Surface-layer scaling of velocity, temperature and transport processes in thermally-driven slope winds

The atmospheric boundary layer (ABL) in mountainous regions is characterised by a variety of airflows, shaped by different landforms, which encompass a range of scales of motion, from synoptic scale flows to very local phenomena. Among them, a particular role is played by the daily-periodic thermally-driven circulation systems developing over the inclines and in the valleys under clear skies and in the absence of major synoptic forcing. These airflows, and turbulence generated therein, affect a variety of processes, including surface-atmosphere exchanges of momentum, energy and mass, and transport across a variety of scales. They may also contribute to the initiation of orographic convection. 

 

The simplest of these wind systems are those which develop over simple slopes, i. e. the so-called slope winds.

 

The structure of turbulence properties and their representation in terms of similarity scaling are still quite debated in the literature.

 

Based on theoretical arguments and on the analysis of data from a variety of field experiments, it is shown that the Obukhov length is still the appropriate lengthscale for the structure of velocity and temperature profiles as well as for the eddy viscosity and eddy diffusivity. However the slope-normal structures of first- and second-order turbulence moments are quite different from those valid for flat horizontal terrains. Also momentum flux and heat flux at the surface are not two independent proerties, bur rather interconnected.

 

Ongoing efforts to pursue further the investigation on these flows within the current initiative TEAMx - Multi-scale transport and exchange processes

in the atmosphere over mountains – programme and experiment (http://www.teamx-programme.org/)  are also presented.