SOLARNET Conference: The Many Scales of the Magnetic Sun

Quasi-static modelling of the Sun’s corona using the magneto-frictional approximation makes predictions of how its large-scale magnetic structure might vary over the solar cycle. Unlike the traditional potential field source surface model, this approach is able to probe the effects of low coronal electric currents and the corresponding free magnetic energy. In particular, ongoing footpoint...

Measurements of solar irradiance and surface magnetic flux sufficiently accurate as to allow assessment of their variability are only available for roughly half a century. Variability on longer time scales is evidenced by proxies. Upon emergence, the magnetic field on the Sun manifests itself as dark (sunspots and pores) and bright (faculae/plage and network) features. The combined effect of...

Solar coronal holes (CHs) are the regions with low coronal emissions and an unbalanced magnetic flux, which led to the common expectation that their magnetic structures are mostly ``open'', or, in other words, extending to infinity. The objective of this study is to examine the CH magnetic structures to verify this expectation. The coronal holes are identified from the synoptic maps...

Variations of the solar magnetic field are the main sources of several manifestations of the solar activity (e.g. flares, CMEs, solar wind). A way to quantify such variations is by means of a physical index, the Ca II K index, which has been proven to be a great proxy for the line-of-sight unsigned magnetic flux density along all phases of the cycle, and not only when sunspots are present.
In...

The solar magnetic field is generated and sustained by the combined action of turbulent convection and differential rotation. This dynamo process can sometimes lead to magnetic cyclic variabilities, like the solar 11 years cycle. Traces of magnetic cycles have also been detected in other solar-like stars, ranging from a few years to a few tens of years. How is the solar cycle period...

Emission in the Ca II H & K spectral lines is sensitive to the changes in the stellar magnetic activity and is a good proxy for studying stellar magnetic fields. This emission is most commonly characterized via the S-index, representing the flux in the Ca II H & K line cores relative to the flux in the nearby continuum. The sources of stellar Ca II emissions are yet to be investigated in...

The solar radiation in the cores of the Mg II h & k spectral lines strongly correlates with solar magnetic activity and global variations of magnetic fields with the solar cycle. This work provides a data-driven model of temporal evolution of the solar full-disk Mg II h & k profiles over the solar cycle. Based on selected 76 IRIS near-UV full-Sun mosaics covering almost the full solar cycle...

Solar dynamo models can explain the production and maintenence of the solar magnetic fields on two different spatial scales: the large-scale solar dynamo, manifested in the cycle-dependent appearance of solar active regions, and the small-scale solar dynamo, driven by the turbulent convective motions close to the solar surface. Disentangling these two mechanisms observationally is extremely...

The total and spectral solar irradiance, TSI and SSI, respectively, vary on many timescales from sub-daily variations to annual, decadal, centennial timescales. The variations of the SSI are also wavelength dependent, with larger relative variations in the EUV/UV and smaller variations in the visible and IR. These irradiance variations allow us to understand, on the one hand, the physics of...

The Sun’s large-scale magnetic field undergoes periodic reversals due to the activity of the dynamo within the solar interior. The evolution of the Sun’s magnetic field has a clear impact on the structure of the corona and solar wind above. Here we show results from the spherical harmonic decomposition of the Sun’s photospheric magnetic field, using WSO, SOHO/MDI and SDO/HMI synoptic...

Differential rotation is a key aspect of the solar dynamo model and is well-established in the Sun's interior and photosphere. However, our understanding of the chromosphere and upper atmosphere's differential rotation is limited and has yielded contradictory results in previous studies. To address this, we utilized a century-long dataset of Ca II K images (1907-2007) from the Kodaikanal Solar...

Recently, there has been consideration of two possible methods for the nonlinear modulation of solar cycle amplitudes. The first mechanism, known as Tilt Quenching (TQ), involves a negative feedback relationship between the cycle amplitude and the mean tilt angle of bipolar active regions relative to the azimuthal direction. The second mechanism, known as Latitude Quenching (LQ), involves a...

The Solar Mean Magnetic Field (SMMF) is the average value of the line-of-sight (LOS) magnetic field considered over the visible hemisphere of the Sun. Various synoptic observations of the solar magnetic field have shown that the SMMF has a periodicity of ~ 27 days, and an amplitude that varies according to the solar cycle, from ±0.2 G during solar minima to ±2 G during solar maxima. It has...

Francesco Berrilli - The Multiscale Magnetic Signature of the Solar Turbulent Magneto-Convection
Andrei Gorobets - Co-existence of self-similarity and anomalous scaling in photospheric turbulent small-scale magnetic fields
Malcolm Druett - Comparing the evolution of mottles and fibrils in a radiation-MHD simulation
Carsten Denker - Instruments for High-resolution Solar Observations
Saida...

The change in the distribution of the magnetic field in the quiet Sun photosphere over the solar cycle could be expected to cause systematic variations in the photospheric thermodynamic structure. This could be due to changes in the dynamics of the convective overshoot or radiative properties. To look for such changes, we use high spatial and spectral resolution spectropolarimetric...

Magnetic helicity as a measure of correlation of the magnetic field and electric current plays an important role in astrophysical magnetohydrodynamics as an inviscid invariant. In the context of solar physics, it is extremely important in several aspects. Firstly, its relaxation time is much longer than the turnover time of the solar turbulence, and therefore, observations of magnetic...

Coronal holes are temporary regions in the solar corona that appear dark in extreme ultraviolet (EUV) and soft X-ray solar images. They have low densities, temperatures, and intensity emissions in comparison to non-coronal hole regions. Magnetic fields within coronal holes are open and unipolar; they originate from the photosphere and extend into interplanetary space. These open magnetic field...

The multiscale dynamics associated with turbulent magneto-convection in physical systems dominated by very high Rayleigh numbers is a challenged topic in the community of astrophysicists and physicists dealing with heat transport by convection. The Sun represents a unique natural laboratory in which to explore turbulent magneto-convection in the hard turbulence regime, a regime associated to...