1. Scale-dependence of magnetic helicity in the solar wind
 assume isotropy to get helicity spectrum
Axel Brandenburg (Nordita/Stockholm)
Kandaswamy Subramanian (IUCAA, Pune)
Andre Balogh (ISSI and Imperial)
Melvyn Goldstein (NASA Goddard, Greenbelt)
Beijing, 31 October 2013
Käpylä+12
Kemel+12
Warnecke+11
Brandenburg+13

2. Dynamo produces bi-helical field
Magnetic helicity spectrum
Southern
hemisphere
Pouquet, Frisch,
& Leorat (1976)

3. Helicity fluxes to alleviate catastrophic quenching
Brandenburg (2005, ApJ)
1046 Mx2/cycle

4. Magnetic helicity flux
EMF and resistive terms still dominant
Fluxes import at large Rm ~ 1000
Rm based on kf
Smaller by 2p

5. Magnetic helicity flux
Gauge-invariant in steady state!
EMF and resistive terms still dominant
Fluxes import at large Rm ~ 1000
Rm based on kf
Smaller by 2p
Del Sordo, Guerrero, Brandenburg (2013, MNRAS 429, 1686)

6. This is how it looks like…
Coronal mass ejections from helical structures
This is how it looks like…
Gibson et al. (2002)

7. Helicity from solar wind
Matthaeus et al. (1982)
Measure correlation function
In Fourier space, calculate
magnetic energy and helicity spectra
 Should be done with Ulysses data away from equatorial plane

8. Measure 2-point correlation tensor
Taylor hypothesis:

9. Ulysses: scaling with distance
Vector helium magnetometer
2 sec resolution
10 pT sensitivity (0.1 mG)
* Fairly isotropic
* Falls off faster than R-2
* Need to compensate
before R averaging
Power similar to US consumption
Energy density similar to ISM

10. Noisy helicity from Ulysses
Taylor hypothesis
Roundish spectra
Southern latitude with opposite sign
Positive H at large k
Brandenburg, Subramanian, Balogh,
Goldstein (2011, ApJ 734, 9)

11. Bi-helical fields from Ulysses
Taylor hypothesis
Broad k bins
Southern latitude with opposite sign
Small/large distances
Positive H at large k
Break point with distance to larger k

12. Latitudinal scaling and trend
Antisymmetric about equator
Decline toward minum

13. Comparison Helicity LS SS + - Dynamo Solar wind
Southern
hemisphere
Field in solar wind is clearly bi-helical
...but not as naively expected
Need to compare with direct and mean-field simulations
Recap of dynamo bi-helical fields
Helicity LS SS
Dynamo + -
Solar wind

14. Shell dynamos with ~CMEs
Warnecke, Brandenburg, Mitra (2011, A&A, 534, A11)
Strong fluctuations, but positive in north

15. Dynamos with exterior  CMEs?
Warnecke, Brandenburg, Mitra (2011, A&A, 534, A11)

16. To carry negative flux: need positive gradient
Brandenburg, Candelaresi, Chatterjee
(2009, MNRAS 398, 1414)
Sign reversal makes sense!

17. Conclusions Magnetic helicity measurable High latitudes ( Ulysses)
Expect bi-helical
Bi-helical fields in dynamo & solar wind
+ sign in wind by turbulent diffusion
also found in CME-like simulations