1. Measurements of lifetimes of high-l solar p-modes in sunspots
Olga Burtseva, Frank Hill and Shukur Kholikov (NSO/GONG)
LoHCo Meeting – Tucson – January 30, 2008

2. Outline Introduction Lifetime measurements technique Analysed data
Lifetimes at solar min and max
Lifetimes in sunspots
Conclusions and future work

3. Introduction
P-mode lifetimes can be determined from the line profile widths in power spectra of global modes ( < 200). For high- interval this method doesn’t work.
One of the tools to determine the lifetimes of high- p-modes is to use absorption of p-modes in sunspots (Braun, Duvall & LaBonte 1987, 1988; Bogdan et al. 1993; Chen, Chou and the TON team 1996).
Time-distance technique is an alternative way to estimate the lifetimes of high- solar acoustic waves.

4. Lifetime measurements technique
The amplitude of the cross-correlation function decreases exponentially with the number of skips
This phenomenon is interpreted as the dissipation of solar p-mode power (D.-Y.Chou et al., 2001)
Lifetimes computed with this method are lifetimes of wave packets (not individual modes)

5. Lifetime measurements technique
The amplitude (A) of the wave packet decreases due to dissipation
Dispersion causes decrease of A and increase of the width (W) of the wave packet
Dispersion doesn’t change the energy of the wave packet (A2W=const) with number of skips (n). Thus:
An and Wn are amplitude and width of the cross-correlation function of the wave packet, en is one skip travel time, Т is lifetime

6. Lifetimes at solar min and max Analysed Data
MDI full disk velocity data: two 512-minute time series at minimum (May 24 and September 18, 1996) and two 512-minute time series at maximum (September 9 and 11, 2000).
- on the selected days in 1996, there is no active regions present in the solar disk.
- on the two days in 2000, there are active regions on the solar disk.
MDI full disk magnetograms to estimate strength of magnetic field.

7. Data analysis
Remapping, tracking, SH decomposition, Gaussian filtering
Phase velocity filtering to isolate wave packets with central0 and ℓ0
Reconstruction of the images and computing of the cross-correlation functions of the wave packets
Region of target points is at the disk center

8. Lifetimes at solar minimum and maximum

9. Lifetimes at solar minimum and maximum
The results show that the lifetime at maximum is systematically shorter than that at minimum.
It is known that magnetic regions absorb or scatter the acoustic waves.
We suppose that exclusion of the strong magnetic field areas from cross-correlation analysis will allow us to conclude if the lifetime change caused by effect of active regions or it changes with solar cycle because of global variations of the properties of the solar plasma with solar cycle.

10. Masking of active regions
B of the quiet regions on the solar disk is upto 30 G, same in both 1996 and 2000.
B in active regions is upto 1000 G.

11. Lifetimes after masking

12. Lifetimes before and after masking

13. Conclusions
The results without masking of active regions show that the lifetime at solar maximum is systematically shorter than that at solar minimum.
After exclusion of active regions lifetime at maximum is still systematically shorter than that at minimum, but by less quantity, as it increases.
Next …
Separate ingoing and outgoing waves, and compare lifetimes.
Compute lifetime in sunspots.

14. Lifetimes in sunspots Analysed Data
GONG and MDI full disk velocity data.

15. Lifetimes in sunspots Analysed DataAR
Sunspot size, deg.
<B>, G
13-Nov-2006
NOAA 10923
5.4
2500
11-Apr-2003
NOAA 10330
4.0
1800
30-Apr-2007
NOAA 10953
3.0
1600
17-Apr-2005
NOAA 10752
2.0
1450

16. Data analysis

17. Lifetimes in sunspots

18. Lifetimes in sunspots

19. Lifetimes in sunspots

20. Lifetimes in sunspots

21. Lifetimes in sunspots

22. Lifetimes in sunspots

23. Conclusions
In the quiet regions: lifetimes of ingoing and outgoing waves are close in most of the cases.
In the sunspots: lifetimes of outgoing waves are shorter in comparison with lifetimes of ingoing waves.
Lifetimes in the sunspots are shorter then the lifetimes in the quiet regions.