scholarly journals Introducing the Sun and SEPs

2021 ◽  
pp. 1-18
Author(s):  
Donald V. Reames
Keyword(s):  
Magnetic Field ◽  
Solar Activity ◽  
Solar Cycle ◽  
Differential Rotation ◽  
Coronal Mass Ejections ◽  
Energetic Particle ◽  
Solar Magnetic Field ◽  
Solar Energetic Particle ◽  
Active Regions ◽  
The Sun

AbstractThe structure of the Sun, with its energy generation and heating, creates convection and differential rotation of the outer solar plasma. This convection and rotation of the ionized plasma generates the solar magnetic field. This field and its variation spawn all of the solar activity: solar active regions, flares, jets, and coronal mass ejections (CMEs). Solar activity provides the origin and environment for both the impulsive and gradual solar energetic particle (SEP) events. This chapter introduces the background environment and basic properties of SEP events, time durations, abundances, and solar cycle variations.

scholarly journals Cosmic-ray propagation around the Sun: investigating the influence of the solar magnetic field on the cosmic-ray Sun shadow

2020 ◽  
Vol 633 ◽  
pp. A83
Author(s):  
J. Becker Tjus ◽  
P. Desiati ◽  
N. Döpper ◽  
H. Fichtner ◽  
J. Kleimann ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Activity ◽  
Solar Cycle ◽  
Cosmic Rays ◽  
Solar Magnetic Field ◽  
Cosmic Ray ◽  
High Energy ◽  
High Solar Activity ◽  
The Sun ◽  
Theoretical Understanding

The cosmic-ray Sun shadow, which is caused by high-energy charged cosmic rays being blocked and deflected by the Sun and its magnetic field, has been observed by various experiments, such as Argo-YBJ, Tibet, HAWC, and IceCube. Most notably, the shadow’s size and depth was recently shown to correlate with the 11-year solar cycle. The interpretation of such measurements, which help to bridge the gap between solar physics and high-energy particle astrophysics, requires a solid theoretical understanding of cosmic-ray propagation in the coronal magnetic field. It is the aim of this paper to establish theoretical predictions for the cosmic-ray Sun shadow in order to identify observables that can be used to study this link in more detail. To determine the cosmic-ray Sun shadow, we numerically compute trajectories of charged cosmic rays in the energy range of 5−316 TeV for five different mass numbers. We present and analyze the resulting shadow images for protons and iron, as well as for typically measured cosmic-ray compositions. We confirm the observationally established correlation between the magnitude of the shadowing effect and both the mean sunspot number and the polarity of the magnetic field during the solar cycle. We also show that during low solar activity, the Sun’s shadow behaves similarly to that of a dipole, for which we find a non-monotonous dependence on energy. In particular, the shadow can become significantly more pronounced than the geometrical disk expected for a totally unmagnetized Sun. For times of high solar activity, we instead predict the shadow to depend monotonously on energy and to be generally weaker than the geometrical shadow for all tested energies. These effects should become visible in energy-resolved measurements of the Sun shadow, and may in the future become an independent measure for the level of disorder in the solar magnetic field.

scholarly journals Low-latitude geomagnetic signatures during major solar energetic particle events of solar cycle-23

2006 ◽  
Vol 24 (12) ◽  
pp. 3569-3583 ◽  
Author(s):  
R. Rawat ◽  
S. Alex ◽  
G. S. Lakhina
Keyword(s):  
Magnetic Field ◽  
Solar Cycle ◽  
Coronal Mass Ejections ◽  
Solar Flares ◽  
Energetic Particle ◽  
Solar Energetic Particle ◽  
Proton Flux ◽  
Main Phase ◽  
Low Latitude ◽  
Solar Cycle 23

Abstract. The frequency of occurrence of disruptive transient processes in the Sun is enhanced during the high solar activity periods. Solar cycle-23 evidenced major geomagnetic storm events and intense solar energetic particle (SEP) events. The SEP events are the energetic outbursts as a result of acceleration of heliospheric particles by solar flares and coronal mass ejections (CMEs). The present work focuses on the geomagnetic variations at equatorial and low-latitude stations during the four major SEP events of 14 July 2000, 8 November 2000, 24 September 2001 and 4 November 2001. These events have been reported to be of discernible magnitude following intense X-ray flares and halo coronal mass ejections. Low-latitude geomagnetic records evidenced an intense main phase development subsequent to the shock impact on the Earth's magnetosphere. Satellite observations show proton-flux enhancements associated with solar flares for all events. Correlation analysis is also carried out to bring out the correspondence between the polar cap magnetic field perturbations, AE index and the variations of low-latitude magnetic field. The results presented in the current study elucidate the varying storm development processes, and the geomagnetic field response to the plasma and interplanetary magnetic field conditions for the energetic events. An important inference drawn from the current study is the close correspondence between the persistence of a high level of proton flux after the shock in some events and the ensuing intense magnetic storm. Another interesting result is the role of the pre-shock southward IMF Bz duration in generating a strong main phase.

scholarly journals The Evolution of the Solar Magnetic Field

2012 ◽  
Vol 10 (H16) ◽  
pp. 86-89 ◽  
Author(s):  
J. Todd Hoeksema
Keyword(s):  
Magnetic Field ◽  
Solar Cycle ◽  
Solar Magnetic Field ◽  
Coronal Holes ◽  
Active Regions ◽  
Statistical Characteristics ◽  
Field Pattern ◽  
Small Scale ◽  
Polar Caps ◽  
Magnetic Elements

AbstractThe almost stately evolution of the global heliospheric magnetic field pattern during most of the solar cycle belies the intense dynamic interplay of photospheric and coronal flux concentrations on scales both large and small. The statistical characteristics of emerging bipoles and active regions lead to development of systematic magnetic patterns. Diffusion and flows impel features to interact constructively and destructively, and on longer time scales they may help drive the creation of new flux. Peculiar properties of the components in each solar cycle determine the specific details and provide additional clues about their sources. The interactions of complex developing features with the existing global magnetic environment drive impulsive events on all scales. Predominantly new-polarity surges originating in active regions at low latitudes can reach the poles in a year or two. Coronal holes and polar caps composed of short-lived, small-scale magnetic elements can persist for months and years. Advanced models coupled with comprehensive measurements of the visible solar surface, as well as the interior, corona, and heliosphere promise to revolutionize our understanding of the hierarchy we call the solar magnetic field.

II. Spots and Intense Flux Tubes

1988 ◽  
Vol 20 (1) ◽  
pp. 58-63
Author(s):  
J.C. Henoux
Keyword(s):  
Magnetic Field ◽  
Solar Activity ◽  
High Resolution ◽  
Solar Magnetic Field ◽  
Solar Physics ◽  
Small Scale ◽  
The Sun ◽  
Flux Tubes ◽  
Flux Concentration ◽  
Scientific Meetings

The development of research on starspots, stellar activity, and the suspected relationship between coronal heating and magnetic field have reenforced the interest of the study of the solar magnetic field and the study of the associated thermodynamic structures. Several proceedings of scientific meetings appeared from 1984 to 1987 (Measurements of Solar Vector Magnetic Fields, 1985 (I); The Hydrodynamics of the Sun, 1984 (II); High Resolution in Solar Physics, 1985 (III); Theoritical Problems in High Resolution Solar Physics, 1985 (IV); Small Scale Magnetic Flux Concentration in the Solar Atmosphere, 1986 (V)). The finding that the solar irradiance in affected by solar activity has renewed interest in photometry of sunspots and faculae. Sunspots have been used for investigating solar differential and meridional motions. Some results are also found in Section III.

scholarly journals Reconstruction of Sun-as-Star Magnetic Field Structure and Evolution Using Filament Observations

1998 ◽  
Vol 167 ◽  
pp. 493-496
Author(s):  
Dmitri I. Ponyavin
Keyword(s):  
Magnetic Field ◽  
Solar Cycle ◽  
Large Scale ◽  
Solar Magnetic Field ◽  
Close Association ◽  
Field Structure ◽  
The Sun ◽  
Magnetic Field Structure ◽  
Large Scale Magnetic Field ◽  
Field Organization

AbstractA technique is used to restore the magnetic field of the Sun viewed as star from the filament distribution seen on Hα photographs. For this purpose synoptic charts of the large-scale magnetic field reconstructed by the McIntosh method have been compared with the Sun-asstar solar magnetic field observed at Stanford. We have established a close association between the Sun-as-star magnetic field and the mean magnetic field inferred from synoptic magnetic field maps. A filtering technique was applied to find correlations between the Sun-as-star and large-scale magnetic field distributions during the course of a solar cycle. The correlations found were then used to restore the Sun-as-star magnetic field and its evolution in the late 1950s and 1960s, when such measurements of the field were not being made. A stackplot display of the inferred data reveals large-scale magnetic field organization and evolution. Patterns of the Sun-as-star magnetic field during solar cycle 19 were obtained. The proposed technique can be useful for studying the solar magnetic field structure and evolution during times with no direct observations.

scholarly journals THE STRUCTURE OF THE SOLAR WIND IN THE HELIOSPHERE DEPENDING ON THE PHASE OF THE SOLAR CYCLE: LARGE-SCALE DYNAMICS OF THE HELIOSPHERIC CURRENT SHEET

2019 ◽  
Vol 47 (1) ◽  
pp. 85-87
Author(s):  
E.V. Maiewski ◽  
R.A. Kislov ◽  
H.V. Malova ◽  
O.V. Khabarova ◽  
V.Yu. Popov ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Solar Activity ◽  
Solar Cycle ◽  
Current Sheet ◽  
Heliospheric Current Sheet ◽  
High Solar Activity ◽  
The Sun ◽  
High Latitudes ◽  
The Magnetic Field

A stationary axisymmetric MHD model of the solar wind has been constructed, which allows us to study the spatial distribution of the magnetic field and plasma characteristics at radial distances from 20 to 400 radii of the Sun at almost all heliolatitudes. The model takes into account the changes in the magnetic field of the Sun during a quarter of the solar cycle, when the dominant dipole magnetic field is replaced by a quadrupole. Selfconsistent solutions for the magnetic and velocity fields, plasma concentration and current density of the solar wind depending on the phase of the solar cycle are obtained. It is shown that during the domination of the dipole magnetic component in the solar wind heliospheric current sheet (HCS) is located in the equatorial plane, which is a part of the system of radial and transverse currents, symmetrical in the northern and southern hemispheres. As the relative contribution of the quadrupole component to the total magnetic field increases, the shape of the HCS becomes conical; the angle of the cone gradually decreases, so that the current sheet moves entirely to one of the hemispheres. At the same time, at high latitudes of the opposite hemisphere, a second conical HCS arises, the angle of which increases. When the quadrupole field becomes dominant (at maximum solar activity), both HCS lie on conical surfaces inclined at an angle of 35 degrees to the equator. The model describes the transition from the fast solar wind at high latitudes to the slow solar wind at low latitudes: a relatively gentle transition in the period of low solar activity gives way to more drastic when high solar activity. The model also predicts an increase in the steepness of the profiles of the main characteristics of the solar wind with an increase in the radial distance from the Sun. Comparison of the obtained dependences with the available observational data is discussed.

scholarly journals Variable Ion Compositions of Solar Energetic Particle Events in the Inner Heliosphere: A Field Line Braiding Model with Compound Injections

2022 ◽  
Vol 924 (1) ◽  
pp. 22
Author(s):  
Fan Guo ◽  
Lulu Zhao ◽  
Christina M. S. Cohen ◽  
Joe Giacalone ◽  
R. A. Leske ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Energetic Particle ◽  
Radial Distance ◽  
Solar Energetic Particle ◽  
The Sun ◽  
Ion Composition ◽  
Source Regions ◽  
Solar Energetic Particle Events ◽  
Composition Ratios ◽  
Inner Heliosphere

Abstract We propose a model for interpreting highly variable ion composition ratios in solar energetic particle (SEP) events recently observed by the Parker Solar Probe (PSP) at 0.3–0.45 au. We use numerical simulations to calculate SEP propagation in a turbulent interplanetary magnetic field with a Kolmogorov power spectrum from large scales down to the gyration scale of energetic particles. We show that when the source regions of different species are offset by a distance comparable to the size of the source regions, the observed energetic particle composition He/H can be strongly variable over more than two orders of magnitude, even if the source ratio is at the nominal value. Assuming a 3He/4He source ratio of 10% in impulsive 3He-rich events and the same spatial offset of the source regions, the 3He/4He ratio at observation sites also vary considerably. The variability of the ion composition ratios depends on the radial distance, which can be tested by observations made at different radial locations. We discuss the implications of these results on the variability of ion composition of impulsive events and on further PSP and Solar Orbiter observations close to the Sun.

scholarly journals A Turbulent History

2021 ◽  
pp. 19-48
Author(s):  
Donald V. Reames
Keyword(s):  
Shock Waves ◽  
Coronal Mass Ejections ◽  
Energetic Particle ◽  
Electron Beams ◽  
Diffusion Theory ◽  
Plasma Temperature ◽  
Solar Energetic Particle ◽  
The Sun ◽  
Suprathermal Ions ◽  
And Diffusion

AbstractLarge solar energetic-particle (SEP) events are clearly associated in time with eruptive phenomena on the Sun, but how? When large SEP events were first observed, flares were the only visible candidate, and diffusion theory was stretched to explain how the particles could spread through space, as widely as observed. The observation of coronal mass ejections (CMEs), and the wide, fast shock waves they can drive, provided better candidates later. Then small events were found with 1000-fold enhancements in 3He/4He that required a different kind of source—should we reconsider flares, or their open-field cousins, solar jets? The 3He-rich events were soon associated with the electron beams that produce type III radio bursts. It seems the radio astronomers knew of both SEP sources all along. Sometimes the distinction between the sources is blurred when shocks reaccelerate residual 3He-rich impulsive suprathermal ions. Eventually, however, we would even begin to measure the source-plasma temperature that helps to better distinguish the SEP sources.

scholarly journals Distinguishing the Sources

2021 ◽  
pp. 49-69
Author(s):  
Donald V. Reames
Keyword(s):  
Magnetic Field ◽  
Energetic Particle ◽  
Solar Energetic Particle ◽  
Active Regions ◽  
High Energy ◽  
Injection Time ◽  
Closed Loops ◽  
Compact Source ◽  
Time Profiles ◽  
Onset Timing

AbstractOur discussion of history has covered many of the observations that have led to the ideas of acceleration by shock waves or by magnetic reconnection in gradual and impulsive solar energetic particle (SEP) events, respectively. We now present other compelling observations, including onset timing, SEP-shock correlations, injection time profiles, high-energy spectral knees, e/p ratios, and intensity dropouts caused by a compact source, that have helped clarify these acceleration mechanisms and sources. However, some of the newest evidence now comes from source-plasma temperatures. In this and the next two chapters, we will find that impulsive events come from solar active regions at ≈ 3 MK, controlling ionization states Q, hence A/Q, and, in most gradual events, shocks accelerate ambient coronal material from ≤1.6 MK. When SEPs are trapped on closed loops they supply the energy for flares. In addition to helping to define their own origin, SEPs also probe the structure of the interplanetary magnetic field.

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