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

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⋅10 22 and 10⋅10 22 Am 2 . 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⋅10 22 Am 2 . 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 F 2 layer, h m F 2 , 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 F 2 layer, N m F 2 , 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 .