SSPVE Discussion Group B Question 5 To what extent is it possible to predict the emergence of active regions before they reach the photosphere, or to predict the rotation of an active region from behind the limb?

Local Helioseismology Three major techniques –Ring Diagrams Large-scale flows show kinetic helicity pattern below flare producers –Time-Distance Sound speed signature seen before AR emergence –Acoustic Holography Provides farside images of ARs

Ring Diagrams - I Three-dimensional power spectrum of solar oscillations Subsurface flow displaces rings No tracking for solar rotation With tracking

Ring Diagrams – II Perform analysis over solar disk Invert for horizontal flows as function of location and depth

Ring Diagrams -III Assuming incompressible flow and using solar model density Derive vertical velocity and fluid dynamics descriptors: divergence, vorticity, helicity, enstrophy

Vorticity below strong flare producers AR AR 10069

Correlation between kinetic helicity and flare activity Recently completed study of 408 ARs: Must have both a strong dipolar vorticity signal deep down and a strong B for high flare activity. Low activity can occur over a wide B range, but is associated with low vorticty.

Temporal behavior of kinetic helicity before a flare

Time-distance Sound is emitted from a location, travels down, and comes back up at some time later and some distance away from the source. The time and distance is influenced by the conditions of the plasma that the wave travels through.

Constructing a T-D plot At a given time T, compute the cross-correlation between a point and annuli centered on the point with different radii D. Repeat for many values of T, plot cross- correlation amplitude as a function of T and D. Can be done approximately by taking the power spectrum of a filtered oscillation power spectrum.

Observed time-distance diagram Cross-correlation function is well described by a Gabor wave packet T (min) Distance (°) T (min) Correlation

T-D diagnostics Changes in travel time are related to subsurface conditions (sound speed, flows) Can be inverted to infer the conditions

AR emergence Sound speed from Time-Distance

Farside imaging Uses acoustic holography Time reverse observed wave field to an impulse at a specific depth Depth can be located at the farside surface Presence of active region causes phase shifts

Farside images of AR /29/05 8/30/05 8/31/05 9/01/05 9/02/05 9/03/05 AR10808

The answer We can see very large regions on the farside, giving up to 14 day warning before appearance on disk (or all-clear signal). We can see large regions form below the surface on the disk, giving 1-5 day warning. We are starting to see that specific flow configurations are likely activity producers and that there may be precursor temporal variations. BUT…

What do we need to do? More statistics, establish confidence levels. Better understanding of flare-related flow characteristics Tighter connection with surface observations – what is the relation between the flow and the surface neutral line? Incorporation of subsurface flows into CME/Flare initiation models Energy analysis – V vs B, is there a CME or SEP? Faster analysis Calibration of farside signal vs activity & B Compare flows and vector magnetograms