Observations of small-scale gravity waves in the equatorial upper mesosphere

Abstract

Using airglow images collected at São João do Cariri (7.4◦S; 36.5◦W) from 2009 to 2010, the spectral characteristics and seasonality in the propagation direction of small-scale gravity waves were studied. There was a preferential propagation direction of the gravity waves to the east during the summer and spring. However, in the autumn and winter, the waves preferred propagate to the north. These observations can be related to the sources of the gravity waves or due to the filtering process of the wind on the vertical propagation of them. When gravity waves propagate in the same direction of the wind, they can reach critical levels and the vertical propagation of the waves are not allowed. Using wind profiles obtained from the Horizontal Wind Model – 14 (HWM-14), it was constructed blocking diagram in each level of the atmosphere tosuch areas where the vertical propagation of gravity waves was not permitted. These blocking regions change substantially along the seasons and can be used to explain the observed patterns in the propagation direction of the gravity waves.