Following from the above discussion, a good example of a maritime Arctic climate is Isfjord Radio (Svalbard) (Figure 8.6). Note first the sharply higher winter air temperatures as compared to Resolute Bay, the polar desert site (Figure 8.5). The maximum summer temperature, however, is similar at about 5 °C. The sites also differ stongly in terms of precipitation. Compared to the summer maximum at Resolute Bay, Isfjord exhibits a distinct autumn/winter precipitation maximum and late spring/early summer minimum. There is also a more even seasonal distribution of cloud cover, ranging from
about 60% in winter to 80% in August and September. This manifests the Atlantic cyclone influences.
The precipitation regime is broadly similar to that of Iceland, well to the south. During autumn/winter, the North Atlantic storm track is strong. Coupled with the availability of abundant oceanic moisture sources and relatively high evaporation rates, precipitation is high. Serreze and Etringer (2003) estimate that, in the vicinity of Iceland, about half of the mean January precipitation is contributed by the large-scale vapor flux convergence and half by surface evaporation.
Figure 6.9 indicates that January mean P — ET in the Svalbard area, representative of winter months, is quite small (0-10 mm). As the change in atmospheric water vapor storage is also small at this time, P — ET is essentially the vapor flux convergence (see Chapter 6 for discussion of the aerological moisture budget). Since the winter vapor flux convergence is so small in the vicinity of Svalbard, this indicates that compared to the Iceland region, correspondingly more of the winter precipitation is derived from surface evaporation.
Extensive cloud cover, open water, latent heat release and poleward heat fluxes associated with frequent cyclone activity combine to keep winter surface temperatures remarkably high given the latitude (roughly 80° N). The North Atlantic storm track is weaker in summer. Because of the weaker temperature contrasts between the ocean and lower atmosphere, surface evaporation declines. Precipitation-generating mechanisms are therefore weaker than in winter. However, cloud cover is still extensive, which moderates the surface air temperature. The June peak value in downwelling solar radiation (about 200 W m—2) is much lower than that for Resolute (about 280 W m—2). This is a result of cloud cover rather than latitude. Although the June cloud fraction is about the same at both locations (70-75%), clouds over Isfjord Radio tend to be optically thicker.
Barrow is also considered by some investigators to fall in the category of an Arctic maritime climate (Figure 8.7), but conditions are quite different from those in the Atlantic sector and are really closer to those for polar desert. Przybylak (2003) properly considers this site to be transitional. Winter temperatures are somewhat higher than those for the Resolute Bay polar desert site. This results in a smaller annual temperature range than for Resolute Bay, but still much greater than at Isfjord Radio. Like Resolute, conditions are quite dry, with less than 5 mm of precipitation (discounting gauge biases) from December through May, and an August maximum of about 23 mm. Compared to Resolute, there is slightly more winter cloud cover.
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