scholarly journals Characteristics of solar wind suprathermal halo electrons

2020 ◽  
Vol 642 ◽  
pp. A130
Author(s):  
M. Lazar ◽  
V. Pierrard ◽  
S. Poedts ◽  
H. Fichtner
Keyword(s):  
Solar Wind ◽  
High Speed ◽  
Solar Wind Speed ◽  
Substantial Reduction ◽  
Comprehensive Description ◽  
Temperature Plasma ◽  
Magnetic Focusing ◽  
Fast Wind ◽  
Outer Corona ◽  
Halo Population

A suprathermal halo population of electrons is ubiquitous in space plasmas, as evidence of their departure from thermal equilibrium even in the absence of anisotropies. The origin, properties, and implications of this population, however, are poorly known. We provide a comprehensive description of solar wind halo electrons in the ecliptic, contrasting their evolutions with heliospheric distance in the slow and fast wind streams. At relatively low distances less than 1 AU, the halo parameters show an anticorrelation with the solar wind speed, but this contrast decreases with increasing distance and may switch to a positive correlation beyond 1 AU. A less monotonic evolution is characteristic of the high-speed winds, in which halo electrons and their properties (e.g., number densities, temperature, plasma beta) exhibit a progressive enhancement already distinguishable at about 0.5 AU. At this point, magnetic focusing of electron strahls becomes weaker and may be counterbalanced by the interactions of electrons with wave fluctuations. This evolution of halo electrons between 0.5 AU and 3.0 AU in the fast winds complements previous results well, indicating a substantial reduction of the strahl and suggesting that significant fractions of strahl electrons and energy may be redistributed to the halo population. On the other hand, properties of halo electrons at low distances in the outer corona suggest a subcoronal origin and a direct implication in the overheating of coronal plasma via velocity filtration.

scholarly journals Interplanetary Response to Solar Long Time-Scale Phenomena

1980 ◽  
Vol 91 ◽  
pp. 105-125
Author(s):  
C. D'Uston ◽  
J. M. Bosqued
Keyword(s):  
Solar Wind ◽  
Time Scale ◽  
High Speed ◽  
Coronal Holes ◽  
Observational Evidence ◽  
Solar Wind Flow ◽  
Speed Solar Wind ◽  
Long Time ◽  
Outer Corona ◽  
High Speed Solar Wind

In this paper, we briefly review the experimental knowledge gained in the recent years on the interplanetary response to solar long-time scale phenomena such as the coronal magnetic structure and its evolution. Observational evidence that solar wind flow in the outer corona comes from the unipolar diverging magnetic regions of the photosphere is discussed along with relations to coronal holes. High-speed solar wind streams observed within the boundary of interplanetary magnetic sectors are associated with these structures. Their boundaries appear as very narrow velocity shears.

Selective acceleration of O+ by drift-bounce resonance in the Earth’s magnetosphere: MMS observations

2020 ◽  
Author(s):  
Satoshi Oimatsu ◽  
Masahito Nosé ◽  
Guan Le ◽  
Stephan A Fuselier ◽  
Robert E Ergun ◽  
...  
Keyword(s):  
Solar Wind ◽  
High Speed ◽  
Solar Wind Speed ◽  
Density Ratio ◽  
Flux Ratio ◽  
Recovery Phase ◽  
Wave Number ◽  
Azimuthal Component ◽  
Time Period ◽  
Speed Solar Wind

<p>We studied O<sup>+</sup>drift-bounce resonance using Magnetospheric Multiscale (MMS) data. A case study of an event on 17 February 2016 shows that O<sup>+</sup> flux oscillations at ~10–30 keV occurred at MLT ~ 5 hr and <em>L</em>~ 8–9 during a storm recovery phase. These flux oscillations were accompanied by a toroidal Pc5 wave and a high-speed solar wind (~550 km/s). The azimuthal wave number (<em>m</em>-number) of this Pc5 wave was found to be approximately –2. The O<sup>+</sup>/H<sup>+</sup> flux ratio was enhanced at ~10–30 keV corresponding to the O<sup>+</sup> flux oscillations without any clear variations of H<sup>+</sup> fluxes, indicating the selective acceleration of O<sup>+</sup> ions by the drift-bounce resonance. A search for the similar events in the time period from September 2015 to March 2017 yielded 12 events. These events were mainly observed in the dawn to the afternoon region at <em>L</em>~ 7–12 when the solar wind speed is high, and all of them were simultaneously identified on the ground, indicating low <em>m</em>-number. Correlation analysis revealed that the O<sup>+</sup>/H<sup>+</sup> energy density ratio has the highest correlation coefficient with peak power of the electric field in the azimuthal component (<em>E<sub>a</sub></em>). This statistical result supports the selective acceleration of O<sup>+</sup> due to the <em>N </em>= 2 drift-bounce resonance.</p>

scholarly journals Solar Wind ∼0.15–1.5 keV Electrons around Corotating Interaction Regions at 1 au

2021 ◽  
Vol 922 (2) ◽  
pp. 198
Author(s):  
Jiawei Tao ◽  
Linghua Wang ◽  
Gang Li ◽  
Robert F. Wimmer-Schweingruber ◽  
Chadi Salem ◽  
...  
Keyword(s):  
Solar Wind ◽  
Solar Wind Speed ◽  
Kinetic Temperature ◽  
Number Density ◽  
Kappa Index ◽  
Corotating Interaction Regions ◽  
Fast Wind ◽  
Magnetic Field Magnitude ◽  
Interaction Regions ◽  
The Relationship

Abstract Here we present a statistical study of the ∼0.15–1.5 keV suprathermal electrons observed in uncompressed/compressed slow and fast solar wind around 59 corotating interaction regions (CIRs) with good measurements by Wind 3DP from 1995 through 1997. For each of these CIRs, we fit the strahl and halo energy spectra at ∼0.15–1.5 keV to a Kappa function with a Kappa index κ and kinetic temperature T eff. We find that the ∼0.15–1.5 keV strahl electrons behave similarly in both slow and fast wind: the strahl number density n s positively correlates with the solar wind electron temperature T e and interplanetary magnetic field magnitude ∣B∣, while the strahl pitch angle width Θ s decreases with the solar wind speed V sw. These suggest that the strahl electrons are generated by a similar/same process at the Sun in both slow and fast wind that produces these correlations, and the scattering efficiency of strahl in the interplanetary medium (IPM) decreases with V sw. The ∼0.15–1.5 keV halo electrons also behave similarly in both slow and fast wind: the halo parameter positively correlates with the corresponding strahl parameter, and the halo number density n h positively correlates only with T e . These indicate that the halo formation process in the IPM retains most of the strahl properties, but it erases the relationship between n s and ∣B∣. In addition, κ in compressed wind distributes similarly to that in uncompressed wind, for both the strahl and halo. It shows that CIRs at 1 au are not a significant/effective acceleration source for the strahl and halo.

scholarly journals Cosmic Ray Signatures of Different Types of Solar Wind Streams

1990 ◽  
Vol 142 ◽  
pp. 259-260
Author(s):  
P.K. Shrivastava ◽  
S.P. Agrawal
Keyword(s):  
Solar Wind ◽  
High Speed ◽  
Solar Wind Speed ◽  
Coronal Holes ◽  
Cosmic Ray ◽  
Cosmic Ray Intensity ◽  
Wind Speeds ◽  
Different Types ◽  
Speed Solar Wind ◽  
High Speed Solar Wind

The earlier concept of average solar wind speed has changed with time. Besides quiet periods of low/average solar wind speeds, two different kinds of solar sources (solar flares and coronal holes) have been identified to produce high speed solar wind streams. In an earlier investigation, it was reported that the high speed streams associated to these sources produce distinctly different effects on the cosmic ray intensity (Venkatesan, et. al., 1982).

Solar cycle variations in differential instrumental responses from ground‑based geomagnetic records

2020 ◽  
Author(s):  
Stuart Gilder ◽  
Michael Wack ◽  
Elena Kronberg ◽  
Ameya Prabhu
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Solar Cycle ◽  
High Speed ◽  
Magnetic Measurements ◽  
Solar Wind Speed ◽  
Maximum Amplitude ◽  
Auroral Oval ◽  
Wide Frequency Range ◽  
The Magnetic Field

<p>We developed a new technique based on differences in instrument responses from ground-based magnetic measurements that extracts the frequency content of the magnetic field with periods ranging from 0.1 to 100 seconds. By stacking hourly averages over an entire year, we found that the maximum amplitude of the magnetic field oscillations occurred near solar noon over diurnal periods at all latitudes except in the auroral oval. Seasonal variability was identified only at high latitude. Long-term trends in field oscillations followed the solar cycle, yet the maxima occurred during the declining phase when high-speed streams in the solar wind dominated. A parameter based on solar wind speed and the relative variability of the interplanetary magnetic field correlated robustly with the ground-based measurements. Our findings suggest that turbulence in the solar wind, its interaction at the magnetopause, and its propagation into the magnetosphere stimulate magnetic field fluctuations at the ground on the dayside over a wide frequency range. Our method enables the study of field line oscillations using the publicly available, worldwide database of geomagnetic observatories.</p>

scholarly journals Quantifying the latitudinal representivity of in situ solar wind observations

2020 ◽  
Vol 10 ◽  
pp. 8 ◽  
Author(s):  
Mathew J. Owens ◽  
Matthew Lang ◽  
Pete Riley ◽  
Mike Lockwood ◽  
Amos S. Lawless
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Wind Speed ◽  
Solar Minimum ◽  
Numerical Models ◽  
Solar Wind Speed ◽  
Cycle Phase ◽  
Model State ◽  
Fast Wind

Advanced space-weather forecasting relies on the ability to accurately predict near-Earth solar wind conditions. For this purpose, physics-based, global numerical models of the solar wind are initialized with photospheric magnetic field and coronagraph observations, but no further observation constraints are imposed between the upper corona and Earth orbit. Data assimilation (DA) of the available in situ solar wind observations into the models could potentially provide additional constraints, improving solar wind reconstructions, and forecasts. However, in order to effectively combine the model and observations, it is necessary to quantify the error introduced by assuming point measurements are representative of the model state. In particular, the range of heliographic latitudes over which in situ solar wind speed measurements are representative is of primary importance, but particularly difficult to assess from observations alone. In this study we use 40+ years of observation-driven solar wind model results to assess two related properties: the latitudinal representivity error introduced by assuming the solar wind speed measured at a given latitude is the same as that at the heliographic equator, and the range of latitudes over which a solar wind measurement should influence the model state, referred to as the observational localisation. These values are quantified for future use in solar wind DA schemes as a function of solar cycle phase, measurement latitude, and error tolerance. In general, we find that in situ solar wind speed measurements near the ecliptic plane at solar minimum are extremely localised, being similar over only 1° or 2° of latitude. In the uniform polar fast wind above approximately 40° latitude at solar minimum, the latitudinal representivity error drops. At solar maximum, the increased variability of the solar wind speed at high latitudes means that the latitudinal representivity error increases at the poles, though becomes greater in the ecliptic, as long as moderate speed errors can be tolerated. The heliospheric magnetic field and solar wind density and temperature show very similar behaviour.

scholarly journals Coronal hole evolution from multi-viewpoint data as input for a STEREO solar wind speed persistence model

2018 ◽  
Vol 8 ◽  
pp. A18 ◽  
Author(s):  
Manuela Temmer ◽  
Jürgen Hinterreiter ◽  
Martin A. Reiss
Keyword(s):  
Solar Wind ◽  
Wind Speed ◽  
High Speed ◽  
Solar Wind Speed ◽  
Coronal Holes ◽  
In Situ Measurements ◽  
False Alarms ◽  
Wind Speed Profile ◽  
Persistence Model

We present a concept study of a solar wind forecasting method for Earth, based on persistence modeling from STEREO in situ measurements combined with multi-viewpoint EUV observational data. By comparing the fractional areas of coronal holes (CHs) extracted from EUV data of STEREO and SoHO/SDO, we perform an uncertainty assessment derived from changes in the CHs and apply those changes to the predicted solar wind speed profile at 1 AU. We evaluate the method for the time period 2008–2012, and compare the results to a persistence model based on ACE in situ measurements and to the STEREO persistence model without implementing the information on CH evolution. Compared to an ACE based persistence model, the performance of the STEREO persistence model which takes into account the evolution of CHs, is able to increase the number of correctly predicted high-speed streams by about 12%, and to decrease the number of missed streams by about 23%, and the number of false alarms by about 19%. However, the added information on CH evolution is not able to deliver more accurate speed values for the forecast than using the STEREO persistence model without CH information which performs better than an ACE based persistence model. Investigating the CH evolution between STEREO and Earth view for varying separation angles over ∼25–140° East of Earth, we derive some relation between expanding CHs and increasing solar wind speed, but a less clear relation for decaying CHs and decreasing solar wind speed. This fact most likely prevents the method from making more precise forecasts. The obtained results support a future L5 mission and show the importance and valuable contribution using multi-viewpoint data.

scholarly journals Solar Wind Plasma Particles Organized by the Flow Speed

Solar Physics ◽  
2020 ◽  
Vol 295 (11) ◽  
Author(s):  
Viviane Pierrard ◽  
Marian Lazar ◽  
Stepan Štverák
Keyword(s):  
Solar Wind ◽  
Solar Wind Speed ◽  
Solar Wind Plasma ◽  
Flow Speed ◽  
Average Value ◽  
The Core ◽  
Fast Wind ◽  
Core Electrons ◽  
Reduced Mobility ◽  
Bulk Speed

AbstractRecent reports of the first data from Parker Solar Probe (PSP) have pointed to a series of links, correlations or anti-correlations between the solar wind bulk speed ($V_{\mathrm{SW}}$ V SW ) and physical properties of plasma particles from less than 0.25 AU in the corona. In the present paper, we describe corresponding and additional links of solar wind properties, at 0.4 AU and 1.0 AU, in an attempt to complement the PSP data and understand their evolution. A detailed analysis is carried out for the main electron populations, comparing the low-energy (thermal) core and the collisionless suprathermal halo. We show that the anti-correlation observed at 0.4 AU between $V_{\mathrm{SW}}$ V SW and the number density (average value) is maintained also at 1 AU for both the core and halo electrons. On the contrary, only the core electrons manifest a clear anti-correlation of the temperature with $V_{\mathrm{SW}}$ V SW , while the halo temperature does not vary much. We also describe the ions, protons and helium, which have a more reduced mobility and their properties exhibit different variations with the solar wind speed. The results are used to shed more light on the mechanisms leading to a differential acceleration of these species and the origin of slow and fast wind modulation.

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