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. Plain Language Summary Large‐scale meteorological disturbances like stratospheric sudden warmings (SSWs) are often of interest for the investigation of a variety of mechanisms and processes that link different regions of the Earth's atmosphere across a wide range of altitudes and latitudes. Earlier studies have shown large and long‐lasting anomalies caused by SSWs in the Earth's daytime ionosphere. In this study, we show that the typical semidiurnal (12‐hr) ionospheric responses in connection with SSWs are caused by the combined effect of solar and lunar semidiurnal migrating tides during the 2009 SSW. The 15‐day oscillation of the semidiurnal variations is indeed a result from the beating between solar and lunar semidiurnal migrating tides, suggesting the importance of strong enhancements in the lunar semidiurnal migrating tide during SSWs. These results improve our understanding of the reasons for day‐to‐day variations in the ionosphere and the role of upward propagation of solar and gravitational lunar‐induced tides from lower altitudes during large‐scale meteorological disturbances. Key Points Investigation of daily ionospheric