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The Magnetic Field at the Inner Boundary of the Heliosphere Around Solar Minimum  

Xuepu Zhao   Submitted: 2010-07-20 13:35

STEREO A and B observations of the radial magnetic field between 1 January 2007 and 31 October 2008 further show significant evidence that in the heliosphere, the ambient radial magnewtic field component with any dynamic effects removed is uniformly distributed. Based on this monopolar nature of the ambient heliospheric field we find that the surface beyond which the magnetic fields are in the monopolar configuration must be spherical, and this spherical surface can be defined as the inner boundary of the heliosphere that separates the monopole-dominated heliospheric magnetic field from the multipole-dominated coronal magnetic field. By using the radial variation of the coronal helmet streamers belts and the horizontal current-current sheet-source surface model we find that the spherical inner boundary of the heliosphere should be located around 14 solar radii near solar minimum phase.

Authors: X. P. Zhao and J. T. Hoeksema
Projects: SoHO-MDI

Publication Status: Accepted for publication in Solar Physics
Last Modified: 2010-07-20 23:40
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Inversion Solutions of the Elliptic Cone Model for Disk Frontside Full Halo Coronal Mass Ejections  

Xuepu Zhao   Submitted: 2007-08-02 10:30

A new algorithm is developed for inverting 6 unknown elliptic cone model parameters from 5 observed CME halo parameters. It is shown that the halo parameter α includes the information on the CME propagation direction denoted by two model parameters. Based on the given halo parameter α , two approaches are presented to find out the CME propagation direction. The two-point approach uses two values of α observed simultaneously by COR1 and COR2 onboard STEREO A and B. The one-point approach combines the value of α with such simultaneous observation as the location of CME-associated flare, which includes the information associated with CME propagation direction. Model validation experiments show that the CME propagation direction can be accurately determined using the two-point approach, and the other four model parameters can also be well inverted, especially when the projection angle is greater than 60°. The propagation direction and other four model parameters obtained using the one-point approach for six disk frontside full halo CMEs appear to be acceptable, though the final conclusion on its validation should be made after STEREO data are available.

Authors: Xuepu Zhao
Projects: SoHO-MDI

Publication Status: Accepted
Last Modified: 2007-08-02 11:11
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The Effect of Differential Rotation of Magnetic Features on Synoptic Frames of the Photospheric Magnetic Flux  

Xuepu Zhao   Submitted: 2007-02-05 13:39

An instantaneous complete global view of the photospheric magnetic field is indispensable to reproduce coronal and heliospheric structures observed at same time from different points by the upcoming STEREO A and B and the Solar Sentinels. To construct a better instantaneous entire solar surface distribution of the photospheric magnetic field, this work first examines the effect of differential rotation of magnetic features on the evolving photospheric magnetic field on the time scale less than one solar rotation, finding that the magnetic elements from a synoptic chart do not cover the entire solar surface at any time within the period of solar rotation; then improve the synoptic frame by including the effect of differential rotation. In the improved synoptic frame or the ``synchronic frame'', all magnetic elements are remapped using fully the heliographic coordinate system at the time of interest. The coronal holes and heliospheric magnetic field polarities reproduced overlying the magnetogram portion of the improved synoptic frame are better than that reproduced using the synoptic frame without the differential rotation correction. To further approximate the photospheric magnetic flux over the entire surface for a later time in order to make better predictions, the synchronic frame with the differential rotation correction should be imported into the flux-dispersal model as an initial, instantaneous, entire-surface distribution of the photospheric magnetic field.

Authors: X. P. Zhao, P. H. Scherrer and J. T. Hoeksema
Projects: SoHO-MDI

Publication Status: Will be submitted to Ap. J.
Last Modified: 2007-02-06 08:22
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The source regions and storm-effectiveness of frontside full halo coronal mass ejections  

Xuepu Zhao   Submitted: 2002-11-19 11:05

Full halo coronal mass ejections (CMEs) erupting from the side of the Sun facing Earth, i.e., frontside full halo CMEs, are considered to be the most likely source of geomagnetic storms. However, this hypothesis has not been tested over a full solar cycle. We compare all frontside full halo CMEs observed during the first half of solar cycle 23, from 1996 to the end of 2000, with moderate or larger storms at Earth. We show that the association of frontside full halo CMEs with such storms tends to decrease from 1997 to 2000, though this decreasing trend is not monotonic. We examine the locations of the frontside full halo CMEs from 1996 to 2000 with respect to two kinds of coronal closed field regions: bipolar closed field regions between opposite-polarity open field regions and unipolar closed field regions between like-polarity open field regions. We find that even during solar maximum when the occurrence frequency of the two kinds of regions is nearly the same, the central positions of the frontside full halo CMEs are mostly located under the bipolar coronal streamer belt, suggesting that most full halo CMEs originate in the bipolar coronal helmet streamers that are sandwiched between coronal holes having opposite magnetic polarity. Because the inclination of the heliospheric current sheet increases towards solar maximum, the fraction of CMEs emitted into the ecliptic decreases and the inclination of associated flux ropes increases. These effects help to explain the solar cycle effect on the storm-effectiveness of frontside full halo CMEs.

Authors: Xuepu Zhao and David Webb
Projects:

Publication Status: Accepted by Jorunal of Geophysical Research - Space Physics
Last Modified: 2002-11-19 14:49
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Abstracts by Author
The Magnetic Field at the Inner Boundary of the Heliosphere Around Solar Minimum
Inversion Solutions of the Elliptic Cone Model for Disk Frontside Full Halo Coronal Mass Ejections
The Effect of Differential Rotation of Magnetic Features on Synoptic Frames of the Photospheric Magnetic Flux
The source regions and storm-effectiveness of frontside full halo coronal mass ejections

Related Pages
MSU Solar Physics.
Max Millennium Science Mail Archive.
Max Millennium Message of the Day Mail Archive.
Max Millennium Flare Catalog

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