Transcript Polar Magnetic Field

Polar Magnetic Field
Elena E. Benevolenskaya
Stanford University
SDO Team Meeting 2009
Overview
• What we know about polar magnetic field?
• Polar magnetic field inferred from
SOHO/MDI data
• SOLIS and HINODE polar magnetic field
• Toward the SDO
History
Babcock & Babcock measured the polar magnetic field in solar cycle 19
(1955).
It is observed the polar magnetic fields is their reversal during the maxima
of 11-year sunspot cycles (Babcock and Livingston, 1958; Babcock, 1959).
To understand the origin of the polar magnetic field reversals many
investigators employed the mean-field dynamo theory
(e.g. Dikpati et al., 2004).
The solar magnetic field and, particularly, the polar magneticfield, is
dominated by small magnetic elements of mixed polarities as has been
shown by Severny (1971).
During the last three cycles the polar magnetic field is continually
decreased (WSO data).
MDI data
Axisymmetrical
Pattern of the
Cycle 23
The polar magnetic field reversal in cycle 23 was
in
CR1975±2 (April 2001) in the North and in
CR1980 ±2 (September 2001) in South.
MDI
WSO
Scientific Task . Polar magnetic field: small-scale and large-scale pattern
Major goals and significance
The polar magnetic field is dominated by small magnetic elements of mixed
polarities, while the Polar Regions may appear as unipolar in low-resolution
magnetograms.
During the solar minimum the polar magnetic field reaches their maxima and is
appeared to be pronounced. The small-scale magnetic elements of the dominant
polarity are coincided with polar faculae which display the solar cycle
dependence. HMI will provide vector magnetic data near the solar limb and
detect the intensity and polarity of small-scale elements more correctly to
compare with line-of-sight component. The local helioseimology produces the
polar synoptic maps of plasma motion near the poles beneath the photosphere
and help to understand dynamics of small scale-elements. The goal of this
investigation is to understand nature of the polar magnetic field and to answer
on the question if any local dynamo is involved in the polar magnetic field
pattern. It is important because of the polar field strength at solar minimum is
perhaps the most important quantitative indicator used to forecast the strength of
the oncoming solar cycle.
MHD simulation and current-free coronal field modeling based on magnetograms
will be carry out for constructing of polar magnetic field above the photosphere
and investigate the configuration of large-scale magnetic fields in solar corona .
One important objective of HMI is to examine these results and to understand
relationship of magnetic configuration of large-scale and small-scale magnetic
field during the solar cycle and define the polar magnetic field.
Science team roles and responsibilities
Dr J.Todd Hoeksema with his student Xudong Sun,
and Dr Elena Benevolenskaya (international
collaborator, Russia) will lead the investigation
team which includes Xu Pu Zhao, K. Hayashi, Y.
Liu, P. H. Scherrer, ………of Stanford University.
They will carry out the investigation by synoptic
analysis, MHD and potential field simulation.
We are welcome!