An Introduction to Helioseismology (Local) 2008 Solar Physics Summer School June 16-20, Sacramento Peak Observatory, Sunspot, NM

Local Helioseismology What is Local helioseismology? –Comparison with Global Helioseismology –History –Why Local Helioseismology Observations for Local Helioseismology The three main methods –Ring diagram analysis –Time Distance –Seismic Holography (seismic imaging) The Space Weather connection

Global Modes A p mode is a standing acoustic wave. Each mode can be described by a spherical harmonic. Quantum numbers n (radial order), l (degree), and m (azimuthal order) identify the mode. -l  m  l

Approximation to plane waves

Global vs Local Global 1.Horizontal interference selects integer values of ℓ 2.Entire sun is sampled 3.Spherical harmonics describe waves 4.Cannot get structure as function of longitude 5.Cannot get non-symmetric latitudinal structure 6.One basic technique 7.Valid for ℓ < ~180 Local 1.No horizontal interference, can have any wavelength 2.Localized volume is sampled 3.Sinusoids or Hankel functions describe waves 4.Longitudinal structure can be determined 5.Non-symmetric latitudinal structure can be determined 6.Several techniques 7.Valid for ℓ > ~180

Helioseismology: A window to the Sun’s Interior

History 1987: Sunspots are observed to absorb p- modes 1988: Ring diagram method is invented 1990: Acoustic holography is invented 1993: Time-distance method is invented

Why local helioseismology ? Infer dynamics and structural parameters of localized areas of the Sun Difference between North and South hemisphere Longitudinal discrimination Meridional circulation Structure and dynamics of active regions and filaments

Observations High spatial resolution velocity or intensity images –Current Instruments: GONG MDI on board of SoHO SOT on board of Hinode –Future: HMI on board of SDO PHI on board of Solar Orbiter

Networks Six stations around the world for continual coverage. 256x256 pixels pixels since 2001 Run from NSO Tucson.

Space Instruments Present Coming Soon…. MDI GOLF VIRGOHMI

Ring Diagram Analysis 1664 min 16 o

Ring-Diagrams analysis Rings of Power l- diagram

Ring-Diagrams analysis No tracking, solar rotation rate of 2000 m/s With tracking to remove rotation

Ring-Diagrams analysis Flow maps

Ring-Diagrams analysis Solar Rotation Confirmation of the solar rotation shear layer from local helioseismology

Ring-Diagrams analysis Meridional Circulation

Ring-Diagrams analysis Meridional Flow: removing surface activity

Ring-Diagrams analysis Meridional Flow

Ring-Diagrams analysis Dynamics of Active regions

AR AR 10069

Ring-Diagrams analysis Helicity and flare production

Time distance Sound travels from a particular location, 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. More resolution that ring- diagrams. Reach deeper layers

Time distance Observed time-distance diagram Cross-correlation function is well described by a Gabor wave packet

Turning points

Time distance Active regions underlying structure

Time distance Meridional Flow 30 Mm 200 Mm 65 Mm 130 Mm

Time distance Sunquakes

EARTHEARTH Seismic holography (seismic imaging) Egression/Ingression Pupil

Seismic holography (seismic imaging) Phase of the Correlation Phase-difference due to: Reduction of gas pressure in magnetic region --> displacement of density variation Sound speed enhancement (evidence from acoustic moats) due to thermal anomalies Inclination of the magnetic field

Seismic holography Prediction capability Carrington Longitude sin(latitude) Active Region NOAA Aug 29  Sep (GONG) AR10808 Sept Source: MLSO K-coronameter

Calibrating the far-side maps Carrington Longitude sin(latitude) Active Region NOAA Aug 29 -> Sep AR10808 Active Region NOAA Oct 31 -> Nov AR10923 sin(latitude)

Calibrating the far-side maps

Rings: easy and intuitive; low spatial resolution and shallow depth range TD: harder; higher spatial resolution and greater depth range, but inversions…. Holography: Similar to TD, but needs a good understanding of the Green’s functions. All methods have a trade-off between depth range and spatial resolution Comparison of methods

Images of activity in the far side of the Sun Flare prediction Emerging active regions Local helioseismology & Space Weather

To Do Huge list!!!! Has links to very detailed lecture notes on helioseismology and solar internal dynamics For more information