Effective Polytropic Index of Small‐Scale and Force‐Free Magnetic Flux Ropes in the Solar Wind

Teh, W.‐L.

doi:10.1029/2021ja029944

Cited by 4 publications

(2 citation statements)

References 38 publications

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“…These other types of structures can occur or be recognized simultaneously with SFRs, and all possess the characteristics of significant field-aligned flow, hence being more dynamic. The internal process, e.g., the evolution of thermodynamics, may differ between quasi-static SFRs and those dynamic structures (Teh 2021). But neither the macroscopic properties, such as the scale size and duration, nor the 2D magnetic configurations exhibit substantial differences (Chen et al 2021).…”

Section: Introductionmentioning

confidence: 99%

Small-scale Magnetic Flux Ropes in Stream Interaction Regions from Parker Solar Probe and Wind Spacecraft Observations

Chen

Allen

et al. 2023

ApJ

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Using in situ measurements from the Parker Solar Probe and Wind spacecraft, we investigate the small-scale magnetic flux ropes (SFRs) and their properties inside stream interaction regions (SIRs). Within SIRs from ∼0.15 to 1 au, SFRs are found to exist in a wide range of solar wind speeds with more frequent occurrences after the stream interface, and the Alfvénicity of these structures decreases significantly with increasing heliocentric distances. Furthermore, we examine the variation of five corresponding SIRs from the same solar sources. The enhancements of suprathermal electrons within these SIRs persist at 1 au and are observed multiple times. An SFR appears to occur repeatedly with the recurring SIRs and is traversed by the Wind spacecraft at least twice. This set of SFRs has similarities in variations of the magnetic field components, plasma bulk properties, density ratio of solar wind alpha and proton particles, and unidirectional suprathermal electrons. We also show, through the detailed time-series plots and Grad–Shafranov reconstruction results, that they possess the same chirality and carry comparable amounts of magnetic flux. Lastly, we discuss the possibility for these recurring SFRs to be formed via interchange reconnection, maintain the connection with the Sun, and survive up to 1 au.

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Section: Introductionmentioning

confidence: 99%

Small-scale Magnetic Flux Ropes in Stream Interaction Regions from Parker Solar Probe and Wind Spacecraft Observations

Chen

Allen

et al. 2023

ApJ

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“…Gosling et al (2010) observed torsional Alfvén wave-embedded SSMFRs within the SW. Shi et al (2021) found the existence of Alfvén waves (proton cyclotron waves) inside (at the outer boundary) SSMFRs at about 0.2 au using PSP measurements. Recently, Teh (2021) studied the thermodynamics of SSMFRs and noted the effective polytropic index closer to 5/3 with torsional Alfvén wave-embedded SSMFRs, as compared to those without. It is believed that SSMFRs are manifestations of solar eruptions similar to magnetic clouds (Feng et al 2008;Cartwright & Moldwin 2010) or local magnetic reconnection in the SW/current sheet (Moldwin et al 1995(Moldwin et al , 2000Cartwright & Moldwin 2008), the solar corona and the SW (Huang et al 2020a), etc.…”

Section: Introductionmentioning

confidence: 99%

Nature of Turbulence inside Small-scale Magnetic Flux Ropes near the Sun: Parker Solar Probe Observations

Shaikh,

Vichare,

Bhaskar

et al. 2023

ApJ

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In this study, we probe the turbulence characteristic within the small-scale magnetic flux ropes (SSMFRs) close to the Sun using Parker Solar Probe (PSP) magnetic field data. The study includes 50 SSMFRs observed by PSP during Encounter 1, 2, and 3 between 35.74 R ☉ and 142.29 R ☉ distance from the Sun. We observed that the average spectral index for all the selected SSMFR events is –1.49 ± 0.21. In line with expectations, we also saw average ∣σ m ∣ values close to zero throughout the inertial range. We also observed that the size of the eddy at the highest frequency is much smaller than the size of the SSMFRs, indicating anisotropy within it. Thus, our finding supports anisotropic models that feature the Iroshnikov–Kraichnan index. Our findings agree with the turbulence properties of the solar wind near the Sun. We also observe low ∼0.1 compressibility, indicating SSMFRs are dominant by Alfvénic fluctuations. In light of this, we believe such an incompressible MHD spectrum results from nonlinear interactions between Alfvénic fluctuations. As a result, our research contributes to understanding the energy cascade process and its transport in solar plasma within the inner heliosphere.

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Evidence for superadiabatic heating and cooling of Alfvénic solar wind

Shaikh

Raghav

Vichare

et al. 2022

Monthly Notices of the Royal Astronomical Society: Letters

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Alfvénic fluctuations are widespread and crucial in various physical processes of space & astrophysical plasma. However, their role in heating and work done remains unexplored. Here, we have used Wind spacecraft’s data situated at 1 AU distance to examine 12 distinct Alfvénic regions using polytropic analysis. The study finds an average polytropic index value α = 2.64, which is consistent with a super-adiabatic behaviour for plasma particles with three effective degrees of freedom (f = 3). Moreover, this study examines several scenarios for plasma particles with different degrees of freedom. We noted that the investigated Alfvénic region could be adiabatic only for plasma particles with f = 1.26 degrees of freedom. In addition to this, for α = 2.64, the ratio of work done to the total heat supply within the system is $\frac{\delta w}{\delta q} = -0.68$, indicating that 68 per cent of the total supplied heat is utilized to accomplish work by the system on the surrounding (expansion phenomena), and the remaining is used to increase the internal energy of the system. As a result, we hypothesized that the Alfvénic plasma region is cooling more than the adiabatic expectation, resulting in super-cooling phenomena. Thus, we propose that the discovered possible super-adiabatic process would be critical in understanding the energy transfer from the Alfvénic zone to the surrounding plasma.

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Effective Polytropic Index of Small‐Scale and Force‐Free Magnetic Flux Ropes in the Solar Wind

Abstract: Magnetic flux ropes in small scales are commonly observed in the solar wind and their durations vary from ∼30 min to ∼12 h (e.g.,

Cited by 4 publications

References 38 publications

Small-scale Magnetic Flux Ropes in Stream Interaction Regions from Parker Solar Probe and Wind Spacecraft Observations

Small-scale Magnetic Flux Ropes in Stream Interaction Regions from Parker Solar Probe and Wind Spacecraft Observations

Nature of Turbulence inside Small-scale Magnetic Flux Ropes near the Sun: Parker Solar Probe Observations

Evidence for superadiabatic heating and cooling of Alfvénic solar wind

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