| Surface temperatures poleward of 60 degreees N are provided by the P-Cube data set for day 90 (March 30) 1988. These temperatures were derived from the AVHRR sensor at a spatial resolution of 100 km. Higher temperatures, indicated by lighter shades of grey, predominate over the open ocean areas of the North Atlantic and Barents Sea, as well as in the Davis Strait between southern Greenland and Canada and over portions of the Bering Sea in the North Pacific. The coldest temperatures are seen over Greenland and the central Arctic ice pack. |
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An image of the precipitable water between the Earth's surface and 850 mb is derived from the TOVS sensor for the P-Cube data set. The highest values, indicated by lighter grey shades, can be identified over the open water regions. Lower values are seen over the Arctic's central ice pack. No data are available over the higher elevations of Greenland but low amounts of precipitable water are observed over land. A good example of this occurs over north central Russia. |
While the science world eagerly awaits NASA's Earth Observing satellite launches, the EOSDIS Distributed Active Archive Centers (DAACs) have been hard at work to ensure availability of high-quality heritage data that enhance the anticipated EOS data streams. For instance, in 1990 when NASA and NOAA teamed to create the Pathfinder Program to generate long time series from existing satellite data sets, it was decided to make Pathfinder data available through the DAACs because, along the way to providing data relevant to global-change research, the Pathfinder investigators were to provide prototype methods for processing and handling large data sets.
The Pathfinder process underscored technical difficulties impeding interdisciplinary data use. Integrating data from different sensors for study is typically awkward because data come in different formats. Reconciling information from multiple sensors can require considerable preparation before data become useful for research purposes. With data inter-use in mind, the Pathfinder program encouraged teams to take a comprehensive approach.
In January 1999, members of three Polar Pathfinder Projects and the National Snow and Ice Data Center (NSIDC) DAAC will bring a groundbreaking example of this idea to fruition. To maximize Polar Pathfinder utility and address the needs of the cryospheric research community, the Special Sensor Microwave/Imager (SSM/I), Advanced Very High Resolution Radiometer (AVHRR), and TIROS-N Operational Vertical Sounder (TOVS) Pathfinder teams coordinated processing activities to create a Polar Pathfinder Sampler that provides a means of studying Arctic ocean, land, ice, and atmosphere interactions at one time.
The Polar Pathfinder data have synchronized file formats and naming conventions, and all data have been projected to the NSIDC Equal-Area Scalable Earth-Grid (EASE-Grid). The fundamental concept of the EASE-Grid is that it provides a basis for a standard, flexible system for working with remote sensing data, independent of the satellite sensor or data type.
The new Polar Pathfinder CD-ROM contains both samples of daily composites of 100-km merged Pathfinder data sets and full-resolution samples of each Polar Pathfinder product. The Sampler features selected animations for previewing large-scale atmospheric and surface-condition changes. In addition, the CD-ROM provides a merged data set from three Pathfinder projects within a low-resolution, multidimensional structure known as the "P-Cube". Containing 16 atmospheric and surface variables, the P-Cube provides data for a range of polar climate research applications, but will be of special interest to investigators dealing with large-scale atmospheric changes, surface heat and mass balance studies, and sea ice modeling.
"P-Cube is a superset of variables from the three sensors," says Drew Rothrock, principal investigator of the NASA EOS interdisciplinary research project, Polar Exchange at the Sea Surface (POLES). "Data can now be compared between instruments and with in situ data. These P-Cube data will be used initially for validation of existing data until they have passed review by the polar science community. Their greatest strength, though, is in providing the beginning of a climatology of interrelated polar variables."
"It's essential to understand the relationships between individual variables," Rothrock says. "For instance, understanding how albedo changes with surface temperature over sea ice becomes trivial using this data set because the information is in a form conducive to climatological analyses."
Numerical models of the planet's general circulation indicate that polar regions are anything but insignificant climatologically. Climate-change projections show polar regions warming faster than lower latitudes. The long-term record indicates that glacial areas have evolved quite differently than tropical climates.
Polar regions respond quickly to changes in climate conditions. Leads, channels of open water within sea ice, and the open ocean at the fluctuating ice margin, respond to incoming solar energy, inducing moisture fluxes that lead to cloud formation and precipitation which ultimately feed back into global atmospheric and oceanic circulation. Earth's ice and snow shape daily weather and human activities around the world. The extent and volume of snow and ice change radically season-to-season and over hundreds of thousands of years, effecting substantial changes in the planet's albedo, weather patterns, water resources, and sea level. But in spite of its climatological significance, "very little data on the three-dimensional state of the Arctic exist Ñ by that I mean ice cover and the atmosphere above it," says Greg Flato, a research scientist at the Canadian Centre for Climate Modeling and Analysis. "It's hard to assess, for example, the way clouds behave, or the way clouds and radiation interact in the Arctic. These interactions may be quite different from the way they occur elsewhere."
The instruments selected to provide Polar Pathfinder data sets provide different and complementary information, Flato points out. "AVHRR provides surface-level imagery in visible and thermal-infrared wavelengths, providing quantitative information on sea ice types. AVHRR suffers because it can't see through clouds."
"The SSM/I provides lower resolution images but it can penetrate cloud cover and, therefore, provides information on sea ice concentration, large-scale surface temperatures and large-scale ice motion. The main purpose of TOVS is to supply information on the atmospheric column above the ice," he says.
"This a rich data set that's going to see a lot of use," he says. "The next step is to make the full data sets available allowing researchers to see how things are evolving over longer periods." NSIDC already distributes SSM/I Pathfinder data. The other Polar Pathfinder data sets are still in production with distribution slated for 1999.
"The primary goal of the Pathfinder Program was to turn out common data sets," Rothrock says. "The Polar Pathfinder Sampler demonstrates the usefulness of doing this with historical data. And, using data from more than one sensor means that a range of variables- cloud fraction, temperature, and albedo- are available over varying times," he says. "One of the most significant outcomes of this project is that people with experience with particular sensors are successfully working with researchers skilled in completely different sensors," Rothrock says. "It is a good multi-sensor data production model for EOS."
The Polar Pathfinder Sampler will be distributed (free) at the January meeting of the American Meteorological Society. To order a copy, please send your postal mailing address, phone, and e-mail address to:
NSIDC User Services
Attn: Polar Pathfinder Sampler
nsidc@kryos.colorado.edu
Campus Box 449
University of Colorado
Boulder, CO 80309-0449 USA
Fax: +1 303-492-2468