Mesoscale Circulations and Surface Energy Balance During Snowmelt in a Regional Climate Model

The Canadian Regional Climate Model has recently been coupled with an advanced, second generation land surface model - the Canadian Land Surface Scheme. In addition, high resolution land cover and soils data sets have been assembled on a 1 km horizontal resolution grid over North America. These data sets, along with the coupled model, provide a powerful tool for the examination of regional climate processes in complex, heterogeneous terrain. In a first application of the new modelling system, simulations of progressively higher horizontal resolution are performed over the Mackenzie Basin for the spring of 1995 in order to determine if turbulent fluxes associated with a heterogeneous land surface can generate mesoscale atmospheric circulations of relevance to the surface energy budget during the critical snow melt period. We have found that shallow, diurnally forced mesoscale circulations associated with surface flux heterogeneity developed regularly throughout the snow melt period in the higher resolution experiments. In one case, a localized down-draft associated with a low level isothermal layer was found to enhance turbulent heat exchange with the underlying snow. The net importance of this process to the overall energy balance of the snowpack did increase with resolution, but remained relatively small for the resolutions considered here.