Polar geomagnetism : developing models of high-latitude geomagnetic fields

• Main Author: Kelly, Gemma
• Other Authors: Holme, Richard; Thomson, Alan W. P.
• Published: University of Liverpool 2013
• Subjects: 538
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.579383

The availability of high-quality data during the past decade has allowed the development of geomagnetic field models which reproduce well the observed field at low to mid latitudes. However, the complexity of un-modelled processes and interactions in the polar ionosphere and magnetosphere causes significant residuals between data and models at high latitudes. Signatures of high latitude currents are clearly visible in the residuals for several recent models in both amplitude and direction, and so are not easily interpretable as field-aligned currents. Motivated by this we identify new techniques to allow more, and better quality, data to be selected for use in field modelling at high latitudes. We also look to include more vector data to improve data uniformity and distribution whilst still avoiding the un-modelled sources of the field, in particular within the auroral oval. We investigate both the use of additional indices in the selection process and a method of locating the highly variable external currents to identify the region where vector data are not selected. By introducing additional criteria we extended the local-time window allowing data density to have greater uniformity in time. We also include vector data at higher latitudes, only using scalar data where we believe external field sources are introducing noise to the data. When using our data selection criteria in the generation of a relatively simply parameterised geomagnetic model we get results that are close to more complex models. For example, we are able to reproduce features of the field seen in CHAOS-4, MF7 and EMAG3, despite only using CHAMP data for a single year. This makes us optimistic for future developments using longer time series.