On the Influence of the Earth's Magnetic Dipole Eccentricity and Magnetospheric Ring Current on the Magnetopause Location

• Published in: Journal of geophysical research. Space physics 2019-02, Vol.124 (2), p.905-914
• Main Authors: Machková, A., Němec, F., Němeček, Z., Šafránková, J.
• Format: Article
• Language: English
• Subjects: Charged particles; corrected Dst index; dipole eccentricity; Earth; Earth magnetosphere; Eccentricity; Empirical models; Field strength; Geomagnetic field; Geomagnetism; Magnetic dipoles; Magnetic fields; Magnetism; Magnetopause; magnetopause location; Magnetospheric currents; Multipoles; ring current; Ring currents
• ISSN: 2169-9380; 2169-9402
• DOI: 10.1029/2018JA026070

We investigate the influence of two typically unconsidered parameters—Earth's magnetic dipole eccentricity and ring current—on the location of the magnetopause. Although empirical magnetopause models generally assume the Earth's magnetic field to be axially symmetric, the terrestrial magnetic dipole is shifted by as much as 500 km out of the Earth's center. Additionally, the magnetic field at the magnetopause is further modified by magnetospheric currents, most importantly by the ring current. In order to quantify the effects related to these phenomena on the magnetopause location, we compare observed magnetopause distances with model distances calculated using a model, which does not take them into account. International Geomagnetic Reference Field is used to describe the dipole eccentricity and relevant multipoles, which results in a statistically observable magnetopause displacement (≈0.2RE) at locations where the magnetic field strength increases/decreases as compared to the dipole field. Additionally, the magnetic field at the magnetopause is modified by the ring current, becoming stronger at the times of a stronger ring current. We use the corrected Dst* index to describe the ring current strength, and we demonstrate that its variation results in a change of the magnetopause stand‐off distance as large as about 0.8RE. We further use the T96 magnetic field model to estimate the total contribution of magnetospheric currents to the magnetic field at the magnetopause and their effects on the magnetopause location. We suggest empirical relations that can be used to incorporate the obtained dependences into existing empirical models of magnetopause location. Key Points Magnetopause distance varies by about 0.2 Earth radii due to nonaxially symmetric magnetic field Magnetopause distance varies by as much as 0.8 Earth radii due to ring current effects Obtained dependences can be incorporated into existing models using suggested empirical relations