Abstract
This paper describes the characteristics and evolving nature of a vigorous thunderstorm density current very early in the morning of 9 May 1981 in Oklahoma. Because the ambient lower atmosphere was stratified, interesting interactions between the outflow current and the ambient environment resulted. The leading portion of the current was modulated by at least three gravity wavelike perturbations of horizontal spacing 12 km which initially coexisted with it. However, as the current evolved, it initiated an undular borelike disturbance which propagated ahead into the stable boundary layer, carrying cold outflow air in large amplitude rolls. Eventually the wave family left the decelerating outflow air in its wake. This borelike disturbance resembles the Australian “morning glory” phenomenon and appears to represent an early stage in the development of a solitary wave family.
The observations resemble other reported morning glories and solitary waves as well their laboratory and numerically simulated counterparts. Comparisons are discussed. This case study is unique not only because it combines Doppler radar, tall tower, and surface mesonet observations, but especially because the period of observation captures the disturbance in its formative stage when it is still very near the density current.
