Using SDO/HMI Magnetograms as a Source of the Solar Mean Magnetic Field Data

Abstract

The solar mean magnetic field (SMMF) provided by the Wilcox Solar Observatory (WSO) is compared with the SMMF acquired by the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamic Observatory (SDO). We found that despite the different spectral lines and measurement techniques used in both instruments the Pearson correlation coefficient between these two datasets equals 0.86 while the conversion factor is very close to unity: B(HMI) = 0.99(2)B(WSO). We also discuss artifacts of the SDO/HMI magnetic field measurements, namely the 12 and 24-hour oscillations in SMMF and in sunspots magnetic fields that might be caused by orbital motions of the spacecraft. The artificial harmonics of SMMF reveal significant changes in amplitude and the nearly stable phase. The connection between the 24-hour harmonic amplitude of SMMF and the presence of sunspots is examined. We also found that opposite phase artificial 12 and/or 24-hour oscillations exist in sunspots of opposite polarities.

On the Variability of the Solar Mean Magnetic Field: Contributions from Various Magnetic Features on the Surface of the Sun

“…Plots of the SMMF and the weighted MMFs corresponding to the different features (as in Equation (3)) on the solar surface are shown in Figure 3 as a function of time, for the entire analysis period. Figure 3(A) shows the peak value of the SMMF to be about 2.5 G that occurred in 2014 December and is consistent with Kutsenko & Abramenko (2016). The dotted vertical line corresponds to 2014 April, which corresponds to the maximum of solar cycle 24.…”

“…These measurements are generally made by letting unfocused light pass through a spectrograph slit (making sure that light from all parts of Sun is integrated) followed by measuring Zeeman splitting of the spectral lines under consideration using a Babcock-type magnetograph. Boberg et al (2002), and more recently Kutsenko & Abramenko (2016), have shown that the SMMF can also be calculated by averaging the full-disk LOS magnetograms provided by the space-based Michelson Doppler Imager (Scherrer et al 1995) on board the Solar and Heliospheric Observatory and the Helioseismic and Magnetic Imager (HMI; Schou et al 2012) on board the Solar Dynamics Observatory, (SDO; Liu et al 2012;Scherrer et al 2012), respectively. This has significantly improved the chances of obtaining such measurements continuously more or less uninterrupted, which otherwise is limited by lack of continuous availability of clear skies in ground-based observations.…”

Role of the background regimes towards the Solar Mean Magnetic Field (SMMF)

“…03.2011 & 30.11.2017 The right panel of figure 1-(A), shows the temporal variation of the SMMF. It is found to have a peak value of about 2.5 G that is consistent with Kutsenko et al (2016). The mean background field ( figure 1-(B)) emulates the SMMF quite distinctly, both peaking around December 2014.…”

Differences in Periodic Magnetic Helicity Injection Behavior between Flaring and Non-flaring Active Regions: Case Study

“…Smirnova et al (2013b,a) found that the amplitude of these oscillations increases rapidly when the field strength exceeds 2000 G in the magnetic fields of ARs. Kutsenko & Abramenko (2016) further argued for the presence of these two artificial oscillations by studying wavelet transform of the solar mean magnetic field measurements. If these oscillations were indeed significant in the helicity components presented in this work, we would expect to see them in the WPS of all ARs, particularly in the non-flaring regions where there are very few periodicities of significant power.…”