High resolution flight observations and numerical simulations: horizontal variability in the wintertime boreal boundary layer

High resolution aircraft observations made along flight tracks over inhomog eneous surface in the late wintertime boreal zone are described and compare d to 2D mesoscale model simulations with surface properties defined at 2km resolution from maps. All observations displayed the expected small-scale t urbulence. On top of that, the near-surface wind speeds (but not directions ) showed mesoscale variations related to local topography and roughness. Up ward (but not downward) SW and LW radiative fluxes and ground temperature a lso displayed mesoscale variability; in SW radiation this was clearly due t o local albedo changes. In the sensible heat flux there was strong horizont al variation near the surface in correlation with surface types. The above observed mesoscale along-track variations were reasonably well represented by the mesoscale model simulation. The track-averaged observed sensible and latent heat flux profiles were in rough agreement with a mixing length app roach, which used the track-averaged wind, temperature and moisture profile s as input (mimicking a first-order turbulence closure scheme of a GCM).