2020/12/24 by Lockwood, Mike, Carl Haines, Haines, Carl +10
Biochemistry, Genetics and Molecular Biology · Physics and Astronomy · #Earth and Planetary Astrophysics (astro-ph.EP) #FOS: Physical sciences #Geomagnetism and Paleomagnetism Studies #Geophysics (physics.geo-ph) #Ionosphere and magnetosphere dynamics #Solar and Space Plasma Dynamics #Space Physics (physics.space-ph)
paper · pdf · doi:10.48550/arxiv.2012.13324
openalex publication_date 2020/12/24 · openalex created_date 2022/07/25 · openalex updated_date 2026/07/28
We use the am, an, as and the a-sigma geomagnetic indices to the explore a\npreviously overlooked factor in magnetospheric electrodynamics, namely the\ninductive effect of diurnal motions of the Earth's magnetic poles toward and\naway from the Sun caused by Earth's rotation. Because the offset of the\n(eccentric dipole) geomagnetic pole from the rotational axis is roughly twice\nas large in the southern hemisphere compared to the northern, the effects there\nare predicted to be roughly twice the amplitude. Hemispheric differences have\npreviously been discussed in terms of polar ionospheric conductivities, effects\nwhich we allow for by studying the dipole tilt effect on time-of-year\nvariations of the indices. The electric field induced in a geocentric frame is\nshown to also be a significant factor and gives a modulation of the voltage\napplied by the solar wind flow in the southern hemisphere of typically a 30%\ndiurnal modulation for disturbed intervals rising to 76% in quiet times. Motion\ntowards/away from the Sun reduces/enhances the directly-driven ionospheric\nvoltages and reduces/enhances the magnetic energy stored in the near-Earth\ntail: 10% of the effect being directly-driven and 90% being in tail energy\nstorage/release. Combined with the effect of solar wind dynamic pressure and\ndipole tilt on the pressure balance in the near-Earth tail, the effect provides\nan excellent explanation of how the observed Russell-McPherron pattern in the\ndriving power input into the magnetosphere is converted into the equinoctial\npattern in average geomagnetic activity (after correction is made for dipole\ntilt effects on ionospheric conductivity), added to a pronounced UT variation\nwith minimum at 02-10UT. In addition, we show that the predicted and observed\nUT variations in average geomagnetic activity has implications for the\noccurrence of the largest events that also show the nett UT variation.\n