The nature of the variability of the Total Electron Content (TEC) over Europe is investigated during 2009 and 2019 Northern Hemisphere (NH) SSW events in this study by using a combination of Global Navigation Satellite System (GNSS) based TEC observations and Thermosphere‐Ionosphere Electrodynamics General Circulation Model (TIE‐GCM) simulations. To simulate the SSW effects in TIE‐GCM, the dynamical fields from the Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension (WACCM‐X) simulations of 2009 and 2019 SSWs are specified at the TIE‐GCM lower boundary. The observed and simulated TEC are in overall good agreement and therefore the simulations are used to understand the sources of mid‐latitude TEC variability during both SSWs. Through comparison of TIE‐GCM simulations with and without geomagnetic forcing, we find that the TEC variability during the 2019 SSW event, was predominantly geomagnetically forced, while for the 2009 SSW, the major variability in TEC was accounted for by the changes in vertically propagating migrating semidiurnal solar (SW2) and lunar (M2) tides. By comparing the TIE‐GCM simulations with and without the SW2 and M2 tides, we find that these semidiurnal tides contribute to
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.
more » « less- NSF-PAR ID:
- 10461059
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Space Weather
- Volume:
- 17
- Issue:
- 5
- ISSN:
- 1542-7390
- Page Range / eLocation ID:
- p. 767-777
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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