Microfronts 1995 and Cases 1999: Boundary Layer Influences on Fronts and Inertial Oscillations

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Processes that occur in the Earth's boundary layer, the relatively shallow layer in contact with the ground, often have a significant effect on atmospheric fronts and are a source of wave motions and atmospheric oscillations. Data available from a previous field investigation in Kansas in 1995 (MICROFRONTS) consists of high frequency hot-wire anemometer winds and both wind and temperature from sonic anemometers mounted on 10 meter tower arrays. Three frontal passages occurred when the instruments were operative. These data, and other lower frequency observations, will continue to be analyzed to determine the kinetic energy dissipation rate and turbulence characteristics that characterize fronts. These motions occur on subgrid spatial and temporal scales of numerical atmospheric models. The turbulent dissipative contributions are either not prescribed or handled ineffectively by all or most models. The present aim is to provide the necessary data analysis and theoretical understanding that is required to ultimately parameterize turbulent dissipation associated with fronts.The passage of fronts and the relatively abrupt change in the height of the boundary layer near sunset appear to be sources for the initiation of internal gravity waves and inertial oscillations. Four years of data from the National Oceanic and Atmospheric Administration wind profiler network, and from three profilers maintained in Kansas by the Argonne National Laboratory, will be analyzed by the rotary spectrum technique. The purpose is to extract properties of atmospheric inertial oscillations, and to develop boundary layer models that will establish the relative importance of fronts and boundary layer depth changes in their occurrence. The role of these oscillations on the dynamics of fronts will continue to be investigated by use of frontogenesis models. The source and characteristics of these oscillations has also been recognized as important for long-range modeling of atmospheric dispersion. Ongoing model development for this purpose is of considerable importance in the prediction of urban air quality.The current data bases will be expanded by participation in a field program to be carried out in southern Kansas in October 1999 (Cooperative Atmosphere-Surface Exchange Study -- 1999). These data will be used with ongoing model developments to both improve and to verify model predictions. The observational arrays are expected to be suitable to acquire data that is required to isolate boundary layer sources for both inertial oscillations and for internal gravity waves.