Separating internal geomagnetic secular variation and long-term magnetospheric field variations

1. Separating internal geomagnetic secular variation and long-term magnetosphericfield variations Monika Korte Deutsches GeoForschungsZentrum GFZ

2. Motivation • Separation of different geomagnetic field sources remains a challenge • Clean data series or models of internal field secular variation on all time scales are important to better understand Earth’s core dynamics and the processes creating and changing the geomagnetic field • On decadal time scales, secular variation and long term magentospheric changes mix • Satellite era data products and field models provide improved separation between them

3. Problem Geomagnetic core fieldsecular variation Picture: Utah State University Long term modulation of magnetospheric ring current by solar activity

4. Data Standard IAGA Dst ring current index – no absolute long-term baseline Comparison of Dst and Rc index used by N. Olsen for global models using CHAMP data MJD

5. Data Differences between Dst and Rc values Comparison of Dst and Rc index used by N. Olsen for global models using CHAMP data MJD

6. Planned project • Choose observatory hourly mean data with long time series (including digitization of some analogue data) • Develop improved ring current index estimation, including separation into direct and induced contribution • Validate against improved indices obtained for or in geomagnetic field models using Swarm (and Champ) data and using Swarm L2 products Magnetic field Improved decadal secular variation estimates through improved elimination of long-term ring current variation from observatory or repeat station data series Aims Ionospheric/Magnetospheric current systems Improved understanding of long-term variability of magnetospheric ring current