Cross helicity of magnetic clouds observed by Parker Solar Probe

2021 ◽  
Author(s):  
Simon Good ◽  
Emilia Kilpua ◽  
Matti Ala-Lahti ◽  
Adnane Osmane ◽  
Stuart Bale ◽  
...  
Keyword(s):  
Solar Wind ◽  
Large Scale ◽  
Mean Field ◽  
Residual Energy ◽  
Magnetic Clouds ◽  
Closed Field ◽  
Twisted Field ◽  
Field Fluctuations ◽  
Field Lines ◽  
Low Amplitude

<p>Magnetic clouds are large-scale transient structures in the solar wind with low plasma <em>β</em>, low-amplitude magnetic field fluctuations, and twisted field lines with both ends often connected to the Sun. We analyse the normalised cross helicity, <em>σ</em><sub>c</sub>, and residual energy, <em>σ</em><sub>r</sub>, in magnetic clouds observed by Parker Solar Probe (PSP). In the November 2018 cloud observed at 0.25 au, a low value of <em>σ</em><sub>c</sub> was present in the cloud core, indicating that wave power parallel and anti-parallel to the mean field was approximately balanced, while the cloud’s outer layers displayed larger amplitude Alfvénic fluctuations with high <em>σ</em><sub>c</sub> values and <em>σ</em><sub>r</sub> ~ 0. These properties are compared and contrasted to those found in clouds observed by PSP at larger heliocentric distances. We suggest that low <em>σ</em><sub>c</sub> is likely a common feature of magnetic clouds given their typically closed field structure, in contrast to the generally higher <em>σ</em><sub>c</sub> found on the open field lines of the solar wind.</p>

scholarly journals Resistive evolution of toroidal field distributions and their relation to magnetic clouds

2019 ◽  
Vol 85 (1) ◽  
Author(s):  
C. B. Smiet ◽  
H. J. de Blank ◽  
T. A. de Jong ◽  
D. N. L. Kok ◽  
D. Bouwmeester
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Magnetic Clouds ◽  
Twisted Field ◽  
Field Lines ◽  
Rotational Transform ◽  
Universal Pattern ◽  
The Magnetic Field

We study the resistive evolution of a localized self-organizing magnetohydrodynamic equilibrium. In this configuration the magnetic forces are balanced by a pressure force caused by a toroidal depression in the pressure. Equilibrium is attained when this low-pressure region prevents further expansion into the higher-pressure external plasma. We find that, for the parameters investigated, the resistive evolution of the structures follows a universal pattern when rescaled to resistive time. The finite resistivity causes both a decrease in the magnetic field strength and a finite slip of the plasma fluid against the static equilibrium. This slip is caused by a Pfirsch–Schlüter-type diffusion, similar to what is seen in tokamak equilibria. The net effect is that the configuration remains in magnetostatic equilibrium whilst it slowly grows in size. The rotational transform of the structure becomes nearly constant throughout the entire structure, and decreases according to a power law. In simulations this equilibrium is observed when highly tangled field lines relax in a high-pressure (relative to the magnetic field strength) environment, a situation that occurs when the twisted field of a coronal loop is ejected into the interplanetary solar wind. In this paper we relate this localized magnetohydrodynamic equilibrium to magnetic clouds in the solar wind.

Ion-scale break of the plasma fluctuation spectra in different large-scale solar wind streams

2021 ◽  
Author(s):  
Maria Riazantseva ◽  
Liudmila Rakhmanova ◽  
Yuri Yermolaev ◽  
Irina Lodkina ◽  
Georgy Zastenker ◽  
...  
Keyword(s):  
Solar Wind ◽  
Large Scale ◽  
Plasma Heating ◽  
Coronal Holes ◽  
Magnetic Clouds ◽  
Alfven Wave ◽  
Slow Solar Wind ◽  
P Value ◽  
High Temporal Resolution ◽  
Turbulent Cascade

<p>Appearance of measurements of the interplanetary medium parameters with high temporal resolution gave rise to a variety of investigations of turbulent cascade at ion kinetic scales at which processes of plasma heating was believed to operate. Our recent studies based on high frequency plasma measurements at Spektr-R spacecraft have shown that the turbulent cascade was not stable and dynamically changed depending on the plasma conditions in different large-scale solar wind structures. These changes was most significant at the kinetic scales of the turbulent cascade. Slow undisturbed solar wind was characterized by the consistency of the spectra to the predictions of the kinetic Alfven wave turbulence model. On the other hand, the discrepancy between the model predictions and registered spectra were found in stream interaction regions characterized by crucial steepening of spectra at the kinetic scales with slopes having values up to -(4-5). This discrepancy was clearly shown for plasma compression region Sheath in front of the magnetic clouds and CIR in front of high speed streams associated with coronal holes. Present study is focused on the break preceding the kinetic scales. Currently the characteristic plasma parameters associated with the formation of the break is still debated. Number of studies demonstrated that the break was consistent with distinct characteristic frequencies for different values ​​of the plasma proton parameter beta βp. Present study consider the ratio between the break frequency determined for ion flux fluctuation spectra according to Spektr-R data and several characteristic plasma frequencies used traditionally in such cases. The value of this ratio is statistically compared for different large-scale solar wind streams. We analyze both the classical spectrum view with two slopes and one break and the spectrum with flattening between magnetohydrodynamic and kinetic scales.  Our results show that for the Sheath and CIR regions characterized typically by βp ≤1 the break corresponds statistically to the frequency determined by the proton gyroradius. At the same time such correspondence are not observed either for the undisturbed slow solar wind with similar βp value or for disturbed flows associated with interplanetary manifestations of coronal mass ejections, where βp << 1. The results also shows that in slow undisturbed solar wind the break is closer to the frequency determined by the inertial proton length. Thus, apparently the transition between streams of different speeds may result in the change of dissipation regimes and plays role in plasma heating at these areas. This work was supported by the RFBR grant No. 19-02-00177a</p>

scholarly journals Dynamical critical scaling of electric field fluctuations in the greater cusp and magnetotail implied by HF radar observations of F-region Doppler velocity

2006 ◽  
Vol 24 (2) ◽  
pp. 689-705 ◽  
Author(s):  
M. L. Parkinson
Keyword(s):  
Solar Wind ◽  
Open Field ◽  
Electric Fields ◽  
Spectral Width ◽  
Hf Radar ◽  
Doppler Velocity ◽  
Closed Field ◽  
Scaling Exponent ◽  
Central Plasma ◽  
Field Lines

Abstract. Akasofu's solar wind ε parameter describes the coupling of solar wind energy to the magnetosphere and ionosphere. Analysis of fluctuations in ε using model independent scaling techniques including the peaks of probability density functions (PDFs) and generalised structure function (GSF) analysis show the fluctuations were self-affine (mono-fractal, single exponent scaling) over 9 octaves of time scale from ~46 s to ~9.1 h. However, the peak scaling exponent α0 was a function of the fluctuation bin size, so caution is required when comparing the exponents for different data sets sampled in different ways. The same generic scaling techniques revealed the organisation and functional form of concurrent fluctuations in azimuthal magnetospheric electric fields implied by SuperDARN HF radar measurements of line-of-sight Doppler velocity, vLOS, made in the high-latitude austral ionosphere. The PDFs of vLOS fluctuation were calculated for time scales between 1 min and 256 min, and were sorted into noon sector results obtained with the Halley radar, and midnight sector results obtained with the TIGER radar. The PDFs were further sorted according to the orientation of the interplanetary magnetic field, as well as ionospheric regions of high and low Doppler spectral width. High spectral widths tend to occur at higher latitude, mostly on open field lines but also on closed field lines just equatorward of the open-closed boundary, whereas low spectral widths are concentrated on closed field lines deeper inside the magnetosphere. The vLOS fluctuations were most self-affine (i.e. like the solar wind ε parameter) on the high spectral width field lines in the noon sector ionosphere (i.e. the greater cusp), but suggested multi-fractal behaviour on closed field lines in the midnight sector (i.e. the central plasma sheet). Long tails in the PDFs imply that "microbursts" in ionospheric convection occur far more frequently, especially on open field lines, than can be captured using the effective Nyquist frequency and volume resolution of SuperDARN radars.

The nature of comets

1987 ◽  
Vol 323 (1572) ◽  
pp. 437-446 ◽  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Large Scale ◽  
Future Research ◽  
Head Region ◽  
Scientific Curiosity ◽  
Halley's Comet ◽  
First Results ◽  
Cometary Material ◽  
Field Lines

The vast scientific campaign associated with the 1986 return of Halley’s Comet has greatly improved and expanded our knowledge of comets. An overview of the first results is presented here with emphasis on the large-scale structure, the chemistry, and the nucleus. Biermann and Alfven’s basic large-scale picture involving the interaction with the solar wind was confirmed. The interaction extends over very large distances and involves the draping of magnetic field lines from the solar wind around the head region. The near-nuclear region is essentially free of magnetic field. The cometary environment is a rich plasma physics laboratory as well as the site of spectacular disconnection events. As Whipple proposed, the chemical composition of the nucleus is largely water, and the breakup of the water molecule produces the large hydrogen-cloud surrounding the comet. Minor constituents with high molecular mass have been observed in the comet. The composition of the dust generally resembles carbonaceous chondrites enriched in the elements H, C, N and O. The interest in the cometary chemistry stems from the belief that cometary material is probably the best remnant of the solar nebula’s original composition. The nucleus is monolithic, as predicted by Whipple’s icy-conglomerate model. Far from spherical, the nucleus is irregular and peanut- or potato-shaped. The surface is very dark, and the emission of gas and dust occurs in jets on the sunward side. Irregular erosion of the surface, which is covered by a dust crust, could lead to many interesting possibilities for outbursts or splitting. Even with our current enhancement of knowledge, comets will continue to excite scientific curiosity. Future research on comets should be very fruitful.

Electrons on closed field lines of lunar crustal fields in the solar wind wake

Icarus ◽  
2015 ◽  
Vol 250 ◽  
pp. 238-248 ◽  
Author(s):  
Masaki N. Nishino ◽  
Yoshifumi Saito ◽  
Hideo Tsunakawa ◽  
Futoshi Takahashi ◽  
Masaki Fujimoto ◽  
...  
Keyword(s):  
Solar Wind ◽  
Closed Field ◽  
Field Lines

scholarly journals Coronal Structure and Solar Wind

1980 ◽  
Vol 91 ◽  
pp. 73-78
Author(s):  
J. N. Tandon
Keyword(s):  
Solar Wind ◽  
Large Scale ◽  
Coronal Holes ◽  
Solar Magnetic Fields ◽  
Coronal Structure ◽  
Active Centers ◽  
Hydromagnetic Wave ◽  
Field Lines ◽  
Open Magnetic Field ◽  
Coronal Structures

Recent observations of large scale coronal structures and solar wind have been studied. The intercorrelation of the two have been qualitatively explained through the focussing of solar-ion streams taking account of the local and general solar magnetic fields. This explains the association of coronal holes with weak, diverging open magnetic field lines and envisages the transfer of hydromagnetic wave energy from nearby active centers to account for the enhanced outflow of solar wind associated with coronal holes.

Small-scale variations of helium abundance in different large-scale solar wind structures

2020 ◽  
Author(s):  
Alexander Khokhlachev ◽  
Maria Riazantseva ◽  
Liudmila Rakhmanova ◽  
Yuri Yermolaev ◽  
Irina Lodkina ◽  
...  
Keyword(s):  
Solar Wind ◽  
Large Scale ◽  
Solar Wind Plasma ◽  
Magnetic Clouds ◽  
Slow Solar Wind ◽  
Small Scale ◽  
Plasma Stream ◽  
Helium Abundance ◽  
Russian Science ◽  
Plasma Parameters

<p>The boundaries between large-scale solar wind streams are often accompanied by sharp changes in helium abundance.  Wherein the high value of relative helium abundance is known as a sign of some large-scale solar wind structures ( for example magnetic clouds). Unlike the steady slow solar wind where the helium abundance is rather stable and equals ~5%, in magnetic clouds its value can grow significantly up to 20% and more, and at the same time helium component becomes more variable.  In this paper we analyze the small-scale variations of solar wind plasma parameters, including the helium abundance variations in different large-scale solar wind streams, especially in magnetic clouds and Sheath regions before them. We use rather long intervals of simultaneous measurements at Spektr-R (spectrometer BMSW) and Wind (spectrometer 3DP) spacecrafts.  We choose the intervals with rather high correlation  level of plasma parameters as a whole to be sure that we are deal with the same plasma stream.  The intervals associated with different large scale-solar wind structures are selected by using of our catalog ftp://ftp.iki.rssi.ru/pub/omni/catalog/. For selected intervals we examine cross-correlation function for Spektr-R and Wind measurements  to reveal the local spatial inhomogeneities by helium abundance which can be observed only at one of spacecrafts, and we determine properties of ones. Such inhomogeneities can be generate by turbulence, which is typically getting more intense in the considered disturbed intervals in the solar wind. The work is supported by Russian Science Foundation grant 16-12-10062.</p>

scholarly journals A comparison between ion characteristics observed by the POLAR and DMSP spacecraft in the high-latitude magnetosphere

2004 ◽  
Vol 22 (3) ◽  
pp. 1033-1046 ◽  
Author(s):  
T. J. Stubbs ◽  
M. Lockwood ◽  
P. Cargill ◽  
M. Grande ◽  
B. Kellett ◽  
...  
Keyword(s):  
Solar Wind ◽  
Probability Distributions ◽  
Average Energy ◽  
Auroral Oval ◽  
Topside Ionosphere ◽  
Closed Field ◽  
Central Plasma ◽  
Ion Energies ◽  
Low Energies ◽  
Field Lines

Abstract. We study here the injection and transport of ions in the convection-dominated region of the Earth's magnetosphere. The total ion counts from the CAMMICE MICS instrument aboard the POLAR spacecraft are used to generate occurrence probability distributions of magnetospheric ion populations. MICS ion spectra are characterised by both the peak in the differential energy flux, and the average energy of ions striking the detector. The former permits a comparison with the Stubbs et al. (2001) survey of He2+ ions of solar wind origin within the magnetosphere. The latter can address the occurrences of various classifications of precipitating particle fluxes observed in the topside ionosphere by DMSP satellites (Newell and Meng, 1992). The peak energy occurrences are consistent with our earlier work, including the dawn-dusk asymmetry with enhanced occurrences on the dawn flank at low energies, switching to the dusk flank at higher energies. The differences in the ion energies observed in these two studies can be explained by drift orbit effects and acceleration processes at the magnetopause, and in the tail current sheet. Near noon at average ion energies of ≈1keV, the cusp and open LLBL occur further poleward here than in the Newell and Meng survey, probably due to convection- related time-of-flight effects. An important new result is that the pre-noon bias previously observed in the LLBL is most likely due to the component of this population on closed field lines, formed largely by low energy ions drifting earthward from the tail. There is no evidence here of mass and momentum transfer from the solar wind to the LLBL by non-reconnection coupling. At higher energies ≈2–20keV), we observe ions mapping to the auroral oval and can distinguish between the boundary and central plasma sheets. We show that ions at these energies relate to a transition from dawnward to duskward dominated flow, this is evidence of how ion drift orbits in the tail influence the location and behaviour of the plasma populations in the magnetosphere. Key words. Magnetospheric physics (magnetopause, cusp and boundary layers; magnetosphere-ionosphere interactions; magnetospheric configuration and dynamic)

scholarly journals Satellite observations of currents and waves in space plasmas

1988 ◽  
Vol 6 (3) ◽  
pp. 503-511 ◽  
Author(s):  
T. A. Potemra ◽  
M. J. Engebretson ◽  
L. J. Zanetti ◽  
R. E. Erlandson ◽  
P. F. Bythrow
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Geomagnetic Field ◽  
Large Scale ◽  
Field Experiments ◽  
Outer Space ◽  
Solar Wind Plasma ◽  
Field Configuration ◽  
The Earth ◽  
Field Lines

When viewed from outer space, the earth's magnetic field does not resemble a simple dipole, but is severely distorted into a comet-shaped configuration by the continuous flow of solar wind plasma. A complicated system of currents flows within this distorted magnetic field configuration called the ‘magnetosphere’ (See figure 1). For example, the compression of the geomagnetic field by the solar wind on the dayside of the earth is associated with a large-scale current flowing across the geomagnetic field lines, called the ‘Chapman-Ferraro’ or magnetopause current. The magnetospheric system includes large-scale currents that flow in the ‘tail’, the ring current that flows at high altitudes around the equator of the earth, field-aligned ‘Birkeland’ currents that flow along geomagnetic field lines into and away from the two auroral regions, and a complex system of currents that flows completely within the layers of the ionosphere, the earth's ionized atmosphere. The intensities of these various currents reach millions of amperes and are closely related to solar activity. The geomagnetic field lines can also oscillate, like giant vibrating strings, at specified resonant frequencies. The effects of these vibrations, sometimes described as ‘standing Alfvén waves’, have been observed on the ground in magnetic field recordings dating back to the beginning of the century. Observations of currents and waves with satellite-borne magnetic field experiments have provided a new perspective on the complicated plasma processes that occur in the magnetosphere. Some of the new observations are described here.

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