Physics
Scientific paper
Aug 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006iaujd...3e..29g&link_type=abstract
Solar Active Regions and 3D Magnetic Structure, 26th meeting of the IAU, Joint Discussion 3, 16-17 August, 2006, Prague, Czech R
Physics
Scientific paper
Magnetic clouds - a subclass of coronal mass ejections distinguished by the smooth rotation of the magnetic field inside the structure - are the most geoeffective solar drivers. The rotation of the magnetic field in magnetic clouds reflects the rotation in their source region on the Sun whose quantitative measure is the magnetic helicity. The helicity in the corona is determined by 2 factors: the helicity transferred from the solar interior, and the helicity generated by the surface differential rotation. The helicity transferred from the interior into the corona is proportional to the squared magnetic flux (maximum in sunspot minimum and minimum at sunspot maximum), and is equal in magnitude and opposite in sign in the two solar hemispheres: positive in the south and negative in the north, independent of the magnetic polarity cycle. The surface differential rotation, fastest at the solar equator and decreasing toward the poles, generates helicity with the same sign: negative in the north and positive in the south. Therefore, magnetic clouds originating from the northern solar hemisphere should contain negative helicity, while the ones originating from the southern hemisphere should have positive helicity, with the total negative helicity over the solar cycle equal to the total positive helicity. However, this "hemispheric helicity rule" is true in only 70-80% of the cases. Moreover, in the last solar cycle the net helicity carried away by magnetic clouds was found to be negative, and the number of the left-handed magnetic clouds was higher than of the right-handed ones. We study the solar differential rotation and find that in cycle 23 the rotation rate was higher and the rotation was more differential in the northern solar hemisphere, consistent with the excess negative helicity carried away by magnetic clouds. We investigate 39 magnetic clouds associated with major geomagnetic storms in the last solar cycle (1997-2001) whose solar sources have been identified. In 27 of them (73%) the magnetic cloud observed at the Earth's orbit with the expected helicity. In 10 out of the 12 cases of violation of the hemispheric helicity rule, the differential rotation in the source region of the magnetic cloud is found to be of the "anti-solar type".
No associations
LandOfFree
Solar differential rotation and helicity of magnetic clouds 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 Solar differential rotation and helicity of magnetic clouds, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Solar differential rotation and helicity of magnetic clouds will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1782410