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) • 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 09/07/19 2
SOLAR MEAN MAGNETIC FIELD (SMMF) 1992 2013 WILC LCOX SOLA LAR OBSERVATORY (WSO) BIRMINGHAM SOLA LAR OSCILLA LLATIONS NETWORK (Bi BiSON) EDDIE ROSS 09/07/19 3
SOLAR MEAN MAGNETIC FIELD (SMMF) TOTAL B (G) TOTAL (PEAK-TO-PEAK) STRONG INTERMEDIATE SMMF (G) WEAK BACKGROUND B (G) PLAGES & NETWORKS B (G) AREA (% DISK) STRONG + INTERMEDIATE INTERMEDIATE STRONG SUNSPOTS B (G) Oct-2010 Apr-2016 2012 2017 Date Year Kutsenko et al. (2017) Solar Phys. Bose and Nagaraju (2018) ApJ EDDIE ROSS 09/07/19 4
SOLAR MEAN MAGNETIC FIELD (SMMF) TOTAL B (G) TOTAL (PEAK-TO-PEAK) STRONG 65% 65% - 95% 95% S SMMF INTERMEDIATE SMMF (G) WEAK FR FROM M ST STRONG & BACKGROUND 89% 89% S SMMF F FRO ROM B (G) INTERM IN ERMED EDIA IATE BA BACKGROUND PLAGES & NETWORKS B (G) AREA (% DISK) STRONG + INTERMEDIATE INTERMEDIATE 2% - 6% 2% 6% A AREA REA 11% S 11% SMMF F FRO ROM STRONG FROM FR M ST STRONG & OTHER OTH SUNSPOTS B (G) INTERM IN ERMED EDIA IATE Oct-2010 Apr-2016 2012 2017 Date Year Kutsenko et al. (2017) Solar Phys. Bose and Nagaraju (2018) ApJ EDDIE ROSS 09/07/19 5
Birmingham Mount Wilson Izaña BIRMINGHAM SOLAR OSCILLATIONS NETWORK (BiSON) Carnarvon Las Campanas Sutherland Narrabri EDDIE ROSS 09/07/19 6
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 EDDIE ROSS 09/07/19 7
POWER SPECTRUM (log-log) Frequency [ μ Hz] EDDIE ROSS 09/07/19 8
POWER SPECTRUM (log-log) Frequency [ μ Hz] 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 EDDIE ROSS 09/07/19 9
POWER SPECTRUM (log-log) Frequency [ μ Hz] Side-bands of aliased power are due to gaps in the data EDDIE ROSS 09/07/19 10
POWER SPECTRUM (log-log) Frequency [ μ Hz] The characteristic timescale of the background gives the lifetime of the ephemeral stochastic background (ERs) EDDIE ROSS 09/07/19 11
PRELIM. RESULTS: ROTATION Synodic rotation: 27.49 ± 0.08 days Sidereal rotation: 25.56 ± 0.07 days Latitude: ~20 ° EDDIE ROSS 09/07/19 12
PRELIM. RESULTS: LIFETIMES & COMPOSITION Lifetime: ARs: 41.7 ± 3.1 days EDDIE ROSS 09/07/19 13
PRELIM. RESULTS: LIFETIMES & COMPOSITION Lifetime: ARs: 41.7 ± 3.1 days ERs: 2.41 ± 0.01 hours Amplitude contribution: ARs: ~ 86 % ERs: ~ 14 % EDDIE ROSS 09/07/19 14
SOLAR CYCLE VARIATION • 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 09/07/19 15
PRELIM. RESULTS: SOLAR CYCLE VARIATION EDDIE ROSS 09/07/19 16
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. EDDIE ROSS 09/07/19 17
THANK YOU FOR YOUR ATTENTION, QUESTIONS? EDDIE ROSS
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