SUBGROUP 1: Surface Solar Magnetic Fields

1
SUB-GROUP 1 Surface Solar Magnetic Fields

• The central question

Can we infer the orientation of Bz of an ICME at
1 AU by focusing on the study of the surface
magnetic fields?

• A. Nindos Examined chirality of source region
  using photospheric magnetograms and coronal
  information (SXT EIT), applied the coronal
  flux-rope model to infer the orientation of the
  leading edge and then compared the result with IP
  measurements..
• Results

• Agreement in 65 (12/19) of cases regarding the
  sign and the
• orientation of the field
• (2) In 8 cases there was no magnetic cloud (MC)
  at 1 AU
• (3) Completion of work using all unambiguously
  identified sources will follow.

2

• V. Yurchyshyn Test with two active region
  cases
• 11/7/04 X2.0 flare and CME event. Erupted
  filament with a magnetic field orientation
  roughly agreeing with the orientation of the MC
• 4/9/01 System of loops disappeared in SXT. Their
  orientation agreed roughly with the
  orientation of the MC at 1 AU.
• NOTE Both exercises are not automatic. Visual
  inspection required.
• Results
• (1) Two cases in which the orientation of the
  erupting feature agreed with MCs' orientation
• Additional test Compared the CME launch speed
  with the Dst index of the subsequent
  disturbances. As a result, Vasyl found that the
  geoeffectiveness of an ICME seems to correlate
  well with the CME's launch speed.

3

• Weve reached a consensus that surface magnetic
  fields are indeed very useful in predicting the
  geoeffectiveness of ICMEs, at least in some of
  the events
• HOWEVER
• We need more reliable ways to infer the coronal
  magnetic fields (calculated or measured)
• We need more reliable MC models
• The task is worthy but currently the technique is
  not able to predict the geoeffectiveness of ICMEs
  on a routine basis. The process is not automatic.

4

• M. K. Georgoulis A quantitative approach based
  solely on the photospheric magnetic fields. An
  array of tools applicable only to vector
  magnetograms
• Resolution of the 180-deg azimuthal ambiguity
• Calculation of the photospheric velocity field
  vector as a solution of the ideal induction
  equation
• Evaluation of the energy-helicity formula in the
  linear force-free approximation. Upgrade to a
  nonlinear force-free method in preparation.

5

• RESULTS
• There seems to be significant quantitative
  difference between flare/CME prolific active
  regions and quiescent active regions in terms of
  the total helicity budget and the percentage of
  the free magnetic energy over the total magnetic
  energy in the configuration
• One case showed distinctive flow differences 30
  min before a M2 flare and a CME
• In one case of an X3 flare the total magnetic
  helicity / free energy decreased after the event,
  thus allowing a lower-limit estimation of the
  events helicity and free energy content

• NOTES
• More active region cases obviously needed
• Large error bars in several cases because of the
  lff approximation
• Obviously, no mention about the geoeffectiveness
  of CMEs. Combined studies required

6

• OVERALL CONSENSUS
• Magnetic helicity is an important tool for
  understanding the process of CME initiation
• However, there are still several gaps in the
  understanding of the CME triggering process
  moreover, several analysis tools need to be
  refined
• We need help! More people need to become
  involved, and more data need to be contributed.
  If the above results are backed up by a
  sufficient statistical sample of cases, a
  promising forecasting ability may emerge