Area averaging of land surface–atmosphere fluxes in NOPEX: challenges, results and perspectives

The NOPEX experimental campaigns dealt with the land-surface-atmosphere exchange of momentum, heat, water and CO2 on local and regional scales. In this paper emphasis is put on the NOPEX experiences with respect to the spatial integration of fluxes of momentum, heat, humidity and CO2 over the mosaic of forest, agricultural land, lakes and mires that make up the southern part of the NOPEX area. It is found that the forest dominates both the regional momentum and heat fluxes but in very different ways. Furthermore, results from a NOPEX experiment in the northern zone of the boreal forest in Finnish Lapland highlights the very unique processes associated with the energy exchange within a forest in wintertime. The interaction of the forest canopy with sunshine provides a considerable energy source, particularly at low solar angles. A considerable improvement in model simulations of fluxes and surface temperature was achieved when this effect and the heat storage of the canopy were taken into account.