ANGEO Annales Geophysicae ANGEO Ann. Geophys. 1432-0576 Copernicus Publications Göttingen, Germany 10.5194/angeo-31-2123-2013 Diurnal variation in gravity wave activity at low and middle latitudes Andrioli V. F. 1 Fritts D. C. 2 Batista P. P. https://orcid.org/0000-0002-5448-5803 1 Clemesha B. R. 1 Janches D. 3 Instituto Nacional de Pesquisas Espaciais – INPE, São José dos Campos, SP, Brazil GATS/Boulder, Boulder, CO, USA Space Weather Lab., Mail Code 674, GSFC/NASA, Greenbelt, MD 20771, USA 29 11 2013 31 11 2123 2135 Copyright: © 2013 V. F. Andrioli et al. 2013 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://angeo.copernicus.org/articles/31/2123/2013/angeo-31-2123-2013.html The full text article is available as a PDF file from https://angeo.copernicus.org/articles/31/2123/2013/angeo-31-2123-2013.pdf

We employ a modified composite day extension of the Hocking (2005) analysis method to study gravity wave (GW) activity in the mesosphere and lower thermosphere using 4 meteor radars spanning latitudes from 7° S to 53.6° S. Diurnal and semidiurnal modulations were observed in GW variances over all sites. Semidiurnal modulation with downward phase propagation was observed at lower latitudes mainly near the equinoxes. Diurnal modulations occur mainly near solstice and, except for the zonal component at Cariri (7° S), do not exhibit downward phase propagation. At a higher latitude (SAAMER, 53.6° S) these modulations are only observed in the meridional component where we can observe diurnal variation from March to May, and semidiurnal, during January, February, October (above 88 km) and November. Some of these modulations with downward phase progression correlate well with wind shear. When the wind shear is well correlated with the maximum of the variances the diurnal tide has its largest amplitudes, i.e., near equinox. Correlations exhibiting variations with tidal phases suggest significant GW-tidal interactions that have different characters depending on the tidal components and possible mean wind shears. Modulations that do not exhibit phase variations could be indicative of diurnal variations in GW sources.

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