Following World War II, France resumed glaciological and geophysical work on the Greenland ice sheet. The Expedition Polaire Francaise (Mission P.E. Victor) operated from Station Centrale at the Eismitte site (70.9° N 40.7° W, 3000 m) during 1949-1950. This set the stage for the French-German-Swiss Expedition Glaciologique Internationale au Groenland (EGIG), which in 1959 surveyed a section through the ice sheet. Resurvey on the two EGIG flow lines in 1969 produced the first evidence of an ongoing change in the ice sheet shape. Important work on the radiation and energy balance of the ice sheet (Ambach, 1963) was also carried out. Station Northice (78.1° N 38.5° W, 2343 m) of the British North Greenland Expedition was occupied from November 1952 to August 1954. Its observations, together with the Station Centrale and EGIG data and the prewar records, provided the bulk of the information on ice sheet climate until the advent of automatic weather stations in the 1980s (Putnins, 1969).
In the 1960s, the Canadian Defence Research Board (DRB) carried out extensive geophysical and glaciological work in Ellesmere Island under G. Hattersley-Smith. Climatological observations were maintained at Tanquary Fjord and also at Lake Hazen (Barry and Jackson, 1969). Numerous field camps of the Canadian Polar Continental Shelf Project, 1974-1993, in the Canadian Arctic Archipelago collected short-term weather observations, and these have recently been assembled into a database. They provide a valuable supplement to the sparse weather station network (Atkinson et al., 2000). Climate studies by the
McGill University, Montreal and the Geographical Institute, ETH, Zuerich were conducted during the Axel Heiberg Expedition, 1961-1985. They were mainly related to glacier research projects but included analyses of tundra energy budgets (Ohmura, 1982).
The first deep ice core was recovered from a 1387 m hole drilled to bedrock in 1966 at Camp Century (71.2° N 61.1° W, 1885 m) in northwest Greenland. For many years, this provided the primary record of glacial and postglacial climate. Additional cores were obtained in Greenland and from ice caps in the Canadian Arctic, but major advances in paleoclimate research resulted from the Greenland Ice Sheet Project 2 (GISP 2) and the European Greenland Ice Core Project (GRIP). Holes drilled in 1989-1993 provided over 3000 m of ice core near Summit (72.6° N 34.6° W). These records had a major impact on our understanding of the climate of the last 130,000 years (Hammer et al., 1997). Especially notable was the recognition of abrupt climatic changes—on time scales only of a decade or so—occurring throughout the late Pleistocene and Holocene intervals.
Among Cold War military programs that yielded climatological information were the "Ptarmigan" flights for Arctic weather reconnaissance, from March 1947 to 1955 (Anonymous, 1950), from Alaska to the North Pole and Project Bird's Eye aerial reconnaissance flights of ice conditions (1962-1967), also to the North Pole. The Ptarmigan flights at the 10,000 ft level observed cloud and ice conditions and used dropson-des for lower tropospheric soundings. Bird's Eye provided data on cloud cover that formed the basis of an improved climatology (Huschke, 1969).
Field studies of the North Water, a polynya in northern Baffin Bay, were conducted by McGill University and the Swiss Federal Institute of Technology (ETH), Zurich from 1972 to 1985 under the leadership of F. Mueller. This work was continued into the late 1990s using mainly satellite remote sensing and modeling studies (Barber et al., 2001).
In the 1980s, there were a number of experiments addressing Arctic ocean-ice-atmosphere interactions and the use of satellite radar data. These included the Marginal Ice Zone Experiment (MIZEX) in 1983, 1984, and 1987 as a direct outcome of POLEX (Mizex '87 Group, 1989), the Labrador Ice Margin Experiment (LIMEX) in 1987 (McNutt et al., 1988), the Coordinated Eastern Arctic Research Experiment (CEAREX) in winter 1988-1989 in the Norwegian-Greenland Sea, and the Leads Experiment (Leadex) in March-April 1992.
In 1988, as a US contribution to the International Geosphere-Biosphere Program (IGBP), the National Science Foundation launched a multidisciplinary program on Arctic System Science (ARCSS). The primary goals are: "to understand the global and regional impacts of the Arctic climate system and its variability, to identify global change impacts on the structure and stability of Arctic ecosystems and to establish the links between environmental change and human activity." Initially, its main components were the Greenland Ice Sheet Project 2 (GISP 2) and one addressing the Paleoclimate of Arctic Lakes and Estuaries (PALE). Then, following a series of workshops, modern process studies were organized for terrestrial and marine systems (ARCSS Workshop Steering Committee, 1990; LAII Science Steering Committee, 1997; ARCSS, 1998). During the 1990s, the Land-Atmosphere-Ice Interactions (LAII) component included several projects that examined climate and environmental changes in the Alaskan Arctic. Responses by plants and frozen ground conditions to recent warming were identified (Serreze et al., 2000). There was also a major focus on trace gas fluxes and the effects on these of changes in climate and associated responses in the soils, vegetation cover, and land cryosphere (Kane and Reeburgh, 1998). From October 1997 to October 1998, an icebreaker was frozen into the Beaufort Sea to support the Surface Heat Budget of the Arctic Ocean (SHEBA) project of ARCSS. Researchers collected data on sea ice, oceanic and atmospheric conditions, and their interactions over an annual cycle, as the vessel drifted from 75° N to 80.5° N. Central concerns of the project are the scaling of in situ field measurements to address parameterization of processes in coupled climate models, and the assessment of surface-based, airborne, and satellite remote sensing data. The project is closely linked to other programs—FIRE and ARM—discussed below.
The US Department of Energy Atmospheric Radiation Measurement (ARM) program includes a Cloud and Radiation Testbed site at Barrow, Alaska, installed in 1997. The objectives are: to describe quantitatively the radiation balance from the surface to the top of the atmosphere; to determine the atmospheric characteristics responsible for this balance; to improve the parameterization of cloud processes in climate models; to evaluate process models used in GCMs; and to provide ground-truth of satellite radiation measurements (Stamnes et al., 1999). Related aircraft, satellite, and in situ measurements of clouds, radiation, and aerosols were carried out over the Beaufort Sea in April-July 1998 during the First ISLSCP Regional Experiment (FIRE) Arctic Clouds Experiment (ACE), in association with the SHEBA ice camp (Curry, 2001).
In Canada, a research group is investigating the Cryospheric System (CRYSYS) and its role in climate. The multi-institute project began in 1988 as a contribution to NASA's Earth Observing System (EOS) program. Various projects are examining the development of parametrizations and the validation of regional to global climate models (http://www.crysys. uwaterloo.ca/).
Recent climate studies in Greenland have been conducted through the Program for Arctic Regional Change Assessment (PARCA) (http://cires.colorado. edu/steffen/parca.html). This NASA project was formally initiated in 1995, combining several investigations begun in 1991, to assess whether airborne laser altimetry could be applied to measure ice-sheet thickness changes. Its primary goal is measuring and understanding the mass balance of the Greenland ice sheet (Thomas and Investigators: PARCA, 2001). Climate-related studies include: shallow ice cores (10-200 m) at many locations to infer recent climate history, atmospheric chemistry, and interannual variability of snow-accumulation rates; investigations of surface energy balance and factors affecting snow accumulation and surface ablation; and installation of a network of automatic weather stations (AWS) around the ice sheet.
In 1997, an Arctic subset of the Comprehensive Ocean-Atmosphere Data Set (COADS) containing marine surface weather reports for the region north of 65° N from ships, drifting ice stations, and buoys was assembled at the Cooperative Institute for Research in Environmental Sciences, University of Colorado. The Arctic subset contains data collected over the years 1950-1995 on air and sea temperature, cloudiness, humidity, and winds (see http://nsidc.org/data/nsidc-0057.html).
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