Scale-dependence of magnetic helicity in the solar wind

Details Scale-dependence of magnetic helicity in the solar wind Scale-dependence of magnetic helicity in the solar wind

2011-01-10

arxiv.org/abs/1101.1709v2

Astrophys. J. 734, 9 (2011)

Astronomy and Astrophysics

Astrophysics

Solar and Stellar Astrophysics

8 pages, 6 figures, ApJ (in press)

Scientific paper

10.1088/0004-637X/734/1/9

We determine the magnetic helicity, along with the magnetic energy, at high latitudes using data from the Ulysses mission. The data set spans the time period from 1993 to 1996. The basic assumption of the analysis is that the solar wind is homogeneous. Because the solar wind speed is high, we follow the approach first pioneered by Matthaeus et al. (1982, Phys. Rev. Lett. 48, 1256) by which, under the assumption of spatial homogeneity, one can use Fourier transforms of the magnetic field time series to construct one-dimensional spectra of the magnetic energy and magnetic helicity under the assumption that the Taylor frozen-in-flow hypothesis is valid. That is a well-satisfied assumption for the data used in this study. The magnetic helicity derives from the skew-symmetric terms of the three-dimensional magnetic correlation tensor, while the symmetric terms of the tensor are used to determine the magnetic energy spectrum. Our results show a sign change of magnetic helicity at wavenumber k~2 AU^{-1} (or frequency nu~2 uHz) at distances below 2.8 AU and at k~30 AU^{-1} (or nu~25 uHz) at larger distances. At small scales the magnetic helicity is positive at northern heliographic latitudes and negative at southern latitudes. The positive magnetic helicity at small scales is argued to be the result of turbulent diffusion reversing the sign relative to what is seen at small scales at the solar surface. Furthermore, the magnetic helicity declines toward solar minimum in 1996. The magnetic helicity flux integrated separately over one hemisphere amounts to about 10^{45} Mx^2/cycle at large scales and to a 3 times lower value at smaller scales.

Affiliated with

Also associated with

No associations

Rating

Scale-dependence of magnetic helicity in the solar wind does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with Scale-dependence of magnetic helicity in the solar wind, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Scale-dependence of magnetic helicity in the solar wind will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-455509