Imprint of a quasi-16-day period in boreal summer through modulation of quasi-2-day wave implying interhemispheric coupling

An interesting case of quasi-2-day wave (Q2DW) amplitude modulation with a quasi-16-day period is investigated using meteor radar winds and global reanalysis data during the 2019 boreal summer. The modulation is found to originate near the equator at 50 km altitude. Presence of a dominant eastward propagating quasi-16-day wave with zonal wavenumber 2 (Q16DWE2) in the austral winter across the zero-wind line near the equator initiates the modulation, as evident in the westward propagating quasi-2-day wave with zonal wavenumber 3 (Q2DWW3). Notably, while no significant Q16DW wave is detected in the boreal summer middle atmospheric winds, the primary Q2DWW3 mode (with amplitudes reaching ~8 m s⁻¹) play a crucial role in carrying the Q16DW signature from the winter to the summer hemisphere. Additionally, the Q16DW appearance in the summer upper mesosphere and lower thermosphere (90–100 km altitude) that is near the dissipation altitude of the Q2DW corroborates a potential link between these two dynamical entities. Overall, the present study highlights a novel mechanism of interhemispheric coupling through planetary wave modulation, offering new insights into the global dynamics of the lower and middle atmosphere.