AIRCRAFT OBSERVATIONS OF THE DEVELOPMENT OF THERMAL INTERNAL BOUNDARY LAYERS AND SCALING OF THE CONVECTIVE BOUNDARY LAYER OVER NON-HOMOGENEOUS LAND SURFACES

摘要

This study investigates the convective boundary layer (CBL) that develops over a non-homogeneous surface under different thermal and dynamic conditions Analyses are based on data obtained from a Russian research aircraft equipped with turbulent sensors during the GAME-Siberia experiment over Yakutsk in Siberia, from April to .June 2000. Mesoscale thermal internal boundary layers (MTIBLs) that radically modified CBL development were observed under unstable atmospheric conditions. It was found that MTIBLs strongly influenced the vertical and horizontal structures of virtual potential temperature, specific humidity and, most notably, the vertical sensible and latent heat fluxes MTIBLs in the vicinity of the Lena River lowlands were confirmed by cloud distributions in satellite pictures. MTIBLs spread through the entire CBL and radically modify its structure if the CBL is unstable, and strong thermal features on the underlying surface have horizontal scales exceeding 10 km, MT-IBL detection is facilitated through the use of special parameters linking shear stress and convective motion. The turbulent structure of the CBL with and without MTIBLs was scaled using the mosaic or flux aggregate approach. A non-dimensional parameter L_(Rau)/L_(hetero) (whereL_(Rau) is Raupach's length and L_(hetero) is the horizontal scale of the surface heterogeneity) estimates the application limit of similarity and local similarity scaling models for the mosaic parts over the surface. Normalized vertical profiles of wind speed, air temperature, turbulent sensible and latent heat fluxes for the mosaic parts with L_(Rau)/L_(hetero) < 1 could be estimated by typical scaling curves for the homogeneous CBL. Traditional similarity scaling models for the CBL could not be applied for the mosaic parts withL_(Rau)/L_(hetero) > 1. For some horizontally non-homogeneous CBLs, horizontal sensible heat fluxes were comparable with the vertical fluxes, The largest horizontal sensible heat fluxes occurred at the top of the surface layer and below the top of the CBL.