Parameters of the Magnetic Flux inside Coronal Holes
The parameters of the magnetic flux distribution inside low-latitude coronal holes (CHs) were analyzed. A statistical study of 44 CHs based on Solar and Heliospheric Observatory (SOHO)/MDI full disk magnetograms and SOHO/EIT 284 Å images showed that the density of the net magnetic flux, B net, does not correlate with the associated solar wind speeds, V x . Both the area and net flux of CHs correlate with the solar wind speed and the corresponding spatial Pearson correlation coefficients are 0.75 and 0.71, respectively. A possible explanation for the low correlation between B net and V x is proposed. The observed non-correlation might be rooted in the structural complexity of the magnetic field. As a measure of the complexity of the magnetic field, the filling factor, f(r), was calculated as a function of spatial scales. In CHs, f(r) was found to be nearly constant at scales above 2 Mm, which indicates a monofractal structural organization and smooth temporal evolution. The magnitude of the filling factor is 0.04 from the Hinode SOT/SP data and 0.07 from the MDI/HR data. The Hinode data show that at scales smaller than 2 Mm, the filling factor decreases rapidly, which means a multifractal structure and highly intermittent, burst-like energy release regime. The absence of the necessary complexity in CH magnetic fields at scales above 2 Mm seems to be the most plausible reason why the net magnetic flux density does not seem to be related to the solar wind speed: the energy release dynamics, needed for solar wind acceleration, appears to occur at small scales below 1 Mm.
KeywordsCoronal holes Solar wind Sun: magnetic fields
Unable to display preview. Download preview PDF.
- Abramenko, V.I.: 2008, In: Wang, P. (ed.) Solar Physics Research Trends, Nova Science Publishers, Inc., New York, 95. Google Scholar
- Baker, D., van Driel-Gesztelyi, L., Kamio, S., Culhane, J.L., Harra, L.K., Sun, J., Young, P.R., Matthews, S.A.: 2008, In: Matthews, S.A., Davis, J.M., Harra, L.K. (eds.) First Results From Hinode, ASP Conf. Ser. 397, 23. Google Scholar
- Harvey, J., Krieger, A.S., Timothy, A.F., Vaiana, G.S.: 1975, Oss. Mem. Oss. Arcetri 104, 50. Google Scholar
- Ireland, J., Gallagher, P.T., McAteer, R.T.J.: 2004, In: Dupree, A.K., Benz, A.O. (eds.), Stars as Suns: Activity, Evolution and Planets, IAU Symp. 219, 255. Google Scholar
- Kamio, S., Hara, H., Watanabe, T., Matsuzaki, K., Shibata, K., Culhane, L., Warren, H.P.: 2007, Publ. Astron. Soc. Japan 59, S757. Google Scholar
- McAteer, R.T.J., Gallagher, P.T., Ireland, J.: 2005, Astrophys. J. 631. Google Scholar
- Schwadron, N.A., McComas, D.J.: 2008, AGU, Fall Meeting, SH13B-1559. Google Scholar
- Shimojo, M.: 2008, AGU, Fall Meeting, SH22A-0836. Google Scholar
- Suematsu, Y.: 2008, AGU, Fall Meeting, SH41B-1623. Google Scholar
- Tarbell, T., Ferguson, S., Frank, Z., Shine, R., Title, A., Topka, K., Scharmer, G.: 1990, In: Stenflo, J.O. (ed.) Solar Photosphere: Structure, Convection, and Magnetic fields, IAU Symp. 138, 147. Google Scholar