A Dynamic Trio: Inertial Oscillation, Deformation Frontogenesis, and the Ekman–Taylor Boundary Layer

Potential temperature and wind profiles obtained during a case of nighttime low-level deformation frontogenesis are examined. The winds in the lowest kilometer over a region in the central United States are shown to be controlled by thermal wind shear in a stable layer above 400 m, in accordance with the Hoskins–Bretherton semigeostrophic frontogenesis model, and by surface-drag-generated shear in the nearly neutral layer below. In this lower layer, the wind profiles are shown to be in good agreement with a simple baroclinic Ekman–Taylor model. The opposite shear in the two layers produces a low-level jet that appears in soundings taken hundreds of kilometers apart. The agreement of the observed profiles with these models is revealed only after a height-dependent inertial oscillation in both layers is removed from the rapidly evolving hourly wind data.