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Solar cycle variation in the peak asymmetry: solar or artefact?. S. J. Jiménez-Reyes IAC . 13-sept-2004. Blue. Red.

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Solar cycle variation in the peak asymmetry solar or artefact l.jpg

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

S. J. Jiménez-Reyes

IAC

13-sept-2004


Variation of peak asymmetry it is real l.jpg

Blue artefact?

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?


Slide3 l.jpg

Blue and red wing measurements artefact?

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.


Slide4 l.jpg

Variation of peak asymmetry. It is real? artefact?

Blue Wing (mA)

D1: 129.7 Vmax

109.8 Vmin

D2a: 155.9

136.0

D2b: 102.9

83.0

Red Wing (mA)

D1: 82.5 Vmax

102.5 Vmin

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.


Variation of peak asymmetry how can we proceed l.jpg

  • Extent the observations of GOLF. artefact?

    • 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?


Golf observations l.jpg

Cycle 23 artefact?

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


Extraction of the mode parameters l.jpg

Nigam & Kosovichev (1998) artefact?

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 l.jpg

Frequency shift of low degree artefact?

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.


Mean change in height and weight l.jpg

No long-term variations artefact?

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.


Variation of peak asymmetry it is real10 l.jpg

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

Variation of peak asymmetry. It is real?


Blue vs red wing l.jpg

-0.68,1.12e-2 artefact?

-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


Time series of 432d long l.jpg

  • 2975 days: artefact?

  • 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 versus mdi 100d and 432d l.jpg

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


Phase difference v v l.jpg

A clear phase difference of around 20 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.º 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


Variation of peak asymmetry summarize l.jpg

  • Extent the observations of GOLF. 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.

    • 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


Artificial data l.jpg

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



Slide19 l.jpg

1. Empirical model of the p-mode simulation:

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 ii l.jpg

Mean asymmetry simulation:

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.


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