Revisiting the modulations of ionospheric solar and lunar migrating tides during the 2009 stratospheric sudden warming by using Global Ionosphere Specification

In this study, Global Ionosphere Specification (GIS) based on Gauss-Markov Kalman filter assimilation of slant total electron content observed from ground-based global positioning system receivers and space-based radio occultation instrumentations is applied to investigate the ionospheric day-to-day tidal variability during the 2009 stratospheric sudden warming (SSW) period. Including the improved daily three-dimensional global electron density distribution from GIS enables us to retrieve the daily solar tidal solution by using least squares tidal analysis. We find prominent reductions followed by enhancements in the amplitude of the solar semidiurnal migrating tide (SW2) after the peak warming, with recurrent phase variations occurring at low magnetic latitudes over a period of about 15 days. This is close to the beating period (15.13 day) between SW2 and lunar semidiurnal (M2), thus suggesting the existence of strong M2, and our results demonstrate that the intensification of M2 exists only during the SSW period. Additionally, M2 acts as the key contributor to make the semidiurnal ionospheric perturbations shift toward later local times. Our tidal analyses of daily GIS thus provide evidence for the combined impact of amplitudes and phases of the SW2 and M2 in producing semidiurnal variations in ionosphere during the 2009 SSW.