Characteristics of Submeso Winds in the Stable Boundary Layer |
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Authors: | Larry Mahrt |
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Institution: | (1) COAS Oregon State University, Corvallis, OR 97331, USA |
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Abstract: | The characteristics of submeso motions in the stable boundary layer are examined using observations from networks of sonic
anemometers with network sizes ranging from a few hundred metres to 100 km. This study examines variations on time scales
between 1 min and 1 h. The analysis focuses on the behaviour of the spectra of the horizontal kinetic energy, the ratios of
the three velocity variances, their kurtosis, the dependence of horizontal variability on time scale, and the inter-relationship
between vertical vorticity, horizontal divergence and deformation. Motions on larger time and space scales in the stable boundary
layer are found to be nearly two-dimensional horizontal modes although the ratio of the vorticity to the divergence is generally
on the order of one and independent of scale. One exception is a small network where stronger horizontal divergence is forced
by a decrease in surface roughness. The horizontal variability, averaged over 1 h, appears to be strongly influenced by surface
heterogeneity and increases with wind speed. In contrast, the time dependence of the horizontal structure on time scales less
than one hour tends to be independent of wind speed for the present datasets. The spectra of the horizontal kinetic energy
and the ratio of the crosswind velocity variance to the along-wind variance vary substantially between networks. This study
was unable to isolate the cause of such differences. As a result, the basic behaviour of the submeso motions in the stable
boundary layer cannot be generalized into a universal theory, at least not from existing data. |
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Keywords: | Mesoscale Nocturnal boundary layer Stable boundary layer Submeso Wind networks |
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