Microbaroms and the Temperature and Wind of the Upper Atmosphere

Abstract

Microbaroms are regular pressure variations of a few microbars (dyn cm?2) produced by the passage of infrasound (?5 see period) radiated from ocean waves. Their amplitudes show prominent diurnal, semidiurnal and seasonal variations that are shown to depend on the presence or absence of one or two atmospheric sound ducts between the surface and an elevation of ?120 km. These ducts depend on the vertical temperature and wind structure of the atmosphere. For our station (Palisades, N.Y.), ducting of sound from the most common source of microbaroms (Atlantic Ocean storms) requires the presence of strong easterly winds at some upper reflection level. Variations (such as tidal) in these winds, as derived from available reports, are shown to account for the observed patterns of microbaroms. In particular, these patterns are shown to be controlled by effects of tidal and seasonal wind variations and stratospheric warmings. Having established the dependence of microbaroms on upper temperature and winds, we use the relationship to interpret these upper atmospheric conditions. Finally, we suggest that use of an expanded ?synoptic? network of infrasound recorders would provide a simple procedure to monitor conditions in the upper atmosphere.