An analysis of gravity wave ducting in the atmosphere: Eckart's resonances in thermal and Doppler ducts

Abstract

We present simple examples of gravity wave ducting due to the background thermal and velocity structure in the atmosphere and examine the consequences of such ducts lying in close proximity. The dispersion curves for individual thermal and Doppler ducts exhibit similar behavior, with normal and inverse dispersion at higher and lower frequencies, respectively, and with smaller phase velocities and larger group velocities for higher modes. In the presence of two ducts of different character, the dispersion curves are given approximately by the intersection of the curves for the individual ducts, with modal character changing dramatically at resonance points near which the dispersion curves for individual ducts cross. Such ducting of gravity wave activity is likely to be a common occurrence in the atmosphere and the oceans and may provide a means of transporting vertically the energy and momentum associated with high‐frequency wave motions.