The Alaskan Arctic Frontal Zone: Forcing by Orography, Coastal Contrast, and the Boreal Forest

Abstract

Experiments have been conducted with a regional climate model to indicate the conditions required to generate preferred regions of frontal activity in the Alaskan region. Several objective methods of frontal identification were first investigated. It was found that· the vertical component of relative vorticity,· a thermal front parameter −∇|∇T850| · n, where T850 is the 850-hPa temperature and n is a unit vector in the direction of the 850-hPa temperature gradient, and· a parameter derived from the Q vector as a measure of vertical motionwere useful in combination to determine the occurrence of fronts. The preferred locations for frontal activity were located to the southern side of the eastern Brooks Range and over the Alaska Range. These diagnostics were then used to characterize frontal frequency in a series of experiments removing topographic and vegetation contrasts. It was found that the removal of the treeline contrast and its associated heating gradient had a small effect on frontal frequency in the immediate vicinity of the tree line, but that the largest impact was in response to the removal of topography, greatly reducing frontal frequency. The coastal contrast was found to have a limited role in synoptic frontal activity in the Alaskan region.