It is believed that the tilt in the bipolar magnetic regions (BMRs) is produced due to a torque induced by the Coriolis force, acting on the diverging flow from the apex of the rising flux tube of the toroidal field in the solar convection zone (SCZ).The BMRs with a strong magnetic field are expected to have reduced tilt as they rise very quickly in the SCZ. This effect can provide the required nonlinear quenching mechanism to suppress the growth of magnetic filed in the dynamo models. Here, we use the magnetograms of the Michelson Doppler Imager (1996–2011) and Helioseismic and Magnetic Imager (2010–2018) to automatically detect the BMRs and look for the signature of tilt quenching. Based on the Bayesian inference method, our results show that the posterior distribution of quenching parameters is Gaussian, and the mean of this distribution agrees with the earlier findings.

Properties of bipolar magnetic regions (BMRs), particularly, the tilt angle play critical roles in generating the observed polar magnetic field and its reversal. Hence, a long-term study of BMR over its lifetime is crucial not only to understand the solar dynamo but also to identify the origin of the properties of BMR. In our work, we have developed an automatic algorithm to detect and track the BMRs from the line-of-sight (LOS) magnetograms of Michelson Doppler Imager (MDI) for the period of Solar Cycle 23 over its lifetime/disk passage. Here, we present the details of our algorithm and the features of BMR, particularly the tilt angle, magnetic field strength and lifetime.

Solar simulations and observations showed that the detection of Earth twins around Sun-like stars is difficult in radial velocities with current methods techniques. The Sun has proved to be very useful to test processes, models, and analysis methods. The convective blueshift effect, dominating for the Sun, decreases towards lower mass stars, providing more suitable conditions to detect low mass planets. We describe the basic processes at work and how we extended a realistic solar model of radial velocity, photometry, astrometry and LogR′HK variability, using a coherent grid of stellar parameters covering a large range in mass and average activity levels. We present selected results concerning the impact of magnetic activity on Earth-mass planet detectability as a function of stellar type. We show how such realistic simulations can help characterizing the effect of stellar activity on RV and astrometric exoplanet detection.

Several problems contribute to difficulties in interpreting transient celestial phenomena as described in Chinese records. Frameworks are an overarching problem. Tianwen, the modern Chinese term for astronomy, in pre-modern times included meteorological phenonemena and was concerned with omenology. Manuscripts that include star charts and comets but also meteorological phenomena and omen reading texts were routinely reframed in modern scholarship to appear as if they included only astronomical content. The scope of pre-modern tianwen, however, was broader than its modern sense. Pre-modern celestial phenomena had political and religious significance. Apparent ambiguity arises from the presence of both meteorological and astronomical phenomena in a single category and from features of the classical Chinese language. Accounting for these problems is essential for research into transient phenomena using historical archives.

We have analyzed the data on yearly mean international sunspot number (RZ) during the period 1610 – 2015 and orbital positions (ecliptic longitudes) of the giant planets in each 10-day interval during the period 1600 – 2099. We determined mean absolute difference ($\overline{\psi _D}$) of the orbital positions of the giant planets in each interval. We find that there exits a good correlation between cycle amplitude (RM, i.e. the maximum value of RZ) and the value of $\overline{\psi _D}$ at cycle maximum, suggesting that on longer time scales low/high solar activity associated with less/large spread in orbital positions of the giant planets (i.e. with a low/high value of $\overline{\psi _D}$).

Here we report our recent prediction of the solar cycle 25 based on a newly developed scheme, which is used to investigate the predictability of the solar cycle over one cycle. The scheme is a combination of the empirical properties of solar cycles and a surface flux transport model to get the possible axial dipole moment evolution at a few years before cycle minimum, by which to get the subsequent cycle strength based on the correlation between the axial dipole moment at cycle minimum and the subsequent cycle strength. We apply this scheme to predict the large-scale field evolution since 2018 onwards. The results show that the northern polar field will keep on increasing, while the southern polar field almost keeps flat by the end of cycle 24. This leads to the cycle 25 strength of 125 ± 32, which is about 10% stronger than cycle 24 according to the mean value.

The tilt angle of a sunspot group is a critical quantity in the surface transport of magnetic flux and the solar dynamo. To contribute long-term databases of the tilt angle, we developed an IDL routine, which allows the user to interactively select and measure sunspot positions and areas on the solar disc. We measured the tilt angles of sunspot groups for solar cycles 19-24 (1954.6-2017.8), using the sunspot drawing database of Kandilli Observatory. The method is similar to that used in the discontinued Mt. Wilson and Kodaikanal databases, with the exception that sunspot groups were identified manually, which has improved the accuracy of the resulting tilt angles. We obtained cycle averages of the tilt angle and compared them with the values from other datasets, keeping the same group selection criteria. We conclude that the previously reported anti-correlation with the cycle strength needs further investigation.

We have analyzed the Debrecen Photoheliographic Data (DPD) and the Solar Optical Observing Network (SOON) sunspot group data during the period 1977 – 2015 and find that during the maximum of solar cycle 23 there is a large difference in the mean meridional motion of sunspot groups determined from DPD and SOON data.

We analyze the flux emergence rate of solar active regions (ARs). Numerical simulations by other authors suggest that the flux emergence rate depends on the AR’s twist. To prove this statement observationally, we make a comparison of the flux emergence rate and twist of 215 emerging ARs. Our results confirm that the correlation exists: the higher the twist the higher the flux emergence rate of an AR. We suppose that the difference in the twist can be caused by chaotic influence of the convective plasma motions on the lifting magnetic flux tube.

The kinematic modeling of the solar convection zone remains the workhorse of the solar dynamo to understand the solar cycle. During the past several years, the major progress in understanding the solar cycle using kinematic models is as follows. (1). The Babcock-Leighton (BL) mechanism was confirmed to be at the essence of the solar cycle. (2). The scatter of sunspot tilt angles is identified as a major cause of solar cycle irregularities. (3). The important roles of the magnetic pumping in the dynamo process are recognized. (4). Some 3D kinematic BL type dynamo models have been developed. As a key part of the solar dynamo loop, the surface observable part of the BL mechanism makes the physics-based solar cycle prediction feasible. Including the effects of the tilt scatter on the polar field generation, the possible strength of the subsequent cycle can be predicted when a cycle starts for a few years.

Predictions of sunspot cycle are important due to their space weather effects. Bhatt et al. (2009) predicted sunspot cycle 24 (Maximum amplitude: 92.8±19.6; Timing:October 2012±4 months) using relative sunspot number (International Sunspot Number), and average geomagnetic activity index aa considering 2008 as the year of sunspot minimum. Owing to the extended solar minimum till 2009, we re-examine our prediction model. Also, the newly calibrated international sunspot number reduces many discrepancies in the old dataset and is available from Solar Influences Data Center (SIDC) website. Considering 2009 as sunspot minimum year and newly calibrated international sunspot number, (i) The annual maximum amplitude of cycle 24 = 118.5±24.4 (observed = 113.3±0.1), (ii) A smoothed monthly mean sunspot number maximum in January 2014±4 months (observed in February 2014). Our prediction method appears to be a reliable indicator for the predictability of cycle 25.

In 1612, Galileo Galilei made very accurate drawings of the solar disk. Currently, 47 of them are in the open access: 9 in May 3 – 11, 35 in June and July, and 3 in late August. Unfortunately, reports have not provided the clock time, which results in uncertainty of sunspots heliographic coordinates. In the present study, we determine the exact time of the drawings by comparing the positions of the same spots from day to day. The time of the observations, which varies from 12 to 16 UT, gives us the direction of the solar rotation axis and the position of the helioequator. Unlike the spots drawn by Christopher Scheiner in 1611 – 1612, none of the analyzed spots lies within the helioequator. This confirms the quality of the Galileo’s drawings.

The poleward magnetic field streams on time-latitude diagram of the photospheric magnetic field of the Sun during 1975–2011 (Kitt Peak NSO, SOLIS NSO, SOHO MDI data) are modeled. We performed simulations in terms of probability density function and bipole orientation according to Joy's law and Hale's cycle. The difference between distributions of leading and trailing fluxes of bipolar sunspots defines the so-called surplus. Finally, magnetic field streams and polar field reversals are a result of meridional drift of a surplus to the poles.

The time-latitude diagram of the photospheric magnetic field of the Sun during 1975-2011 (Kitt Peak NSO, SOLIS NSO, SOHO MDI data) is analyzed using Gnevysvev's idea of impulsed structure of sunspot cycle and a flux transport concept. It is demonstrated that poleward migrations of magnetic trailing polarities are closely associated with the impulses of sunspot activity. We use a fitting procedure to reconstruct the sunspot impulses and poleward magnetic field surges. We compare our results for Cycle 22 model with the time-latitude diagram of the photospheric magnetic field of the Sun.

Observational data concerning the long-term history of cyclic solar activity as recorded in sunspot and isotopic data are discussed in the context of solar dynamo theory. In particular, a simple dynamo model based on differential rotation and the mirror asymmetry of convection with random fluctuations of dynamo governing parameters is shown to reproduce some basic features of the solar magnetic activity evolution.

Commission 12 covers research on the internal structure and dynamics of the Sun, the “quiet” solar atmosphere, solar radiation and its variability, and the nature of relatively stable magnetic structures like sunspots, faculae and the magnetic network. There is considerable productive overlap with the other Commissions of Division II as investigations move progressively toward the fertile intellectual boundaries between traditional research disciplines. In large part, the solar magnetic field provides the linkage that connects these diverse themes. The same magnetic field that produces the more subtle variations of solar structure and radiative output over the 11 yr activity cycle is also implicated in rapid and often violent phenomena such as flares, coronal mass ejections, prominence eruptions, and episodes of sporadic magnetic reconnection.

The last three years have again brought significant progress in nearly all the research endeavors touched upon by the interests of Commission 12. The underlying causes for this success remain the same: sustained advances in computing capabilities coupled with diverse observations with increasing levels of spatial, temporal and spectral resolution. It is all but impossible to deal with these many advances here in anything except a cursory and selective fashion. Thankfully, the Living Reviews in Solar Physicsacute; has published several extensive reviews over the last two years that deal explicitly with issues relevant to the purview of Commission 12. The reader who is eager for a deeper and more complete understanding of some of these advances is directed to http://www.livingreviews.org for access to these articles.