Observations of Planetary Mixed Rossby–Gravity Waves in the Upper Stratosphere

Abstract

Observational evidence is presented for planetary scale (zonal wave number 1?2) mixed Rossby?gravity (MRG) waves in the equatorial upper stratosphere (35?50 km). These waves are detected in Limb Infrared Monitor of the Stratosphere (LIMS) measurements as coherently propagating temperature maxima of amplitude 0.1?0.3 K, which are antisymmetric (out of phase) about the equator, centered near 10°?15° north and south latitude. These features have vertical wavelengths of order 10?15 km, periods near 2?3 days, and zonal phase velocities close to 200 m s?1. Both eastward and westward propagating waves are found, and the observed vertical wavelengths and meridional structures are in good agreement with the MRG dispersion relation. Theoretical estimates of the zonal accelerations attributable to these waves suggest they do not contribute substantially to the zonal momentum balance in the middle atmosphere.