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Solar cycle variation in the peak asymmetry: solar or artefact?PowerPoint Presentation

Solar cycle variation in the peak asymmetry: solar or artefact?

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Solar cycle variation in the peak asymmetry: solar or artefact?

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Solar cycle variation in the peak asymmetry: solar or artefact?

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Solar cycle variation in the peak asymmetry: solar or artefact?

S. J. Jiménez-Reyes

IAC

13-sept-2004

Blue

Red

The convective overshoot in the photosphere makes the asymmetries less negative. It should be stronger in the blue period, when observations are sensitive to variations close to the base of the photosphere.

Our previous studies (Jiménez Reyes et al. 2003) uncovered a clear evidence for a systematic variation over the solar cycle. However, such conclusion ignores any potential contribution from the change in operating configuration through the GOLF lifetime.

Blue Red

?

Variation of peak asymmetry. It is real?

Blue and red wing measurements

A one year modulation is visible due to the orbital velocity of the spacecraft.

This is what we can expect if the changes are due to the measurements make at different depths in the solar atmosphere.

Variation of peak asymmetry. It is real?

Blue Wing (mA)

D1:129.7Vmax

109.8Vmin

D2a:155.9

136.0

D2b:102.9

83.0

Red Wing (mA)

D1: 82.5Vmax

102.5Vmin

D2a:108.8

128.7

D2b: 55.8

75.7

Given the annual variation of the line-of-sight velocity of the spacecrafts we should see a periodic modulation in the asymmetry variations. Indeed, this modulation should be of the order of height difference between both operating configurations. However, such height-dependent is not found.

- Extent the observations of GOLF.
- Analyze the results obtained from both configuration modes separately.
- Compare results obtained from time series with larger length.

- Perform a contemporaneous analysis of different datasets such as MDI, BiSON, etc.
- Study a possible progressive intensity contamination of the velocity measurement (phase difference V-V).
- Carry out a realistic simulation of the GOLF signal.

Variation of peak asymmetry. How can we proceed?

Cycle 23

Note that in terms of level of solar activity, there is not overlapping between blue and red-wing periods.

Blue

Red

Blue

- 2975 days:
- Start: 1996 April 11
- End: 2004 June 2
- Duty cycle: 92%
- Series of 100-days
- Shifted 25 days
- 116 – 4 = 112 series
- l=0, 1, 2 and 3
- f=2.4 to 3.4 mHz

GOLF observations

Nigam & Kosovichev (1998)

Maximum height

Width

Fractional asymmetry

Central frequency

Extraction of the mode parameters

- Rotational splitting fixed to 400 nHz.
- Same linewidth for all the components of the multiplets.
- Fixed theoretical values for the instrumental sensitivity.
- Same peak asymmetry for both multiplets.

This is a traditional peak fitting in the sense that the asymmetrical frequency shifts of the multiplet is not taken into account.

Frequency shift of low degree

Using this results it is possible to identify some of the main characteristics of the solar magnetic fields. Thus, differential analysis of the frequency shifts of different low-degree modes can provide information on the distribution of high-latitude fields.

No long-term variations

Mean change in height and weight

The result found could be explained on the basis of changes in damping affecting both the mode with and the velocity power.

The new data confirms our previous results. We do not find any dramatic variation between both operating configuration modes.

Variation of peak asymmetry. It is real?

-0.68,1.12e-2

-0.07,7.95e-1

-0.65,1.57e-4

-0.40, 1.74e-1

-0.38, 1.44e-1

-0.83,1.99e-8

0.60,3.06e-2

-0.02,9.40e-1

0.57,1.34e-3

0.77, 1.87e-03

0.84, 3.93e-05

0.92, 2.45e-12

Blue...

Red...

All...

Blue vs Red wing

- 2975 days:
- Start: 1996 May 5
- Duty cyle: 87%
- Series of 432-days
- Shifted 216 days
- 14 series
- l=0, 1, 2 and 3
- f=1.8 to 3.7 mHz
- Given the higher SNR, we have fitted an asymmetry parameter for each mode degree.

Time series of 432d long

GOLF vs MDI. 100d and 432d

We can confirm an asymmetry variation of l=1,3 in both datasets although the peak-to-peak change does not agree. The higher sensitivity found for GOLF might arises from an additional contribution due to the observed depth in the solar atmosphere.

GOLF versus MDI. 100d and 432d

A clear phase difference of around 20º between both operating configurations is found, which coincides with initial estimations (Pallé et al. 1999). However, we did not find any trend of this parameter with time.

In principle, the variation of the asymmetry could be explained as part of a progressive intensity contamination of the velocity measurement. When Ic b

Let suppose first, that the long-term asymmetry variation is due to the observed depth in the solar atmosphere.

Can be explained the short-term variation as part of an intensity contamination?

We compute the phase difference between two simultaneous velocity measurements (GOLF-MDI)

Phase difference V-V

- Extent the observations of GOLF.
- Analize the results obtained from both configuration modes separately.
- Compare results obtained from time series with larger different length.

- Perform a contemporaneous of different datasets such as MDI.
- Study a possible progresive intensity contamination of the velocity measurement (phase difference V-V).
- Carry out a realistic simulation of the GOLF signal.

CONFIRMED

CONFIRMED

CONFIRMED

PARTIALLY

CONFIRMED

CONFIRMED

???????

Variation of peak asymmetry.

Summarize

Different issues need to take into account in the simulation:

- The asymmetrical frequency shifts of the multiplets (l=2 and 3).
- The window function (BiSON and GONG).
- Possible systematic bias in the peak asymmetry determination.
- Variation with the SNR of the power spectra.
- Leakage from higher mode degrees, mainly from l=4 and 5.

Artificial data

What about l=4 and 5?

1. Empirical model of the p-mode

parameters extracted from previous

results.

2. Empirical model of the p-mode parameter variations normalized to the Radio Flux changes.

(l,m)=(2,0)

(l,m)=(2,2)

Artificial data

3. Relative instrumental sensitivity up to l=5 (theoretical values)

4. Asymmetrical frequency shifts of the multiplets (l=2 and 3).

Artificial data. Results (i)

Mean asymmetry

Mean noise

Artificial data. Results (ii)

The leakage from l=4 and 5 might affect the asymmetry determination of l=0,2 since the level of noise cannot be estimated correctly.