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1.
Viviane Pierrard Milan Maksimovic Joseph Lemaire 《Astrophysics and Space Science》2001,277(1-2):195-200
Electron velocity distribution functions (VDF) observed in the low speed solar wind flow are generally characterized by ‘core’
and ‘halo’ electrons. In the high speed solar wind, a third population of ‘strahl’ electrons is generally observed. New collisional
models based on the solution of the Fokker-Planck equation can be used to determine the importance of the different electron
populations as a function of the radial distance. Typical electron velocity distribution functions observed at 1 AU from the
Sun are used as boundary conditions for the high speed solar wind and for the low speed solar wind. Taking into account the
effects of external forces and Coulomb collisions with a background plasma, suprathermal tails are found to be present in
the electron VDF at low altitudes in the corona when they exist at large radial distances.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
2.
The electron distribution functions from the solar corona to the solar wind are determined in this paper by considering the
effects of the external forces, of Coulomb collisions and of the wave – particle resonant interactions in the plasma wave
turbulence. The electrons are assumed to be interacting with right-handed polarized waves in the whistler regime. The acceleration
of electrons in the solar wind seems to be mainly due to the electrostatic potential. Wave turbulence determines the electron
pitch-angle diffusion and some characteristics of the velocity distribution function (VDF) such as suprathermal tails. The
role of parallel whistlers can also be extended to small altitudes in the solar wind (the acceleration region of the outer
corona), where they may explain the energization and the presence of suprathermal electrons. 相似文献
3.
The plasmapause formation physical mechanisms are recalled: (i) the MHD convection mechanism, based on the original idea that
the plasmapause coincides with the last closed equipotential (LCE) of the magnetospheric convection electric field or with
the last closed streamline (LCS) of the equatorial plasma, and (ii) the interchange mechanism, which is based on peeling off
the plasmasphere as a result of substorm associated enhancements of the night side convection velocity, leading to an enhanced
centrifugal acceleration in the outermost layers of the plasmasphere. The plasmapause positions, predicted by these alternative
theories, were numerically determined for two different magnetospheric empirical electric field models: (i) the Volland-Stern-Maynard-Chen
(VSMC) and (ii) McIlwain E5D models, both of which are Kp-dependent. The predicted positions and overall shape of the equatorial plasmapause cross-sections are confronted to those
derived from decades of whistler and satellite observations including the EUV observations during the substorm of June 27,
2001. It is found that the VSMC electric field model and the LCS plasmapause formation theory less correspond to whistler
measurements and in-situ satellite observations than the E5D model and the interchange plasmapause formation mechanism.
Published in Russian in Geomagnetizm i Aeronomiya, 2008, Vol. 48, No. 5, pp. 579–597.
The article was translated by the authors. 相似文献
4.
An understanding of solar variability over a broad spectral range and broad range of timescales is needed by scientists studying Earth’s climate. The Total and Spectral Solar Irradiance Sensor (TSIS) Spectral Irradiance Monitor (SIM), is designed to measure solar spectral irradiance (SSI) with unprecedented accuracy from 200 nm to 2400 nm. SIM started daily observations in March 2018. To maintain its accuracy over the course of its anticipated 5-year mission and beyond, TSIS SIM needs to be corrected for optical degradation, common for solar viewing instruments. The differing long-term trends of various independent solar-irradiance records attest to the challenge at hand.
The correction of TSIS SIM for optical degradation is based on piecewise linear fits that bring the three instrument channels into agreement. It is fundamentally different to the correction applied to the TSIS SIM predecessor on SORCE. The correction facilitates reproducibility, uncertainty estimation and is measurement-based. Corrected, integrated TSIS SIM SSI agrees with independent observations of total solar irradiance to within 45 ppm as well as various solar-irradiance models. TSIS SIM SSI is available at: http://lasp.colorado.edu/lisird/.
相似文献5.
Milan Maksimovic Viviane Pierrard Joseph Lemaire 《Astrophysics and Space Science》2001,277(1-2):181-187
We present the basics of the exospheric models of the solar wind acceleration. In these models the plasma is assumed fully
collisionless above a typical altitude in the corona. The solar wind is accelerated by the interplanetary electrostatic potential
which is needed to warrant the equality of the proton and electron fluxes. These models suggest that the fast wind emanating
from the polar regions could be due to the presence of non-thermal electron distributions in the corona.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
6.
I.A. Barghouthi V. Pierrard A.R. Barakat J. Lemaire 《Astrophysics and Space Science》2001,277(3):427-436
A Monte Carlo simulation is used to study the effects of Kappa H+distributions in the polar wind. We consider the gravity, the polarization electric field, the divergence of geomagnetic field
lines and Coulomb collisions of H+ in a background of O+ ions. The aim is to study the consequences of a velocity distribution function with an enhanced high energy tail instead
of a Maxwellian distribution as assumed in earlier Monte Carlo simulations. The transformation of the velocity distribution
function of H+ ions as a function of the altitude is presented. Effects resulting from the acceleration of the particles by the polarization
electric field and from Coulomb collisions depend on the energy of the particles. Coulomb collisions mainly affect low energy
particles while high energy particles are more efficiently accelerated by the upward directed ambipolar electric field. The
combination of both effects results in double-hump velocity distribution functions developing in the transition region. We
study consequences of suprathermal tails distributions on the shape of the double-hump and on the moments of the velocity
distribution function.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
7.
In the present paper, the proton velocity distribution function (VDF) in the solar wind is determined by numerically solving the kinetic evolution equation. We compare the results obtained when considering the effects of external forces and Coulomb collisions with those obtained by adding effects of Alfvén wave turbulence. We use Fokker–Planck diffusion terms to calculate the Alfvénic turbulence, which take into account observed turbulence spectra and kinetic effects of the finite proton gyroradius. Assuming a displaced Maxwellian for the proton VDF at the simulation boundary at 14 solar radii, we show that the turbulence leads to a fast (within several solar radii) development of the anti-sunward tail in the proton VDF. Our results provide a natural explanation for the nonthermal tails in the proton VDFs, which are often observed in-situ in the solar wind beyond 0.3 AU. 相似文献
8.
We study the velocity-space quasi-linear diffusion of the solar wind protons driven by oblique Alfvén turbulence at proton kinetic scales. Turbulent fluctuations at these scales possess the properties of kinetic Alfvén waves (KAWs) that are efficient in Cherenkov-resonant interactions. The proton diffusion proceeds via Cherenkov kicks and forms a quasi-linear plateau – the nonthermal proton tail in the velocity distribution function (VDF). The tails extend in velocity space along the mean magnetic field from 1 to (1.5?–?3) V A, depending on the spectral break position, on the turbulence amplitude at the spectral break, and on the spectral slope after the break. The most favorable conditions for the tail generation occur in the regions where the proton thermal and Alfvén velocities are about equal, V Tp/V A≈1. The estimated formation times are within 1?–?2 h for typical tails at 1 AU, which is much shorter than the solar wind expansion time. Our results suggest that the nonthermal proton tails, observed in situ at all heliocentric distances >?0.3 AU, are formed locally in the solar wind by the KAW turbulence. We also suggest that the bump-on-tail features – proton beams, often seen in the proton VDFs, can be formed at a later evolutional stage of the nonthermal tails by the time-of-flight effects. 相似文献
9.
10.
The plasma particle velocity distributions observed in the solar wind generally show enhanced (non-Maxwellian) suprathermal
tails, decreasing as a power law of the velocity and well described by the family of Kappa distribution functions. The presence
of non-thermal populations at different altitudes in space plasmas suggests a universal mechanism for their creation and important
consequences concerning plasma fluctuations, the resonant and nonresonant wave – particle acceleration and plasma heating.
These effects are well described by the kinetic approaches where no closure requires the distributions to be nearly Maxwellian.
This paper summarizes and analyzes the various theories proposed for the Kappa distributions and their valuable applications
in coronal and space plasmas. 相似文献