Long-term variability of the low latitude mesospheric SAO and QBO and their relation with stratospheric QBO

Abstract

Long term variations of low-latitude mesospheric semi-annual oscillation (MSAO) and quasi-biennial oscillation (MQBO) in the zonal wind are studied using observations available from 1977 to 2006. The MQBO showed large inter-annual variability in the phase difference between 77.5 km and 72.5 km indicating such variability in eddy viscosity. Association of these oscillations with stratospheric quasi-biennial oscillation (SQBO) is investigated. In general, the MQBO at 77.5 km is out-of-phase with SQBO and this relation fails during strong and long SQBO. The MSAO at 72.5 km and 77.5 km generally shows strong westward phase during strong eastward phase of SQBO. The most striking feature observed in the present study is the strong modulation of the MSAO by MQBO revealing a non-linear type of interaction with presence of sidebands of the MSAO.