4.1 Mesoscale motions and their influence on turbulence in stable conditions

Monday, 9 June 2008: 3:30 PM
Aula Magna (Aula Magna)
Larry Mahrt, NorthWest Research Associates, Inc., Corvallis, OR

In weak-wind conditions, the wind field and shear-generation of turbulence become dominated by mesoscale motions, generally of unknown origin, particularly in the stable boundary layer. The distinction between the turbulence and mesoscale motions may become more obscure compared to stronger winds and fully developed turbulence. This partitioning problem is examined in terms of changes of flow characteristics with scale using fast response data from towers and networks of stations.

We also examine the characteristics of mesoscale motions in terms of time-space relationships. The mesoscale motions on the smaller scales tend to be more wavy, or distorted by the large-scale flow. Mesoscale motions on larger scales tend to be more two-dimensional and less influenced by the large-scale flow. The interaction between the turbulence and mesoscale motions on different time and space scales is explored.

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