Exploring the Properties of the Electron Strahl at 1 AU as an Indicator of the Quality of the Magnetic Connection Between the Earth and the Sun

The Sun ◽

Number Density ◽

Intensity Changes ◽

The Magnetic Field ◽

Region Plasma

In this report some properties of the electron strahl at 1 AU are examined to assess the strahl at 272 eV as an indicator of the quality of the magnetic connection of the near-Earth solar wind to the Sun. The absence of a strahl has been taken to represent either a lack of magnetic connection to the corona or the strahl not surviving to 1 AU owing to scattering. Solar-energetic-electron (SEE) events can be used as indicators of good magnetic connection: examination of 216 impulsive SEE events finds that they are all characterized by strong strahls. The strahl intensity at 1 AU is statistically examined for various types of solar-wind plasma: it is found that the strahl is characteristically weak in sector-reversal-region plasma. In sector-reversal-region plasma and other slow wind, temporal changes in the strahl intensity at 1 AU are examined with 64 s resolution measurements and the statistical relationships of strahl changes to simultaneous plasma-property changes are established. The strahl-intensity changes are co-located with current sheets (directional discontinuities) with strong changes in the magnetic-field direction. The strahl-intensity changes at 1 AU are positively correlated with changes in the proton specific entropy, the proton temperature, and the magnetic-field strength; the strahl-intensity changes are anti-correlated with changes in the proton number density, the angle of the magnetic field with respect to the Parker-spiral direction, and the alpha-to-proton number-density ratio. Reductions in the strahl intensity are not consistent with expectations for a simple model of whistler-turbulence scattering. Reductions in the strahl intensity are mildly consistent with expectations for Coulomb scattering, however the strongest-observed plasma-change correlations are unrelated to Coulomb scattering and whistler scattering. The implications of the strahl-intensity-change analysis are that the change in the magnetic-field direction at a strahl change represents a change in the magnetic connection to the corona, resulting in a different strahl intensity and different plasma properties. An outstanding question is: Does an absence of an electron strahl represent a magnetic disconnection from the Sun or a poor strahl source in some region of the corona?

The Sun

The Sun's Influence on Climate ◽

10.23943/princeton/9780691153834.003.0003 ◽

2015 ◽

Author(s):

Joanna D. Haigh ◽

Peter Cargill

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Solar Atmosphere ◽

Space Weather ◽

Extreme Ultraviolet ◽

The Sun ◽

Base Level ◽

Earth’S Climate ◽

The Magnetic Field ◽

Terrestrial Magnetic Field

This chapter discusses how there are four general factors that contribute to the Sun's potential role in variations in the Earth's climate. First, the fusion processes in the solar core determine the solar luminosity and hence the base level of radiation impinging on the Earth. Second, the presence of the solar magnetic field leads to radiation at ultraviolet (UV), extreme ultraviolet (EUV), and X-ray wavelengths which can affect certain layers of the atmosphere. Third, the variability of the magnetic field over a 22-year cycle leads to significant changes in the radiative output at some wavelengths. Finally, the interplanetary manifestation of the outer solar atmosphere (the solar wind) interacts with the terrestrial magnetic field, leading to effects commonly called space weather.

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.

Magnetic clouds' structure in the magnetosheath as observed by Cluster and Geotail: four case studies

Annales Geophysicae ◽

10.5194/angeo-32-1247-2014 ◽

2014 ◽

Vol 32 (10) ◽

pp. 1247-1261 ◽

Cited By ~ 7

Author(s):

L. Turc ◽

D. Fontaine ◽

P. Savoini ◽

E. K. J. Kilpua

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Magnetic Fields ◽

Bow Shock ◽

Field Direction ◽

Magnetic Clouds ◽

Field Orientation ◽

The Impact ◽

Abstract. Magnetic clouds (MCs) are large-scale magnetic flux ropes ejected from the Sun into the interplanetary space. They play a central role in solar–terrestrial relations as they can efficiently drive magnetic activity in the near-Earth environment. Their impact on the Earth's magnetosphere is often attributed to the presence of southward magnetic fields inside the MC, as observed in the upstream solar wind. However, when they arrive in the vicinity of the Earth, MCs first encounter the bow shock, which is expected to modify their properties, including their magnetic field strength and direction. If these changes are significant, they can in turn affect the interaction of the MC with the magnetosphere. In this paper, we use data from the Cluster and Geotail spacecraft inside the magnetosheath and from the Advanced Composition Explorer (ACE) upstream of the Earth's environment to investigate the impact of the bow shock's crossing on the magnetic structure of MCs. Through four example MCs, we show that the evolution of the MC's structure from the solar wind to the magnetosheath differs largely from one event to another. The smooth rotation of the MC can either be preserved inside the magnetosheath, be modified, i.e. the magnetic field still rotates slowly but at different angles, or even disappear. The alteration of the magnetic field orientation across the bow shock can vary with time during the MC's passage and with the location inside the magnetosheath. We examine the conditions encountered at the bow shock from direct observations, when Cluster or Geotail cross it, or indirectly by applying a magnetosheath model. We obtain a good agreement between the observed and modelled magnetic field direction and shock configuration, which varies from quasi-perpendicular to quasi-parallel in our study. We find that the variations in the angle between the magnetic fields in the solar wind and in the magnetosheath are anti-correlated with the variations in the shock obliquity. When the shock is in a quasi-parallel regime, the magnetic field direction varies significantly from the solar wind to the magnetosheath. In such cases, the magnetic field reaching the magnetopause cannot be approximated by the upstream magnetic field. Therefore, it is important to take into account the conditions at the bow shock when estimating the impact of an MC with the Earth's environment because these conditions are crucial in determining the magnetosheath magnetic field, which then interacts with the magnetosphere.

Plasma Flow and Solar Wind Acceleration in Non-Radial Coronal Magnetic Fields

Symposium - International Astronomical Union ◽

10.1017/s0074180900030151 ◽

1983 ◽

Vol 102 ◽

pp. 473-477

Author(s):

H. Biernat ◽

N. Kömle ◽

H. Rucker

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Plasma Flow ◽

Coronal Holes ◽

Expansion Velocity ◽

The Sun ◽

Solar Wind Acceleration ◽

Coronal Magnetic Fields ◽

Field Lines ◽

In the vicinity of the Sun — especially above coronal holes — the magnetic field lines show strong non-radial divergence and considerable curvature (see e.g. Kopp and Holzer, 1976; Munro and Jackson, 1977; Ripken, 1977). In the following we study the influence of these characteristics on the expansion velocity of the solar wind.

Cassini observations of magnetic holes in the solar wind and Saturn magnetosheath

10.5194/egusphere-egu2020-100 ◽

2020 ◽

Author(s):

Tomas Karlsson ◽

Lina Hadid ◽

Michiko Morooka ◽

Jan-Erik Wahlund

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Field Strength ◽

Magnetic Field Strength ◽

High Time Resolution ◽

Scale Size ◽

Background Magnetic Field ◽

Cycle Dependence ◽

We present the first Cassini observations of magnetic holes on the near-Saturn solar wind and magnetosheath, based on data from the MAG magnetometer. We conclude that magnetic holes (defined as isolated decreases of at least 50% compared to the background magnetic field strength) are common in both regions. We present statistical properties of the magnetic holes, including scale size, depth of the magnetic field reduction, orientation, change in magnetic field direction over the holes, and solar cycle dependence. For magnetosheath magnetic holes, also high-time resolution density measurements from the LP Langmuir probe are available, allowing us to study the anti-correlation of density and magnetic field strength in the magnetic holes. We compare to recent results from MESSENGER observations from Mercury orbit, and finally discuss the possible importance of magnetic holes in solar wind-magnetosphere interaction at Saturn.

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

Journal of Oceanological Research ◽

10.29006/1564-2291.jor-2019.47(1).25 ◽

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 ◽

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.

Evidence for Plasma Heating at Thin Current Sheets in the Solar Wind

The Astrophysical Journal ◽

10.3847/2041-8213/ac4701 ◽

2022 ◽

Vol 924 (2) ◽

pp. L22

Author(s):

Zilu Zhou ◽

Xiaojun Xu ◽

Pingbing Zuo ◽

Yi Wang ◽

Qi Xu ◽

...

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Plasma Heating ◽

Current Sheets ◽

Proton Temperature ◽

Fast Wind ◽

Wind Spacecraft ◽

Slow Wind ◽

Abstract Plasma heating at thin current sheets in the solar wind is examined using magnetic field and plasma data obtained by the WIND spacecraft in the past 17 years from 2004 to 2019. In this study, a thin current sheet is defined by an abrupt rotation (larger than 45°) of the magnetic field direction in 3 s. A total of 57,814 current sheets have been identified, among which 25,018 current sheets are located in the slow wind and 19,842 current sheets are located in the fast wind. Significant plasma heating is found at current sheets in both slow and fast wind. Proton temperature increases more significantly at current sheets in the fast wind than in the slow wind, while the enhancement in electron temperature is less remarkable at current sheets in the fast wind. The results reveal that plasma heating commonly exists at thin current sheets in the solar wind regardless of the wind speed, but the underlying heating mechanisms might be different.

Statistical Differences of Magnetic Field Kinks Observed by PSP and WIND

10.5194/egusphere-egu21-14696 ◽

2021 ◽

Author(s):

Chuanpeng Hou ◽

Xingyu Zhu ◽

Rui Zhuo ◽

Jiansen He

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Radial Velocity ◽

Slow Solar Wind ◽

Number Density ◽

Ion Temperature ◽

Group I ◽

Rotational Discontinuity ◽

Background Magnetic Field ◽

Parker Solar Probe&#8217;s (PSP) observations near the sun show the extensive presence of magnetic field kinks (switchback for large kinks) in the slow solar wind. These kinks are usually accompanied by the enhancement of radial solar wind velocity and ion temperature, increasing or decreasing of number density. The magnetic field kinks have also been observed by WIND and Ulysses to exist near and beyond 1 AU, respectively. In this study, we statistically analyze the property difference of magnetic field kinks observed by PSP and WIND. We obtain the following four points of results. (1) Inside the PSP-kinks, the radial velocity and protons&#8217; temperature increase while density shows enhancement or descent. However, inside the WIND-kinks, besides the slight enhancement of radial velocity, the density and temperature show no obvious change compared with the outside plasma. (2) By employing the Walen-test of kinks, we find that, R components of some PSP-kinks but not all satisfy the rotational discontinuity (RD) features, while the three components of most WIND-kinks well match the RD features. (3) The correlation between magnetic field and velocity inside the PSP-kinks and WIND-kinks does not show significant differences. (4) Both the PSP-kinks and WIND-kinks can be divided into two groups based on the histograms of &#952;Bn, where B is the background magnetic field, and n is the normal direction of kink. The first group (group-I) has &#952;Bn concentrating around 20&#176; for PSP-kinks and 30&#176; for WIND-kinks, indicating that the satellites were crossing the same kinked interplanetary magnetic field (IMF) from the upstream to the downstream. The second group (group-II) has &#952;Bn concentrating around 90&#176; for PSP-kinks and WIND-kinks, suggesting that the satellites were crossing an interface between the unkinked and kinked IMF regions. Our findings help better understanding the nature of kinks and provide the observational basis for testifying models about radial propagation and evolution of magnetic field kinks.

On the alignment of plasma anisotropies and the magnetic field direction in the solar wind

Journal of Geophysical Research Atmospheres ◽

10.1029/ja082i035p05555 ◽

1977 ◽

Vol 82 (35) ◽

pp. 5555-5562 ◽

Cited By ~ 8

Author(s):

J. R. Asbridge ◽

S. J. Bame ◽

W. C. Feldman ◽

J. T. Gosling ◽

N. F. Ness

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Field Direction ◽

Statistical analysis of the accelerated H2O ions above 1 keV: the comet 67P/Churyumov–Gerasimenko observed by the Rosetta spacecraft.

10.5194/egusphere-egu21-378 ◽

2021 ◽

Author(s):

Tsubasa Kotani ◽

Masatoshi Yamauchi ◽

Hans Nilsson ◽

Gabriella Stenberg-Wieser ◽

Martin Wieser ◽

...

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Statistical Analysis ◽

The Sun ◽

Ion Composition ◽

Solar Winds ◽

Comet Activity ◽

Parallel Acceleration ◽

Comet 67P ◽

The ESA/Rosetta spacecraft has studied the comet 67P/Churyumov-Gerasimenko for two years. Rosetta Plasma Consortium's Ion Composition Analyser (RPC/ICA) detected comet-origin water ions that are accelerated to > 100 eV.&#160; Majority of them are interpreted as ordinary pick-up acceleration&#160; by the solar wind electric field perpendicular to the magnetic field during low comet activity [1,2]. As the comet approaches the sun, a comet magnetosphere is formed, where solar winds cannot intrude.However,&#160; some water ions are accelerated to > 1 keV even in the magnetosphere [3]. Using RPC/ICA data during two years [4], we investigate the acceleration events > 1 keV where solar winds are not observed, and classify dispersion events with respect to the directions of the sun, the comet, and the magnetic field.&#160; Majority of these water ions show reversed energy-angle dispersion. Results of the investigation also show that these ions are flowing along the (enhanced) magnetic field, indicating that the parallel acceleration occurs in the magnetosphere.In this meeting, we show a statistical analysis and discuss a possible acceleration mechanism.References[1] H. Nilsson et al., MNRAS 469, 252 (2017), doi:10.1093/mnras/stx1491[2] G. Nicolau et al., MNRAS 469, 339 (2017), doi:10.1093/mnras/stx1621[3] T. Kotani et al., EPSC, EPSC2020-576 (2020), https://doi.org/10.5194/epsc2020-576[4] H. Nilsson et al., Space Sci. Rev., 128, 671 (2007), DOI: 10.1007/s11214-006-9031-z&#160;