Radiation Conditions

In the history of actinometric measurements in the Arctic, five phases can be distinguished:

Phase 1. The 19lh ccnniry. During this period, measurements of solar radiation were made using ordinary thermometers, i.e. the difference between tiic readings of thermometers with shaded and exposed bulbs, placed in the sun and in the shade, was used to estimate the intensity of radiation. According to Gavrilova (1963) the first such measurements were made during the expeditions of John Franklin to the polar sea in the years 1825, 1826, and 1827 (Franklin 1828). Later on, using the same method, measurements were conducted during different expeditions to the Arctic (Solar Radiation..., 1876; Report of the International..., 1885; Observations of the International..., 1886).

Phase 2. The end of 19th century - the Second international Polar Year (1932/1933). For actinometric measurements, the date of the construction of the first pyranometer by Angstrom at the end of the 19lh century was very important. Wcstman conducted the first measurements using this instrument at Trcurenbcrg Bay in Spitsbergen in 1899-1900 (Westman 1903). A greater number of measurements during this period were carried out in the 1920s and at the beginning of 1930s (e.g. Kalitin 1921, 1924, 1929; Götz 1931; Mosby 1932; Georgi 1935; Kopp 1939; Wegener 1939). All these actinometric measurements were, however, of a temporary and episodic character. At the end of this period most scientists knew that the establishment of a network of stations was necessary in order to determine the radiation regime of the Arctic.

Phase 3. The Second International Polar Year - 1950. In this period in the years 1932-1933 the first continuous actinometric observations were made simultaneously at a number of stations. The second important event was the organisation of an actinometric network in the Soviet Arctic (six stations).

Phase 4. 1950 - the start of the satellite era (ca. 1972). This period (mainly in the 1950s) saw the establishing of most of the actinometric stations which now exist in the Arctic. The majority of them (about 20) are located in the Russian Arctic (see Figure 1 in Gavrilova 1963). In addition, since 1950, regular observations have been carried out in the central Arctic by the drifting stations "Severnyy Polyus" (Volkov 1958; Sychev 1959).

Phase 5. Satellite era - the present. In this period, besides standard in situ actinometric observations, different remote sensing techniques have become increasingly popular, especially those using satellites. These new methods are especially important for the Arctic, where the network of meteorological stations, as we know, is scarce. They permit the calculation of incoming solar radiation, albedo, and outgoing long-wave terrestrial radiation loss - all the necessary components of the net radiation of the earth-atmosphere system (see Cracknell 1981; Lo 1986; Harris 1987; Schweiger et al. 1993). On a global scale, several satellite-based data sets exist (International Satellite Cloud Climatology Project, Earth Radiation Budget Experiment), which have been used recently for projects such as the calculation of Surface Radiation Budget (Whitlock et al. 1993). In recent years, satellite-based methods have also been used to retrieve surface radiative fluxes for small areas (Parlow 1992; Scherer 1992; Duguay 1993). For this purpose Landsat satellites are best, due to satellite orbit and sensor resolution (Haefliger 1998). For greater areas the data received from NOAA AVHRR (Advanced Very High Resolution Radiometer) and SSM/I (Special Sensor Microwave/Imager) are most useful for calculations of short-wave and long-wave surface radiative fluxes. Such studies have been conducted for the Fram Strait area (Kergomard et al. 1993) and the Greenland Ice Cap (Haefliger 1998).

Although, it is possible to find a great quantity of literature and points of view on the different aspects of the radiation regime in the Arctic, our knowledge about the climatology of the radiation balance and its components is still meagre. This is especially true of the central Arctic and Greenland Ice Sheet regions. The main reason for this is the sparse network of actinometric stations in the Arctic. From the different sources presenting radiation conditions in the study area, especially those in the form of charts, the reader should know that the isolines drawn give only a rough approximation of the real situation. In many cases, the charts were based on theoretical calculations. It is hoped, however, that in the future, satellite remote sensing techniques will help to collect data sets of surface (and other) radiative fluxes for the Arctic with much greater temporal and spatial resolution than we have today.

Gavrilova (1963), Marshunova and Chcrnigovskii (1971), and Ohmura (1981, 1982) gave excellent reviews of the historical development in radiation studies up to about 1980. Therefore, there is no need to repeat this here again. However, some more important elaborations, from a climatological point of view, should be mentioned here, together with some new works which appeared after Ohmura*s reviews. If is rather unquestionable that the role played by Soviet (Russian) climatologists in investigations into the radiation regime in the Arctic was, and probably still is, the greatest. The most important works published by Russians are the following: Kalitin (1940, 1945), Marshunova (1961), Budyko (1963), Gavrilova (1963), Chernigovskii and Marshunova (1965), Stepanova (1965), Marshunova and Chernigovskii (1971), Gorskhov (1980), Makshtas (1984), Atlas Arktiki (1985) and Khrol (1992).

From the non-Russian authors, without doubt the greatest contribution in investigations of radiation and heat balance of the Arctic and their components has been made by the staff of the Arctic Meteorology Research Group, Department of Climatology, McGill University in Montreal, and in particular Vowinckel and Orvig. Their results were first published in the McGill University Scientific Reports, Publications in Meteorology (Larson and Orvig 1962; Vowinckel and Orvig 1962, 1963, 1964a, 1965; Vowinckel 1964a, b; Vowinckel and Taylor 1964) and in shorter versions in a series of papers published in Archiv für Meteorologie, Geophysik und Bioklimatologie (Vowinckel and Orvig 1964b, c, d, 1966; Vowinckel and Taylor 1965). All these papers were later used by Vowinckel and Orvig in the preparation of some fragments of their best known work published in the series of the World Survey of Climatology (Vowinckel and Orvig 1970). A good summary of the heat budget of the earth-atmosphere system in the Arctic, based mainly on above-mentioned sources, has been provided by Fletchcr (1965). Of the other important works, in particular those which give the spatial distribution of radiation balance and its components only for the Canadian Arctic, one should mention the publications of Maxwell (1980), McKay and Morris (1985), and Woo and Young (1996), among others. In recent years intensive investigations of radiation conditions on the Greenland Ice Sheet have been mainly carried out by the Institute for Atmosphere and Climate at the Swiss Federal Institute of Technology in Zürich using satellite techniques (Ohmura et al. 1991, 1992; Konzclmann 1994; Konzelmann and Ohmura 1995; Haefliger 1998).

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