The dependence of the coupled magnetosphere‐ionosphere‐thermosphere system on the Earth's magnetic dipole moment

Abstract

The strength of the Earth's magnetic field changes over time. We use simulations with the Coupled Magnetosphere‐Ionosphere‐Thermosphere model to investigate how the magnetosphere, upper atmosphere, and solar quiet (Sq) geomagnetic variation respond as the geomagnetic dipole moment M varies between 2⋅1022 and 10⋅1022 Am2. We find that the magnetopause stand‐off distance and the cross‐polar cap potential increase, while the polar cap size decreases, with increasing M. Their dependence on M is stronger than predicted by previous studies. We also show for the first time that the shape of the magnetosphere starts to change for M ≤ 4⋅1022 Am2. This may be due to enhanced magnetopause erosion and/or to strong changes in the ionospheric conductance, which affect the field‐aligned currents and the magnetic fields they create in the magnetosphere, thus modifying the magnetic pressure inside the magnetosphere. E × B drift velocities, Joule heating power, the global mean thermospheric temperature and the global mean height of the peak of the ionospheric F2 layer, hmF2, all increase with increasing M for low dipole moments, but all decrease with increasing M for larger dipole moments. The peak electron density of the F2 layer, NmF2, shows the opposite behavior. The Sq amplitude decreases with increasing M and this dependence can be roughly described by a power law scaling. Most scaling relations show a weak dependence on the solar activity level, which is likely associated with a change in the relative contributions to the Pedersen conductance from the upper and lower ionosphere, which scale differently with M.

Long-term variation in the upper atmosphere as seen in the geomagnetic solar quiet daily variation

“…Elias et al (2010) reported that a decrease of the magnetic field causes an increase in the Sq amplitude because of an enhancement in the ionospheric conductivities. Using the CMIT model, Cnossen et al (2012) confirmed that an increase in the ionospheric conductivities could generate long-term trends in the Sq amplitude of a similar order of magnitude to observed trends associated with a reduction in the dipole moment over the past century. Moreover, near the dip equator, the variations in the inclination of the magnetic field lead to a significant change in the Sq amplitude because the Cowling conductivity [Hirono 1952] is very sensitive to the inclination of the magnetic field.…”

How changes in the tilt angle of the geomagnetic dipole affect the coupled magnetosphere‐ionosphere‐thermosphere system

“…The main aim of this work is to gain a better insight in the role of the dipole tilt angle in the MIT system and the mechanisms by which changes in tilt angle affect this system. This will help with understanding the effects of the more complex magnetic field changes that have occurred historically and complements two previous studies in which we examined the effects of changes in the dipole moment on the MIT system [ Cnossen et al , 2011, 2012]. A few simulations done with rather strong dipole tilts of 30°–60° are also interesting from a geological perspective, giving an idea of what the MIT system could be like during times of geomagnetic excursions, although in those cases the magnetic field is not necessarily dipolar.…”

Filtering ionosphere parameters to detect trends linked to anthropogenic effects

“…These trends were attributed to solar extreme ultraviolet (EUV) radiation changes (Adler et al 1997;Yamazaki and Yumoto 2012), geomagnetic activity variations (Mikhailov and Marin 2001;Danilov 2002;Mikhailov 2001Mikhailov , 2006, the increase in greenhouse gas concentration (Bremer 1992(Bremer , 1998Upadhyay and Mahajan 1998;Ulich and Turunen 1997;Jarvis et al 1998), and/or secular variations of the Earth's main magnetic field (Foppiano et al 1999;Elias and Adler 2006;Elias 2009;Yue et al 2008;Richmond 2008, 2013;Cnossen et al 2012).…”