Study of alpha particle properties across rarefaction regions

Mapping Intimacies ◽

10.5194/egusphere-egu21-2864 ◽

2021 ◽

Author(s):

Tereza Durovcova ◽

Jana Šafránková ◽

Zdeněk Němeček

Keyword(s):

Solar Wind ◽

Wind Speed ◽

Alpha Particle ◽

Solar Wind Speed ◽

Coronal Holes ◽

Distribution Functions ◽

Alpha Particles ◽

Slow Solar Wind ◽

The Sun ◽

Wind Source

Two large-scale interaction regions between the fast solar wind emanating from coronal holes and the slow solar wind coming from streamer belt are usually distinguished. When the fast stream pushes up against the slow solar wind ahead of it, a compressed interaction region that co-rotates with the Sun (CIR) is created. It was already shown that the relative abundance of alpha particles, which usually serve as one of solar wind source identifiers can change within this region. By symmetry, when the fast stream outruns the slow stream, a corotating rarefaction region (CRR) is formed. CRRs are characterized by a monotonic decrease of the solar wind speed, and they are associated with the regions of small longitudinal extent on the Sun. In our study, we use near-Earth measurements complemented by observations at different heliocentric distances, and focus on the behavior of alpha particles in the CRRs because we found that the large variations of the relative helium abundance (AHe) can also be observed there. Unlike in the CIRs, these variations are usually not connected with the solar wind speed and alpha-proton relative drift changes. We thus apply a superposed-epoch analysis of identified CRRs with a motivation to determine the global profile of alpha particle parameters through these regions. Next, we concentrate on the cases with largest AHe variations and investigate whether they can be associated with the changes of the solar wind source region or whether there is a relation between the AHe variations and the non-thermal features in the proton velocity distribution functions like the temperature anisotropy and/or presence of the proton beam.

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Solar wind and kinetic heliophysics

Annales Geophysicae ◽

10.5194/angeo-36-1607-2018 ◽

2018 ◽

Vol 36 (6) ◽

pp. 1607-1630 ◽

Cited By ~ 5

Author(s):

Eckart Marsch

Keyword(s):

Solar Wind ◽

Interplanetary Space ◽

Coronal Holes ◽

Heavy Ion ◽

Alfven Waves ◽

Distribution Functions ◽

Slow Solar Wind ◽

Alfvén Waves ◽

The Sun ◽

Collisionless Dissipation

Abstract. This paper reviews recent aspects of solar wind physics and elucidates the role Alfvén waves play in solar wind acceleration and turbulence, which prevail in the low corona and inner heliosphere. Our understanding of the solar wind has made considerable progress based on remote sensing, in situ measurements, kinetic simulation and fluid modeling. Further insights are expected from such missions as the Parker Solar Probe and Solar Orbiter. The sources of the solar wind have been identified in the chromospheric network, transition region and corona of the Sun. Alfvén waves excited by reconnection in the network contribute to the driving of turbulence and plasma flows in funnels and coronal holes. The dynamic solar magnetic field causes solar wind variations over the solar cycle. Fast and slow solar wind streams, as well as transient coronal mass ejections, are generated by the Sun's magnetic activity. Magnetohydrodynamic turbulence originates at the Sun and evolves into interplanetary space. The major Alfvén waves and minor magnetosonic waves, with an admixture of pressure-balanced structures at various scales, constitute heliophysical turbulence. Its spectra evolve radially and develop anisotropies. Numerical simulations of turbulence spectra have reproduced key observational features. Collisionless dissipation of fluctuations remains a subject of intense research. Detailed measurements of particle velocity distributions have revealed non-Maxwellian electrons, strongly anisotropic protons and heavy ion beams. Besides macroscopic forces in the heliosphere, local wave–particle interactions shape the distribution functions. They can be described by the Boltzmann–Vlasov equation including collisions and waves. Kinetic simulations permit us to better understand the combined evolution of particles and waves in the heliosphere.

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Solar Wind and Kinetic Heliophysics

10.5194/angeo-2018-36 ◽

2018 ◽

Cited By ~ 1

Author(s):

Eckart Marsch

Keyword(s):

Solar Wind ◽

Interplanetary Space ◽

Coronal Holes ◽

Heavy Ion ◽

Alfven Waves ◽

Distribution Functions ◽

Slow Solar Wind ◽

Alfvén Waves ◽

The Sun ◽

Collisionless Dissipation

Abstract. This lecture reviews recent aspects of solar wind physics and elucidates the role Alfvén waves play in solar wind acceleration and turbulence, which prevail in the low corona and inner heliosphere. Our understanding of the solar wind has made considerable progress based on remote sensing, in-situ measurements, kinetic simulation and fluid modeling. Further insights are expected from such missions as the Parker Solar Probe and Solar Orbiter. The sources of the solar wind have been identified in the chromospheric network, Transition region and corona of the sun. Alfvén waves excited by reconnection in the network contribute to the driving of turbulence and plasma flows in funnels and coronal holes. The dynamic solar magnetic field causes solar wind variations over the solar cycle. Fast and slow solar wind streams, as well as transient coronal mass ejections are generated by the sun’s magnetic activity. Magnetohydrodynamic turbulence originates at the sun and evolves into interplanetary space. The major Alfvén waves and minor magnetosonic waves, with an admixture of pressurebalanced structures at various scales, constitute heliophysical turbulence. Its spectra evolve radially and develop anisotropies. Numerical simulations of turbulence spectra have reproduced key observational features. Collisionless dissipation of fluctuations remains a subject of intense research. Detailed measurements of particle velocity distributions have revealed non-maxwellian electrons, strongly anisotropic protons and heavy ion beams. Besides macroscopic forces in the heliosphere local wave-particle interactions shape the distribution functions. They can be described by the Boltzmann–Vlasov equation including collisions and waves. Kinetic simulations permit us to better understand the combined evolution of particles and waves in the heliosphere.

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Analysis of Quasistationary Solar Wind Stream Forecasts for 2010–2019

Meteorologiya i Gidrologiya ◽

10.52002/0130-2906-2021-3-58-66 ◽

2021 ◽

Vol 3 ◽

pp. 58-66

Author(s):

Yu. S. Shugai ◽

Keyword(s):

Solar Wind ◽

Wind Speed ◽

High Speed ◽

Solar Rotation ◽

Solar Wind Speed ◽

Coronal Holes ◽

Slow Solar Wind ◽

Stream Velocity ◽

Solar Wind Stream ◽

Time Model

A real-time model for predicting the quasistationary solar wind speed at the near-Earth orbit is presented. The forecast of the high-speed solar wind stream velocity is obtained with an empirical model linking the areas of coronal holes to the solar wind speed. The forecast of the slow solar wind is based on data on the observed solar wind speed from the previous solar rotation. Over the whole analyzed period from May 2010 to December 2019, the coefficient of correlation between the observed and predicted solar wind speed values is 0.45, and the standard deviation is 88 km/s. The accuracy of forecasting the speed of quasistationary solar wind streams is comparable to the results of foreign models.

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Alpha particle thermodynamics in the inner heliosphere fast solar wind

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834900 ◽

2019 ◽

Vol 623 ◽

pp. L2 ◽

Cited By ~ 12

Author(s):

D. Stansby ◽

D. Perrone ◽

L. Matteini ◽

T. S. Horbury ◽

C. S. Salem

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Alpha Particle ◽

Distribution Functions ◽

Alpha Particles ◽

Perpendicular Direction ◽

The Sun ◽

Fast Solar Wind ◽

Field Parallel ◽

The Magnetic Field

Context. Plasma processes occurring in the corona and solar wind can be probed by studying the thermodynamic properties of different ion species. However, most in situ observations of positive ions in the solar wind are taken at 1 AU, where information on their solar source properties may have been irreversibly erased. Aims. In this study we aim to use the properties of alpha particles at heliocentric distances between 0.3 AU and 1 AU to study plasma processes occurring at the points of observation, and to infer processes occurring inside 0.3 AU by comparing our results to previous remote sensing observations of the plasma closer to the Sun. Methods. We reprocessed the original Helios positive ion distribution functions, isolated the alpha particle population, and computed the alpha particle number density, velocity, and magnetic field perpendicular and parallel temperatures. We then investigated the radial variation of alpha particle temperatures in fast solar wind observed between 0.3 AU and 1 AU. Results. Between 0.3 AU and 1 AU alpha particles are heated in the magnetic field perpendicular direction and cooled in the magnetic field parallel direction. Alpha particle evolution is bounded by the alpha firehose instability threshold, which provides one possible mechanism to explain the observed parallel cooling and perpendicular heating. Closer to the Sun our observations suggest that the alpha particles undergo heating in the perpendicular direction, whilst the large magnetic field parallel temperatures observed at 0.3 AU may be due to the combined effect of double adiabatic expansion and alpha particle deceleration inside 0.3 AU.

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Solar wind speed within 20RSof the Sun estimated from limb coronal mass ejections

Journal of Geophysical Research Atmospheres ◽

10.1029/2005ja011249 ◽

2006 ◽

Vol 111 (A1) ◽

Cited By ~ 10

Author(s):

Tomoko Nakagawa ◽

Nat Gopalswamy ◽

Seiji Yashiro

Keyword(s):

Solar Wind ◽

Wind Speed ◽

Coronal Mass Ejections ◽

Solar Wind Speed ◽

The Sun

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The role of aerodynamic drag in dynamics of coronal mass ejections

Proceedings of the International Astronomical Union ◽

10.1017/s1743921309029391 ◽

2008 ◽

Vol 4 (S257) ◽

pp. 271-277

Author(s):

Bojan Vršnak ◽

Dijana Vrbanec ◽

Jaša Čalogović ◽

Tomislav Žic

Keyword(s):

Solar Wind ◽

Wind Speed ◽

Coronal Mass Ejections ◽

Weather Forecasting ◽

Aerodynamic Drag ◽

Interplanetary Space ◽

Solar Wind Speed ◽

Standard Form ◽

The Sun

AbstractDynamics of coronal mass ejections (CMEs) is strongly affected by the interaction of the erupting structure with the ambient magnetoplasma: eruptions that are faster than solar wind transfer the momentum and energy to the wind and generally decelerate, whereas slower ones gain the momentum and accelerate. Such a behavior can be expressed in terms of “aerodynamic” drag. We employ a large sample of CMEs to analyze the relationship between kinematics of CMEs and drag-related parameters, such as ambient solar wind speed and the CME mass. Employing coronagraphic observations it is demonstrated that massive CMEs are less affected by the aerodynamic drag than light ones. On the other hand, in situ measurements are used to inspect the role of the solar wind speed and it is shown that the Sun-Earth transit time is more closely related to the wind speed than to take-off speed of CMEs. These findings are interpreted by analyzing solutions of a simple equation of motion based on the standard form for the drag acceleration. The results show that most of the acceleration/deceleration of CMEs on their way through the interplanetary space takes place close to the Sun, where the ambient plasma density is still high. Implications for the space weather forecasting of CME arrival-times are discussed.

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On the Drag parameter of ICME propagation models

10.5194/egusphere-egu2020-21007 ◽

2020 ◽

Author(s):

Gianluca Napoletano ◽

Raffaello Foldes ◽

Dario Del Moro ◽

Francesco Berrilli ◽

Luca Giovannelli ◽

...

Keyword(s):

Solar Wind ◽

Travel Time ◽

Initial Conditions ◽

Solar Wind Speed ◽

Distribution Functions ◽

Model Parameters ◽

Wind Condition ◽

The Sun ◽

The Earth ◽

External Fluid

ICME (Interplanetary Coronal Mass Ejection) are violent phenomena of solar activity that affect the whole heliosphere and the prediction of their impact on different solar system bodies is one of the primary goals of the planetary space weather forecasting. The travel time of an ICME from the Sun to the Earth can be computed through the Drag-Based Model (DBM), which is based on a simple equation of motion for the ICME defining its acceleration as a=-&#915;(v-w)v-w, where a and v are the CME acceleration and speed, w is the ambient solar-wind speed and &#915; is the so-called drag parameter (Vrs&#780;nak et al., 2013). In this framework, &#915; depends on the ICME mass and cross-section, on the solar-wind density and, to a lesser degree, on other parameters. The typical working hypothesis for DBM implies that both &#915; and w are constant far from the Sun. To run the codes, forecasters use empirical input values for &#915; and w, derived by pre-existent knowledge of solar-wind condition and by solving the &#8220;inverted problem&#8221; (where the ICME travel time is known and the unknowns are &#915; and/or w). In the 'Ensemble' approaches (Dumbovich et al., 2018; Napoletano et al. 2018), the uncertainty about the actual values of such inputs are rendered by Probability Distribution Functions (PDFs), accounting for the values variability and our lack of knowledge. Among those PDFs, that of &#915; is poorly defined due to the relatively scarce statistics of recorded values.&#160;Employing a list of past ICME events, for which initial conditions when leaving the Sun and arrival conditions at the Earth are known, we employ a statistical approach to the Drag-Based Model to determine a measure of &#915; and w for each case. This allows to obtain distributions for the model parameters on experimental basis and, more importantly, to test whether different conditions of relative velocity to the solar wind influence the value of the drag efficiency, as it must be expected for solid objects moving into an external fluid. In addition, we perform numerical simulations of a solid ICME-shaped structure moving into the solar-wind modelled as an external fluid. Outcomes from these simulations are compared with our experimental results, and thus employed to interpret them on physical basis.

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Understanding Solar Wind Formation by Identifying the Origins of In Situ Observations

10.5194/egusphere-egu21-6200 ◽

2021 ◽

Author(s):

Samantha Wallace ◽

Nicholeen M. Viall ◽

Charles N. Arge

Keyword(s):

Solar Wind ◽

Solar Wind Speed ◽

Source Region ◽

Heliospheric Current Sheet ◽

Slow Solar Wind ◽

The Sun ◽

Flux Transport ◽

Model Driven ◽

In Situ Observations

Solar wind formation can be separated into three physical steps &#8211; source, release, and acceleration &#8211; that each leave distinct observational signatures on plasma parcels.&#160; The Wang-Sheeley-Arge (WSA) model driven by Air Force Data Assimilative Photospheric Flux Transport (ADAPT) time-dependent photospheric field maps now has the ability to connect in situ observations more rigorously to their precise source at the Sun, allowing us to investigate the physical processes involved in solar wind formation. &#160;&#160;In this talk, I will highlight my PhD dissertation research in which we use the ADAPT-WSA model to either characterize the solar wind emerging from specific sources, or investigate the formation process of various solar wind populations. &#160;In the first study, we test the well-known inverse relationship between expansion factor (fs) and observed solar wind speed (vobs) for solar wind that emerges from a large sampling of pseudostreamers, to investigate if field line expansion plays a physical role in accelerating the solar wind from this source region.&#160; We find that there is no correlation between fs and vobs at pseudostreamer cusps. In the second study, we determine the source locations of the first identified quasiperiodic density structures (PDSs) inside 0.6 au. Our modeling provides confirmation of these events forming via magnetic reconnection both near to and far from the heliospheric current sheet (HCS) &#8211; a direct test of the Separatrix-web (S-web) theory of slow solar wind formation.&#160; In the final study, we use our methodology to identify the source regions of the first observations from the Parker Solar Probe (PSP) mission.&#160; Our modeling enabled us to characterize the closest to the Sun observed coronal mass ejection (CME) to date as a streamer blowout.&#160; We close with future ways that ADAPT-WSA can be used to test outstanding questions of solar wind formation.

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