Solar Physics

Lopin, Igor

2023 Solar Physics

doi: 10.1007/s11207-023-02197-4

Slow-mode standing waves are examined in the model of a bent magnetic slab with a plasma flow directed along curved magnetic field lines. The dispersion relation is obtained and studied both numerically and analytically regarding the principal slow mode. It is found that flow decreases the longitudinal oscillating motions and increases the radial kink-like motions, both produced by the principal slow mode. This feature may result in the development of Kelvin-Helmholtz instability when the flow speed exceeds the critical value, and this threshold depends on the azimuthal number m\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$m$\end{document}. When flow exists, a quasi-stationary wave structure that satisfies the footpoint boundary conditions has the form of a propagating wave modulated by a sinusoidal envelope. The corresponding eigenfrequencies of oscillations are found to decrease with increasing flow speed until u<cTi\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$u< c_{Ti}$\end{document}. The results obtained are used for seismological estimation of a plasma flow speed in coronal fan loops experiencing slow mode oscillations.

Nagovitsyn, Yury; Pevtsov, Alexei; Osipova, Aleksandra

2023 Solar Physics

doi: 10.1007/s11207-023-02204-8

It is shown that the average meridional velocities of sunspot groups linearly depend on their average longitudinal velocities (solar rotation) with a high correlation coefficient of -0.95. The relationship differs for small, short-lived and large, long-lived groups. The meridional motions of sunspots do not have any pronounced global distribution law with latitude, but depend on their individual longitudinal velocities in a rotating coordinate system close to the Carrington one. The found relations indicate that the Coriolis force may play a role in driving the meridional motions of sunspot groups.

Skumanich, Andrew

2023 Solar Physics

doi: 10.1007/s11207-023-02199-2

This memoire covers my life history starting with my family’s background and their immigration to the US. It continues with my childhood, my early education, and my introduction to science. It then covers my professional research career including a variety of institutions and areas of physics ending ultimately in solar physics.

Izquierdo-Guzmán, I.; González-Avilés, J. J.; Guzmán, F. S.

2023 Solar Physics

doi: 10.1007/s11207-023-02202-w

We simulate the evolution of reconnection in solar flares to study the influence of magnetic-field strength and thermal conduction on the dynamics of the magnetic-reconnection and energy-conversion processes. For this, we solve the 2.5D resistive magnetohydrodynamics (MHD) equations with thermal conduction on a domain that contains the chromosphere–corona interface. The flare is triggered at a null point where a Gaussian resistivity distribution is maximum, and further evolution is tracked. The parameter space considers magnetic-field strength [B0\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$B_{0}$\end{document}] between 22 G and 50 G, and thermal conductivity [κ\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$\kappa $\end{document}] in the range from zero to 10−11\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$10^{-11}$\end{document} W m−1K−7/2\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$^{-7/2}$\end{document}. In this parameter space, we find that the magnetic field determines the reconnection rate, which can change by a 100% in the range of B0\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$B_{0}$\end{document}, whereas thermal conduction can induce a rate change of at most 10%. We also measure the evolution of magnetic, internal, and kinetic energies in a region just above the reconnection point and measure their interplay. For all simulations, magnetic energy dominates initially and relaxes on a time scale of about 20 seconds. In this interval, the magnetic energy drops by ≈50%\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$\approx 50\%$\end{document}, whereas the internal energy grows by ≈100%\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$\approx 100\%$\end{document}. During the process, part of the energy becomes kinetic, which pushes the reconnection jet upwards and is bigger for the bigger B0\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$B_{0}$\end{document} and smaller κ\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$\kappa $\end{document}.

Calisir, M. Ali; Yazici, H. Tayfun; Kilcik, Ali; Yurchyshyn, Vasyl

2023 Solar Physics

doi: 10.1007/s11207-023-02198-3

We present a comprehensive analysis of the physical parameters and relationships of umbral dots (UDs), which assists in our understanding of the physical properties of the Sun. This study is based on a detailed analysis of UDs detected in 12 umbras belonging to 10 different sunspots using high-resolution data recorded by the Goode Solar Telescope at Big Bear Solar Observatory. We obtained the physical parameters (total intensity, diameter, eccentricity, lifetime, and dynamic velocity) of each UD and calculated correlation coefficients using linear and nonlinear approaches to reveal the relationships between these parameters. We found that: i) The diameter of UDs vary between 92.2 km and 246.5 km, the eccentricity varies between 0.02 and 0.65, the lifetimes of UDs vary from 0.75 to 120.00 min and the dynamic velocities vary from 0.01 km s−1 to 3.80 km s−1. ii) The intensity–diameter and diameter–eccentricity relationships show the highest degree of correlation, while the lowest linear correlation was obtained for the diameter–lifetime relationship and the lowest nonlinear correlation was obtained for the eccentricity–lifetime relationship. iii) In general, the nonlinear correlation coefficients are higher than the linear correlation without exception. iv) The linear and nonlinear correlation coefficients are very close to each other in the case of the diameter–eccentricity relation. v) While the average diameter, intensity, and eccentricity are related to the umbral area, the average lifetime and dynamic velocity of UDs are not dependent on the umbral area.

Kotzé, Pieter

2023 Solar Physics

doi: 10.1007/s11207-023-02203-9

An analysis has been made of the behaviour of the 27-day and 13.5-day periodicities in proton, C, and O galactic-cosmic-ray (GCR) particles at different energies as observed by the Advanced Composition Explorer (ACE) and SOHO (Solar and Heliospheric Observatory) spacecraft during both Solar Cycles 23 and 24. In addition, the behaviour of the 27-day and 13.5-day periods in the solar-wind-modulation parameter ζ\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$\zeta $\end{document} = BIMF × VSW has been investigated during the same time interval to determine the existence of a possible solar-polarity dependence. Ground-based neutron-monitor (NM) observations, corresponding to different rigidity cutoff [RC] parameters, were also studied to determine the temporal behaviour of both the 27-day and 13.5-day periods during Cycles 23 and 24, revealing a statistically significant solar-polarity correlation. The Lomb–Scargle periodogram technique has been employed to extract spectral information from the above-mentioned observations for each individual year from 2001 – 2009 (Cycle 23) and 2010 – 2019 (Cycle 24). Daily mean energetic ACE and SOHO particle measurements are used to identify how both the 27-day and 13.5-day periodicities vary during each individual year during these cycles as a function of particle mean energy. This spectral analysis of proton, C, and O galactic-cosmic-particle data at different energies revealed that both the 27-day and 13.5-day periods are stronger during the minimum of Solar Cycle 24/25 when A > 0 (solar dipole pointing North) in comparison to the minimum of Cycle 23/24 when A < 0 (solar dipole pointing South) at certain energy levels. This showed a particularly strong energy-dependent behaviour for both periodicities. This article reports for the first time an annual time- and energy-dependent behaviour of both the 27-day and 13.5-day periodicities in daily-mean galactic cosmic particles observed by spacecraft and ground-based neutron monitors during consecutive Solar Cycles 23 and 24, corresponding to opposite solar-magnetic-field orientations. Periodicity behaviour in heliospheric solar-wind data corroborate these results in general.

Mikhalyaev, B. B.; Derteev, S. B.; Shividov, N. K.; Sapraliev, M. E.; Bembitov, D. B.

2023 Solar Physics

doi: 10.1007/s11207-023-02196-5

In this article we study the properties of acoustic waves in the rarefied high-temperature plasma of the solar corona, assuming that the heating and cooling of the plasma has a well-defined description. We consider a constant heating function supposing that the heating processes are generally established. For the radiative-loss function, a number of values are taken, which have been found using the CHIANTI code. On their basis, an analytical expression of the function in the form of a cubic interpolation has been worked out. We analyze the dispersion relation for linear acoustic waves. The heating and cooling function, introduced along with the classical expression of the thermal conductivity, allows us to obtain some specific results about their properties. In other words, a model of non-adiabatic acoustic waves with field-aligned thermal conduction, CHIANTI-based radiative cooling and constant heating function is constructed. Using the available observational data on compression waves, we can set the problem of finding the parameters of the coronal plasma. The model allows to specify the temperature range at which the thermal instability of waves is possible and to draw some conclusions about their damping. The coronal temperatures considered can be divided into intervals from 0.5 to 0.98 MK and from 4.57 to 8.38 MK, where the radiation function increases, and intervals from 0.98 to 4.57 MK and from 8.38 to 10 MK, where the radiation function decreases. With constant heating, at large wavelengths, acoustic waves can be unstable in the decreasing interval from 1.38 to 3.15 MK. In the increasing intervals, they may have a zero real part of the oscillation frequency and thus become non-propagating, also subject to a large wavelength. In some cases, the plasma density has a significant effect on the damping of acoustic oscillations due to heating and cooling. A change in density within the same order can lead to the fact that the heating and cooling effects prevail over the effect of thermal conductivity on long-wave perturbations.

Schrijver, C. J. (Karel)

2023 Solar Physics

doi: 10.1007/s11207-023-02200-y

This invited memoir looks back on my scientific career that straddles the solar and stellar branches of astrophysics, with sprinklings of historical context and personal opinion. Except for a description of my life up to my Ph.D. phase, the structure is thematic rather than purely chronological, focusing on those topics that I worked on throughout substantial parts of my life: stars like the Sun and the Sun-as-a-star, surface field evolution, coronal structure and dynamics, heliophysics education, and space weather. Luck and a broadly inquisitive frame of mind shaped a fortunate life on two continents, taking me from one amazing mentor, colleague, and friend to another, working in stimulating settings to interpret data from state-of-the-art space observatories.

Richardson, I. G.; St. Cyr, O. C.; Burkepile, J. T.; Xie, H.; Thompson, B. J.

2023 Solar Physics

doi: 10.1007/s11207-023-02192-9

We report on the first comprehensive study of the coronal mass ejections (CMEs) associated with ∼25 MeV\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$\sim 25\text{ MeV}$\end{document} solar energetic-proton (SEP) events in 1980 – 2013 observed in the low/inner corona by the Mauna Loa Solar Observatory (MLSO) Mk3 and Mk4 coronameters. Where possible, these observations are combined with space-based observations from the Solar Maximum Mission C/P, P78-1 SOLWIND, or SOHO/LASCO coronagraphs. The aim of the study is to understand directly measured (rather than inferred from proxies) CME motions in the low to midcorona and their association with SEP acceleration, and hence attempt to identify early signatures that are characteristic of SEP acceleration in ground-based CME observations that may be used to warn of impending SEP events. Although we find that SEP events are associated with CMEs that are on average faster and wider than typical CMEs observed by MLSO, a major challenge turns out to be determining reliable estimates of the CME dynamics in the low corona from the 3-min cadence Mk3/4 observations since different analysis techniques can produce inconsistent results. This complicates the assessment of what early information on a possible SEP event is available from these low-coronal observations.

Owens, Mathew J.; Lockwood, Mike; Barnard, Luke A.; Yardley, Stephanie L.; Hietala, Heli; LaMoury, Adrian T.; Vuorinen, Laura

2023 Solar Physics

doi: 10.1007/s11207-023-02193-8

Earth’s orbit and rotation produces systematic variations in geomagnetic activity, most notably via the changing orientation of the dayside magnetospheric magnetic field with respect to the heliospheric magnetic field (HMF). Aside from these geometric effects, it is generally assumed that the solar wind in near-Earth is uniformly sampled. But systematic changes in the intrinsic solar wind conditions in near-Earth space could arise due to the annual variations in Earth heliocentric distance and heliographic latitude. In this study, we use 24 years of Advanced Composition Explorer data to investigate the annual variations in the scalar properties of the solar wind, namely the solar wind proton density, the radial solar wind speed and the HMF intensity. All parameters do show some degree of systematic annual variation, with amplitudes of around 10 to 20%. For HMF intensity, the variation is in phase with the Earth’s heliocentric distance variation, and scaling observations for distance largely explains the observed variation. For proton density and solar wind speed, however, the phase of the annual variation is inconsistent with Earth’s heliocentric distance. Instead, we attribute the variations in speed and density to Earth’s heliographic latitude variation and systematic sampling of higher speed solar wind at higher latitudes. Indeed, these annual variations are most strongly ordered at solar minimum. Conversely, combining scalar solar wind parameters to produce estimates of dynamic pressure and potential power input to the magnetosphere results in solar maximum exhibiting a greater annual variation, with an amplitude of around 40%. This suggests Earth’s position in the heliosphere makes a significant contribution to annual variations in space weather, in addition to the already well-studied geometric effects.

Javaraiah, J.

2023 Solar Physics

doi: 10.1007/s11207-023-02201-x

Study of the tilt angles of solar bipolar magnetic regions is important because the tilt angles have an important role in the solar dynamo. We analyzed the data on tilt angles of sunspot groups measured at the Mt. Wilson Observatory (MWOB) during the period 1917 – 1986 and Kodaikanal Observatory (KOB) during the period 1906 – 1986. We binned the daily tilt-angle data during each of the Solar Cycles 15 – 21 into different 5∘\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$5^{\circ }$\end{document}-latitude intervals and calculated the mean value of the tilt angles in each latitude interval and the corresponding standard error. We fitted these binned data to Joy’s law (increase of the tilt angle with latitude), i.e. the linear relationship between tilt angle and latitude of an active region. The linear least-square fit calculations were carried out by taking into account the uncertainties in both the abscissa (latitude) and ordinate (mean tilt angle). The calculations were carried out by using both the tilt-angle and area-weighted tilt-angle data in the whole sphere, northern hemisphere, and southern hemisphere during the whole period and during each individual solar cycle. We find a significant difference (north–south asymmetry) between the slopes of Joy’s laws recovered from northern and southern hemispheres’ whole-period MWOB data of area-weighted tilt angles. Only the slope obtained from the southern hemisphere’s MWOB data of a solar cycle is found to be reasonably well anticorrelated to the amplitude of the solar cycle. In the case of area-weighted tilt-angle data, a good correlation is found between the north–south asymmetry in the slope of a solar cycle and the amplitude of the solar cycle. The corresponding best-fit linear equations are found to be statistically significant.