Ted Scambos and Matthew Cross presented reports on remote sensing and data management issues, respectively.
The broad ITASE plan is to determine the last 200 years of global climate, atmospheric composition, and aerosols as recorded in the Antarctic Ice Sheet. This will be accomplished by a series of traverses across both the East and West Antarctic ice sheets during which the upper few 10s of meters will be cored, and several ancillary measurements made in the vicinity. This upper layer records several parameters of importance to global climate (e.g., chemistry, isotopes, accumulation), and is an indicator of variations in climate in Antarctica. This record will greatly add to our current understanding of global change over the last few hundred years derived from other sources, and will provide an essential baseline for the interpretation and comparison of the deeper Antarctic ice core records.
The planned traverses for the ITASE program are shown in Figures 1 and 2. Figure 1 presents the East Antarctic traverses, and Figure 2, the West. The U.S. contribution will be in West Antarctica, consisting of three transects beginning in 1999. The routes were selected as representative of all climate zones in West Antarctica, while maximizing information already collected from previous transects, cores and remote weather stations. Remote sensing is expected to be an integral part of the ITASE effort, contributing to route and site selection, and extending parameters measured during the traverses to cover the rest of the continent. In turn, the ITASE traverses also contribute to the development of remote sensing, by providing ground truth and validation information. In some cases, the ITASE remote sensing effort will consist of identifying and modifying existing sources of information for ITASE objectives. In other cases, the ITASE remote sensing effort will undertake a research effort to develop a new or improved algorithm. Expected results from the remote sensing effort are a photoclinometric improvement to existing digital elevation models, grain size mapping from image data, and most importantly, accumulation rate mapping from a combination of passive microwave data and weather satellite imagery.
Figure 1. presents the East Antarctic traverses for the ITASE program.
Figure 2. presents the West Antarctic traverses for the ITASE program.
A suggested data management scheme for US ITASE would be similar in look and feel to the NSF-funded GISP2 project, where a focal point for the coordination of science and data collection would exist at the University of New Hampshire. A long-term data archive and management plan would be implemented by major data center within the U.S. NSIDC has opened a discussion with ITASE as a possible site for this long-term function. The proposed international focal point for data management is the Australian National Antarctic Data Center, located in Kingston, Tasmania.
If you have further questions about the US ITASE project, please contact Ted Scambos (firstname.lastname@example.org).
The Nansen Environmental and Remote Sensing Center (NERSC) is an independent research institute affiliated with the University of Bergen. NERSC was founded in 1986 by Prof. Ola M. Johannessen, who has served as its director since its inception. NERSC conducts basic and applied environmental research funded by national and international governmental agencies, research councils, and industry. NERSC's aim is to make a significant contribution to understanding, monitoring, and forecasting of the environment especially the marine environment on regional to global scales. A significant portion of NERSC research is concerned with the cryosphere, especially sea ice variability and processes in the marginal ice zone.
The Center's regional emphasis is on the Arctic and the Nordic seas (the Greenland, Iceland, and Norwegian seas). In the most recent years, NERSC has extended its focus into the Siberian marginal seas, particularly the Kara Sea. In part, this reflects the establishment of an affiliated institute in St. Petersburg, the Nansen International Environmental and Remote Sensing Center (NIERSC). NIERSC was founded by NERSC in 1992, in cooperation with the St. Petersburg Research Center for Ecological Safety of the Russian Academy of Sciences, the Environmental Research Institute of Michigan (USA), the Max Planck Institute for Meteorology (Germany), and in collaboration with the CEC Joint Research Center (Italy).
NERSC conducts studies using both observations and models. Observational data analyzed at the center consist of instrumental and in situ data, including those obtained in dedicated oceanographic field campaigns, as well as satellite remote sensing data. Remote sensing studies at NERSC emphasize the use of active and passive microwave satellite data.
Active microwave data from the European Remote Sensing satellites, ERS-1 and 2, are used for science and applications. Scientifically, C-band (5.6 cm) synthetic aperture radar (SAR) backscatter data are analyzed to study open ocean features and SAR imaging mechanisms associated with wind and waves at the sea surface, as well as sea ice processes, particularly meso-scale processes such as ice edge eddies in the Greenland and Barents seas. SAR ice signature studies are being conducted in conjunction with in situ ice observations in the Barents and Kara seas. The application of ERS SAR data to practical problems has resulted in the establishment of a near-real-time ice monitoring service based primarily on such data. Several demonstration projects focusing on the Northern Sea Route along the northern Siberian coast (in historical perspective, termed the Northeast Passage) have been conducted since 1991. As result of such projects, NERSC has acquired and archived several thousand SAR scenes from the Arctic and sub-Arctic marine environment.
Passive microwave data are being used to study the variability of the global sea ice covers. The input data are Nimbus-7 SMMR and DMSP SSM/I brightness temperature data on CD-ROM produced and issued by NSIDC. The time period is 1978-present. The research team at NERSC computes sea ice concentrations using the NORSEX and NASA Team algorithms, then derives and analyzes parameters such as ice extent, ice area, water area, and overall ice concentration. NERSC first analyzed the SMMR and SSM/I data separately; the results were published by Johannessen et al. (Nature, 376:126-127, 1995). A subsequent analysis using a merged SMMR-SSM/I sea ice time series is presently in review. In either case, statistically-significant negative trends are detected in the Arctic, with no changes yet evident in the Antarctic. This hemispheric asymmetry is consistent with that seen in many recent general circulation model (GCM) greenhouse warming simulations. The estimated negative slopes of 32,000 and 36,000 km2 per year in Arctic ice extent and ice area, 1978-95, represent decreases of 4.5% and 5.7% over the 16.8 year period.
Related research plans for the near future include extending the sea ice time series with future passive microwave data as issued by NSIDC. The spatial and temporal aspects of the derived trends will also be investigated in detail. Additionally, other climatically-sensitive cryospheric variables, such as the snow cover, ice sheets, and permafrost areas, may be investigated using active and passive microwave data. Longer-term climate variability will be estimated using time series of cryospheric data such as Greenland ice sheet isotope composition and sea ice observations. These studies will include data archived and issued at NSIDC, as well as from collaborators at the University of Copenhagen and elsewhere.
In addition to remote sensing and other observational research, NERSC has a burgeoning modelling and data assimilation group, focusing on ocean models related to global climate processes, regional-scale coupled ice-ocean models, studies of the carbon cycle and ocean uptake of CO2, deep water formation near the Greenland Sea ice edge, and the potential transport of radionuclides in the Kara Sea.
For further information, please contact NERSC on the internet: http://www.nrsc.no:8001, or NERSC, Edvard Griegsvei 3a, 5037 Solheimsvik, Norway, or telephone: +47 55 29 72 88 (phone), or +47 55 20 00 50 (fax).
The fourth meeting of the RADARSAT/National Ice Center working group was held on 24 and 25 April at NSIDC. Participants from the National Ice Center, NOAA/NESDIS, the Alaska SAR Facility, the Jet Propulsion Laboratory, Atmospheric Environment Service Canada, the Naval Research Laboratory, Vexcel Corporation, and the University of Kansas met to share information on the status of the hardware and software systems that will deliver RADARSAT data and on issues surrounding data ordering and access.
The working group got its start planning for the operational use of RADARSAT within the NOAA CoastWatch program and at the National Ice Center (NIC) in Suitland, MD. Since the launch of ERS-1 in 1991, NIC has come to rely on satellite SAR data for ice analysis. This is because of the distinctiveness of different stages of ice development in SAR imagery, the imagery's high resolution, and the instrument's ability to image through clouds. The only drawback has been the narrow (100km) swath of ERS-1. Analysts got a detailed look at the ice, but for a relatively small area. The launch by NASA of the Canadian RADARSAT satellite on November 4, 1995, has changed that. Bruce Ramsay, AES Canada, showed a mosaic of RADARSAT ScanSAR imagery that mapped the ice cover of the Beaufort Sea and Canadian Arctic up to the pole. The 500km-wide swath allowed the mosaic to be constructed over just 3 days. RADARSAT's utility for routing icebreakers has already been demonstrated in a joint US/Canadian project briefed by NIC's Steve Rutherford. Imagery and analyses were sent to the US Coast Guard icebreaker Mackinaw on Lake Superior by modem within 3 hours of the receipt of the data at the Gatineau satellite station. The demonstration was so successful that analysts judged aerial reconnaissance to be unnecessary. One outcome was that ScanSAR appears superior to ERS-1 for discriminating ice from water; possibly a result of using imagery at higher incidence angles than ERS-1's 23 degrees.
NIC and the NOAA Satellite Active Archive will receive about 70 500km-square images per week from the Alaska SAR Facility. NIC will also use imagery from Canada in an exchange agreement with the Canadian Ice Service, and will receive imagery from the Norwegian Tromso station covering the Barents Sea. At peak times, NIC will be receiving about 3 gigabytes of data each day. It will be impossible to manually analyze that volume of data. The status of ice type mapping algorithms, including an expert system being developed at the University of Kansas, was discussed, with an eye toward use of those algorithms at NIC. NIC will begin using RADARSAT intensively this fall.
You can find out more about these activities on the World Wide Web: