首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
The photo-ionization produced in the night-time E region by the total stellar u.v. continuum is considered. It is shown to be approximately equal to that produced by the scattered Lyman β above about 115 km.  相似文献   

2.
The paper describes the phenomenon of afternoon depression of the geomagnetic H field on quiet days near the magnetic equator in the Indian zone. These events occur most frequently around 1600 solar hr and are localized in longitude; sometimes, not seen at stations separated by even 2 hr LT. The geomagnetic disturbance tends to decrease or destroy the identity of the phenomenon. The latitudinal extent of these events is confined to the equatorial electrojet region. The events do not seem to be caused mainly by the Moon, but their occurrences are modified by the lunar age, being most frequent around new and full Moon. These events are associated with the disappearance of the q type of Es over the Equator for periods during which the H field is below the night-time level. The currents responsible for these events flow westward in the E-region and are within few degrees centred near the magnetic equator.  相似文献   

3.
A self-consistent, time-dependent numerical model of the aurora and high-latitude ionos-phere has been developed. It is used to study the response of ionospheric and atmospheric properties in regions subjected to electron bombardment. The time history of precipitation events is arbitrarily specified and computations are made for a variety of electron spectral energy distributions and flux magnitudes. These include soft electron precipitation, such as might occur on the poleward edge of the auroral oval and within the magnetospheric cleft, and harder spectra representative of particle precipitation commonly observed within and on the equatorward edge of the auroral oval. Both daytime and night-time aurorae are considered. The results of the calculations show that the response of various ionospheric and atmospheric parameters depends upon the spectral energy distribution and flux magnitudes of the precipitating electrons during the auroral event. Various properties respond with different time constants that are influenced by coupling processes described by the interactive model. The soft spectrum aurora affects mainly the ionospheric F region, where it causes increases in the electron density, electron temperature and the 6300 Å red line intensity from normal quiet background levels during both daytime and night-time aurora. The fractional variation is greater for the night-time aurora. The hard spectrum aurorae, in general, do not greatly affect the F-2 region of the ionosphere; however, in the F-1 and E regions, large increases from background conditions are shown to occur in the electron and ion temperatures, electron and ion densities, airglow emission rates and minor neutral constituent densities during the build-up phase of the auroral event. During the decay phase of the aurora, most of these properties decrease at nearly the same rate as the specified particle precipitation flux. However, some ionospheric and atmospheric species have a long memory of the auroral event. The odd nitrogen species N(4S) and NO probably do not ever reach steady-state densities between auroral storms.  相似文献   

4.
The topology of the boundaries of penetration (or inversely the boundaries of the forbidden regions) of 90° pitch angle equatorial protons with energies less than 100 keV are explored for an equatorial convection E-field which is directed in general from dawn to dusk. Due to the dependence of drift path on energy (or magnetic moment) complex structural features are expected in the proton energy spectra detected on satellites since the penetration distance of a proton is not a monotonically increasing or decreasing function of energy. During a storm when the convection E is enhanced, model calculations predict elongations of the forbidden regions analogous to plasmatail extensions of the plasmasphere. Following a reduction in the convection field, spiral-structured forbidden regions can occur. Structural features inherent to large scale convection field changes may be seen in the noselike proton spectrograms observed near dusk by instrumentation on the satellite Explorer 45 (S3) (Smith and Hoffman, 1974). These nose events are modelled by using an electric field model developed originally by Volland (1973). The strength of the field is related to Kp through night-time equatorial plasmapause measurements.  相似文献   

5.
Quantitative estimates of ionization sources that maintain the night-time E- and F-region ionosphere are given. Starlight (stellar continuum radiation in the spectral inverval 911–1026 Å) and resonance scattering of solar Ly-β into the night sector are the most important sources in the E-region and are capable of maintaining observable electron densities of order (1–4) × 103 cm?3. Starlight ionization rates have substantial variations (factors of 2–4) with latitude and time of year since the brightest stars in the night sky occur in the southern Milky Way and Orion regions. In the lower F-region the major O+ source in the equatorial ionosphere is 910 Å radiation from the O+ recombination in the F2-region, whereas in the extratropical ionosphere interplanetary 584 Å radiation only exceeds resonance scattering of solar 584 and 304 Å radiation as the dominant O+ source during the month of December.  相似文献   

6.
Intensities of auroral hiss generated by the Cerenkov radiation process by electrons in the lower magnetosphere are calculated with respect to a realistic model of the Earth's magnetosphere. In this calculation, the magnetic field is expressed by the “Mead-Fairfield Model” (1975), and a static model of the iono-magnetospheric plasma distribution is constructed with data accumulated by recent satellites (Alouette-I, -II, ISIS-I, OGO-4, -6 and Explorer 22). The energy range of hiss producing electrons and the frequency range of the calculated VLF are 100–200 keV, and 2–200 kHz, respectively. Intensities with a maximum around 20 kHz, of the order of 10?14 W/m2/Hz1 at the ground seem to be ascribable to the incoherent Cerenkov emission from soft electrons with a differential energy spectrum E?2 having an intensity of the order of 108cm?2/sec/sr/eV at 100 eV. It is shown that the frequency of the maximum hiss spectral density at geomagnetic latitudes 80° on the day-side and 70° on the night-side is around 20 kHz for the soft spectrum (～E?2) electrons, which shifts toward lower frequency (～10 kHz) for a hard spectrum (～E?1·2) electrons. The maximum hiss intensity produced by soft electrons is more than one order higher than that of hard electron produced hiss. The higher rate of hiss occurrence in the daytime side, particularly in the soft electron precipitation zone in the morning sector, and the lesser occurrence of auroral hiss in night-time sectors must be, therefore, due to the local time dependence of the energy spectra of precipiating electrons rather than the difference in the geomagnetic field and in the geoplasma distributions.  相似文献   

7.
Energetic electron fluxes from more than two years of ASPERA-3 observations are organized in different coordinate systems for the investigation of asymmetries in the global dynamics of the Martian magnetosphere. A clear asymmetry is found in the distribution of high-flux events with respect to the solar wind convective electric field (Esw) direction. These events are frequently detected below the average magnetic pile-up boundary (MPB) location at the terminator region of the hemisphere to which the Esw points and extend toward the tail. A detailed investigation of the electron fluxes at the terminator region also reveals that the largest contribution to this Esw asymmetry comes from locations of moderate or strong crustal fields. These observations have implications about reconnection processes in the terminator and provide new insight on magnetic anomaly effects in the global dynamics of the Mars-solar wind interaction.  相似文献   

8.
The effect of frictional heating by means of neutral winds on the ion and electron temperature in the undisturbed ionosphere is studied theoretically by solving a system of basic ionospheric and atmospheric equations. The study shows that both the electron and ion temperatures are increased in the night-time ionosphere through friction. In the region between 150 and 200 km Ti may exceed T6 by as much as 130°. The increase of Ti due to friction amounts to about 100–200°, depending on the atmospheric model employed in calculating the neutral wind velocity. It is illustrated that frictional heating may be very important for the determination of the neutral temperature from measured ion temperature values.  相似文献   

9.
Detailed studies of the daytime E-region critical frequency at Aberystwyth (geomagnetic latitude +56°) show clear evidence for changes associated with both the axially-symmetric (Dst) and asymmetric (DS) components of the disturbance magnetic field. Comparison of the sensitivity of the E-region peak density to these two influences shows that the changes cannot entirely (if at all) be ascribed to the influence of electric currents in the region. It is suggested that a major role is played by dynamical influences associated with the neutral air “storm circulation” which distributes the energy fed into the auroral region to lower latitudes.  相似文献   

10.
  相似文献   

11.
The paper describes a comparison of vertical electron drift in the F-region (Vz) measured by VHP incoherent scatter radar at Jicamarca with the corresponding variations of geomagnetic horizontal field (H) and the maximum frequency reflected from The Es layer (Es) at Huancayo during the geomagnetic storm period 7–9 March, 1970. The Vz is generally upward during the daytime at the equator, but during 7–9, March, 1970, Vz was negative for brief periods associated with negative bays in H. These periods of abnormally low or of downward Vz correspond closely with the period of complete disappearance of the q type of Es layer. The magnetic bays associated with the intensification of ring current do not affect the equatorial Es- q and it is only the negative bays in H at the equator due to the ionospheric current flowing westward, that cause sudden disappearance of Es? q. It is suggested that the q type of Es is due to cross-field instability created in the electrojet region due to interaction of northward magnetic field and vertical upward Hall polarization electric field when the plasma density gradient is upward. The sudden disappearances of Es? q are due to the reversal of the horizontal electric field in the equatorial ionosphere and thereby due to the reversal of the equatorial electrojet currents. These reversals of electric field may be due to the imposition on the normal Sq field of another westward electric field.  相似文献   

12.
Assuming a certain horizontal distribution of the convection field at a certain altitude above the ionosphere, the associated electric field and current distributions in a vertical plane are calculated using a model with finite current-dependent conductivity along the magnetic field lines. It is seen that given the kind of horizontal distribution of E6 commonly observed by polar-orbiting satellites at inverted-V electron precipitation events, the calculated distribution of E∥ is able to reproduce the basic spatial structure of the precipitation. It is also seen that the combined effect of a locally increased ionization within auroral forms and a large potential difference (ΔV)∥ along the magnetic field lines at higher altitudes is a strong reduction of E6 within the auroral forms. From the basic features of the electric field, it is concluded that an interpretation of auroral precipitation in terms of a static E∥ may require a mechanism that can support a large (ΔV)∥ even at relatively weak current densities and at the same time allow local enhancements of the parallel conductivity within the region of non-zero E∥. It is suggested that the magnetic mirroring combined with gyro-resonant wave-particle interactions may be a suitable mechanism.  相似文献   

13.
Generation of auroral kilometric radiation (AKR) in the auroral acceleration region is studied. It is shown that auroral kilometric radiation can be generated by the backscattered electrons trapped in the acceleration region via a cyclotron maser process. The parallel electric field in the acceleration region is required to be distributed over 1–2 RE. The observed AKR frequency spectrum can be used to estimate the altitude range of the auroral acceleration region. The altitudes of the lower and upper boundaries of the acceleration region determined from the AKR data are respectively ～2000 and ～9000 km.  相似文献   

14.
  相似文献   

15.
Two Skylark rockets carrying ion and R.F. electron probes, lithium and sodium vapourisers and proton precession magnetometers were launched from Woomera, Australia in November and December 1965 and made at least four encounters with sporadic E ionization. A magnetic field minimum was detected on only one of these encounters, and the minimum was found to be 2–3 km below the observed ion layer. The wind measurements deduced from observations of the vapour trails indicated that the sporadic E layer occurred in a region of ion divergence.  相似文献   

16.
Damped hydromagnetic eigenmodes are calculated numerically for a simple inhomogeneous plasma that is assumed to be contained within rigid perfectly conducting walls, and subject only to Joule dissipation. It is found that E∥ must be included in order to obtain well-behaved damped eigenmodes that include resonant field lines, even though E∥ is relatively very small. The thickness of the resonant region in the equatiorial plane, estimated from the model, is of order 10?3 of an L number, which seems about two orders of magnitude too small to match observed long period micropulsations. The fact that mid-latitude micropulsations sometimes lead in phase at the lower latitudes is shown probably to be an effect of the local increase in resonant period with latitude.  相似文献   

17.
By the test particle method, we have investigated the kinematic characteristics of the electrons in the reconnecting current sheet with a guiding magnetic field Bz after they are accelerated by the supper-Dreicer electric field Ez. Firstly, the influence of the guiding magnetic field Bz on the particle acceleration is discussed under the assumption that Bz is constant in magnitude but different in orientation with respect to the electric field. In this case, the variation of the Bz direction directly leads to the variation of electron trajectories and makes electrons leave the current sheet along different paths. If Bz is parallel to Ez, the pitch angles of the accelerated electrons are close to 180°. If Bz is anti-parallel to Ez, the pitch angles of the accelerated electrons are close to 0°. The orientation of the guiding magnetic field just makes the electric field accelerate selectively the electrons in different regions, but does not change the energy distribution of electrons, and the finally derived energy spectrum is the common power-law spectrum E?γ. In typical coronal conditions, γ is about 2.9. The further study indicates that the magnitude of γ depends on the strengths of the guiding magnetic field and reconnecting electric field, as well as the scale of the current sheet. Then, the kinematic characteristics of the accelerated electrons in the current sheet with multiple X-points and O-points are also studied. The result indicates that the existences of the X-points and O-points have the particles constrained in the accelerating region to obtain the maximum acceleration, and the final energy spectrum has the characteristics of multi-power law spectra.  相似文献   

18.
The dependence of the occurrence probabilities of ionosonde sporadic-E parameters f0Es and fbEs on probing frequency is analyzed for wintertime for day and night for two Southern Hemisphere stations. The ionosonde data indicate that significant changes have taken place over the period 1958–1983 suggesting that Es has become increasingly dense and also less patchy.  相似文献   

19.
On the basis of quasi-linear theory of ion-acoustic turbulence it is shown that the angular and energy distribution of the electron spectra observed in quasi-static inverted-V structures are natural products of electron heating and runaway processes occuring in a region of current-driven turbulence located at h ≈ 1 Re. The power law population J ∞ E?γ, with γ ≈ 1 observed in the energy range ~ 25–1000 eV, is interpreted as a quasi-stationary distribution of suprathermal electrons interacting resonantly with the ion sound waves. This spectrum is generated in the turbulent region and convectively transported earthward along the magnetic field lines. Field-aligned intense electron fluxes with collimation angle < 10° are explained as due to particles escaping from the turbulent region through the runaway cone—a characteristic feature of velocity-space in ion-acoustic turbulence. A complete, new interpretation of the observed electron spectra is given on the basis of the proposed physical acceleration mechanism along with many other implications of this theory.  相似文献   

20.
Assuming that the formation of the ring current belt is a direct consequence of an enhanced crosstail electric field and hence of an enhanced convection, we calculate the total ring current kinetic energy (KR) and the ring current energy injection rate (UR) as a function of the cross-tail electric field (ECT); the cross-tail electric field is assumed to have a step function-like increase. The loss of ring current particles due to recombination and charge-exchange is assumed to be distributed over the whole ring current region. It is found that: (1) the steady-state ring current energy KR is approximately linearly proportional to ECT; (2) the characteristic time tc for KR to reach the saturation level is 3–4 h; (3) the injection rate UR is proportional to ECTβ where β ? 1.33?1.52; and (4) the characteristic time tp for UR to reach the peak value is 1–2 h and the peak UR value is 50% higher than the steady-state value. Since β is now determined specifically for an enhanced convection, an observational determination of the relationship between ECT(or φCT) and UR is essential to a better understanding of ring current formation processes. If the observed β is greater than 1.5, additional processes (e.g. an injection of heavy ions from the ionosphere to the plasma sheet and subsequently to the ring current region) may be required.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号