Further Study of the Atmospheric Gravity Waves over the Eastern Seaboard on 18 March 1969

Abstract

Washington, D. C., microbarograph records for 18 March 1969 reveal gravity-wave-associated pressure oscillations which appear to be directly related to upper tropospheric wave structure observed at the same time with a Wallops Island 10-cm wavelength radar. The consistency between the two sets of data provides new observational support for a hypothesis of long standing in the microbarograph community; namely, that shear instability in the upper tropospheric flow is indeed the mechanism responsible for the generation of such waves. The comparison presented here suggests that microbarograph arrays might be useful adjuncts to future radar studies of upper tropospheric wave dynamics, supplying such wave parameters as phase velocity and wavelength in favorable cases. A closer examination of the radar data pertinent to this event reveals an apparent vertical wave phase variation, permitting a very approximate and somewhat uncertain estimate of the wave-associated vertical flux of horizontal momentum, which is found to be ?4 dyn cm?2. While approximate, this illustrative calculation yields a value several times greater than the annual average flux at temperate latitudes, and since microbarograph data show such events to be fairly common wintertime phenomena, we are tempted to infer that wave generation by shear instability in the upper tropospheric air flow and the resulting vertical momentum transport may be an important element of the global atmospheric momentum budget. More extensive and conclusive studies are obviously indicated.