Helioseismology is the study of the Sun's internal structure and dynamics through observations of its resonant oscillation modes. The document discusses how helioseismology has provided insights into changes that occur within the Sun's convection zone over the course of the solar cycle. Observations of changes in oscillation frequencies and amplitudes have revealed shifts in subsurface flows and magnetic activity throughout the convection zone. However, the exact mechanisms driving these changes remain unclear. Improved observations from instruments like SDO may help constrain dynamo models by providing more detailed views of structural variations close to the Sun's surface.

1. Helioseismology and the Solar Cycle
- Rachel Howe - 2006
Mads L. Severinsen, Kristian Jerslev & Lars V. T. Occhionero
- d. 18. Maj 2010

2. Introduktion
 Direct observations of Solar Activity → From
Photosphere
 Activity originates from within the Convective
Zone
 Measure of solar interior → Helioseismology

3. Helioseismology 101
 Sun oscillates in Spherical Harmonic
Oscillations
Y l
m
 ,=−1m
clm Pl
m
cosei m

4. Helioseismology 101
l = 1, m = 0 l = 10, m = 5

5. Helioseismology 101
 l = 0
 l = 2
 l = 20
 l = 25
 l = 75

6. Helioseismology 101
 gravity modes
 Surface gravity
modes
 pressure modes
(acoustic)

7. Article Data
Sun as a Star l < 4 Whole Sun
Medium Degree l < 300 10''
High Degree l > 200 Very Local

8. Article Data

9. Changes in interior dynamics
- Torsional oscillation change

10. Changes in interior dynamics
- Phase and amplitude changes
Observations
 Changes in torsional
oscillation during period
 Possible changes all way
through convection zone
 Zonal flows: constrains
dynamo models
 Changes in meridional
flow oserved through
high l oscillations

11. Changes in mode-parameters
- Frequency shifts

12. Changes in mode-parameters
- Frequency shifts

13. Changes in mode-parameters
- Mechanisms
 Clear change in frequency as function of
activity and time
 No clear mechanism
 Not only a magnetic effect

14. Changes in mode-parameters
- Amplitude and Width

15. Changes in mode-parameters
- Width and Amplitude
Results:
 Damping due to surface activity
 Width and amplitude inversly related to lifetime

16. Subsurface structural changes
 Subsurface changes still unknown
– High l-modes drown in surface variations
– High l-modes hard to observe
 Better results with SDO ?
 We can only see the outermost part of surface
(R=99%)

17. Conclusion
 Chance to look into the Sun's Convection zone
 Gives experimental data to dynamo-model
confinement
 See changes in the suns hydrodynamics during
cycles