Advection in the Coastal Hudson Bay Lowlands, Canada. I. The Terrestrial Surface Energy Balance

Abstract

The effects of advection, from a cold polar sea to a warmer terrestrial surface, on the energy balance in the surface boundary layer are reported. Results indicate that mesoscale advective influences are strongly developed. Over a 10-km coastal zone, Bowen ratios (I) decrease exponentially inland, 2.7 fold during onshore winds and 1.8 fold during offshore winds. This decrease is due both to boundary layer adjustments to a new surface under onshore winds and to horizontal and vertical convergence and divergence in the atmosphere under all wind conditions. Horizontal convergence and divergence is most evident near the coast. The former is most common during periods of low wind speed and the latter during stronger winds. The strongest mesoscale advective impacts on the turbulent fluxes occur within 10 km of the coast. Although in hummocky tundra, the surface may appear to be saturated because of standing water, the drier hummocks serve to reduce the average surface vapor pressure substantially below saturation and thus to reduce the latent heat flux.