. Compendium of meteorology. Meteorology. Fig. 6.—Average 700-mb contours (ft) and isotherms (°C) during January. to the areas of excessive sea-level pressure, as previously noted over northern Baffin Bay and over the Kara Sea, on the Weather Bureau "normal" map. With the in- troduction of more realistic perturbations in the circum- polar westerfies over these areas came an equally logical intensification and southward displacement of the east Asiatic cyclonic cell. It is suggested that the intensity of the American cefl will be exceeded by that of the Asiatic cell only during the an
. Compendium of meteorology. Meteorology. Fig. 6.—Average 700-mb contours (ft) and isotherms (°C) during January. to the areas of excessive sea-level pressure, as previously noted over northern Baffin Bay and over the Kara Sea, on the Weather Bureau "normal" map. With the in- troduction of more realistic perturbations in the circum- polar westerfies over these areas came an equally logical intensification and southward displacement of the east Asiatic cyclonic cell. It is suggested that the intensity of the American cefl will be exceeded by that of the Asiatic cell only during the anomalous absence, or com- plete enclosure, of the Barents-Kara perturbation. The cold-season cyclonic circulation over northern arctic America, being mainly a dynamic system of cold dry air, is relatively cloud free except during periods of reintensification. SEASONAL VARIATIONS IN ARCTIC AIR Variations over Northern Arctic America. The fore- going summary of average circulation patterns, and the geographical location of the American Arctic, indicate that all the large-scale air currents will have been sub- jected to arctic influences before their arrival over this region. The region itself provides the cold source area of arctic air masses affecting central and eastern North America. Variations in the observed properties of arctic air are directly related to the seasonal variations of the underlying surfaces and the air flow over them. The. -60° -40' -20" 0°C 20 -40' -30" -20' -10' 0"C Fig. 7.—Average soundings over northern arctic America. July. The average sounding for July, based on 28 ascents to the 250-mb level obtained at the Eurelia station during July 1947, shows the midsummer struc- ture of arctic air over ice-free interior areas. Because of the predominantly cool and moist underlying surface conditions, the regional air mass is maritime arctic in summer. There is a characteristic surface inversion over the pacli ice and cold water, but convective
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