Solar Spectral Irradiance (SSI) provides information about various properties of the solar atmosphere, including physical, chemical, thermal, and dynamic aspects. However, its importance extends beyond this, as solar emission in EUV wavelengths is the primary source of energy input to planetary atmospheres, significantly impacting their structure, composition, and dynamics, particularly in the Ionosphere-Thermosphere-Mesosphere (ITM) system. To study the impact of SSI on planetary atmospheres, it is important to provide long and continuous SSI time series. In the case of Earth, this can be used in ITM models to understand their impact. Since the photospheric magnetic flux drives the solar irradiance variability, it is possible to use the magnetic field to model the Solar Spectral Irradiance (SSI), e.g., the COronal DEnsity and Temperature (CODET) model. It is a physics-based model that uses the relationship between the magnetic field, density, temperature, and EUV emission. This work shows the most recent results and applications, e.g., new SSI time series in Earth’s exosphere and at Mars’ distances. New perspectives and improvements are also discussed.

We present a study of the evolution of two types of coronal holes (CHs) in the solar minimum of 24/25, which was preceded by a prolonged minimum of 23/24 and a weak 24 solar cycle. The goal of the study is to clarify whether the behavior of CHs during this period is also unusual? The study is based on the material of observations obtained by SDO/AIA/193. The Heliophysics Events Knowledgebase was used to localize the CHs and calculate their areas. Analysis of the evolution of the areas of polar and non-polar CHs in solar minimum 24/25 revealed a number of features. The hemispheric asymmetry is evident both in solar activity indices and in the localization of maxima of polar and non-polar CH areas. The hemispheric area imbalance is minimal for polar CHs and pronounced in the regions of non-polar CHs and sunspots. This is consistent with the general concept of polar CHs as the main source of the Sun’s dipole magnetic field. The areas of polar CHs significantly exceed the areas of non-polar CHs and make a significant contribution to the total area of all CHs in the solar disk. It is concluded that the dynamics of polar and nonpolar CHs suggests that the 24/25 minimum is rather close to earlier minima than to the 23/24 minimum.

The formation of highly structured, spatially localized complex structures during solar flux emergence facilitates adaptation of topological methods, extending the research of emerging macroscopic MHD fluxes into knots, links and braids. Combining mathematical considerations, remote images and in situ satellite observations at solar vicinity, we construct new characteristics of those braided/knotted magnetic structures, applying Braid and Knot Theory to physical configurations, deducing their topological invariants, constraining the evolution and stability while delineating the relaxation path to magnetized equilibria.

Total solar eclipses are popular targets for amateur astronomers. At the same time, the eclipses are still scientifically important to observe the solar corona. Therefore, the eclipses are a good chance for amateurs to participate in scientific observations. In fact, some of amateur astronomers in Japan have been carried out scientific observations at the total solar eclipses collaborating with professional solar scientists over more than ten years. Some scientific results have been produced from the collaboration. We present here our collaborative activities as a practical example of citizen science.

The profile of the differential rotation together with the sign of the alpha-effect determine the dynamo wave direction. In early models of the solar dynamo the dynamo wave often leads to a poleward migration of the activity belts. Flux transport by the meridional flow or the effect of the surface shear layer are possible solutions. In a model including the corona, we show that various migrations can be obtained by varying the properties of the corona. A new dynamo of Babcock-Leighton type also leads to the correct equatorward migration by the non-linear relation between flux density and rise time of the flux.

Solar eruptions are due to a sudden destabilization of force-free coronal magnetic fields. But the detailed mechanisms which can bring the corona towards an eruptive stage, then trigger and drive the eruption, and finally make it explosive, are not fully understood. A large variety of storage-and-release models have been developed and opposed to each other since 40 years. For example, photospheric flux emergence vs. flux cancellation, localized coronal reconnection vs. large-scale ideal instabilities and loss of equilibria, tether-cutting vs. breakout reconnection, and so on. The competition between all these approaches has led to a tremendous drive in developing and testing all these concepts, by coupling state-of-the-art models and observations. Thanks to these developments, it now becomes possible to compare all these models with one another, and to revisit their interpretation in light of their common and their different behaviors. This approach leads me to argue that no more than two distinct physical mechanisms can actually initiate and drive prominence eruptions: the magnetic breakout and the torus instability. In this view, all other processes (including flux emergence, flux cancellation, flare reconnection and long-range couplings) should be considered as various ways that lead to, or that strengthen, one of the aforementioned driving mechanisms.

Coronal Mass Ejections (CMEs) are one of the most violent phenomena found on the Sun. One model to explain their occurrence is the flux rope ejection model where these magnetic structures firt form in the solar corona then are ejected to produce a CME. We run simulations coupling two models. The Global Non-Linear Force-Free Field (GNLFFF) evolution model to follow the quasi-static formation of a flux rope and MHD simulations for the production of a CME through the loss of equilibrium and ejection of this flux rope in presence of solar gravity and density stratification. Our realistic multi-beta simulations describe the CME following the flux rope ejection and highlight the decisive role played by the gravity stratification on the CME propagation speed.

Using maximum brightness of coronal bright point's (CBP) as a criterion, we separate them on two categories: dim CBPs, associated with areas of a quiet Sun, and bright CBPs, associated with an active Sun. This study reports on characteristics of two types of CBPs and their evolution.

Magnetohydrodynamic turbulence has been proposed as a mechanism for the heating of coronal active regions, and has therefore been actively investigated in recent years. According to this scenario, a turbulent regime is driven by footpoint motions. The energy being pumped this way into active region loops, is efficiently transferred to small scales due to a direct energy cascade. The ensuing generation of fine scale structures, which is a natural outcome of turbulent regimes, helps to enhance the dissipation of either waves or DC currents.

We present an updated overview of recent results on turbulent coronal heating. To illustrate this theoretical scenario, we simulate the internal dynamics of a coronal loop within the reduced MHD approximation. The application of a stationary velocity field at the photospheric boundary leads to a turbulent stationary regime after several photospheric turnover times. This regime is characterized by a broadband power spectrum and energy dissipation rate levels compatible with the heating requirements of active region loops. Also, the energy dissipation rate displays a complex superposition of impulsive events, which we associate to the so-called nanoflares. A statistical analysis yields a power law distribution as a function of their energies, which is consistent with those obtained from observations. We also study the distributions of peak dissipation rate and duration of these events.

This article is a study of a family of nonlinear force-free magnetic fields (FFMFs), in Cartesian geometry under assumption of translational symmetry, as simple models of the magnetic fields in the solar corona. For this configuration all the physical quantities are invariant under translations in a fixed direction to be the direction Oz of a Cartesian coordinate system. Two classes of exact analytic solutions for the steady state are obtained. These solutions may be helpful in understanding the physics involved in the transition from the low-confinement to the high-confinement mode in tokamaks. In particular, they can be employed for stability investigations, which would be of relevance to magnetic confinement systems. Further, the obtained solutions may have several applications in the study of solar photosphere, the solar corona, as well as astrophysical plasmas.

The magnetic field of the Sun and the plasma properties of its atmosphere, such as temperature, density and waves in the solar corona, determine the origin, energetics and evolution of the solar wind. The solar wind comes in three main kinds, as steady fast streams, variable slow flows and transient fast coronal mass ejections, with all being closely associated with the structure and activity of the coronal magnetic field that evolves on a multitude scales. This tutorial paper places emphasis on the observed and measured characteristics of the solar wind sources and their magnetic structure. The boundary conditions in the magnetically closed corona, in the transiently opening corona, and in the lastingly open corona (funnels and holes) will be discussed, and their influences on and consequences for the interplanetary solar wind be addressed. The resulting three-dimensional structure of the solar wind and its evolution over the solar cycle are also briefly discussed.

The solar corona – one of the most spectacular celestial shows and yet one of the most challenging puzzles – exhibits a spectrum of structures related to both the quiet Sun and active regions. In spite of dramatic differences in appearance and physical processes, all these structures share a common origin: they are all related to the solar magnetic field. The origin of the field is beneath the turbulent convection zone, where the magnetic field is not a master but a slave, and one can wonder how much the coronal magnetic field “remembers” its dynamo origin. Surprisingly, it does. We will describe several observational phenomena that indicate a close relationship between coronal and sub-photospheric processes.