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 1995

2001
•
1024 pixels
since 2001
•
Run from NSO
Tucson.
Space Instruments
1996

Present
Coming Soon….
MDI GOLF VIRGO
HMI
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
Ring

Diagrams analysis
Dynamics of Active regions
AR 10486
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
E
A
R
T
H
Seismic holography (seismic imaging)
P
t
t
t
z
G
d
t
d
t
z
H
)
,
(
)
,
,
,
,
(
)
,
,
(
2
r
r
r
r
r
Egression/Ingression
Pupil
Seismic holography (seismic imaging)
Phase of the
Correlation
)
,
,
(
)
,
,
(
)
,
,
(
t
z
H
t
z
H
dt
z
C
r
r
r
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

10808
Aug 29
卥瀠㤠㈰〵 ⡇低䜩
AR10808
Sept 7 2005
Source: MLSO K

coronameter
Calibrating the far

side maps
Carrington Longitude
sin(latitude)
Active Region NOAA

10808
Aug 29

> Sep 9 2005
AR10808
Active Region NOAA

10923
Oct 31

> Nov 10 2006
AR10923
sin(latitude)
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
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