TY - JOUR
T1 - Parameters of the magnetic flux inside coronal holes
AU - Abramenko, Valentyna
AU - Yurchyshyn, Vasyl
AU - Watanabe, Hiroko
N1 - Funding Information:
Acknowledgements Authors thank Spiro Antiochos, Len Fisk, Dennis Haggerty, Marco Velli, Yi-Ming Wang, Thomas Zurbuchen and the entire LWS/TR&T Heliospheric Focus Team for helpful discussions and initiation of this research. We also thank Rob Markel for valuable assistance in during the inversion process, and anonymous referees whose criticism and comments led to a significant improvement of the manuscript. We thank the ACE MAG and SWEPAM instrument teams and the ACE Science Center for providing the ACE data. SOHO is a project of international cooperation between ESA and NASA. Hinode is a Japanese mission developed and launched by ISAS/JAXA, collaborating with NAOJ as a domestic partner, NASA and STFC (UK) as international partners. Scientific operation of the Hinode mission is conducted by the Hinode science team organized at ISAS/JAXA. This team mainly consists of scientists from institutes in the partner countries. Support for the post-launch operation is provided by JAXA and NAOJ (Japan), STFC (UK), NASA (USA), ESA, and NSC (Norway). Hinode SOT/SP inversions were conducted at NCAR under the framework of the Community Spectro-polarimtetric Analysis Center (CSAC; http://www.csac.hao.ucar.edu/). This work was supported by NASA NNX07AT16G grant, and NSF grant ATM-0716512.
PY - 2009/1
Y1 - 2009/1
N2 - 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, Bnet, does not correlate with the associated solar wind speeds, Vx. 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 Bnet and Vx 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.
AB - 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, Bnet, does not correlate with the associated solar wind speeds, Vx. 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 Bnet and Vx 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.
KW - Coronal holes
KW - Solar wind
KW - Sun: magnetic fields
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U2 - 10.1007/s11207-009-9433-7
DO - 10.1007/s11207-009-9433-7
M3 - Article
AN - SCOPUS:74449086310
SN - 0038-0938
VL - 260
SP - 43
EP - 57
JO - Solar Physics
JF - Solar Physics
IS - 1
ER -