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Register a new userGround-based Observations of the Solar Sources of Space Weather (Invited Review)
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Monitoring of the Sun and its activity is a task of growing importance in the frame of space weather research and awareness. Major space weather disturbances at Earth have their origin in energetic outbursts from the Sun: solar flares, coronal mass ejections and associated solar energetic particles. In this review we discuss the importance and complementarity of ground-based and space-based observations for space weather studies. The main focus is drawn on ground-based observations in the visible range of the spectrum, in particular in the diagnostically manifold H$alpha$ spectral line, which enables us to detect and study solar flares, filaments, filament eruptions, and Moreton waves. Existing H$alpha$ networks such as the GONG and the Global High-Resolution H$alpha$ Network are discussed. As an example of solar observations from space weather research to operations, we present the system of real-time detection of H$alpha$ flares and filaments established at Kanzelhohe Observatory (KSO; Austria) in the frame of the ESA Space Situational Awareness programme. During the evaluation period 7/2013 - 11/2015, KSO provided 3020 hours of real-time H$alpha$ observations at the SWE portal. In total, 824 H$alpha$ flares were detected and classified by the real-time detection system, including 174 events of H$alpha$ importance class 1 and larger. For the total sample of events, 95% of the automatically determined flare peak times lie within $pm$5 min of the values given in the official optical flares reports (by NOAA and KSO), and 76% of the start times. The heliographic positions determined are better than $pm$5$^circ$. The probability of detection of flares of importance 1 or larger is 95%, with a false alarm rate of 16%. These numbers confirm the high potential of automatic flare detection and alerting from ground-based observatories.
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The solar group at the National Astronomical Observatory of Japan is conducting synoptic solar observations with the Solar Flare Telescope. While it is a part of a long-term solar monitoring, contributing to the study of solar dynamo governing solar activity cycles, it is also an attempt at contributing to space weather research. The observations include imaging with filters for H$alpha$, Ca K, G-band, and continuum, and spectropolarimetry at the wavelength bands including the He I 1083.0 nm / Si I 1082.7 nm and the Fe I 1564.8 nm lines. Data for the brightness, Doppler signal, and magnetic field information of the photosphere and the chromosphere are obtained. In addition to monitoring dynamic phenomena like flares and filament eruptions, we can track the evolution of the magnetic fields that drive them on the basis of these data. Furthermore, the magnetic field in solar filaments, which develops into a part of the interplanetary magnetic cloud after their eruption and occasionally hits the Earth, can be inferred in its pre-eruption configuration. Such observations beyond mere classical monitoring of the Sun will hereafter become crucially important from the viewpoint of the prediction of space weather phenomena. The current synoptic observations with the Solar Flare Telescope is considered to be a pioneering one for future synoptic observations of the Sun with advanced instruments.
In this article, we insist on the importance and the challenges of the prediction of solar eruptive phenomena including flares, coronal mass ejections (CME), and filament eruptions fully based on the ground-based telescopes. It is true that satellites data are indispensable for the space weather prediction, but they are vulnerable to the space weather effects. Therefore, the ground-based telescopes can be complementary to them from the viewpoint of space weather prediction. From this view point, one possible new flare prediction method that makes use of H-alpha, red wings, and blue wings images obtained by the SDDI/SMART, the ground-based telescope at Hida Observatory, is presented. And in order to show the possibility for the actual operation based on that method, the recent progress of CHAIN project, the international observation network, is mentioned in terms of their outcomes and capacity buildings.
The Suns outer atmosphere is heated to temperatures of millions of degrees, and solar plasma flows out into interplanetary space at supersonic speeds. This paper reviews our current understanding of these interrelated problems: coronal heating and the acceleration of the ambient solar wind. We also discuss where the community stands in its ability to forecast how variations in the solar wind (i.e., fast and slow wind streams) impact the Earth. Although the last few decades have seen significant progress in observations and modeling, we still do not have a complete understanding of the relevant physical processes, nor do we have a quantitatively precise census of which coronal structures contribute to specific types of solar wind. Fast streams are known to be connected to the central regions of large coronal holes. Slow streams, however, appear to come from a wide range of sources, including streamers, pseudostreamers, coronal loops, active regions, and coronal hole boundaries. Complicating our understanding even more is the fact that processes such as turbulence, stream-stream interactions, and Coulomb collisions can make it difficult to unambiguously map a parcel measured at 1 AU back down to its coronal source. We also review recent progress -- in theoretical modeling, observational data analysis, and forecasting techniques that sit at the interface between data and theory -- that gives us hope that the above problems are indeed solvable.
We review the presence and signatures of the non-equilibrium processes, both non-Maxwellian distributions and non-equilibrium ionization, in the solar transition region, corona, solar wind, and flares. Basic properties of the non-Maxwellian distributions are described together with their influence on the heat flux as well as on the rates of individual collisional processes and the resulting optically thin synthetic spectra. Constraints on the presence of high-energy electrons from observations are reviewed, including positive detection of non-Maxwellian distributions in the solar corona, transition region, flares, and wind. Occurrence of non-equilibrium ionization is reviewed as well, especially in connection to hydrodynamic and generalized collisional-radiative modelling. Predicted spectroscopic signatures of non-equilibrium ionization depending on the assumed plasma conditions are summarized. Finally, we discuss the future remote-sensing instrumentation that can be used for detection of these non-equilibrium phenomena in various spectral ranges.
Total solar irradiance (TSI) has been monitored from space since 1978. The measurements show a prominent variability in phase with the solar cycle, as well as fluctuations on timescales shorter than a few days. However, the measurements were done by multiple and usually relatively short-lived missions making the possible long-term trend in the TSI highly uncertain. While the variability in the UV irradiance is clearly in-phase with the solar cycle, the phase of the variability in the visible range has been debated. In this paper, we aim at getting an insight into the long-term trend of TSI since 1996 and the phase of the solar irradiance variations in the visible part of the spectrum. We use independent ground-based full-disc photometric observations in Ca~II~K and continuum from the Rome and San Fernando observatories to compute the TSI since 1996. We follow the empirical San Fernando approach based on the photometric sum index. We find a weak declining trend in the TSI of -7.8$^{+4.9}_{-0.8}times10^{-3}$ Wm$^{-2}$y$^{-1}$ between the 1996 and 2008 activity minima, while between 2008 and 2019 the reconstructed TSI shows no trend to a marginally decreasing (but statistically insignificant) trend of -0.1$^{+0.25}_{-0.02}times10^{-3}$ Wm$^{-2}$y$^{-1}$. The reference TSI series used for the reconstruction does not significantly affect the determined trend. The variation in the blue continuum (409.2 nm) is rather flat, while the variation in the red continuum (607.1 nm) is marginally in anti-phase, although this result is extremely sensitive to the accurate assessment of the quiet Sun level in the images. These results provide further insights into the long-term variation of the total solar irradiance. The amplitude of the variations in the visible is below the uncertainties of the processing, which prevents an assessment of the phase of the variations.
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