Observações da onda de 10 dias nos ventos da mesosfera tropical austral e em média latitude boreal.

Abstract

This work presents a study of planetary wave with a period of quasi 10 days identified in neutral wind measurements of the upper mesosphere and lower thermosphere region (known as the MLT region, from 80 to 100 km). In order to study the interannual variability and the characteristics of the 10-day wave, wind measurements obtained from meteor radars have been used, which are located in tropical latitudes of the southern and in the middle latitude of the northern hemispheres, that is, in Cachoeira Paulista (22.7◦S; 45.0◦W) and São João do Cariri (7.4◦S; 36.5◦O), Brazil, and in Collm (51◦N; 13◦E), Germany. The time series were generated from about two decades of observations in Cachoeira Paulista (1999-2008 and 2012-2019) and nearly one decade in São João do Cariri (2004-2009 and 2018-2019) and Collm (2004-2015). The interannual variability and the seasonal character of quasi 10-day oscillations were analyzed from the vertical structure of the amplitudes estimated using harmonic analysis in the least squares sense. Quasi 10-day wave signatures were observed during the austral winter (between July and September) in the zonal component in both sites (Cachoeira Paulista and São João do Cariri). During the boreal winter (between January and February), the amplitudes in Collm were observed in both wind components, and these were higher than those verified during the southern hemisphere winter. Events were also identified in the zonal component during the autumn and spring equinoxes in both hemispheres, however, the amplitudes estimated in the southern hemisphere were higher than those in the northern hemisphere. Thus, the appearance of the wave presented a regularity in almost all years analyzed during the autumn, winter and spring seasons in both hemispheres. Between June and September there was no wave activity in wind components at 51°N. The amplitudes estimated in the zonal component were higher in all years than those in the southern component in both hemispheres. Attention was given to events with large amplitudes, which presented vertical descending phase structures and vertical wavelengths consistent with those already reported.