Latest Results from GONG: Helioseismic Studies of the Solar Cycle and Space Weather. Frank Hill Dec. 3, 2009 NAOC, Beijing. Outline. Brief overview of helioseismology The GONG system Latest results Future H α observations. Helioseismology.
Dec. 3, 2009
=Global helioseismology data reduction
Three spherical harmonics
Time signal for 3 modes
Observed Doppler shift movie
3-d Fourier power spectrum of 16° patches
Spectrum sliced at constant frequency
Close analogy to terrestrial seismology
Cross-correlation amplitude as a function of time and distance from a source
Ray paths from a source
The interference pattern from an object
Waves emitted by subsurface sources are observed on the surface
Waves are “time-reversed” to image the sources at a chosen depth
Overall average duty cycle: 0.849
Last year: 0.893
No day without data since July 2001
W. Livingston & M. Penn
Jain & Tripathy
The temporal evolution of mean frequency shifts (bottom panel) and activity indices represented by sunspot number (top panel) and 10.7 cm radio flux (middle panel). The quantities are calculated on a time scale of nine days and cover the period of May 7, 1995 to Dec 11, 2008. Both the magnitude and the fluctuations of the frequency shifts of this minimum are smaller than those of the last cycle.
Temporal evolution of GONG intermediate-degree frequency shifts (red) calculated from 72 day time series during the (a) previous (cycle 22/23) and (b) current (cycle 23/24) minima of the solar cycle. The blue line represents the linearly scaled 10.7 cm radio flux (F10.7). The dash-dot and dash-dot-dot-dot lines in both panels of the figure display the minimum value in activity and frequency shifts between the cycle 22/23, respectively. Note that the frequency shifts are anti-correlated during the current minimum, unlike the previous one. This is also seen in MDI data.
Relative to 2000 maximum
Sound speed is roughly 20 m/s slower compared to 1996 minimum
Independent of separation near surface effect
Implies either much cooler layers (T/T 0.5%) or lower B
Consistent with reduced irradiance and very low activity
See Howe et al. (2000; Science 287, 2456)
Courtesy R. Howe
Symmetric global inversion
Courtesy R. Howe
Howe et al 2005
Cycle 24 flow is weaker during its rise phase below the surface
Clear north/south asymmetry
Courtesy R. Ulrich
Line of sight coronal hole plot
Synoptic coronal hole plot
Synoptic field plot
Line of sight synoptic field plot
North polar view
Line of sight view
10-min magnetic field average
10-min magnetic field standard deviation
10-min intensity average
Weights for synoptic map
From December 12 2006: Mosaic plot of line-of-sight field changes over a four-hour period centered at 1829UT, the start time of a X6.5 flare in AR10930. Each plot corresponds to one pixel, and the mosaic covers most of AR10930. There is a systematic pattern to the changes, which should yield information about flare mechanisms. Courtesy G. Petrie, J. Harvey, J. Sudol.
Partial rings – apparent suppression in some directions
Rings suppressed in direction towards active region
Information on active region dynamics contained in 3-d power spectrum
Also shows apparent suppression (retrograde here)
Irene Gonzalez-Hernandez & Charlie Lindsey have developed a calibration between the far-side phase shift and the magnetic field strength (above).
It is now possible to create “magnetograms” of the far side (above images), but without polarity information.
A comparison of the current far-side maps (on the right) and the new improved version on the left. The improved ones have been created from four maps over two days, which strengthens the persistent features and reduces the noise. Thus, some faint features that could not be reliably identified as active regions in the original maps have become candidate regions. These are identified with a red circle and a number that quantifies the probability that the feature is an active region.
Temporal variation in disk-averaged far-side phase shift (Courtesy I. GonzálezHernández).
Temporal variation in lag of low-degree autocorrelation function peak – could be applied to asteroseismic observations (courtesy S. Kholikov).
Solid line: vertical velocity averaged over all 801 regions and all ring daysFilled squares: regions with emerging flux – the 25% with highest increase in flux Filled circles: regions with decaying flux – the 25% with greatest decrease in flux Open squares: the rest (50% of regions)Emerging flux: strong upflows in deeper layers, weaker downflows near the surface.Decaying flux: stronger downflows
801 active regions, vertical flow and flux values for complete disk passage. Courtesy R. Komm
Below: vorticity (twisting motions). Pattern shows two horizontal “tornadoes” with opposite sense of rotation. This pattern is under every active region that produces large numbers of X-class flares.
Above: Sound speed: red is relatively high, blue is low. The variations are caused by either temperature or magnetic field.
Komm & Hill
A superposed epoch analysis for active regions associated with X-class flares (red), M-class flares (blue), and C-class flares (cyan). Shown in green is an average value for active regions that do
Henthorn & Reinard
For M- and X-class flares
Heidke scores for surface magnetic field alone are 0.07-0.15
Existing GONG Calibration assembly
Existing instrument cover mounting rail
The details of the spectral structures are related to the rates of rotation, translation, expansion, etc. of the features on the disk.
Spectra of a synthetic rotating Gaussian
Spectra of area A on the image (an erupting filament)
Spectra of a growing and translating Gaussian
Can derive the relationships and then use the spectra for statistical studies of filament dynamics.