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1.
The plasma oscillations that can be observed by the French incoherent scatter system have small phase velocities and are excited by low energy photoelectrons, typically 2–5 eV. Consequently, the method used to determine the energy photoelectron distribution from plasma line measurements made at other observatories (e.g. Cicerone, 1974) cannot be applied here: it is necessary to chose a model energy distribution with a small number of parameters. The energy shape of the flux is assumed Maxwellian and the angular shape is assumed linear with the cosine of the pitch angle. Total flux values and mean energies are obtained as a function of altitude, in agreement with other determinations, and the difference between upshifted and downshifted plasma line intensities lead to the determination of the anisotropy of the photoelectron flux.  相似文献   

2.
The ambient photoelectron spectrum below 300 km has been studied for a sample of 500 AE-E orbits taken during the period 13 December 1975 to 24 February 1976. During this solar minimum period, the average and maximum Σ Kp were 19 and 35 respectively. The agreement between the measured spectral shape and several recent calculations is extremely good. The daytime photoelectron spectrum below 300 km from 1 to 100 eV is illustrated by a number of spectra. Detailed 0–32 eV spectra are presented at various altitudes and solar zenith angles. High resolution 10–32eV spectra show the widths of the photoelectron lines in the spectrum and the variation of the linewidth and intensity with altitude. Data from the entire 500 orbit sample are combined into plots of the average flux over a number of altitude ranges up to 300 km at various local times and solar zenith angles. The data show that the photoelectron flux below 300 km is remarkably constant (typical variation less than ±50%) over a period of several months. The photoelectron lines between 20 and 30 eV are extremely sharp when the total plasma density is low but broaden significantly at high altitudes as the plasma density builds up during the day. The N2 vibration-rotation excitation dip at 2.3 eV is strongest at the lowest altitudes and decreases with increasing altitude and plasma density. The absolute accuracy of the experiment is discussed in detail and a correction factor for previously published AE-E fluxes is given.  相似文献   

3.
Calculations of the steady-state photoelectron energy and angular distribution in the altitude region between 120 and 1000 km are presented. The distribution is found to be isotropic at all altitudes below 250 km, while above this altitude anisotropies in both pitch angle and energy are found. The isotropy found in the angular distribution below 250 km implies that photoelectron transport below 250 km is insignificant, while the angular anisotropy found above this altitude implies a net photoelectron current in the upward direction. The energy anisotropy above 500 km arises from the selective backscattering of the low energy photoelectron population of the upward flux component by Coulomb collisions with the ambient ions. The total photoelectron flux attains its maximum value between about 40 and 70 km above the altitude at which the photoelectron production rate is maximum. The displacement of the maximum of the equilibrium flux is attributed to an increasing (with altitude) photoelectron lifetime. Photoelectrons at altitudes above that where the flux is maximum are on the average more energetic than those below that altitude. The flux of photoelectrons escaping to the protonosphere at dawn was found to be 2.6 × 108 cm?2 sec?1, while the escaping flux at noon was found to be 1.5 × 108 cm?2 sec?1. The corresponding escaping energy fluxes are: 4.4 × 109 eV cm?2 sec?1 and 2.7 × 109 eV cm?2 sec?1.  相似文献   

4.
First results from wideband (electron phase energies of 5–51 eV), high-resolution (0.1 eV) spectral measurements of photoelectron–enhanced plasma lines made with the 430 MHz radar at Arecibo Observatory are presented. In the F region, photoelectrons produced by solar EUV line emissions (He II and Mg IX) give rise to plasma line spectral peaks/valleys. These and other structures occur within an enhancement zone extending from electron phase energies of 14–27 eV in both the bottomside and topside ionosphere. However, photoelectron–thermal electron Coulomb energy losses can lead to a broadened spectral structure with no resolved peaks in the topside ionosphere. The plasma line energy spectra obtained in the enhancement zone exhibit a unique relation in that phase energy is dependent on pitch angle; this relation does not exist in any other part of the energy spectrum. Moreover, large fluctuations in the difference frequency between the upshifted and downshifted plasma lines are evident in the 14–27 eV energy interval. At high phase energies near 51 eV the absolute intensities of photoelectron-excited Langmuir waves are much larger than those predicted by existing theory. The new measurements call for a revision/improvement of plasma line theory in several key areas.  相似文献   

5.
The ambient photoelectron spectrum above 300 km has been measured for a sample of 500 AE-E orbits during the period 13 December 1975 to 24 February 1976 corresponding to solar minimum conditions. The 24 h average and maximum ΣKp were 19 and 35, respectively. The photoelectron flux above 300 km was found to have an intensity and energy spectrum characteristic of the 250–300 km production region only when there was a low plasma density at the satellite altitude. Data taken at local times up to 3 h after sunrise were of this type and the escaping flux was observed to extend to altitudes above 900 km with very little modification, as predicted by several theoretical calculations. The flux at high altitudes was found to be extremely variable throughout the rest of the day, probably as a result of attenuation and energy loss to thermal plasma along the path of the escaping photoelectrons. This attenuation was most pronounced where the photoelectrons passed through regions of high plasma density associated with the equatorial anomaly. At altitudes of 600 km, the photoelectron fluxes ranged from severely attenuated to essentially unaltered—depending on the specific conditions, Photoelectron fluxes from conjugate regions were often less attenuated than those observed arriving from the high density regions immediately below. Comparison of the observed attenuations, photoelectron line broadening, and energy loss due to coulomb scattering from the thermal plasma with rough calculations based on stopping power and transmission coefficients of thermal plasma for fast electrons yielded order of magnitude agreement—satisfactory in view of the large number of assumptions necessary for the calculations. Overall, the impression of the high altitude photoelectron flux which emerges from this work is that the fluxes are extremely variable as a consequence of interactions with the thermal plasma whose density is in turn affected by electrodynamic and neutral wind processes in the underlying F region.  相似文献   

6.
Photoelectron flux in the energy range 6–70 eV coming from the sunlight conjugate ionosphere has been measured directly by the rocket borne low energy electron spectrometer in the altitude region of 210–350 km. Pitch angle distribution of the measured flux is nearly isotropic, the flux decreasing slightly with pitch angle. The photoelectron fluxes measured at 350 km at the energies of 15 and 30 eV are 3 × 106 and 1 × 106 (cm2 s str eV)?1 respectively which decrease to 1 × 106 and 1 × 105 at 250 km at the same energies. These values are consistent with the vertical profile of the 630 nm airglow intensity measured simultaneously. The fluxes obtained near apogee show peaks in the range 20–30 eV which also appear in the daytime photoelectron flux, indicating reduced loss of electrons during the passage from the conjugate ionosphere through the plasmasphere at the low geomagnetic latitude where observation was made. Photoelectron fluxes observed below the apogee height are compared to the calculated fluxes to investigate the interaction of electrons with the atmospheric species during the passage in the ionosphere. Calculated fluxes obtained by using continuous slowing-down approximation and neglecting pitch angle scattering are in good agreement with the observations although there still remain disagreements in detailed comparison which may be ascribed to the assumptions inherent in the calculation and/or to the uncertainties of the input data for the calculation.  相似文献   

7.
A numerical model of current F-region theory is use to calculate the diurnal variation of the mid-latitude ionospheric F-region over Millstone Hill on 23–24 March 1970, during quiet geomagnetic conditions. From the solar EUV flux, the model calculates at each altitude and time step primary photoelectron spectra and ionization rates of various ion species. The photoelectron transport equation is solved for the secondary ionization rates, photoelectron spectra, and various airglow excitation rates. Five ion continuity equations that include the effects of transport by diffusion, magnetospheric-ionospheric plasma transport, electric fields, and neutral winds are solved for the ion composition and electron density. The electron and ion temperatures are also calculated using the heating rates determined from chemical reactions, photoelectron collisions, and magnetospheric-ionospheric energy transport. The calculations are performed for a diurnal cycle considering a stationary field tube co-rotating with the Earth; only the vertical plasma drift caused by electric fields perpendicular to the geomagnetic field line is allowed but not the horizontal drift. The boundary conditions used in the model are determined from the incoherent scatter radar measurements of Te, Ti and O+ flux at 800km over Millstone Hill (Evans, 1971a). The component of the neutral thermospheric winds along the geomagnetic field has an important influence on the overall ionospheric structure. It is determined from a separate dynamic model of the neutral thermosphere, using incoherent scatter radar measurements.The calculated diurnal variation of the ionospheric structure agrees well with the values measured by the incoherent scatter radar when certain restrictions are placed on the solar EUV flux and model neutral atmospheric compositions. Namely, the solar EUV fluxes of Hinteregger (1970) are doubled and an atomic oxygen concentration of at least 1011cm3 at 120 km is required for the neutral model atmosphere. Calculations also show that the topside thermal structure of the ionosphere is primarily maintained by a flow of heat from the magnetosphere and the night-time F2-region is maintained in part by neutral winds, diffusion, electric fields, and plasma flow from the magnetosphere. The problem of maintaining the calculated night-time ionosphere at the observed values is also discussed.  相似文献   

8.
Assuming that the unidimensional distribution function of the photoelectron flux can be determined from plasma line intensity measurement, it is shown that the photoelectron flux distribution is not uniquely determined if additional hypotheses are not made. The limitations of the inversion procedure are shown: in particular, plasma line measurements cannot allow the determination of more than the first two Legendre components of the photoelectron flux. Experimental procedures for this determination are finally reviewed.  相似文献   

9.
Photoelectrons of ionospheric origin have been observed for the first time at high altitudes (up to 7RE geocentric distance) using the suprathermal plasma analysers (SPA) on the GEOS satellites. At such high altitudes the photoelectron flux is confined within a few degrees of the magnetic field direction. We show how this flux may be identified and extracted from the background which is a combination of locally produced photoelectrons and ambient plasma. GEOS-2 results are presented to illustrate the “turn-on” of the photoelectron flux at dawn in the ionosphere. Data from GEOS-1 are used to study the behaviour of the photoelectron flux with equatorial geocentric distance from 3 to 7RE. The results compare favourably with theoretical models and with ionospheric observations at mid latitudes.  相似文献   

10.
Results of measurements of the energy distribution of thermal electrons below 1 eV in a midlatitude upper atmosphere are presented and compared with some recent measurements at other places. Measurements are based on the Druyvesteyn method using Langmuir probes.In the periods without solar light, distribution does not depart much from Maxwellian above 0.3 eV. Below 0.2 eV, depletion and sometimes double humps are seen. In the periods with solar light, bumps are sometimes observed on the high energy tail at altitudes between 100 and 160 km. Energy distribution in the F layer above 180 km fits the Maxwellian distribution rather well. The reason for the appearance of such non-thermal electrons at lower altitudes may be due to super-elastic collisions with vibrationally excited nitrogens.  相似文献   

11.
Observations and computer calculations of OI 7774 airglow emissions excited by conjugate photoelectrons have been carried out. The observations were made at McDonald Observatory, Texas using a 2m grille spectrometer from December 1972 to June 1973. The zenithal emission intensity during conjugate photoelectron precipitation was fairly constant at 2–4 R until conjugate sunset, after which it diminished steadily and ceased near a conjugate solar zenith angle (χc) of 105 ± 3°. A predawn enhancement in both OI 7774 and [OI] 6300 was observed to commence near χc ～ 102°.The computations utilize the two-stream technique of Nagy and Banks (1970) to obtain the escaping photoelectron flux and the local excitation rates of the oxygen emissions. Good agreement with the observations is obtained for the dependence of the emission rate on conjugate solar zenith angle. A lack of agreement in absolute intensity may not be due entirely to uncertainties in the excitation cross section. The discrepancy may indicate significant magnetospheric scattering of photoelectrons with energy greater than 15 eV.  相似文献   

12.
The influence of low-frequency electrostatic turbulence on the flux of precipitating magnetospheric electrons is analyzed in the framework of the quasilinear kinetic equation. It is shown that an electron population in a turbulent region, with an electric field parallel to the ambient magnetic field, can be separated into two parts by introducing a pitch angle dependent runaway velocity vr(θ). Lower energy electrons with parallel velocity v∥ < vr are effectively scattered by plasma waves, so that they remain in the main population and are subjected to an anomalous transport equation. A distribution function f ∞ v?4 (or the particle flux vs energy J ∞ E?1) is established in this velocity range. Faster electrons with v∥ ? vr are freely accelerated by a parallel electric field, so that they contribute directly to hot electron fluxes which are observed at ionospheric altitudes. New expressions are derived for the magnetic-field aligned current and the electron energy flux implied by this model. These expressions agree well with empirical relations observed in auroral inverted-V structures.  相似文献   

13.
HEOS-2 low energy electron data (10 eV–3.7 keV) from the LPS Frascati plasma experiment have been used to identify three different magnetospheric electron populations. Magnetosheathlike electron energy spectra (35–50 eV) are characteristic of the plasma mantle, entry layer and cusps from the magnetopause down to 2–3 RE Plasma sheet electrons (energy > 1 keV) are found at all local times, with strong intensities in the early morning quadrant and weaker intensities in the afternoon quadrant. The plasma sheet shows a well defined inner edge at all local times and latitudes, the inner edge coinciding probably with the plasmapause. The plasma sheet does not reach the magnetopause, but it is separated from it by a boundary layer electron population that is very distinct from the other two electron populations, most electrons having energies 100–300 eV.We map these three electron populations from the magnetopause down to the high latitude near earth regions, by making use of the HEOS-2 low latitude inbound passes and the high latitude outbound passes (in Solar Magnetic (SM) coordinates). The boundary layer extends along the magnetopause up to 5–7 RE above the equator; at higher latitudes it follows the magnetic lines of force and it is found closer and closer to the earth, so that it has the same invariant latitudes of the system 1 currents observed by Iijima and Potemra (1976) in their region 1. The plasma sheet can be mapped into their region 2 and the cusp-entry layer-plasma mantle can be mapped into their cusp currents region. The boundary layer is observed for any Interplanetary Magnetic Field (IMF) direction. We speculate that magnetosheath particles penetrate into the magnetosphere everywhere along the magnetopause. The electron energization, however, is observed only in the boundary layer, on both dawn and dusk side and could be due to the polarization electric field at magnetopause generated by the magnetosheath plasma bulk motion in the region where such motion is roughly perpendicular to the magnetospheric magnetic field. The electron energization is absent in the regions (entry layer and plasma mantle) where the sheath plasma motion is roughly parallel or antiparallel to the magnetospheric magnetic field.  相似文献   

14.
The determination of the origin of cosmic rays with observed energies in excess of 1017 eV that exceed the expected energies of cosmic rays accelerated by supernova remnants in the galaxy is a pressing problem in modern astrophysics. Hypernova remnants are one of the possible galactic sources of cosmic rays with energies of up to 1019 eV. Hypernovae constitute a class of extremely powerful supernova explosions, whose supposed progenitors are massive Wolf-Rayet stars. We analyze the special aspects of acceleration of cosmic rays in hypernova remnants that expand in wind bubbles of Wolf-Rayet progenitor stars. We show that these cosmic rays may attain maximum energies of 1018 eV even with a relatively conservative choice of acceleration parameters and account for tens of percent of the total cosmic ray flux observed in the vicinity of the earth in the energy range of 1016–1018 eV if the galactic hypernova explosion rate in the modern epoch reaches ? S ～ 10?4 year?1.  相似文献   

15.
A laboratory plasma experiment has been built to study the eruption of arched magnetic flux ropes (AMFRs) in the presence of a large magnetized plasma. This experiment simulates the eruption of solar AMFRs in two essential steps: i) it produces an AMFR (n=6.0×1012 cm?3, $T_{\rm e} = 14~\mathrm{eV}$ , B≈1 kilo-gauss, L=0.51 m) with a persistent appearance that lasts several Alfvén transit times using a lanthanum hexaboride (LaB6) plasma source, and ii) it generates controlled plasma flows from the footpoints of the AMFR using laser beams. An additional LaB6 plasma source generates a large magnetized plasma in the background. The laser-generated flows trigger the eruption by injecting dense plasma and magnetic flux into the AMFR. The experiment is highly reproducible and runs continuously with a 0.5 Hz repetition rate; hence, several thousand identical loop eruptions are routinely generated and their spatio-temporal evolution is recorded in three-dimensions using computer-controlled movable probes. Measurements demonstrate striking similarities between the erupting laboratory and solar arched magnetic flux ropes.  相似文献   

16.
Observed magnetospheric asymmetries which occur in response to the y-component of the IMF are discussed in terms of the open model of the magnetosphere. The torque which the IMF exerts on the magnetosphere about the Earth-Sun axis results in asymmetric addition of open flux tubes to the tail lobes about the noon-midnight meridian. In response an IMF-associated By field appears across the tail lobes. The ratio between internal and external By fields will generally be same as the ratio between internal and external electric fields. If the tail flux asymmetry is related to an asymmetric distribution of the field normal to the tail magnetopause then an asymmetry in tail lobe electric field and plasma populations will immediately result, as observed. If the flux asymmetry is associated with a twist in the tail then the By field will appear but not necessary the electric field and plasma asymmetries. Generally both effects may occur together. Simple open tail lobe models are derived which demonstrate the asymmetry effects. These represent more physically satisfactory models of the tail and its plasma populations than available hitherto, but they remain somewhat unrealistic in a number of respects. Finally, it is shown that the observed asymmetry effects on closed (auroral zone) field lines may be at least qualitatively accounted for if the cross-magnetosphere IMF-associated By field pervades not only the open but also the closed field line regime, as may be generally expected.  相似文献   

17.
The Electron Spectrometer (ELS) instrument of the ASPERA-3 package on the Mars Express satellite has recorded photoelectron energy spectra up to apoapsis (∼10,000 km altitude). The characteristic photoelectron shape of the spectrum is sometimes seen well above the ionosphere in the evening sector across a wide range of near-equatorial latitudes. Two numerical models are used to analyze the characteristics of these high-altitude photoelectrons. The first is a global, multi-species MHD code that produces a 3-D representation of the magnetic field and bulk plasma parameters around Mars. It is used here to examine the possibility of magnetic connectivity between the high-altitude flanks of the martian ionosheath and the subsolar ionosphere. It is shown that some field lines in this region are draped interplanetary magnetic lines while others are open field lines (connected to both the IMF and the crustal magnetic field sources). The second model is a kinetic electron transport model that calculates the electron velocity space distribution along a selected, non-uniform, magnetic field line. It is used here to simulate the high-altitude ELS measurements. It is shown that the photoelectrons are essentially confined to the source cone, as governed by magnetic field inhomogeneity along the field line. Reasonable agreement is shown between the data and the model results, and a method is demonstrated for inferring properties of the local and photoelectron source region magnetic field from the ELS measurements. Specifically, the number of sectors in which photoelectrons are measured is a function of the magnetic field intensity ratio and the field's angle with respect to the detector plane. In addition, the sector of the photoelectron flux peak is a function of the magnetic field azimuthal angle in the detector plane.  相似文献   

18.
Based on data from the SONG and SPR-N multichannel hard electromagnetic radiation detectors onboard the CORONAS-F space observatory and the X-ray monitors onboard GOES satellites, we have distinguished the thermal and nonthermal components in the X-ray spectrum of an extreme solar flare on January 20, 2005. In the impulsive flare phase determined from the time of the most efficient electron and proton acceleration, we have obtained parameters of the spectra for both components and their variations in the time interval 06:43–06:54 UT. The spectral index in the energy range 0.2–2 MeV for a single-power-law spectrum of accelerated electrons is shown to have been close to 3.4 for most of the time interval under consideration. We have determined the time dependence of the lower energy cutoff in the energy spectrum of nonthermal photons E γ0(t) at which the spectral flux densities of the thermal and nonthermal components become equal. The power deposited by accelerated electrons into the flare volume has been estimated using the thick-target model under two assumptions about the boundary energy E 0 of the electron spectrum: (i) E 0 is determined by E γ0(t) and (ii) E 0 is determined by the characteristic heated plasma energy (≈5kT (t)). The reality of the first assumption is proven by the fact that plasma cooling sets in at a time when the radiative losses begin to prevail over the power deposited by electrons only in this case. Comparison of the total energy deposited by electrons with a boundary energy E γ0(t) with the thermal energy of the emitting plasma in the time interval under consideration has shown that the total energy deposited by accelerated electrons at the beginning of the impulsive flare phase before 06:47 UT exceeds the thermal plasma energy by a factor of 1.5–2; subsequently, these energies become approximately equal and are ～(4–5) × 1030 erg under the assumption that the filling factor is 0.5–0.6.  相似文献   

19.
This is the second of two papers which together provide a detailed statistical analysis of the low-energy (1-eV–100-keV) geosynchronous plasma environment. In this paper, data on the ion environment between ～1 eV and 80 keV are statistically analysed. About 50 days of 10-min averages of the first 4 moments of the ion distribution function from the University of California at San Diego low-energy plasma detectors on the ATS-5 and ATS-6 geosynchronous satellites are studied in terms of: occurrence frequency, local time variations, Kp variations, injection events, and intercomparisons among the 4 moments. Variations in the 4 moments can be explained by assuming the existence of 2 dominant plasma populations (the plasmasphere and ring current) upon which are superimposed plasma injection events. In conjunction with this analysis, the accuracy of the 4-moment representation for ions was tested and, unlike that for electrons, found to be limited by the energy band-pass of the instrumentation and by a lack of knowledge of the angular anisotropies and ionic composition. Even so, these limitations are outweighed by the utility and compactness of the method. A technique for correcting the limited energy band-pass of the instrumentation is presented in the Appendix.  相似文献   

20.
The upper ionospheres of Mars and Venus are permeated by the magnetic fields induced by the solar wind. It is a long-standing question whether these fields can put the dense ionospheric plasma into motion. If so, the transterminator flow of the upper ionosphere could explain a significant part of the ion escape from the planets atmospheres. But it has been technically very challenging to measure the ion flow at energies below 20 eV. The only such measurements have been made by the ORPA instrument of the Pioneer Venus Orbiter reporting speeds of 1-5 km/s for O+ ions at Venus above 300 km altitude at the terminator ( [Knudsen et al., 1980] and [Knudsen et al., 1982]). At Venus the transterminator flow is sufficient to sustain a permanent nightside ionosphere, at Mars a nightside ionosphere is observed only sporadically. We here report on new measurements of the transterminator ion flow at Mars by the ASPERA-3 experiment on board Mars Express with support from the MARSIS radar experiment for some orbits with fortunate observation geometry. We observe a transterminator flow of O+ and O2+ ions with a super-sonic velocity of around 5 km/s and fluxes of 0.8×109/cm2 s. If we assume a symmetric flux around the terminator this corresponds to an ion flow of 3.1±0.5×1025/s half of which is expected to escape from the planet. This escape flux is significantly higher than previously observed on the tailside of Mars. A possible mechanism to generate this flux can be the ionospheric pressure gradient between dayside and nightside or momentum transfer from the solar wind via the induced magnetic field since the flow velocity is in the Alfvénic regime. We discuss the implication of these new observations for ion escape and possible extensions of the analysis to dayside observations which may allow us to infer the flow structure imposed by the induced magnetic field.  相似文献   

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