Explorer 35 observations of solar-wind electron density, temperature, and anisotropy

Serbu, G. P.

doi:10.1029/ja077i010p01703

Cited by 16 publications

(8 citation statements)

References 23 publications

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“…If we concentrate on the trailing edges of these streams, where dynamical effects are minimal, there is a tendency for Tc to be lower locally when U is higher. This effect is consistent with the weak, inverse correlations between T core and the bulk speed reported by Serbu (1972) andFeldman _gtal.. (1975) on the basis of 1 AU observations. All of these correlations are consistent with expansive collisional cooling and compressive heating of a "classical gas".…”

Section: Observational Support Of Theoretically Expected Correlationssupporting

confidence: 80%

A theory of local and global processes which affect solar wind electrons 2. Experimental support

Scudder¹,

Olbert²

1979

J. Geophys. Res.

158

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We have extended the theoretical considerations of Scudder and Olbert (1979) (hereafter paper I) to show from the microscopic characteristics of the Coulomb cross section that there are three natural subpopulations for plasma electrons: the subthermals with local kinetic energy E < kTc; the transthermals with kT < E < 7 kT and the extrathermals E > 7 kT c . We present experimental support from three experimental groups on three different spacecraft in the interplanetary medium over a radial range for the five interrelations projected in paper I between solar wind electron properties and changes in the interplanetary medium: 1) subthermals respond primarily to local changes (compressions and rarefactions) in stream dynamics; 2) the extrathermal fraction of the ambient electron density should be anti-correlated with the asymptotic bulk speed; 3) the extrathermal "temperature" should be anti-correlated with the local wind speed at 1 AU; 4) the heat flux carried by electrons should be anti-correlated with the local bulk speed; and 5) the extrathermal differ ential "temperature" should be nearly independent of radius within 1 AU.From first principles and the spatial inhomogeneity of the plasma we show that the velocity dependence of Coulomb collisions in the solar wind plasma produces a bifurcation in the solar wind electron distribution function at a transition energy, E*. This energy is theoretically shown to scale with the local thermal (tp core) temperature as E*(r) A 7 kT c(r).This scaling is observationally supported over the radial range from 0.45 to 0.9 AU by Mariner 10 data and IMP data acquired at 1 AU. The extra thermals, defined on the basis of Coulomb collisions, is synonymous with 3 the subpopulation previously labeled in the literature as the "halo" or shot" component. If the transition energy should be required to equal the polarization potential energy, e(r), for all radii beyond the observer, (as motivated by Mariner 10 data) the thermal electrons should obey a polytrope law with index Y = 7/6. In this circumstance the polarization potential is equal to the specific enthalpy: e4(r) = [y/(y-1)] kTc(r).This relation probably does not obtain in the corona, inside r < 10-20 RQ (of. Paper I). In the asymptotic spherically symmetric solar wind the inverse power law index for radial variation required for the thermal electrons should be a = 1/3 which is consistent with the recent in situ determinations between 0.45 and 03 AU. We thus provide the first self-consistent argument for associating E*(r) with e0(r). This theoretical asymptotic (r -) thermal electron temperature variation is between the conduction dominated (2Z7) and the inviscid solution (2/5). In the proximity of the ecliptic the ratio of the thermal electron Coulomb mean free path to scale length is shown to decrease with increasing radial distance. By contrast, over the solar poles the same asymptotic tempera ture and density variations iiply that the, Coulomb thermal mean free path will increase with increasing radial distance.A strai...

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Section: Observational Support Of Theoretically Expected Correlationssupporting

confidence: 80%

A theory of local and global processes which affect solar wind electrons 2. Experimental support

Scudder¹,

Olbert²

1979

J. Geophys. Res.

158

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“…Hollweg and V61k argued that this was an attractive instability because of its ability simultaneously to reduce both the electron and the proton anisotropies and to cool the electrons and heat the protons, but (60) is probably only rarely satisfied in the solar wind; Serbu [1972] has found some circumstances when it may occur, however. At this point we digress for a moment to mention a third instability that is similar to the two fire hose instabilities discussed above, except that it is driven by anisotropies in the sense of pz > p•.…”

Section: However There Are a Number Of Reasons Why We Do Not Feel Thmentioning

confidence: 87%

Waves and instabilities in the solar wind

Hollweg¹

1975

Reviews of Geophysics

144

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We present a review of waves and instabilities in the solar wind, concentrating on those aspects that are likely to play important roles in influencing the dynamic and thermodynamic states of the general solar wind expansion. We consider in particular the roles played by various waves and instabilities in influencing the heating and expansion of the solar wind, the angular momentum of the solar wind, the solar wind thermal anisotropy, the heating and flow of alpha particles in the solar wind, the interstellar neutral particles that become ionized in the solar wind, and the ‘fluidlike behavior’ of the solar wind. We include a brief review of the properties of the hydromagnetic wave modes, concentrating particularly on the Alfvén mode, which has been observed to contribute significantly to the microscale fluctuations of the solar wind. But we also present a summary of observational evidence pertaining to the presence and action in the solar wind of waves and instabilities that are not among the hydromagnetic modes.

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“…Present descriptions of electrons in the solar wind [Wolfe and McKibbin,. 1968;Montgomery et al, 1968;Ogilvie et al, 1971;Montgomery, 1972a;Serbu, 1972;Feldman et al, 1973a;Scudder et al, 1973] are not as complete as those of the ions [Hundhausen et al, 1970; see also Hundhausen, 1972, for a comprehensive review] because of the relative difficulty in measuring electron velocity distributions. This paper is intended to reduce this deficiency by presentihg detailed results of interplanetary electron measurements using the Los Alamos Scientific Laboratory (LASL) Imp 6, 7, and 8 plasma analyzers.…”

Section: Introductionmentioning

confidence: 99%

Solar wind electrons

Feldman¹,

Asbridge²,

Bame³

et al. 1975

J. Geophys. Res.

712

527

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Average characteristics of solar wind electron velocity distributions as well as the range and nature of their variations are presented. The measured distributions are generally symmetric about the heat flux direction and are adequately parameterized by the superposition of a nearly bi‐Maxwellian function which characterizes the low‐energy electrons and a bi‐Maxwellian function which characterizes a distinct, ubiquitous component of higher‐energy electrons. An alternate self‐consistent description of the higher‐energy component is presented in terms of an unbound population of hot electrons with energy greater than some breakpoint energy of ≃60 V. The largest‐scale parameter variations appear to come most often in association with high‐speed streams. The salient electron parameter variations associated with these structures are presented and discussed. The mechanism by which interplanetary electrons conduct heat is convection of the hot component relative to the bulk speed. Arguments are presented which favor the local regulation of the solar wind heat flux at 1 AU.

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Explorer 35 observations of solar-wind electron density, temperature, and anisotropy

Cited by 16 publications

References 23 publications

A theory of local and global processes which affect solar wind electrons 2. Experimental support

A theory of local and global processes which affect solar wind electrons 2. Experimental support

Waves and instabilities in the solar wind

Solar wind electrons

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