Investigating the non-Quiet Time Magnetic Diurnal Variation Field – Using Observatory Data, CM4 and the RC Index as Tools.

Abstract:

We investigate and analyse the behaviour of the external field variations of the geomagnetic field for days away from quiet time using worldwide observatory station data, the CM4 model and the RC index. Despite the model reasonably predicting the ground variation of the diurnal field for days away from quiet time (especially outside the period the CM4 data covers and the lack of active data in the original model dataset) as our results shows, it also reveals the inability of the external field description included in the model to sufficiently explain the rapid variations seen for days away from quiet time.

In trying to explain the behaviour of the rapid variations seen in our data for days away from quiet time, we investigate the use of the RC index as a better tool for describing the external field variations (instead of Dst). Our results showed that the residuals of the X component of our data include a strong component in rapid variations related to large scale external field variations arising from magnetospheric ring current. The comparison between the X component residuals of our observatory station data and that of the RC index showed good correlation and coherence, which is seen in the high cross-correlation coefficients between the X component of our observatory data residuals and the RC index globally. This shows the rapid variation signals for days away from quiet time to be large scale, and the RC index a better representation of rapid variations globally, for days away from quiet time.