An Introduction to Helioseismology(Local)

2008 Solar Physics Summer SchoolJune 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

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• 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 LocalGlobal1. Horizontal interference

selects integer values of ℓ 2. Entire sun is sampled3. Spherical harmonics

describe waves4. Cannot get structure as

function of longitude5. Cannot get non-

symmetric latitudinal structure

6. One basic technique7. Valid for ℓ < ~180

Local

1. No horizontal interference, can have any wavelength

2. Localized volume is sampled3. Sinusoids or Hankel

functions describe waves4. Longitudinal structure can

be determined5. Non-symmetric latitudinal

structure can be determined6. Several techniques7. 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 1995-2001

• 1024 pixels since 2001

• Run from NSO Tucson.

Space Instruments1996 - Present

Coming Soon….

MDI GOLF VIRGO HMI

Ring Diagram Analysis

1664 min

16o

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 analysisFlow maps

Ring-Diagrams analysisSolar Rotation

Confirmation of the solar

rotation shear layer from

local helioseismolog

y

Ring-Diagrams analysisMeridional Circulation

Ring-Diagrams analysisMeridional Flow: removing surface activity

Ring-Diagrams analysisMeridional Flow

Ring-Diagrams analysisDynamics of Active regions

Ring-Diagrams analysisDynamics of Active regions

AR 10486

AR 10069

Ring-Diagrams analysisHelicity 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 distanceActive regions underlying structure

Time distanceMeridional Flow

30 Mm

200 Mm

65 Mm

130 Mm

Time distanceSunquakes

EARTH

Seismic holography (seismic imaging)

∫∫ ′′′′′′= ±± PtttzGdtdtzH ),(),,,,(),,( 2 rrrrr ψ

Egression/Ingression

Pupil

Seismic holography (seismic imaging)

Phase of the Correlation

),,(),,(),,( ττ += −+∫ tzHtzHdtzC rrr

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 holographyPrediction capability

Carrington Longitude

sin

(lati

tud

e)

Active Region NOAA-10808

Aug 29 Sep 9 2005 (GONG)

AR10808

Sept 7 2005

Source: MLSO K-coronameter

Calibrating the far-side maps

Carrington Longitude

sin

(lati

tud

e)

Active Region NOAA-10808

Aug 29 -> Sep 9 2005

AR10808

Active Region NOAA-10923

Oct 31 -> Nov 10 2006

AR10923

sin

(lati

tud

e)

Calibrating the far-side maps

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!!!!

http://www.hao.ucar.edu/summerschool/program.html

•Has links to very detailed lecture notes on helioseismology and solar internal dynamics

For more information