Signature of a 120-day oscillation in the MLT winds and tides over São João do Cariri (7.4oS, 36.5oW)

Abstract

A conspicuous and intermittent signature of a 120-day oscillation is found in the winds and tides in the mesosphere and lower thermosphere (MLT) over a Southern hemispheric equatorial station, São João do Cariri (7.4oS, 36.5oW) for the first time using meteor radar observations during the interval 2004–2008. The intermittent 120-day modulation can be as high as 10 m/s in the MLT winds. However, the seasonal component of the concerned periodicity, i.e. terannual oscillation is relatively smaller in amplitude (<4 m/s) than the instantaneous component. The oscillation feature is also investigated for the dominant tides. The 120-day modulation amplitude is higher (maximum ~ 5 m/s) in the diurnal and semidiurnal tides and relatively smaller in the terdiurnal tide (peak ~ 2 m/s). The intermittent behavior of the particular oscillation in wind and absence in temperature may imply it to be a feature of the MLT wind circulation. Proximity of period may also indicate a possible contribution from the lower atmospheric intraseasonal oscillation to some extent at times. Furthermore, existence of the same periodicity in the solar UV flux may indicate a plausible indirect solar connection with the MLT circulation although direct solar influence cannot be ascertained. The evident imprint of the oscillation in the MLT wind and tides accentuates the need of further extensive studies to lend valuable insights of the underlying physical processes/mechanisms associated to their relationship hitherto remained unexplored.