Quasi 16‐Day Wave Signatures in the Interhemispheric Field Aligned Currents: A New Perspective Toward Atmosphere‐Ionosphere Coupling

Quasi 16‐day waves (Q16DWs) are a prominent and recurrent phenomenon in the middle atmosphere, typically observed over winter mid and high latitudes. This study investigates the intense Q16DW event during the 2018–2019 Northern Hemisphere (NH) winter, and explores its propagation in the middle atmosphere and its notable influence on the E‐region ionosphere. Long‐term geopotential height estimates of Aura Microwave Limb Sounder (MLS) reveal that the wave activity under consideration exhibited the largest amplitudes in the mesosphere for past 16 years. An analysis of wind data obtained from medium frequency (MF) and meteor radars, as well as from Modern‐Era Retrospective analysis for Research and Applications, Version 2 (MERRA‐2) reanalysis, reveals the presence of a westward‐propagating Q16DW with zonal wavenumber 1 exhibiting notable asymmetry about the equator, with the majority of the wave activity being confined to the NH. The prominently large amplitudes and vertical wavelengths of the wave suggest potential for the wave propagation to extend deep into the E‐region ionosphere. Swarm satellite observations reveal concurrent ∼16‐day oscillations in the eastward component of the geomagnetic field at low latitudes. These oscillations can be attributed to the periodic variations in interhemispheric field‐aligned currents (IHFACs). The ∼16‐day oscillations in the IHFACs are likely a consequence of asymmetric wind‐dynamo action, which is directly or indirectly associated with the Q16DW. These findings suggest that planetary waves originating in the middle atmosphere can cause interhemispheric coupling in the ionosphere. Plain Language Summary This study examines the strong quasi‐16‐day wave activity that occurred during the winter of 2018–2019 over mid‐to‐high latitudes. A data set consisting of medium frequency (MF) and meteor radar winds, reanalysis data, Aura Microwave Limb Sounder (MLS) and Swarm geomagnetic field measurements is utilized to characterize the wave. The simultaneous occurrence of wave signatures in the middle atmosphere and the ionosphere suggests some atmosphere‐ionosphere coupling. The wave signatures observed in the eastward component of the geomagnetic field are attributed to interhemispheric field‐aligned currents. Key Points Strong quasi‐16‐day wave signatures in middle atmospheric temperatures and winds during the northern hemispheric winter of 2018–2019 Simultaneous occurrence of the wave in the eastward component of the geomagnetic