Long-term heliospheric current sheet oscillation
Abstract
The large scale (dipolar) solar magnetic field is known to be asymmetric in the North-South direction. According to spacecraft observations, the southern hemisphere magnetic field has been stronger during the five last solar activity cycles. Magnetic flux balance requires the northern magnetic field to cover a wider area, thus the heliospheric current sheet (HCS) is shifted southward since at least 1960-s. This in turn leads to a dominance of the ecliptic interplanetary magnetic field (IMF) with the polarity of the northern solar hemisphere. High-latitude geomagnetic variations allow one to infer IMF polarity before the satellite era. Using very long datasets of ground magnetic observations, we reconstruct IMF polarities back to 1844 and present estimates of the annual polarity disbalance. The results suggest that the HCS was shifted northward from cycles 14 (or 15) to cycle 19. With less confidence, we speculate that in cycles 9-13 the HCS was shifted southward. Surprisingly, HCS flips occur when the growth/decline phase of the centennial activity cycle changes.
- Publication:
-
43rd COSPAR Scientific Assembly. Held 28 January - 4 February
- Pub Date:
- January 2021
- Bibcode:
- 2021cosp...43E.927V