The contribution of the Russell‐McPherron effect to the semiannual variation in thermospheric density

Lockwood, M. ORCID: https://orcid.org/0000-0002-7397-2172, Scott, C. J. ORCID: https://orcid.org/0000-0001-6411-5649, O'Donoghue, J. ORCID: https://orcid.org/0000-0002-4218-1191, Owens, M. J. ORCID: https://orcid.org/0000-0003-2061-2453 and Barnard, L. A. ORCID: https://orcid.org/0000-0001-9876-4612 (2026) The contribution of the Russell‐McPherron effect to the semiannual variation in thermospheric density. Journal of Geophysical Research: Space Physics, 131 (5). e2025JA034732. ISSN 2169-9402 doi: 10.1029/2025ja034732

Abstract/Summary

A number of external sources and internal circulation mechanisms have been proposed to explain the well‐known semiannual variation in global mean thermospheric densities. We use the polarity of the ‐component (dawn to dusk) of the Interplanetary Magnetic Field (IMF) in the Geocentric Solar Equatorial (GSEQ) frame to identify the influence, via geomagnetic currents, of the Russell‐McPherron (R‐M) effect on solar wind‐to‐magnetosphere energy coupling. Using data from 1996 to 2025, our best estimate is that for an IMF component of magnitude or greater, more than half of the semiannual variation in global averages of thermospheric density at altitudes between and is externally driven by the R‐M effect and the associated geomagnetic activity and that other effects that do not depend on the IMF ‐component, such as the “spoon” mechanism or upward energy transport from below by waves and tides, are responsible for the remainder. For all data, including quieter geomagnetic conditions, our best estimate is that the R‐M mechanism contributes 20% of the semiannual variation of thermospheric densities.

Item Type	Article
URI	https://centaur.reading.ac.uk/id/eprint/130104
Identification Number/DOI	10.1029/2025ja034732
Refereed	Yes
Divisions	Science > School of Mathematical, Physical and Computational Sciences > Department of Meteorology
Publisher	American Geophysical Union
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