1. What drives space weather and what has helicity got to do with it?...or assorted thoughts and questionsof a confused PhD student 19/03/2019 Reko Hynönen1 1Aalto-yliopisto Reko.Hynonen@aalto.fi

2. Purpose of this talk

3. Solar features • Strong magnetic flux • Active regions: simple and complex • Flares • Flux of magnetic helicity?

4. Solar features • Strong magnetic flux • Active regions: simple and complex • Flares • Flux of magnetic helicity? • Open field lines • High-speed solar wind streams • With high Alfvénicity / cross helicity • CH: Relation to helicity?

5. Solar features • Strong magnetic flux • Active regions: simple and complex • Flares • Flux of magnetic helicity? • Flares and coronal mass ejections • Transfer of magnetic helicity? • Open field lines • High-speed solar wind streams • With high Alfvénicity / cross helicity • CH: Relation to helicity?

6. Solar wind structures

7. Solar wind structures • Slow, high-density solar wind • High velocity shear • typically low cross helicity • Origin unclear: • One of the source regions:helmet streamers

8. Solar wind structures • Slow, high-density solar wind • High velocity shear • typically low cross helicity • Origin unclear: • One of the source regions:helmet streamers • Fast, low-density solar wind • Low velocity shear • typically high cross helicity • Origin: Coronal holes

9. Solar wind structures • Slow, high-density solar wind • High velocity shear • typically low cross helicity • Origin unclear: • One of the source regions:helmet streamers • Fast, low-density solar wind • Low velocity shear • typically high cross helicity • Origin: Coronal holes

10. Space weather events Energy!  Energy Energy!

11. Space weather events Reconnection! Energy!  Energy Energy! Reconnection!

12. Space weather events Reconnection! Energy! Dungey cycle  Energy Energy! Reconnection!

13. Space weather events Dungey cycle Reconnection! Energy! Dungey cycle  Energy Energy! Reconnection!

14. Space weather events Reconnection! Energy! Dungey cycle  Energy Energy! Reconnection!

15. Space weather events • Geomagnetic storms • Enhancement of ring current • Equatorial, global activity • Measured by storm disturbance indices, like Dst Reconnection! Energy! Dungey cycle  Energy Energy! Reconnection!

16. Space weather events • Geomagnetic storms • Enhancement of ring current • Equatorial, global activity • Measured by storm disturbance indices, like Dst • Substorms • Activity of auroral region (both poles) • Local phenomena • Measured by substorm / electrojet current indices, like AE Reconnection! Energy! Dungey cycle  Energy Energy! Reconnection!

17. Space weather events • Measuring Dst index • Four magnetic stations around equator

18. Space weather events

19. Space weather events