Impact of Arctic treeline on synoptic climate

The position of the Arctic treeline has been associated with the preferred location of Arctic fronts that demarcate the boundary between Arctic arid p olar air masses. It has been argued that differences in summer energy balan ce, particularly in sensible heating, across treeline between forest arid t undra may help determine the location of these frontal zones. Our observati ons of the energy balance at treeline show that the daily averaged summer h eating contrast between treeline forest and tundra is an order of magnitude less than that previously proposed and that the influence on the atmospher e is confined to a shallow layer. In addition, maximum heating contrasts oc curred in spring rather than in summer when the Arctic frontal zone is best expressed. Hence energy-balance contrasts at treeline are unlikely to be t he major determinant of the position of the Arctic front.