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  • Uncertainty Estimates of Solar Wind Prediction Using HMI Photospheric Vector and Spatial Standard Deviation Synoptic Maps
    Sol. Phys. (IF 2.503) Pub Date : 2020-10-08
    B. Poduval, G. Petrie, L. Bertello

    The solar wind prediction is based on the Wang and Sheeley (Astrophys. J. 365, 372, 1990) empirical relationship between the solar wind speed observed at 1 AU and the rate of magnetic flux tube expansion (FTE) between the photosphere and the inner corona, where the FTE is computed using coronal models (e.g. the current sheet source surface (CSSS) and the potential field source surface models). These

  • Probabilistic Inversions for Time–Distance Helioseismology
    Sol. Phys. (IF 2.503) Pub Date : 2020-10-07
    Jason Jackiewicz

    Time–distance helioseismology is a set of powerful tools to study localized features below the Sun’s surface. Inverse methods are needed to robustly interpret time–distance measurements, with many examples in the literature. However, techniques that utilize a more statistical approach to inferences, and that are broadly used in the astronomical community, are less-commonly found in helioseismology

  • The Solar Event of 14 – 15 July 2012 and Its Geoeffectiveness
    Sol. Phys. (IF 2.503) Pub Date : 2020-10-06
    Agnieszka Gil, Renata Modzelewska, Szczepan Moskwa, Agnieszka Siluszyk, Marek Siluszyk, Anna Wawrzynczak, Mariusz Pozoga, Lukasz Tomasik

    During Solar Cycle 24, which started at the end of 2008, the Sun was calm, and there were not many spectacular geoeffective events. In this article, we analyze the geomagnetic storm that happened on 15 July 2012 during the 602nd anniversary of the Polish Battle of Grunwald, thus we propose this event to be called the “Battle of Grunwald Day Storm”. According to NOAA scale, it was a G3 geomagnetic storm

  • Predicting the Shape of Solar Cycle 25 Using a Similar-Cycle Method
    Sol. Phys. (IF 2.503) Pub Date : 2020-10-06
    Zhanle Du

    A similar-cycle method is applied in predicting the shape of Solar Cycle 25, through a more scientific definition to select similar cycles. Using the current solar minimum \(R_{\mathrm{min}}(25)\) as a reference, the six most similar cycles to Solar Cycle 25 are found to be Cycles 24, 15, 12, 14, 17, and 10 (in that order). The monthly values of sunspot-number series for the whole of Cycle 25 are predicted

  • Development of a Method for Determining the Search Window for Solar Flare Neutrinos
    Sol. Phys. (IF 2.503) Pub Date : 2020-10-06
    K. Okamoto, Y. Nakano, S. Masuda, Y. Itow, M. Miyake, T. Terasawa, S. Ito, M. Nakahata

    Neutrinos generated during solar flares remain elusive. However, after 50 years of discussion and search, the potential knowledge unleashed by their discovery keeps the search crucial. Neutrinos associated with solar flares provide information on otherwise poorly known particle acceleration mechanisms during a solar flare. For neutrino detectors, the separation between atmospheric neutrinos and solar

  • Identifying Flux Rope Signatures Using a Deep Neural Network
    Sol. Phys. (IF 2.503) Pub Date : 2020-10-06
    Luiz F. G. dos Santos, Ayris Narock, Teresa Nieves-Chinchilla, Marlon Nuñez, Michael Kirk

    Among the current challenges in space weather, one of the main ones is to forecast the internal magnetic configuration within interplanetary coronal mass ejections (ICMEs). The classification of such an arrangement is essential to predict geomagnetic disturbances. When a monotonic and coherent magnetic configuration is observed, it is associated with the result of a spacecraft crossing a large flux

  • Solar Flare Build-Up and Release
    Sol. Phys. (IF 2.503) Pub Date : 2020-10-06
    Hugh S. Hudson

    Flares and coronal mass ejections should follow a pattern of build-up and release, with the build-up phase understood as the gradual addition of stress to the coronal magnetic field. Recently Hudson (Mon. Not. Roy. Astron. Soc. 491, 4435, 2020) presented observational evidence for this pattern in two isolated active regions from 1997 and 2006, finding a correlation between the waiting time after the

  • CMEchaser, Detecting Line-of-Sight Occultations Due to Coronal Mass Ejections
    Sol. Phys. (IF 2.503) Pub Date : 2020-10-06
    Golam Shaifullah, Caterina Tiburzi, Pietro Zucca

    We present a python-based tool to detect the occultation of back-ground sources by foreground solar coronal mass ejections. The tool takes as input standard celestial coordinates of the source and translates those to the helioprojective plane, and is thus well suited for use with a wide variety of background astronomical sources. This tool provides an easy means to search through a large archival dataset

  • Three-Dimensional Simulations of Solar Wind Preconditioning and the 23 July 2012 Interplanetary Coronal Mass Ejection
    Sol. Phys. (IF 2.503) Pub Date : 2020-09-29
    Ravindra T. Desai, Han Zhang, Emma E. Davies, Julia E. Stawarz, Joan Mico-Gomez, Pilar Iváñez-Ballesteros

    Predicting the large-scale eruptions from the solar corona and their propagation through interplanetary space remains an outstanding challenge in solar- and helio-physics research. In this article, we describe three-dimensional magnetohydrodynamic simulations of the inner heliosphere leading up to and including the extreme interplanetary coronal mass ejection (ICME) of 23 July 2012, developed using

  • Solar wind transient currents: statistical properties and impact on Earth’s magnetosphere
    Sol. Phys. (IF 2.503) Pub Date : 2020-09-24
    Robert Newman, Dmitri Vainchtein, Anton Artemyev

    Solar wind discontinuities carry intense transient currents and significantly contribute to the turbulent spectrum and plasma heating. The most-investigated characteristics of these discontinuities are the magnetic field configuration and the current density, whereas plasma characteristics attract less attention. In this study, we utilize eight years of ARTEMIS spacecraft observations in the solar

  • Revisiting the Amplitude of Solar Cycle 9: The Case of Sunspot Observations by W.C. Bond
    Sol. Phys. (IF 2.503) Pub Date : 2020-09-22
    V. M. S. Carrasco, M. C. Gallego, R. Arlt, J. M. Vaquero

    William Cranch Bond, director of the Harvard College Observatory in mid-19th century, carried out detailed sunspot observations during the period 1847–1849. We highlight Bond was the observer with the highest daily number of sunspot groups observed in Solar Cycle 9 recording 18 groups on 26 December 1848 according to the current sunspot group database. However, we have detected significant mistakes

  • Twin Null-Point-Associated Major Eruptive Three-Ribbon Flares with Unusual Microwave Spectra
    Sol. Phys. (IF 2.503) Pub Date : 2020-09-22
    V. V. Grechnev, N. S. Meshalkina, A. M. Uralov, A. A. Kochanov, S. V. Lesovoi, I. I. Myshyakov, V. I. Kiselev, D. A. Zhdanov, A. T. Altyntsev, M. V. Globa

    On 23 July 2016 after 05:00 UTC, the first 48-antenna stage of the Siberian Radioheliograph detected two flares, M7.6 and M5.5, which occurred within half an hour in the same active region. Their multi-instrument analysis reveals the following. The microwave spectra were flattened at low frequencies and the spectrum of the stronger burst had a lower turnover frequency. Each flare was eruptive, emitted

  • Analysis of Large Deflections of Prominence–CME Events during the Rising Phase of Solar Cycle 24
    Sol. Phys. (IF 2.503) Pub Date : 2020-09-09
    M. Valeria Sieyra, Mariana Cécere, Hebe Cremades, Francisco A. Iglesias, Abril Sahade, Marilena Mierla, Guillermo Stenborg, Andrea Costa, Matthew J. West, Elke D’Huys

    The analysis of the deflection of coronal mass ejection (CME) events plays an important role in the improvement of the forecasting of their geo-effectiveness. Motivated by the scarcity of comprehensive studies of CME events with a focus on the governing conditions that drive deflections during their early stages, we performed an extensive analysis of 13 CME events that exhibited large deflections during

  • Forecasting the Daily 10.7 cm Solar Radio Flux Using an Autoregressive Model
    Sol. Phys. (IF 2.503) Pub Date : 2020-09-08
    Zhanle Du

    As an important proxy of the solar extreme ultraviolet radiation from the upper chromosphere and lower corona, the 10.7 cm solar radio flux (F10.7) has a wide range of applications in models of the thermosphere and ionosphere. Forecasting F10.7 has already become a routine business in space weather services. In this study, we analyzed the predictive power of autoregressive (AR) models with orders \(p=15\) – 1005

  • Estimate of Plasma Temperatures Across a CME-Driven Shock from a Comparison Between EUV and Radio Data
    Sol. Phys. (IF 2.503) Pub Date : 2020-09-08
    Federica Frassati; Salvatore Mancuso; Alessandro Bemporad

    In this work, we analyze the evolution of an EUV wave front associated with a solar eruption that occurred on 30 October 2014, with the aim of investigating, through differential emission measure (DEM) analysis, the physical properties of the plasma compressed and heated by the accompanying shock wave. The EUV wave was observed by the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory

  • The Interconnection between the Periodicities of Solar Wind Parameters Based on the Interplanetary Magnetic Field Polarity (1967–2018): A Cross Wavelet Analysis
    Sol. Phys. (IF 2.503) Pub Date : 2020-09-07
    M. A. El-Borie; A. M. El-Taher; A. A. Thabet; A. A. Bishara

    In this article, we have examined the possible interconnection and phase asynchrony between the periodicities of solar wind parameters (solar wind velocity \(V\), plasma density \(N\), and dynamic pressure \(P\)), and the interplanetary magnetic field (IMF) magnitude \(B\), taking into account the polarity state, toward (\(T\)) and away (\(A\)) from the Sun, of the IMF. For this purpose, the daily

  • Time Series Analysis of Photospheric Magnetic Parameters of Flare-Quiet Versus Flaring Active Regions: Scaling Properties of Fluctuations
    Sol. Phys. (IF 2.503) Pub Date : 2020-09-07
    Eo-Jin Lee; Sung-Hong Park; Yong-Jae Moon

    Time series of photospheric magnetic parameters of solar active regions (ARs) are used to answer the question whether scaling properties of fluctuations embedded in such time series help to distinguish between flare-quiet and flaring ARs. We examine a total of 118 flare-quiet and 118 flaring AR patches, Helioseismic and Magnetic Imager Active Region Patches (called HARPs), which were observed from

  • Multiwavelength Analysis of the Kinematics of a Long Duration Flare-CME Event on 27 January 2012
    Sol. Phys. (IF 2.503) Pub Date : 2020-09-07
    G. Selvarani; S. Prasanna Subramanian; A. Shanmugaraju; K. Suresh

    We present a detailed analysis of a long-duration flare associated with a coronal mass ejection (CME) event that occurred on 27 January 2012 in the active region (AR) 11402. We analyze the kinematics of the CME and the close relationship between the flare, radio burst, and CME. We used STEREO (Solar Terrestrial Relations Observatory)/EUVI A (Extreme Ultraviolet Imager) and white light data from STEREO

  • Correlations of Sunspot Physical Characteristics during Solar Cycle 23
    Sol. Phys. (IF 2.503) Pub Date : 2020-09-03
    Adriana Valio; Eduardo Spagiari; Mauricio Marengoni; Caius L. Selhorst

    The behavior of sunspots is governed by the magnetic dynamo acting deep within the convection zone of the Sun. Therefore, knowledge of sunspot physical characteristics and how they evolve in time during a solar cycle can help to improve our understanding of the solar magnetic behavior. This work analyzes the physical characteristics of sunspots during the Solar Activity Cycle 23, detected using computer

  • Analysis of the Helical Kink Stability of Differently Twisted Magnetic Flux Ropes
    Sol. Phys. (IF 2.503) Pub Date : 2020-09-01
    M. Florido-Llinas; T. Nieves-Chinchilla; M. G. Linton

    Magnetic flux ropes (MFRs) are usually considered to be the magnetic structure that dominates the transport of helicity from the Sun into the heliosphere. They entrain a confined plasma within a helically organized magnetic structure and are able to cause geomagnetic activity. The formation, evolution, and twist distribution of MFRs are issues subject to strong debate. Although different twist profiles

  • Solar 11-Year Cycle Signal in Stratospheric Nitrogen Dioxide—Similarities and Discrepancies Between Model and NDACC Observations
    Sol. Phys. (IF 2.503) Pub Date : 2020-09-01
    Shuhui Wang; King-Fai Li; Diana Zhu; Stanley P. Sander; Yuk L. Yung; Andrea Pazmino; Richard Querel

    NOx (NO2 and NO) plays an important role in controlling stratospheric ozone. Understanding the change in stratospheric NOx and its global pattern is important for predicting future changes in ozone and the corresponding implications on the climate. Stratospheric NOx is mainly produced by the reaction of N2O with the photochemically produced O(1D) and, therefore, it is expected to vary with changes

  • How Good Is the Bipolar Approximation of Active Regions for Surface Flux Transport?
    Sol. Phys. (IF 2.503) Pub Date : 2020-09-01
    Anthony R. Yeates

    We investigate how representing active regions with bipolar magnetic regions (BMRs) affects the end-of-cycle polar field predicted by the surface flux transport model. Our study is based on a new database of BMRs derived from the SDO/HMI active region patch data between 2010 and 2020. An automated code is developed for fitting each active region patch with a BMR, matching both the magnetic flux and

  • Reconstructing Highly-twisted Magnetic Fields
    Sol. Phys. (IF 2.503) Pub Date : 2020-08-26
    Victor M. Demcsak; Michael S. Wheatland; Alpha Mastrano; Kai E. Yang

    We investigate the ability of a nonlinear force-free code to calculate highly-twisted magnetic field configurations using the Titov and Démoulin (Astron. Astrophys. 351:707, 1999) equilibrium field as a test case. The code calculates a force-free field using boundary conditions on the normal component of the field in the lower boundary, and the normal component of the current density over one polarity

  • Spectral Analysis of Forbush Decreases Using a New Yield Function
    Sol. Phys. (IF 2.503) Pub Date : 2020-08-17
    M. Livada; H. Mavromichalaki

    The Forbush decreases of the cosmic ray intensity observed on 24 December 2014 and on 8 September 2017 were chosen for cosmic ray spectral analysis. At first an analytical study of the solar and geomagnetic parameters of these events was carried out due to the fact that both are typical cosmic ray events. Hourly cosmic ray data of the neutron monitor stations obtained from the high-resolution neutron

  • Modeling Differential Faraday Rotation in the Solar Corona
    Sol. Phys. (IF 2.503) Pub Date : 2020-08-14
    Jason E. Kooi; Molly E. Kaplan

    For decades, radio remote-sensing techniques have been used to probe the plasma structure of the solar corona at distances of 2 – \(20~\mathrm{R}_{\odot }\). Measurement of Faraday rotation, the change in the polarization position angle of linearly polarized radiation as it propagates through a magnetized plasma, has proven to be one of the best methods for determining the coronal magnetic-field strength

  • Distinguishing the Rigidity Dependences of Acceleration and Transport in Solar Energetic Particles
    Sol. Phys. (IF 2.503) Pub Date : 2020-08-13
    Donald V. Reames

    In solar energetic particle (SEP) events, the power-law dependence of element abundance enhancements on their mass-to-charge ratios [\(A/Q\)] provides a new tool that measures the combined rigidity dependences from both acceleration and transport. Distinguishing between these two processes can be challenging. However, the effects of acceleration dominate when SEP events are small or when the ions propagate

  • Sunspot Records by Antonio Colla Just After the Dalton Minimum
    Sol. Phys. (IF 2.503) Pub Date : 2020-08-11
    V. M. S. Carrasco; C. Bertolin; F. Domínguez-Castro; L. de Ferri; M. C. Gallego; J. M. Vaquero

    Antonio Colla was a meteorologist and astronomer who made sunspot observations at the Meteorological Observatory of the Parma University (Italy). He carried out his sunspot observations from 1830 to 1843, just after the Dalton Minimum. We have recovered 71 observation days for this observer. Unfortunately, many of these records are qualitative and we could only obtain the number of sunspot groups and/or

  • Coronal Electron Density Fluctuations Inferred from Akatsuki Spacecraft Radio Observations
    Sol. Phys. (IF 2.503) Pub Date : 2020-08-11
    D. Wexler; T. Imamura; A. Efimov; P. Song; L. Lukanina; H. Ando; E. Jensen; J. Vierinen; A. Coster

    Trans-coronal radio observations were taken during the 2011 observing campaign of the Akatsuki spacecraft through superior conjunction. The observed X-band (8.4 GHz) signals exhibit frequency fluctuations (FF) that are produced by temporal variations in electron density along the radio ray path. A two-component model for interpretation of the FF is proposed: FF scales largely with acoustic wave amplitude

  • Comparative Study and Development of Two Contour-Based Image Segmentation Techniques for Coronal Hole Detection in Solar Images
    Sol. Phys. (IF 2.503) Pub Date : 2020-08-07
    Sanmoy Bandyopadhyay; Saurabh Das; Abhirup Datta

    The study of solar coronal holes (CHs) is important in the understanding of solar physics and the prediction of space weather events, which have significant impact on space-based instruments, communication and navigation systems. With the availability of the multi-wavelength Atmospheric Imaging Assembly (AIA) instrument on board Solar Dynamics Observatory (SDO) satellite, a large volume of high-resolution

  • A High-Efficiency and High-Accuracy Polarimeter for Solar Magnetic Field Measurements
    Sol. Phys. (IF 2.503) Pub Date : 2020-08-06
    Deqing Ren; Zijian Han; Jing Guo

    Solar activity is dominated by the magnetic field. Nowadays, a polarimeter is a mandatory tool to measure solar magnetic fields, which are generally faint and correspond to a polarization of an order of \(10^{-2}\)–\(10^{-4}\). As such, polarization measurements of high efficiency with a high accuracy are crucial to investigate faint magnetic fields. Here we propose a high-efficiency and high-accuracy

  • On the Expansion Speed of Coronal Mass Ejections: Implications for Self-Similar Evolution
    Sol. Phys. (IF 2.503) Pub Date : 2020-08-04
    L. A. Balmaceda; A. Vourlidas; G. Stenborg; O. C. St. Cyr

    A proper characterization of the kinematics of coronal mass ejections (CMEs) is important not only for practical purposes, i.e. space weather forecasting, but also to improve our current understanding of the physics behind their evolution in the middle corona and into the heliosphere. The first and core step toward this goal is the estimation of the three main components of the CME speeds, namely the

  • Dependence of Major Geomagnetic Storm Intensity ( Dst ≤ − 100 $\mathrm{Dst}\le -100$ nT) on Associated Solar Wind Parameters
    Sol. Phys. (IF 2.503) Pub Date : 2020-08-04
    Gui-Ming Le; Gui-Ang Liu; Ming-Xian Zhao

    We investigate the influence of various solar wind parameters on the intensity of the associated major geomagnetic storm. SYM-Hmin was used to indicate the intensity of major geomagnetic storms, while \(I(B_{s})\), \(I(E_{y})\) and \(I(Q)\) were used to indicate the time integrals of the southward interplanetary magnetic field component (\(B_{s}\)), the solar wind electric field (\(E_{y}\)), and Q

  • Magnetic and Velocity Field Topology in Active Regions of Descending Phase of Solar Cycle 23
    Sol. Phys. (IF 2.503) Pub Date : 2020-08-03
    R. A. Maurya; A. Ambastha

    We analyze the topology of photospheric magnetic fields and sub-photospheric flows of several active regions (ARs) that are observed during the peak to descending phase of Solar Cycle 23. Our analysis shows clear evidence of hemispheric preferences in all the topological parameters such as the magnetic, current and kinetic helicities, and the ‘curl-divergence’. We found that 68%(67%) ARs in the northern

  • Identifying 8 mm Radio Brightenings During the Solar Activity Minimum
    Sol. Phys. (IF 2.503) Pub Date : 2020-07-29
    Juha Kallunki; Merja Tornikoski; Irene Björklund

    Strong solar radio brightenings have been extensively studied in the past, and their correlation to the sunspots and active regions are already well known. But even when the Sun is ostensibly quiet, there is practically always some activity that can be detected in the radio domain. In this article we investigate these semi-active features at 8 mm using the radio telescope at Aalto University Metsähovi

  • Editorial: Solar Wind at the Dawn of the Parker Solar Probe and Solar Orbiter Era
    Sol. Phys. (IF 2.503) Pub Date : 2020-07-29
    Giovanni Lapenta; Andrei Zhukov; Lidia van Driel-Gesztelyi

    Solar Wind 15 brought together almost 250 experts from all continents of the world to discuss the current trends and future perspectives of the research on the Sun and its solar wind. The present article collection recaptures some of the highlights of their contributions.

  • Evolution of Coronal Mass Ejections and the Corresponding Forbush Decreases: Modeling vs. Multi-Spacecraft Observations
    Sol. Phys. (IF 2.503) Pub Date : 2020-07-29
    Mateja Dumbović; Bojan Vršnak; Jingnan Guo; Bernd Heber; Karin Dissauer; Fernando Carcaboso; Manuela Temmer; Astrid Veronig; Tatiana Podladchikova; Christian Möstl; Tanja Amerstorfer; Anamarija Kirin

    One of the very common in situ signatures of interplanetary coronal mass ejections (ICMEs), as well as other interplanetary transients, are Forbush decreases (FDs), i.e. short-term reductions in the galactic cosmic ray (GCR) flux. A two-step FD is often regarded as a textbook example, which presumably owes its specific morphology to the fact that the measuring instrument passed through the ICME head

  • Investigation of the Middle Corona with SWAP and a Data-Driven Non-Potential Coronal Magnetic Field Model.
    Sol. Phys. (IF 2.503) Pub Date : 2020-07-27
    Karen A Meyer,Duncan H Mackay,Dana-Camelia Talpeanu,Lisa A Upton,Matthew J West

    The large field-of-view of the Sun Watcher using Active Pixel System detector and Image Processing (SWAP) instrument onboard the PRoject for Onboard Autonomy 2 (PROBA2) spacecraft provides a unique opportunity to study extended coronal structures observed in the EUV in conjunction with global coronal magnetic field simulations. A global non-potential magnetic field model is used to simulate the evolution

  • Small Size Ground Level Enhancements During Solar Cycle 24
    Sol. Phys. (IF 2.503) Pub Date : 2020-07-27
    Leonty I. Miroshnichenko; Chuan Li; Victor G. Yanke

    We continue the systematical empirical search for small size ground level enhancements (GLEs) (also called “hidden” or sub-GLEs) using data from ground-based instruments for Solar Cycle 24. The starting point of this research is the hypothesis that small size GLEs may be indicative of the acceleration of solar energetic particles (SEPs) by shocks driven by coronal mass ejections (CMEs). A crucial parameter

  • Investigation of the Hemispheric Asymmetry in Solar Flare Index During Solar Cycle 21 – 24 from the Kandilli Observatory
    Sol. Phys. (IF 2.503) Pub Date : 2020-07-23
    Soumya Roy; Amrita Prasad; Koushik Ghosh; Subhash Chandra Panja; Sankar Narayan Patra

    The hemispheric asymmetry of the solar-flare index during 1976 – 2018 from the Kandilli Observatory is studied in this investigation. The temporal duration covers Solar Cycles 21 – 23 and almost the whole of Solar Cycle 24. Different methodologies, such as cross-correlation analysis, rescaled-range analysis, empirical mode decomposition, and date-compensated discrete Fourier transform, have been used

  • The Evolution over Time and North–South Asymmetry of Sunspots and Solar Plages for the Period 1910 to 1937 Using Data from Ebro Catalogues
    Sol. Phys. (IF 2.503) Pub Date : 2020-07-23
    V. de Paula; J. J. Curto

    In this work, we analysed both the evolution over time and the north–south (N-S) asymmetry of certain solar features with regards to their morphological type and area. We examined and compared simultaneously 4212 photospheric sunspot groups and 5781 chromospheric solar plage groups using data from the Ebro Observatory catalogues for the period 1910–1937. We found that the most frequently recorded groups

  • Forward Synthesis of Polarized Emission in Target DKIST Coronal Lines Applied to 3D MURaM Coronal Simulations
    Sol. Phys. (IF 2.503) Pub Date : 2020-07-20
    Thomas Schad; Gabriel Dima

    Self-consistent magnetohydrodynamic simulations of the solar corona with fine (\(\lesssim10\) km) grid scales are now being realized in parallel to advancements in high-resolution coronal spectropolarimetry provided by the National Science Foundation’s Daniel K. Inouye Solar Telescope (DKIST). We investigate the synthesis of polarized emission in the presence of apparent coronal fine structure exhibited

  • Self-consistent Nonlinear Force-Free Field Reconstruction from Weighted Boundary Conditions
    Sol. Phys. (IF 2.503) Pub Date : 2020-07-17
    A. Mastrano; K. E. Yang; M. S. Wheatland

    Photospheric vector magnetogram data are often used as boundary conditions for force-free coronal magnetic field extrapolations. In general, however, vector magnetogram data are not consistent with the force-free assumption. In this article, we demonstrate a way to deal with inconsistent boundary data, by generalizing the “self-consistency procedure” of Wheatland and Régnier (Astrophys. J. Lett.700

  • Magnetic Field, Electron Density and Their Spatial Scales in Zebra Pattern Radio Sources
    Sol. Phys. (IF 2.503) Pub Date : 2020-07-15
    L. V. Yasnov; M. Karlický

    Zebra patterns (zebras) play an important role in the plasma diagnostics during solar flares. Considering their double plasma resonance (DPR) model, we present an improved method for the determination of the gyro-harmonic numbers of the zebra stripes that are essential in determining the electron density and magnetic field strength in zebra sources. Furthermore, we present the magnetic field and density

  • Synoptic Measurements of Electron Temperature and Speed in the Solar Corona with Next Generation White-Light Coronagraph
    Sol. Phys. (IF 2.503) Pub Date : 2020-07-15
    Nelson Reginald; Jeffrey Newmark; Lutz Rastaetter

    Current white-light coronagraphs measure polarized brightness (pB) of the solar corona using a single bandpass filter to measure the density of electrons. However, future coronagraphs can be modified to take pB images through four bandpass filters to measure density, temperature and speed of electrons. In this article, we use a spherical three dimensional coronal model of the Bastille Day coronal mass

  • Solar Flare Forecasting Using Time Series and Extreme Gradient Boosting Ensembles
    Sol. Phys. (IF 2.503) Pub Date : 2020-07-14
    T. Cinto; A. L. S. Gradvohl; G. P. Coelho; A. E. A. da Silva

    Space weather events may cause damage to several types of technologies, including aviation, satellites, oil and gas industries, and electrical systems, leading to economic and commercial losses. Solar flares belong to the most significant events, and refer to sudden radiation releases that can affect the Earth’s atmosphere within a few hours or minutes. Therefore, it is worth designing high-performance

  • Multilevel Observations of the Oscillations in the First Active Region of the New Cycle
    Sol. Phys. (IF 2.503) Pub Date : 2020-07-14
    A. A. Chelpanov; N. I. Kobanov

    For the first time, a multiwavelength investigation of the oscillation dynamics in a solar facula from its birth to decay was carried out. We performed spectral observations of active region NOAA 12744 at the Horizontal Solar Telescope of the Sayan Solar Observatory in the H\(\alpha \), He i 10830 Å, and Si i 10827 Å lines. We used Solar Dynamics Observatory (SDO) line-of-sight magnetic field data

  • New Types of the Chromospheric Anemone Microflares: Case Study
    Sol. Phys. (IF 2.503) Pub Date : 2020-07-13
    Yurii V. Dumin; Boris V. Somov

    Chromospheric anemone microflares (AMFs) are transient solar phenomena whose emission regions have a multi-ribbon configuration. As distinct from the so-called “atypical” solar flares, also possessing a few ribbons, the temporal and spatial scales of AMFs are a few times less, and the configuration of their ribbons is more specific (star-like). The previously reported AMFs had typically three or, less

  • Sun-to-Earth Observations and Characteristics of Isolated Earth-Impacting Interplanetary Coronal Mass Ejections During 2008 – 2014
    Sol. Phys. (IF 2.503) Pub Date : 2020-07-09
    D. Maričić; B. Vršnak; A. M. Veronig; M. Dumbović; F. Šterc; D. Roša; M. Karlica; D. Hržina; I. Romštajn

    A sample of isolated Earth-impacting interplanetary coronal mass ejections (ICMEs) that occurred in the period January 2008 to August 2014 is analyzed to study in detail the ICME in situ signatures, with respect to the type of filament eruption related to the corresponding CME. Observations from different vantage points provided by the Solar and Heliospheric Observatory (SOHO) and the Solar Terrestrial

  • The STIX Aspect System (SAS): The Optical Aspect System of the Spectrometer/Telescope for Imaging X-Rays (STIX) on Solar Orbiter
    Sol. Phys. (IF 2.503) Pub Date : 2020-07-03
    A. Warmuth; H. Önel; G. Mann; J. Rendtel; K. G. Strassmeier; C. Denker; G. J. Hurford; S. Krucker; J. Anderson; S.-M. Bauer; W. Bittner; F. Dionies; J. Paschke; D. Plüschke; D. P. Sablowski; F. Schuller; V. Senthamizh Pavai; M. Woche; D. Casadei; S. Kögl; N. G. Arnold; H.-P. Gröbelbauer; D. Schori; H. J. Wiehl; A. Csillaghy; O. Grimm; P. Orleanski; K. R. Skup; W. Bujwan; K. Rutkowski; K. Ber

    The Spectrometer/Telescope for Imaging X-rays (STIX) is a remote sensing instrument on Solar Orbiter that observes the hard X-ray bremsstrahlung emission of solar flares. This paper describes the STIX Aspect System (SAS), a subunit that measures the pointing of STIX relative to the Sun with a precision of \(\pm 4''\), which is required to accurately localize the reconstructed X-ray images on the Sun

  • Coronal Photopolarimetry with the LASCO-C2 Coronagraph over 24 Years [1996 – 2019]
    Sol. Phys. (IF 2.503) Pub Date : 2020-07-01
    Philippe Lamy; Antoine Llebaria; Brice Boclet; Hugo Gilardy; Michael Burtin; Olivier Floyd

    We present an in-depth characterization of the polarimetric channel of the Large-Angle Spectrometric COronagraph/LASCO-C2 onboard the Solar and Heliospheric Observatory (SOHO). The polarimetric analysis of the white-light images makes use of polarized sequences composed of three images obtained though three polarizers oriented at \(+60^{\circ }\), \(0^{\circ }\), and \(-60^{\circ }\), complemented

  • Long- and Short-Term Evolutions of Magnetic Field Fluctuations in High-Speed Streams
    Sol. Phys. (IF 2.503) Pub Date : 2020-07-01
    Gilbert Pi; Alexander Pitňa; Zdenek Němeček; Jana Šafránková; Jih-Hong Shue; Ya-Hui Yang

    High-speed streams (HSSs) are believed to be only slightly affected by different interactions on their path from the Sun to Earth and thus the analysis of their observations can provide information on the structure and temporal variations of the magnetic field and plasma parameters at the source region. We have chosen three coronal holes supplying 14 HSSs recorded by Wind in 2008. For each HSS, we

  • Nonaxisymmetric Component of Solar Activity: the Vector of the Longitudinal Asymmetry
    Sol. Phys. (IF 2.503) Pub Date : 2020-06-30
    E. S. Vernova; M. I. Tyasto; D. G. Baranov; O. A. Danilova

    The vector representation of sunspots is used to study the nonaxisymmetric features of the solar activity distribution (sunspot data from Greenwich–USAF/NOAA, 1874–2016). Each sunspot is represented by a polar vector with modulus equal to the sunspot area and the phase equal to the sunspot heliolongitude. The vector sum of these individual vectors defines both the magnitude of the longitudinal asymmetry

  • Observation of Differential Rotation Within a Sunspot Umbra During an X-Class Flare
    Sol. Phys. (IF 2.503) Pub Date : 2020-06-30
    Richard Grimes; Balázs Pintér; Huw Morgan

    Sunspots and their dynamics dominate the magnetic topology and evolution of both the photosphere and the overlying coronal active regions. Thus a comprehensive understanding of their behaviour is essential to understanding the solar magnetic field. A new technique is presented for applying multiple ellipse fits as a method for rotation tracking of sunspot umbrae. The method is applied to a sunspot

  • Randomness in Sunspot Number: A Clue to Predict Solar Cycle 25
    Sol. Phys. (IF 2.503) Pub Date : 2020-06-30
    Bharati Kakad; Raj Kumar; Amar Kakad

    Forecasting of solar activity is extremely important, due to its impact on our space-based technology. In recent years, we have observed a continuous decline in the peak sunspot number for Solar Cycles (SCs) 21 to 24. We are more curious about peak activity of SC 25 because if the solar activity weakens further, then it may be an indication of new extended minima. So far, the daily sunspot-number data

  • Validity of Nonlinear Force-Free Field Optimization Reconstruction
    Sol. Phys. (IF 2.503) Pub Date : 2020-06-29
    G. V. Rudenko; I. S. Dmitrienko

    We evaluate the validity of Nonlinear Force Free Field (NLFFF) reconstruction performed with Optimization class (OPTI) codes. We present a postprocessing method that removes the inevitable non-solenoidality of the magnetic field calculated by OPTI codes, which is caused by the noticeable role played by the gradient of the gas pressure in the force balance at photospheric heights, and by some of the

  • EMD and LSTM Hybrid Deep Learning Model for Predicting Sunspot Number Time Series with a Cyclic Pattern
    Sol. Phys. (IF 2.503) Pub Date : 2020-06-22
    Taesam Lee

    The prediction of a time series such as climate indices and the sunspot number (SSN) with long-term oscillatory behaviors has been a challenging task due to the complex combination of oscillations. Frequency extraction algorithms have been developed to separate a time series into different oscillation components according to frequency, such as empirical model decomposition (EMD) and wavelet analysis

  • Short-Term Periodicities Observed in Neutron Monitor Counting Rates
    Sol. Phys. (IF 2.503) Pub Date : 2020-06-22
    A. López-Comazzi; J. J. Blanco

    Neutron monitor counting rates and solar wind velocity, interplanetary magnetic field, sunspot number and total solar irradiance measurements from 2013 to 2018 corresponding to the end of solar maximum and the decreasing phase of the Solar Cycle 24 have been used. The main objective is to check whether the periodicities observed in the cosmic rays are affected by the magnetic rigidity or the height

  • Model Fitting of Wind Magnetic Clouds for the Period 2004 – 2006
    Sol. Phys. (IF 2.503) Pub Date : 2020-06-22
    R. P. Lepping; C.-C. Wu; D. B. Berdichevsky; A. Szabo

    We give the results of parameter fitting of the magnetic clouds (MCs) observed by the Wind spacecraft for the three year period – 2004 to the end of 2006 (the “Present period”) using the force-free MC model of Lepping, Jones, and Burlaga (J. Geophys. Res.95, 11957, 1990). There were 19 MCs identified in the Present period, which was mainly in the declining phase of the solar cycle. The long-term occurrence

  • Radio Sounding Measurements of the Solar Corona Using Giant Pulses of the Crab Pulsar in 2018
    Sol. Phys. (IF 2.503) Pub Date : 2020-06-19
    Munetoshi Tokumaru; Kaito Tawara; Kazuhiro Takefuji; Mamoru Sekido; Toshio Terasawa

    Observations of the Crab pulsar at 327 MHz were made at the Toyokawa Observatory of the Institute for Space-Earth Environmental Research, during the solar occultation in mid-June 2018 to investigate the coronal plasma density in the weak sunspot cycle, Cycle 24. The dispersion measurements (DMs) were determined using giant pulses detected from observations of the Crab pulsar. The systematic increase

  • A New Tool for Predicting the Solar Cycle: Correlation Between Flux Transport at the Equator and the Poles
    Sol. Phys. (IF 2.503) Pub Date : 2020-06-18
    Susanta Kumar Bisoi; P. Janardhan

    Magnetic flux cancellation on the Sun plays a crucial role in determining the way in which the net magnetic flux changes in every solar cycle, affecting the large scale evolution of the coronal magnetic field and heliospheric environment. We have investigated the correlation between the solar magnetic flux cancelled at the equator and the solar magnetic flux transported to the poles by comparing the

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