Global Gravity Wave Variances from Aura MLS: Characteristics and Interpretation

Satellite microwave radiometry emerges as a useful technique to measure gravity wave (GW) induced temperature perturbations in the stratosphere and mesosphere. Aura MLS (Microwave Limb Sounder) is one of the latest microwave sensors that employ limb technique for atmospheric temperature sounding. This paper presents GW observations with Aura MLS 118-GHz radiance measurements at 12 altitude levels between 21 and 51 km. The observed GW variances are contributed mostly from waves with vertical wavelengths > 5 km and horizontal wavelengths of 150-300 km. Aura MLS is sensitive to wave propagation direction due to the narrow instrument beamwidth and unique viewing geometry. MLS observes significant poleward GW propagation in the high-latitude upper stratosphere. In the lower stratosphere the GW variances show a maximum in the tropics, a feature consistent with radiosonde and other high-resolution satellite observations. The time series of MLS GW variance show that the quasi-biennial oscillation (QBO) has significant impacts on the variances at 21.7 km. The tropical variance enhancement is split by equatorial low values into double latitude bands during the eastward shear phase but maintains as a single stronger peak during the westward shear phase. Correlated with the QBO-modulated zonal mean wind, the northern high-latitude variance appears to be weaker in the 2005-2006 winter than in the 2004-2005 winter.