The occurrence of microbarograph-detected gravity waves compared with the existence of dynamically unstable wind shear layers

Abstract

Records from microbarograph arrays at Boulder, Colorado, and Washington, D. C., for December 1971 through March 1972 and at Boulder for June 1972 through August 1972 are analyzed for gravity wave events. Rawinsonde soundings from Denver, Colorado, and Dulles International Airport near Washington, D. C., are examined for corresponding times to determine the existence of dynamically unstable (defined by small Richardson number) wind shear layers in the atmosphere. Comparison of these two sets of data indicates that at least one half of the 280 gravity wave events detected and analyzed are shear-induced. Further, the ratio of the average wavelength of a shear-induced gravity wave to shear layer thickness is found to be close to theoretical estimates based on linear perturbation theory. It is also indicated that shear layers may be likely to generate gravity waves because the layer has an almost dry adiabatic lapse rate (small Brunt-Vaisala frequency) rather than because it has a large wind shear. Finally, further study is desirable on the question of why the wind shear mechanism is not responsible for a larger number of the gravity waves that are seen on the microbarograph.