soliton_only_finescale
Small-scale meandering associated with a wave-like oscillation

The term meandering motions normally refers to unpredictable constant changing of wind direction due to submeso motions.  Such changes could be associated with any of the above submeso motions but is often associated with wave-like behavior. While meandering usually applies to nocturnal conditions, submeso motions with very weak daytime winds can also lead to wind direction meandering in the daytime with weak large scale flow.

Meandering is a commonly used term in the pollution/dispersion community where the term has no specific physical/dynamical meaning beyond shifting of the wind direction back and forth. Meandering often refers to changes on time scales greater than ten minutes and, therefore, is more often in the mesoscale regime  rather than the submeso regime. Layers of different flow direction may lead to significant vertical shear and intermittent generation of turbulence. Meandering modes are best viewed from an overhead position.

The following video shows a variety of motions that cause meandering of the wind direction, vertical wind direction shear, divergence and transient flow around obstacles.

Meandering is normally  considered to be smoothly changing changing wind direction, but sudden embedded wind shifts are common.  The two following videos show such wind shifts.  The wind shifts are often preceded by brief rising motion suggesting horizontal convergence and microfrontal type behavior.  These motions were observed with significant winds within hilly terrain.

DISPERSION:   In the most stable conditions, when concentrations of atmospheric contaminates can be large, dispersion is slow and often confined to thin layers near the ground.  In such important cases, a release of harmful material will be transported in a variety of wind directions due to meandering of the wind direction.  Plume models will not be of use in these cases.  Networks of data have been used to construct dispersion animations which provide examples of time and space distribution of the contaminants.

Advertisements