Meteorological Tower, Microbarograph Array, and Sodar Observations of Solitary-like Waves in the Nocturnal Boundary Layer

Abstract

Five short-duration disturbances of the stable nocturnal boundary layer, ranging in depth from about 15 m to over 500 m, were observed using a 300 m meteorological tower, 2 sodars, and a 4-station microbarograph array. Four of the events showed characteristic pulse-like sodar signatures; the fifth occurred within the minimum range of the sodars. We show that the events have the characteristics expected of strongly nonlinear deep-fluid internal solitary waves that are transporting and recirculating cold air at a supercritical velocity. The unique sodar signatures, tracing out the form of the waves, are attributed to small-scale turbulent temperature inhomogeneities marking the boundary of the recirculating air as it is transported through the ambient nocturnal boundary layer by the wave. All the events are shown to deviate from the Benjamin-Davis-Ono (BDO) theory, because of their amplitude/wavelength and amplitude/stable layer thickness ratios are considerably larger than normally thought appropriate for the weakly nonlinear BDO theory. These events exhibit characteristics that are consistent with those predicted by the nonlinear theory of Tung et al.