Critical level interaction of a gravity wave with background winds driven by a large-scale wave perturbation

As part of the Maui-Mesosphere and Lower Thermosphere program, data from the Utah State University Mesospheric Temperature Mapper (MTM) and the University of Illinois Meteor Wind Radar (MWR) have been used to investigate wave-driven dynamical interactions in the upper mesosphere at low latitudes. On 29 June 2003, short-period (∼20 min) gravity waves (GWs) were imaged in the MTM in the near-infrared OH and O₂ airglow emissions for most of the night from 0700 to 1500 UT. The GWs were observed to disappear rapidly in the O₂ data (peak altitude: ∼94 km) around 1400 UT but remained evident in the lower altitudes OH data (∼87 km) for a further 30 min. Coincident background wind variations measured by the MWR suggest that the GW disappearance at the O₂ layer was most probably caused by a critical level (CL) interaction. However, at the OH layer, the GW fading may also have been due to wave saturation and instabilities. During this period (1400-1500 UT), no significant change in OH and O₂ rotational temperatures were measured by the MTM; however, the background winds centered on the airglow layers were observed to increase by ∼10 m/s. The background wind acceleration from the disappearing gravity waves estimated from the airglow observations was larger below the CL than at the CL, consistent with the wind variation observed by the MWR.