A New Look at the Summer Arctic Frontal Zone

Crawford, Alexander Michael Dominic

Graduate Thesis Or Dissertation

A New Look at the Summer Arctic Frontal Zone Public Deposited

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Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/k3569466m

Abstract

A notable characteristic of the summertime Arctic is the existence of a narrow band of strong horizontal temperature gradients spanning the coastlines of Siberia, Alaska, and western Canada that extends through a considerable depth of the troposphere. Past research has associated this summer Arctic Frontal Zone (AFZ) with contrasts in atmospheric heating between the Arctic Ocean and snow-‐free land, with its regional strength strongly influenced by topography. However, little is known about its variability, and questions persist regarding possible links with heating contrasts along the boreal forest-‐tundra ecotone. Output from the latest generation of global atmospheric reanalyses is used to better constrain and define the summer AFZ, including its spatial and seasonal characteristics. The relative importance of different factors linked to its variability are evaluated, and long-‐term trends in monthly AFZ strength are examined. The summer AFZ is present in at least some areas from May through August and reaches its peak strength in July. It is manifested aloft as a separate Arctic jet feature at about 300 hPa. The summer AFZ is clearly associated with differential atmospheric heating, as evidenced by the sharp difference in surface energy balance terms between the Arctic Ocean and adjacent land. No evidence is found of links between the summer AFZ and the boreal forest-‐tundra ecotone. Interannual variations in monthly strength of the summer AFZ are spatially heterogeneous and primarily dependent on factors affecting temperature over land, especially variability in cloud cover, surface wind direction, and snow cover extent. Local variability in sea ice concentration is also important through its control on temperatures over coastal seas. Snow cover is primarily important to monthly AFZ strength in May and June, while sea ice is more important in July and August. Throughout the period 1979 to 2012, monthly June AFZ strength increased throughout most of Eurasia. This strengthening is likely related to amplification of Arctic atmospheric warming over land from snow cover loss.

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