An Introduction to Helioseismology (Local)

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Nov 16, 2013 (3 years and 11 months ago)

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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



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