ACTIVE AND EPHEMERAL REGIONS IN THE SOLAR MEAN MAGNETIC FIELD - - PowerPoint PPT Presentation

ACTIVE AND EPHEMERAL REGIONS IN THE SOLAR MEAN MAGNETIC FIELD

EDDIE ROSS

W.J. CHAPLIN, G.R. DAVIES, Y.P . ELSWORTH, S.J. HALE, R. HOWE

EDDIE ROSS

SOLAR MEAN MAGNETIC FIELD (SMMF)

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• The SMMF is the mean line-of-sight magnetic field of the

Sun-as-star.

• The SMMF varies with the solar activity cycle from ~2 G

(solar max.) to ~0.2 G (solar min.).

• The SMMF has a strong rotational component.
• However, the main source of the SMMF is not well-

understood!

EDDIE ROSS

SOLAR MEAN MAGNETIC FIELD (SMMF)

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1992 2013 WILC LCOX SOLA LAR OBSERVATORY (WSO) BIRMINGHAM SOLA LAR OSCILLA LLATIONS NETWORK (Bi BiSON)

SOLAR MEAN MAGNETIC FIELD (SMMF)

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Bose and Nagaraju (2018) ApJ Kutsenko et al. (2017) Solar Phys.

TOTAL BACKGROUND PLAGES & NETWORKS SUNSPOTS TOTAL (PEAK-TO-PEAK) STRONG INTERMEDIATE WEAK STRONG + INTERMEDIATE INTERMEDIATE STRONG

AREA (% DISK) SMMF (G) Date Oct-2010 Apr-2016 Year 2012 2017 B (G) B (G) B (G) B (G)

SOLAR MEAN MAGNETIC FIELD (SMMF)

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Bose and Nagaraju (2018) ApJ Kutsenko et al. (2017) Solar Phys.

TOTAL BACKGROUND PLAGES & NETWORKS SUNSPOTS TOTAL (PEAK-TO-PEAK) STRONG INTERMEDIATE WEAK STRONG + INTERMEDIATE INTERMEDIATE STRONG

AREA (% DISK) SMMF (G) Date Oct-2010 Apr-2016 Year 2012 2017 B (G) B (G) B (G) B (G)

2% 2% - 6% 6% A AREA REA FR FROM M ST STRONG & IN INTERM ERMED EDIA IATE 65% 65% - 95% 95% S SMMF FR FROM M ST STRONG & IN INTERM ERMED EDIA IATE 11% 11% S SMMF F FRO ROM OTH OTHER 89% 89% S SMMF F FRO ROM BA BACKGROUND

Mount Wilson Las Campanas Izaña Birmingham Sutherland Narrabri Carnarvon

BIRMINGHAM SOLAR OSCILLATIONS NETWORK (BiSON)

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OBJECTIVES

Analyse, for the first time, over 20 years of high-cadence (40- second) observations of the SMMF from BiSON. We present an analysis of the SMMF in the frequency domain which aimed to:

• Investigate the rotation periods
• Investigate the lifetimes of features
• Determine the main source of the SMMF
• Investigate the solar cycle variation of the SMMF background

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POWER SPECTRUM (log-log)

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Frequency [μHz]

POWER SPECTRUM (log-log)

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The central frequency of the peaks gives the rotation period of active magnetic field regions (ARs) The line width of the peaks gives the lifetime of ARs

Frequency [μHz]

POWER SPECTRUM (log-log)

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Side-bands of aliased power are due to gaps in the data

Frequency [μHz]

POWER SPECTRUM (log-log)

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The characteristic timescale

• f

the background gives the lifetime of the ephemeral stochastic background (ERs)

Frequency [μHz]

• PRELIM. RESULTS: ROTATION

Synodic rotation: 27.49 ± 0.08 days Sidereal rotation: 25.56 ± 0.07 days Latitude: ~20°

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• PRELIM. RESULTS: LIFETIMES &

COMPOSITION

Lifetime: ARs: 41.7 ± 3.1 days

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• PRELIM. RESULTS: LIFETIMES &

COMPOSITION

Lifetime: ARs: 41.7 ± 3.1 days ERs: 2.41 ± 0.01 hours Amplitude contribution: ARs: ~ 86 % ERs: ~ 14 %

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SOLAR CYCLE VARIATION

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• The SMMF was segmented into 3-month intervals.
• In each temporal segment, matched sinusoids to the peak

frequencies in the power spectra were removed from the time- series, leaving the background component.

• The background component was then modelled using a zero-

centred Lorentzian.

EDDIE ROSS

• PRELIM. RESULTS: SOLAR CYCLE

VARIATION

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SUMMARY

• Frequency domain analysis for the first time of sub-minute

cadence observations of the SMMF .

• Lifetime of ARs: 41.7 ± 3.1 days
• Lifetime of ERs: 2.41 ± 0.01 hours
• SMMF dominated by ARs: ~ 86 % AR flux / ~ 14 % ER flux
• We see variation in the RMS amplitude and lifetime of the

weak-background field correlated to the solar cycle.

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THANK YOU FOR YOUR ATTENTION, QUESTIONS?

EDDIE ROSS