Abstract

The strength of the Earth’s magnetic field changes over time. Over the past 800,000 years the Earth’s magnetic dipole moment has fluctuated between values of 1e22 Am2 to 10e22 Am2, with the current value being approximately 7.7e22 Am2. While the present-day magnetic field is relatively strong in a geological context, the dipole moment has been steadily decreasing since ~1840 at a rate of 5-7% per century. If this declining trend continues, we can thus expect a considerably weaker magnetic field over centuries to come. A change in the magnetic field strength has consequences for the Earth’s magnetosphere, ionosphere, and thermosphere. Based on simulations with the Coupled Magnetosphere-Ionosphere-Thermosphere (CMIT) model, I will show how a range of magnetospheric and upper atmospheric variables change as a function of the geomagnetic dipole moment and derive scaling relations where possible. The influence of the background solar activity level is also investigated. Finally, I will discuss to what extent changes in magnetic field strength may have contributed to observed long-term trends in the ionospheric F2 layer and the solar quiet (Sq) current system.