Determination of Solar Energetic Particle anisotropies based on four-sector measurements - Study based on STEREO/SEPT in preperation of SolO/EPT

With the launch of Solar Orbiter (SolO) Solar Energetic Particles (SEPs) can be observed at a radial distance of 0.284 to 0.9 AU and an inclination out of the ecliptic up to 34 degree. The properties of SEP observations carry information about their source at the Sun as well as their transport through the interplanetary medium. Their energy is mostly determined close to the Sun. As SEPs propagate outward along the Interplanetary Magnetic Field (IMF) the pitch-angle with respect to the local field is systematically focused due to the radially decreasing IMF. However, stochastic changes are induced by scattering at fluctuations of the IMF. Often the first order anisotropy of SEPs is calculated to disentangle imprints of source and transport. Strong anisotropies indicate periods of weak pitch-angle scattering. Although many modeling and observational studies are based on the anisotropy, its uncertainty is often neglected which could result in inaccurate conclusions. Therefore, we propose a new method based on a bootstrap approach where we consider (1) directional instrument responses, (2) the variation of the magnetic field, and (3) the stochastic nature of detection. Here, we present our procedure and final results for different SEP events using measured data of the IMF and particle fluxes by the Solar Electron and Proton Telescope (SEPT) on board of each STEREO spacecraft. The SEPT provides four viewing directions with a view cone of 0.66 sr each on a three axis stabilized spacecraft. In contrast the Electron and Proton Telescope (EPT) on board SolO also consists of four viewing directions but each telescope has a much smaller view cone of 0.21 sr. Due to the very similar instrument setup we can apply our method both to the SEPT and EPT.

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The evolution of inverted magnetic fields through the inner heliosphere

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa951 ◽

2020 ◽

Vol 494 (3) ◽

pp. 3642-3655 ◽

Cited By ~ 2

Author(s):

Allan R Macneil ◽

Mathew J Owens ◽

Robert T Wicks ◽

Mike Lockwood ◽

Sarah N Bentley ◽

...

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Radial Distance ◽

Occurrence Rate ◽

Slow Solar Wind ◽

The Sun ◽

Radial Evolution ◽

In Transit ◽

The Magnetic Field ◽

Inner Heliosphere

ABSTRACT Local inversions are often observed in the heliospheric magnetic field (HMF), but their origins and evolution are not yet fully understood. Parker Solar Probe has recently observed rapid, Alfvénic, HMF inversions in the inner heliosphere, known as ‘switchbacks’, which have been interpreted as the possible remnants of coronal jets. It has also been suggested that inverted HMF may be produced by near-Sun interchange reconnection; a key process in mechanisms proposed for slow solar wind release. These cases suggest that the source of inverted HMF is near the Sun, and it follows that these inversions would gradually decay and straighten as they propagate out through the heliosphere. Alternatively, HMF inversions could form during solar wind transit, through phenomena such velocity shears, draping over ejecta, or waves and turbulence. Such processes are expected to lead to a qualitatively radial evolution of inverted HMF structures. Using Helios measurements spanning 0.3–1 au, we examine the occurrence rate of inverted HMF, as well as other magnetic field morphologies, as a function of radial distance r, and find that it continually increases. This trend may be explained by inverted HMF observed between 0.3 and 1 au being primarily driven by one or more of the above in-transit processes, rather than created at the Sun. We make suggestions as to the relative importance of these different processes based on the evolution of the magnetic field properties associated with inverted HMF. We also explore alternative explanations outside of our suggested driving processes which may lead to the observed trend.

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Starspots Magnetic field by transit mapping

Proceedings of the International Astronomical Union ◽

10.1017/s1743921314002129 ◽

2013 ◽

Vol 9 (S302) ◽

pp. 220-221

Author(s):

Adriana Válio ◽

Eduardo Spagiari

Keyword(s):

Magnetic Field ◽

Light Curve ◽

Field Component ◽

Solar Magnetic Field ◽

Line Of Sight ◽

The Sun ◽

Using Data ◽

The Magnetic Field ◽

Spot Temperature

AbstractSunspots are important signatures of the global solar magnetic field cycle. It is believed that other stars also present these same phenomena. However, today it is not possible to observe directly star spots due to their very small sizes. The method applied here studies star spots by detecting small variations in the stellar light curve during a planetary transit. When the planet passes in front of its host star, there is a chance of it occulting, at least partially, a spot. This allows the determination of the spots physical characteristics, such as size, temperature, and location on the stellar surface. In the case of the Sun, there exists a relation between the magnetic field and the spot temperature. We estimate the magnetic field component along the line-of-sight and the intensity of sunspots using data from the MDI instrument on board of the SOHO satellite. Assuming that the same relation applies to other stars, we estimate spots magnetic fields of CoRoT-2 and Kepler-17 stars.

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

The Astrophysical Journal ◽

10.3847/1538-4357/ac3233 ◽

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.

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The expected imprint of flux rope geometry on suprathermal electrons in magnetic clouds

Annales Geophysicae ◽

10.5194/angeo-27-4057-2009 ◽

2009 ◽

Vol 27 (10) ◽

pp. 4057-4067 ◽

Cited By ~ 4

Author(s):

M. J. Owens ◽

N. U. Crooker ◽

T. S. Horbury

Keyword(s):

Magnetic Field ◽

Magnetic Flux ◽

Pitch Angle ◽

Flux Rope ◽

Magnetic Clouds ◽

Magnetic Field Direction ◽

Magnetic Flux Rope ◽

Suprathermal Electron ◽

Angle Scattering ◽

The Magnetic Field

Abstract. Magnetic clouds are a subset of interplanetary coronal mass ejections characterized by a smooth rotation in the magnetic field direction, which is interpreted as a signature of a magnetic flux rope. Suprathermal electron observations indicate that one or both ends of a magnetic cloud typically remain connected to the Sun as it moves out through the heliosphere. With distance from the axis of the flux rope, out toward its edge, the magnetic field winds more tightly about the axis and electrons must traverse longer magnetic field lines to reach the same heliocentric distance. This increased time of flight allows greater pitch-angle scattering to occur, meaning suprathermal electron pitch-angle distributions should be systematically broader at the edges of the flux rope than at the axis. We model this effect with an analytical magnetic flux rope model and a numerical scheme for suprathermal electron pitch-angle scattering and find that the signature of a magnetic flux rope should be observable with the typical pitch-angle resolution of suprathermal electron data provided ACE's SWEPAM instrument. Evidence of this signature in the observations, however, is weak, possibly because reconnection of magnetic fields within the flux rope acts to intermix flux tubes.

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Dependence of pitch-angle scattering rates and loss timescales on the magnetic field model

Geophysical Research Letters ◽

10.1029/2009gl041639 ◽

2010 ◽

Vol 37 (5) ◽

pp. n/a-n/a ◽

Cited By ~ 51

Author(s):

Ksenia G. Orlova ◽

Yuri Y. Shprits

Keyword(s):

Magnetic Field ◽

Pitch Angle ◽

Field Model ◽

Angle Scattering ◽

Magnetic Field Model ◽

The Magnetic Field ◽

Scattering Rates

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Alfvénic versus non-Alfvénic turbulence in the inner heliosphere as observed by Parker Solar Probe

10.5194/egusphere-egu21-12876 ◽

2021 ◽

Author(s):

Marco Velli ◽

Chen Shi ◽

Olga Panasenco ◽

Anna Tenerani ◽

Victor Reville ◽

...

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Radial Distance ◽

Velocity Spectrum ◽

The Sun ◽

Mhd Turbulence ◽

Great Opportunity ◽

Depth Analysis ◽

Slow Wind ◽

The Magnetic Field

Parker Solar Probe (PSP) measures the magnetic field and plasma parameters of the solar wind at unprecedentedly close distances to the Sun, providing a great opportunity to study the early-stage evolution of magnetohydrodynamic (MHD) turbulence in the solar wind. Here we use PSP data to explore the nature of solar wind turbulence focusing on the Alfv&#233;nic character and power spectra of the fluctuations and their dependence on heliocentric distance and context (i.e., large-scale solar wind properties), aiming to understand the role that different effects such as source properties, solar wind expansion, and stream interaction might play in determining the turbulent state. We carried out a statistical survey of the data from the first five orbits of PSP with a focus on how the fluctuation properties at the large MHD scales vary with different solar wind streams and the distance from the Sun. A more in-depth analysis from several selected periods is also presented. Our results show that as fluctuations are transported outward by the solar wind, the magnetic field spectrum steepens while the shape of the velocity spectrum remains unchanged. The steepening process is controlled by the age of the turbulence, which is determined by the wind speed together with the radial distance. Statistically, faster solar wind has higher Alfv&#233;nicity with a more dominant outward propagating wave component and more balanced magnetic and kinetic energies. The outward wave dominance gradually weakens with radial distance, while the excess of magnetic energy is found to be stronger as we move closer toward the Sun. We show that the turbulence properties can significantly vary from stream to stream even if these streams are of a similar speed, indicating very different origins of these streams. Especially, the slow wind that originates near the polar coronal holes has much lower Alfv&#233;nicity compared with the slow wind that originates from the active regions and pseudostreamers. We show that structures such as the heliospheric current sheet and wind stream velocity shears can play an important role in modifying the properties of the turbulence.*The PSP Team:&#160;Stuart D.Bale, &#160;Justin Kasper, Kelly Korreck, J. W. Bonnell, Thierry Dudok de Wit, Keith Goetz, Peter R. Harvey, Robert J. MacDowall, David Malaspina, Marc Pulupa, Anthony W.Case, Davin Larson, &#160;Jenny Verniero, Roberto Livi, Michael Stevens, PhyllisWhittlesey, Milan Maksimovic, and Michel Moncuquet

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Non-Markovian Pitch-angle Scattering as the Origin of Particle Superdiffusion Parallel to the Magnetic Field

The Astrophysical Journal ◽

10.3847/1538-4357/abb951 ◽

2020 ◽

Vol 903 (2) ◽

pp. 105

Author(s):

Gaetano Zimbardo ◽

Silvia Perri

Keyword(s):

Magnetic Field ◽

Pitch Angle ◽

Angle Scattering ◽

The Magnetic Field

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Emergence of Twisted Magnetic Flux Related Sigmoidal Brightening

International Astronomical Union Colloquium ◽

10.1017/s0252921100064630 ◽

2000 ◽

Vol 179 ◽

pp. 263-264

Author(s):

K. Sundara Raman ◽

K. B. Ramesh ◽

R. Selvendran ◽

P. S. M. Aleem ◽

K. M. Hiremath

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Magnetic Flux ◽

Ultra Violet ◽

Active Regions ◽

Morphological Properties ◽

Energy Storage And Conversion ◽

The Sun ◽

X Rays ◽

The Magnetic Field

Extended AbstractWe have examined the morphological properties of a sigmoid associated with an SXR (soft X-ray) flare. The sigmoid is cospatial with the EUV (extreme ultra violet) images and in the optical part lies along an S-shaped Hαfilament. The photoheliogram shows flux emergence within an existingδtype sunspot which has caused the rotation of the umbrae giving rise to the sigmoidal brightening.It is now widely accepted that flares derive their energy from the magnetic fields of the active regions and coronal levels are considered to be the flare sites. But still a satisfactory understanding of the flare processes has not been achieved because of the difficulties encountered to predict and estimate the probability of flare eruptions. The convection flows and vortices below the photosphere transport and concentrate magnetic field, which subsequently appear as active regions in the photosphere (Rust & Kumar 1994 and the references therein). Successive emergence of magnetic flux, twist the field, creating flare productive magnetic shear and has been studied by many authors (Sundara Ramanet al.1998 and the references therein). Hence, it is considered that the flare is powered by the energy stored in the twisted magnetic flux tubes (Kurokawa 1996 and the references therein). Rust & Kumar (1996) named the S-shaped bright coronal loops that appear in soft X-rays as ‘Sigmoids’ and concluded that this S-shaped distortion is due to the twist developed in the magnetic field lines. These transient sigmoidal features tell a great deal about unstable coronal magnetic fields, as these regions are more likely to be eruptive (Canfieldet al.1999). As the magnetic fields of the active regions are deep rooted in the Sun, the twist developed in the subphotospheric flux tube penetrates the photosphere and extends in to the corona. Thus, it is essentially favourable for the subphotospheric twist to unwind the twist and transmit it through the photosphere to the corona. Therefore, it becomes essential to make complete observational descriptions of a flare from the magnetic field changes that are taking place in different atmospheric levels of the Sun, to pin down the energy storage and conversion process that trigger the flare phenomena.

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