Abstract
AbstractThis paper describes long‐term changes in the geomagnetic lunar (L) and solar (S) daily variations. We analyze the eastward component of the geomagnetic field observed at eight midlatitude stations during 1903–2012. The amplitude and phase for the semidiurnal component of the L and S variations are examined. Both L and S amplitudes correlate with the solar activity index F10.7, revealing a prominent 11 year solar cycle. In both cases, the correlation is slightly better with than F10.7. The sensitivity of the L variation to solar activity is comparable with that of the S variation. The solar cycle effect is also found in the phase of the S variation but not apparent in the phase of the L variation. The ratio in the amplitude of the L to S variation shows a long‐term decrease (approximately 10% per century), which may be due to a reduction in lunar tidal waves from the lower atmosphere to the upper atmosphere in association with climate change.
Highlights
When solar-terrestrial disturbances are absent, records of the Earth’s magnetic field on the ground show regular daily variations, which are primarily composed of 24, 12, 8, and 6 h spectral components
It is well understood that solar quiet (Sq) variations are a consequence of electric currents flowing in the dynamo region of the ionosphere, where the neutral wind drives a electromotive force through the ionospheric wind dynamo mechanism [Richmond, 1995a; Richmond and Maute, 2014]
The variations are largely similar at different stations, indicating that long-term variations are dominated by global changes
Summary
When solar-terrestrial disturbances are absent, records of the Earth’s magnetic field on the ground show regular daily variations, which are primarily composed of 24, 12, 8, and 6 h spectral components. Those variations are commonly known as solar quiet (Sq) variations [Chapman and Bartels, 1940; Matsushita, 1967; Campbell, 2003]. Satellite measurements of solar tides in the dynamo region can be found in the literature [McLandress et al, 1996; Forbes et al, 2008] Another important parameter for Sq currents is the electrical conductivity of the ionosphere. Ionospheric conductivities vary with the ionospheric plasma density, as well as the strength of the Earth’s main magnetic field Takeda and Araki [1985]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
