The Variation of Magnetospheric Resonance with Changing Geomagnetic Conditions

Like any closed physical system, the Earth's magnetosphere can support resonant phenomena. Standing waves are able to form along closed magnetic field lines, whose frequencies can be measured by applying the cross-phase technique to magnetometer data. These frequencies depend on the structure and plasma content of the Earth's magnetosphere.

In this work, we have applied the cross-phase technique to ten years of magnetometer observations and then used the OMNI solar wind dataset to try to understand under what conditions the standing waves are excited. By understanding the probability of resonance, we can make many inferences on the behaviour of the magnetosphere and try to understand its response to changing solar wind and geomagnetic conditions. Results include a difference in the conditions required to excite Pc4 and Pc5 frequencies, as well as latitude-dependent responses to disturbed conditions. By analysing this wealth of data, it is also possible to infer what the sources of the waves are.

We can also measure how the frequencies change in value with geomagnetic conditions. This can potentially tell us about the changing structure of the magnetosphere and its plasma content. It is found that the frequencies of magnetic field lines decrease during disturbed conditions, despite the magnetosphere being compressed.