1. GONG Measurements – Pre-eruptive signatures
Frank Hill, Rudi Komm and the GONG Team

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 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

7. 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

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

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