July Arctic Front in North America
Abstract: Boundaries between air masses, frontal zones, are associated with vegetation boundaries. Using gridded climate reanalysis data, we analyse the air masses and frontal zones of North America in relation to the atmospheric circulation and vegetation productivity. The position of the July Arctic front varies significantly through the period 1948-2007, with a mean position similar to that found by Bryson (1966). The variability of the frontal position can be associated with changes in the general circulation; when the Arctic Oscillation (AO) and Southern Oscillation Index (SOI) are positive (negative), the position of the July Arctic front is further north (south). There is also more spatial variability in the July Arctic frontal position in eastern versus western North America. The location of the frontal zone affects the vegetation through impacts on vegetative production; when the July Arctic front is north (south) of the mean position, the boreal forest and tundra vegetation is more (less) productive. Contrary to other studies that have identified changes in air mass frequency distributions and properties in several regions in response to global warming, we could not find clear evidence of significant changes in the position of the Arctic front in recent years.
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