Level Method

Figure 8.4 Map of estimated mean annual sublimation for the Greenland Ice Sheet. Positive values mean transfer from the surface to the atmosphere (from Box and Steffen, 2001, by permission of AGU).

Figure 8.4 Map of estimated mean annual sublimation for the Greenland Ice Sheet. Positive values mean transfer from the surface to the atmosphere (from Box and Steffen, 2001, by permission of AGU).

In the polar deserts, mean annual temperatures are quite low and only exceed the freezing point in one or two summer months. Mean winter month temperatures are typically —30 to —35 °C, while means of the warmest month, generally July, are typically 1 to 5 °C. The fairly low summer maxima, while partly a function of latitude, are also due to persistent multiyear sea ice along the northern coasts of Greenland and the Canadian Arctic Archipelago, and around many of the Siberian islands. Areas in the continental interior of the Arctic and sub-Arctic can have similar (or even lower) winter air temperatures than polar desert, but July mean temperatures are considerably higher, yielding a pronounced annual temperature range.

Polar desert climates have been described for Peary Land, North Greenland (Putnins, 1969), Ellesmere Island (Lotz and Sagar, 1963; Barry and Jackson, 1969; Alt et al., 2000), Devon Island (Courtin and Labine, 1977), the northern Taymyr Peninsula and the Siberian Arctic Islands (Korotkevich, 1972). The areas in Peary Land and the Canadian Arctic Archipelago are characterized by high continentality with monthly mean temperatures in the winter months of —30 °Cor below and July values of 4-5 °C. In Severnaya Zemlya, mean annual air temperatures are —13 to —16 °C. Means for the winter months of —28 to —33 °C compare to those of around 1 °C in summer. Even in July, frost is recorded on 18 days. Climatic differences between coastal weather stations and inland sites like Lake Hazen and Tanquary Fiord on Ellesmere Island have been pointed out by Jackson (1959b) and Barry and Jackson (1969). Based on six years of data, Alt et al. (2000) show that mean July temperatures average 3 °C higher in the interior of the Fosheim Peninsula at Hot Weather Creek than at Eureka on the coast. In winter, inland temperatures are 1.5-3.5 °C lower than at the coast.

Especially striking are variations in the frequency of extreme minimum temperatures. On Ellesmere Island, the frequency of minima below —45 °C during February 1950-60 was 21% at Eureka but less than 2% at Alert (Hagglund and Thompson, 1964). These are both coastal sites. By comparison, Lake Hazen, an inland site, recorded minima of —45 °C or below on all but three days in December 1957 (Jackson, 1959b).

In some inland areas, summer conditions are surprisingly mild. Remarkably for the latitude, there are 65 frost-free days at Tanquary Fiord (81.4° N, 71.9° W) and 70 at Bronlunds Fiord on Greenland (82° N, 30.5° W). One could conceivably grow lettuce. Over the period 1989-93, the melt season (days with mean temperatures above freezing) at Eureka ranged from 72 to 95 days. At Hot Weather Creek, the corresponding values are 74 to 96 days (Alt et al., 2000).

As the above results imply, topoclimates and microclimates are strongly developed in many polar desert areas. It is not uncommon for the local topography to give rise to foehn conditions and resulting spells of high summer temperatures. Air temperatures of 18 °C have been recorded under these conditions on the eastern lowlands of the New Siberian Islands (L. S. Berg, cited by Golubchikov) and in Tanquary Fiord, Ellesmere Island (Barry and Jackson, 1969). Extremes of around 28 °C reported from the interior of Wrangel Island (Golubchikov, 1996) may arise from occasional warm air incursions from the Siberian lowlands combined with foehn effects.

Precipitation in polar desert areas is low and occurs mainly as snow. On Ellesmere Island, mean daily precipitation on summer days with measurable amounts is between 0.8 and 1.5 mm with maximum falls typically around 4-8 mm at Eureka (Alt et al., 2000). On rare occasions, summer precipitation can be associated with convective storms. Annual precipitation is typically 100-300 mm. Winter snow depths are generally around 200-400 mm but highly variable. Exposed parts of the surface may be blown free of snow for most of the winter. In other areas, drifting may result in a fairly deep snowpack. Where drifting is especially pronounced and in sheltered areas, snow can linger through the summer.

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