INERTIAL OSCILLATIONS AND A PARAMETERIZATION OF THE EVOLVING STABLE BOUNDARY LAYER

Inertial oscillations, with a frequency equal to the Coriolis parameter, have been observed in conjunction with the evening transition of the boundary layer, and have been proposed as a mechanism for the genesis of the low-level wind maximum in the nocturnal boundary layer (Blackadar 1957). Inertial oscillations also appear to influence dispersion in the stable boundary layer (Singh et al 1996).

Wind profiler data has revealed the presence of inertial oscillations in the vicinity of fronts (Ostdiek and Blumen 1997). Data from a 915 MHz wind profiler in the Argonne Boundary Layer Experiment (ABLE) array, located in southeastern Kansas, has been analyzed for the presence of inertial oscillations generated by the evening transition. During the 30-day CASES97 field experiment, we found two nights with inertial oscillations at many height gates, with an average amplitude of ~ 4 ms-1. There is a strong variation of the amplitude of these inertial oscillations with height; this variation resembles that found by previous investigators (Ostdiek and Blumen 1997). The maximum amplitude tends to be at 300-600 m; the amplitude sharply decreases below that height while gradually decreasing above that height until reaching the maximum height of the daytime convective boundary layer. We rarely find nocturnal inertial oscillations above the maximum height of the daytime convective boundary layer.

A model of the stable boundary layer will be used with this dataset. We adapt a common model development presented by Mahrt (1981), Tjemkes and Duynkerke (1989), and Singh et al (1993). The new aspect of this work is to use the observed inertial oscillations to parameterize the vertical momentum flux in terms of a horizontal eddy diffusion coefficient following the work of Young et al (1982). The effect on the evening transition by the new parameterization will be presented together with properties of horizontal dispersion within the evolving stable boundary layer.

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