. Compendium of meteorology. Meteorology. 1020 \ \ W \ 1 AVERAGE PRESSURE JULY ' Fig. 1.—Average sea-level pressure (mb) during July. the circulation patterns in this midsummer period of minimum thermal contrast between the polar and tem- perate zones. The circumpolar belt of low pressure is at its highest latitude in this month, with a definite extension of cyclonic activity toward the North Pole itself, although a feeble anticyclonic circulation persists over the congested pack-ice area northwest of the Canadian Archipelago and over the northeast Green- land-Fridtjof Nansen Land area. Along
. Compendium of meteorology. Meteorology. 1020 \ \ W \ 1 AVERAGE PRESSURE JULY ' Fig. 1.—Average sea-level pressure (mb) during July. the circulation patterns in this midsummer period of minimum thermal contrast between the polar and tem- perate zones. The circumpolar belt of low pressure is at its highest latitude in this month, with a definite extension of cyclonic activity toward the North Pole itself, although a feeble anticyclonic circulation persists over the congested pack-ice area northwest of the Canadian Archipelago and over the northeast Green- land-Fridtjof Nansen Land area. Along the Laptev Sea coast line, the contrast between warm air from the in- terior of Siberia and cool air from the pack ice is sufficient to maintain persistent cyclonic activity. Weak disturbances, originally associated with poleward thrusts of North Atlantic maritime air masses, may here be reintensified to resume their eastward pro- gression toward the similar but milder thermal gradients along the arctic coast of Canada. It has been mentioned that the July chart retains the best features derived by prior research of other arctic specialists [1, 6, 19]. The more widely circulated pub- lication, "Normal Weather Maps, Northern Hemi- sphere, Sea-Level Pressure," [20] has presented a differ- ent pattern for July, especially over northern arctic America. With a 1017-mb isobar encircling the well- substantiated col area (average pressure less than 1013 mb) of the North Pole, and with little hint of a semi- permanent cyclonic system over northern Baffin Bay, the "40-yr normal July" could be very misleading. However "abnormal" the recent Julys may have ap- peared to be in this area, expedition reports indicate that midsummers over a hundred years ago were more dominated by cyclonic than by anticyclonic conditions. Because of the simple thermal aspects of the July circulation scheme and the annual return to relatively the same percentages of ice-covered or
Size: 1774px × 1409px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookcollectionbiodivers, booksubjectmeteorology
