GONG Measurements

1
GONG Measurements Pre-eruptive signatures

• Frank Hill, Rudi Komm and the GONG Team
• fhill_at_noao.edu

2
What is GONG?

• The Global Oscillation Network Group
• Deployed in 1995 to continually observe solar
  oscillations and infer internal solar structure
  and dynamics (helioseismology)
• Six instruments located around the world

3
What does GONG observe?

• Full-disk Doppler velocity, line-of-sight
  magnetic field, and intensity
• Uses Ni I 676.8-nm spectral line
• Solar image is 800x800 pixels (2.5 pixels)
• One data set every 60 sec at each site
• Semi-automated operation

4
GONG temporal coverage
1995
2007
Overall average duty cycle 0.849 Last year
0.893 No day without data since July 2001 Data
loss due to instrumental problems is 0.02
5
GONG Space Weather Products

• High-cadence (60 sec) surface magnetic field
  measurements and field extrapolations provide
  rapid changes in the field geometry
• Images of far-side magnetic field from
  helioseismology show large active regions see
  poster S-14 by Irene Gonzalez-Hernandez
• Helioseismology ring diagrams can measure
  subsurface vorticity, which is an excellent flare
  indicator, and may be able to predict the time of
  flare onset
• Considering adding 1 pixel high-cadence (15-60
  sec) full-disk H? imaging

6
Helioseismology

• Sun is filled with 5,000,000 distinct sound waves
• Sound is trapped in a cavity defined by the
  internal thermal structure
• Each wave samples a different range of depths
• Can invert wave properties to infer internal
  conditions, such as bulk plasma velocity

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Ring Diagrams - I

• Three-dimensional power spectrum of solar
  oscillations
• Subsurface flow displaces rings

No tracking for solar rotation
With tracking
8
Ring Diagrams II

• Perform analysis over solar disk

• Invert for horizontal flows as function of
  location and depth

On a single day, can reach 60 in heliocentric
longitude and latitude.
9
Flows below strong flare producers
AR 10069
AR 10486
10
Flare activity, vorticity and B
Each point identifies the observed vorticity and
surface magnetic field strength B for a unique
active region. Filled symbols multiple
flares Open symbols single flare Sample
approximately 700 active regions covering
2001-2004
11
Flare occurrence probabilities as a function of
vorticity and surface magnetic field
The vorticity and surface B measurements are
placed in bins, each containing 28 unique active
regions. The numbers in the bins are the
percentage of active regions with at least one
flare with a magnitude above the indicated class.
Colors indicate the probability levels in steps
of 10, white is 0.
12
Temporal behavior of kinetic helicity before a
flare
Time history of kinetic helicity (KH) below 9
solar areas preceding the Halloween flare. The
flaring region was located in the ellipse. The KH
was anomalously high before the flare, then
abruptly decreased at the time of the flare. The
KH may be a predictor of strong flares. Different
colors indicate different depths.
13
Next steps

• Fully test added value of combining vorticity
  with surface magnetic field measurements
• Beginning collaboration with KD Leka, G Barnes
  and A Reinard to apply discriminant analysis and
  investigate correlation with spot complexity
• Start statistical analysis of temporal predictor
• Develop automated pipeline at remote sites to
  estimate the vorticity below active regions on an
  8-hour cadence would produce six observations
  per 24 hours
• Work with NOAA towards an operational product
• GONG facing funding challenges, uncertain future
  could result in loss of a useful space weather
  asset