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1.
2.
Accurate observations of the elevation angle of arrival of 20 MHz signals from the polar orbiting satellite Beacon-B for a 20 month period have provided transmission ionograms which may be reduced to give Hp, the scale height at the peak of the ionosphere. Noon seasonal averages of Hp are 1.35 (in winter) to 1.55 (in summer) times greater than the scale height obtained from bottom-side ionograms. A comparison of scale height at the peak with routine measurements of total content and peak electron density indicates that the O+/H+ transition level is above 1000 km during the day but comes down to about 630 km on winter nights. A predawn peak in the overall scale height (∝ total content/peak density) is caused by a lowering of the layer to a region of increased recombination and is magnified in winter by low O+/H+ transition levels. After sunrise in winter and equinoxes the overall scale height is less than the scale height at the peak, implying an outwards flux of ionisation which lasts for about three hours. The summer evening increase in ƒ0F2 requires both a cooling and a raising of the layer for its occurrence.  相似文献   

3.
In this paper the question is examined of how the v.l.f. radio-waves are guided along the magnetic field. Energy passes through the magnetic field under two sets of conditions. Corresponding to the “nose-whistlers” explained by Helliwell, the first one occurs when the wave-normal itself is in the direction of the magnetic field. This does not happen in the second case when the remarkable property is also shown that all frequencies are propagated at the same velocity V0 = cƒH/2ƒ0H gyrofrequency, ƒ0 frequency of the plasma). Considerations of energy point out that, if such a propagation is not easily observable in the case of an isotropic emission, it is not the same thing for an emission produced by erenkov effect, which is able to produce all energy by this mode of propagation, provided the particle's velocity has a low fixed value (˜ 10,000 km/sec in the exosphere). All frequencies being emitted at the same time and following the same path wtih the same velocity, we can explain the broadband noise observed during the reception of whistlers. The required velocity of particles is exactly the velocity V0. This coincidence is explained in an appendix, and extended to other anisotropic media.  相似文献   

4.
N. Hiotelis   《New Astronomy》2002,7(8):531-539
We present density profiles, that are solutions of the spherical Jeans equation, derived under the following two assumptions: (i) the coarse grained phase-density follows a power-law of radius, ρ/σ3r, and (ii) the velocity anisotropy parameter is given by the relation βa(r)=β1+2β2 (r/r*)/[1+(r/r*)2] where β1, β2 are parameters and r* equals twice the virial radius, rvir, of the system. These assumptions are well motivated by the results of N-body simulations. Density profiles have increasing logarithmic slopes γ, defined by γ=−d ln ρ/d ln r. The values of γ at r=10−2.5rvir, a distance where the systems could be resolved by large N-body simulations, lie in the range 1.0–1.6. These inner values of γ increase for increasing β1 and for increasing concentration of the system. On the other hand, slopes at r=rvir lie in the range 2.42–3.82. A model density profile that fits well the results at radial distances between 10−3rvir and rvir and connects kinematic and structural characteristics of spherical systems is described.  相似文献   

5.
A theoretical model is proposed for interpreting the coherent emissionmechanism of solar radio moving type IV bursts. Energetic electrons produced in flares captured by an expanding and rising magnetic flux tube exhibit a beam-like distribution of velocities on the top of the flux tube. These excite beaming plasma instability and directly amplifies O-mode electromagnetic waves. The instability growth rate sensitively depends on the coronal plasma parameter, ƒpece and the beam-temperature Tb. This can qualitatively explain the high brightness temperature and high degree of polarization as well as the broad spectrum observed in this type of solar radio bursts.  相似文献   

6.
The existence of sidereal semidiurnal variation of cosmic-ray intensity in a rigidity region 102-103 GV has been reported by many researchers, but there is no consensus of opinion on its origin. In this paper, using the observed semidiurnal variations in a rigidity range (300–600 GV) with 10 directional muon telescopes at Sakashita underground station (geog. lat. = 36°, long. = 138°E, DEPTH = 80 m.w.e.), the authors determine the magnitudes (η1, η2) and directions (a1, a2) of the first- and second-order anisotropies in the following galactic cosmic-ray intensity distribution (j)
jdp = j0{1 + η1P1(cos χ1) + η2P2(cos χ2)}dp
, where Pnis the nth order spherical function and χn is the pitch angle of cosmic rays with respect to an. For the determination, the influence of cosmic-ray's heliomagnetospheric modulation, geomagnetic deflection and nuclear interaction with the terrestrial material and also of the geometric configuration of the telescopes are taken into account. Usually, the semidiurnal variation is produced by the second-order anisotropy. The present observation, however, requires also the first-order anisotropy which usually produces only the diurnal variation, but can produce also the semidiurnal variation as a result of the heliospheric modulation. The first- and second-order anisotropies are characterized with η1) > 0 and η2 < 0 have almost the same direction (a1 a2) specified by the right ascension ( 0.75 h) and declination (δ 50°S) and, therefore, they can be expressed, as a whole, by an axis-symmetric anisotropy of loss-cone type (i.e. deficit intensities in a cone). It is noteworthy that this anisotropy approximately coincides with that inferred from the air shower observation at Mt Norikura in the rigidity region 104 GV.  相似文献   

7.
It is shown that the arguments advanced by Shaw(1) to demonstrate that the absorption of radio waves in the ionosphere is controlled by the currents causing geomagnetic variations are unsound. Further the method used by Bandyopadhyay(2) in deducing the nondeviative absorption leads to too high a proportion of this absorption in the total. The two D-regions model proposed by Rumi(3) is also unsatisfactory in several respects. In all three papers, error arises because of the neglect of the deviative absorption in E-region. The reason for this neglect may be because of the resemblance between the frequency variation of E-region deviative absorption and that of the non-deviative absorption, except in the immediate vicinity of ƒ0E.  相似文献   

8.
We discuss the possibility of exciting whistler mode waves (WMWs) in the Earth's ionosphere, by using two high frequency beams of electromagnetic waves (f1f2) suitably orientated to the geomagnetic field Ho, so that a non-linear resonant interaction can take place in the natural ionospheric plasma, approximately at the altitude of the F2 maximum electron density. Within the limitations imposed by ionospheric inhomogeneities in the interaction region, it should be possible to excite a WMW which propagates along a predetermined direction, e.g. parallel to Ho.

If we assumef1 andf2 to be approx 30 MHz (i.e. well above the ionospheric plasma frequency), this method would make it possible to select and vary the frequency range of the excited WMW up to a few hundreds kHz without substantial alterations to the high frequency transmitting system.

Since the two beams should form an angle close to 90° to the direction of propagation of the WMW, this technique may prove particularly suitable for active wave experiments at low geomagnetic latitudes, where the geometry of the geomagnetic field limits the feasibility of direct wave injection experiments.

Using the results of theoretical calculations of the three wave coupling coefficients, it will be shown that the transmitters required to produce WMWs with field strengths comparable to that of naturally occurring strong whistlers are substantial, but feasible.  相似文献   


9.
We use a 1-D chemical diffusive model, in conjunction with the measured neutral atmospheric structure, to analyze the Voyager RSS electron density, ne, profiles for the ionospheres of Jupiter and Saturn. As with previous studies we find serious difficulties in explaining the ne measurements. The model calculates ionospheres for both Jupiter and Saturn with ne peaks of 10 times the measured peaks at altitudes which are 900–1000 km lower than the altitude of peaks in the RSS electron densities. Based on our knowledge of neutral atmospheric structure, ionization sources, and known recombination mechanisms it seems that, vibrational excitation of H2 must play some role in the conversion of slowly radiatively recombining H+ ions to the relatively more rapidly recombining H2+ and H3+ ions. In addition, vertical ion flow induced by horizontal neutral winds or electric fields probably also play some role in maintaining the plasma peaks observed both for Jupiter and Saturn to be at high altitudes. For the ionosphere of Saturn, the electron densities are affected by a putative influx of H2O molecules, ΦH2O, from the rings. To reproduce the RSS V2 exit ne results model requires an influx of ΦH2O 2 × 107 molecules cm−2 s−1 without invoking H2f vibrational excitation. To maintain the model ne peak at the measured altitude vertical plasma drift maintained by meridional winds or vertical electric fields is required. The amounts of H2O are consistent with earlier estimates of Connerney and Waite (1984) and do not violate any observational constraints.  相似文献   

10.
Reflection and transmission coefficients of MHD waves are obtained at a stable, plane interface which separates two compressible, perfectly conducting media in relative motion to each other. The coefficients are evaluated for representative conditions of the quiettime, near-Earth magnetopause. The transmission coefficient averaged over a hemispherical distribution of incident waves is found to be 1–2 per cent. Yet the magnitude of the energy flux deposited into the magnetosphere in a day averaged over a hemispherical distribution of waves having amplitudes of say 2–3 gamma, is estimated to be of the order 1022 erg. Therefore the energy input of MHD waves must contribute significantly to the energy budget of the magnetosphere. The assumption that the boundary surface is a tangential discontinuity with no curvature limits the present theory to hydromagnetic frequencies higher than about 10−1 Hz. The ion gyrofrequencies for the models assumed here lie above 2 × 10−1 Hz. Therefore the present treatment applies to MHD waves near 10−1 Hz.  相似文献   

11.
Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) on the Mars Express (MEX) spacecraft has made numerous measurements of the Martian surface and subsurface. However, all of these measurements are distorted by the ionosphere and must be compensated before any analysis. We have developed a technique to compensate for the ionospheric distortions. This technique provides a powerful tool to derive the total electron content (TEC) and other higher-order terms of the limited expansion of the plasma dispersion function that are related to overall shape of the electron column profile. The derived parameters are fitted by using a Chapman model to derive ionospheric parameters like n0, electron density primary peak (maximum for solar zenith angle (SZA) equal 0), and the neutral height scale H.

Our estimated ionospheric parameters are in good agreement with Mars Global Surveyor (MGS) radio-occultation data. However, since MARSIS does not have the observation geometry limitations of the radio occultation measurements, our derived parameters extend over a large range of SZA for each MEX orbit.

The first results from our technique have been discussed by Safaeinili et al. [2007, Estimation of the total electron content of the Martian ionosphere using radar sounder surface echoes. Geophys. Res. Lett. 34, L23204, doi:10.1029/2007GL032154].  相似文献   


12.
It is shown that the dynamics of the plasmapause, the plasmasphere plasma tails, the plasma sheet and the magnetosheath boundaries of the geomagnetosphere may be investigated by means of the geostationary version of the differential phase method, by which a signal transmitted from a sounding station (a geostationary satellite) and received by a response station on the Earth may be transformed, allowing the sign of the frequency shift and of the phase lag to be changed. Information on the location, the motion of the magnetospheric plasma discontinuities and the concentration drop at their boundaries may be obtained from measurements carried out on board the geostationary satellite of the phase difference of the sounding and response signals ΔΦ, the time of its increase Δt and the phase difference change rate (fast beating frequency Δƒ = ΔΦ/2π Δt). The establishment of communication between appropriately spaced ground stations and a satellite with a quasi-polar orbit allows the midlatitude plasmapause dynamics, and those of the ionosphere trough, polar cusp boundaries and of polar cap inhomogeneities to be studied. Equipment with a stability of 10−11–10−12 is needed for the most dynamical events (for ΔΦ= 10−4 tens of rad. and for Δƒ= 10−5 tens of Hz) occurring in the radio path during storms.  相似文献   

13.
Inspection of recent spectra presented by Sivjee (1983) show evidence of the 0–4 and 0–5 bands of the N2(c41Σu+a1Πg) Gaydon-Herman system. In conjunction with earlier spectra, it is now possible that this band system is a significant auroral component, with an intensity approx. 7% that of the N2 2P system. The absence in aurorae of the potentially far stronger N2(c41Σu+X1Πg) system is discussed. It is that the O2(A3Σu+X3Σg) band system is indiscernible in Sivjee's auroral spectra, under conditio the foreground nightglow is expected to be clearly visible. On the other hand, at least one relatively strong O2(A3Δua1Δg) band appears to be present in these spectra.  相似文献   

14.
对中俄联合火星星-星电离层掩星技术体制进行了分析和介绍,采用三维射线追踪方法对电离层掩星事件的电波观测值进行了模拟计算,并利用模拟的掩星观测数据进行了电子密度廓线反演,结果说明仿真算法可靠.利用仿真的方法,分别对掩星电波相位观测误差和卫星轨道误差等带来的反演误差进行了个例计算和分析,结果得到:5%周的相位测量误差对白天电离层掩星探测结果的影响可以忽略,而夜间电子密度测量的绝对误差小于4×108 m-3;卫星轨道误差对掩星的主要影响是导致电离层高度抬升或下降.结果表明,中俄联合火星电离层掩星探测技术体制先进,可望获得高精度的电子密度廓线;其技术体制也可以用于月球电离层环境的探测.  相似文献   

15.
A comparison covering more than three decades is made between the seasonal variation of radar meteor influx and seasonal variations in the occurrence probabilities of ionosonde sporadic-E parametersƒ0Es and ƒbEs for different diurnal intervals at two Southern Hemisphere stations. The analyses show that for medium intensity 3Em type sporadic-E no clear correlation with major Southern Hemisphere meteor shower activity exists. This finding which does not support some earlier shorter period surveys suggests the need for further work into the aeronomy of Es source ions.  相似文献   

16.
It is shown that electrostatic fields parallel (E11) to the geomagnetic field cannot be the major mechanism that accelerates charged particles to auroral energies. Principal arguments are that electron and proton precipitation occur simultaneously, and also that precipitated electrons with energies less than 100 eV are found to accompany the electrons with energies of 1–10 keV that excite auroral luminosity. It is further shown that essentially all the ambient plasma in an entire tube of flux is required to sustain this intense low-energy precipitation, and this places a severe constraint on any replenishment process. It is found that generally the upper limit to (E11) throughout the auroral regions of the ionosphere and magnetosphere is of order 10 μV/m and it may be appreciably less. Relevant measurements are reviewed briefly. It is concluded that while there may occasionally be significant E11 fields, they play only a minor role-if any-in auroral phenomena.  相似文献   

17.
We present a quantitative analysis of CO thermal emissions discovered on the nightside of Titan by Baines et al. [2005. The atmospheres of Saturn and Titan in the near-infrared: First results of Cassini/VIMS. Earth, Moon, and Planets, 96, 119–147]. in Cassini/VIMS spectral imagery. We identify these emission features as the P and R branches of the 1-0 vibrational band of carbon monoxide (CO) near 4.65 μm. For CH3D, the prominent Q branch of the ν2 fundamental band of CH3D near 4.55 μm is apparent. CO2 emissions from the strong v3 vibrational band are virtually absent, indicating a CO2 abundance several orders of magnitude less than CO, in agreement with previous investigations. Analysis of CO emission spectra obtained over a variety of altitudes on Titan's nightside limb indicates that the stratospheric abundance of CO is 32±15 ppm, and together with other recent determinations, suggests a vertical distribution of CO nearly constant at this value from the surface throughout the troposphere to at least the stratopause near 300 km altitude. The corresponding total atmospheric content of CO in Titan is 2.9±1.5×1014 kg. Given the long lifetime of CO in the oxygen-poor Titan atmosphere (0.5–1.0 Gyr), we find a mean CO atmospheric production rate of 6±3×105 kg yr−1. Given the lack of primordial heavy noble gases observed by Huygens [Niemann et al., 2005. The abundances of constituents of Titan's atmosphere from the GCMS on the Huygens probe. Nature, 438, 779–784], the primary source of atmospheric CO is likely surface emissions. The implied CO/CH4 mixing ratio of near-surface material is 1.8±0.9×10−4, based on an average methane surface emission rate over the past 0.5 Gyr of 1.3×10−13 gm cm−2 s−1 as required to balance hydrocarbon haze production via methane photolysis [Wilson and Atreya, 2004. Current state of modeling the photochemistry of Titan's mutually dependent atmosphere and ionosphere. J. Geophys. Res. 109, E06002 Doi:10.1029/2003JE002181]. This low CO/CH4 ratio is much lower than expected for the sub-nebular formation region of Titan and supports the hypothesis [e.g., Atreya et al., 2005. Methane on Titan: photochemical-meteorological-hydrogeochemical cycle. Bull. Am. Astron. Soc. 37, 735] that the conversion of primordial CO and other carbon-bearing materials into CH4-enriched clathrate-hydrates occurs within the deep interior of Titan via the release of hydrogen through the serpentinization process followed by Fischer–Tropsch catalysis. The time-averaged predicted emission rate of methane-rich surface materials is 0.02 km3 yr−1, a value significantly lower than the rate of silicate lava production for the Earth and Venus, but nonetheless indicative of significant active geological processes reshaping the surface of Titan.  相似文献   

18.
One of the problems in reconstructing the real ionosphere from an ionogram is the occurrence of a ‘valley,’ where electron density decreases with altitude and make a non-monotonic profile. For the case of the Earth ionosphere, the ordinary and extraordinary ray data, accompanied with an empirical model, based on the observations, are necessary to obtain a mathematical solution for a ‘valley,’ such as the region between the E and F layers. MARSIS/MEX is a topside sounder designed to observe the ionosphere of Mars. Some ‘valley’ structures were found in the ionograms measured by MARSIS. The echoes of the extraordinary ray are not available owing to the absence of the strong magnetic field on Mars. Therefore, it is difficult to have a mathematical solution for the valleys in the Martian ionosphere. In this paper, a least square method with a simple model is presented to solve the ‘valley’ problem in the topside ionosphere of Mars. The electron density profiles with ‘valleys’ observed by the Radio Occultation experiment onboard MGS are used to rebuild the virtual depths at MARSIS frequencies. The reconstructed electron density profile by the least square method with a simple model from the rebuilt virtual depth curve is compared with the original electron density profile. It is proved that this method can reproduce small valleys in the profile of the Martian ionosphere well.  相似文献   

19.
Continuous records of the electron content of the ionosphere, from 1965 to 1970, are used to obtain power spectra covering periods from 30 sec to 2 yr at latitudes of 34°S and 42°S. At periods up to 5 min, amplitudes were less than 0.2 per cent of the total electron content. Variations produced by gravity waves were very common in the range 20–80 min, with no preferred periods. The r.m.s. amplitude per octave A0 was about 1015 electrons/m2, or 0.6 per cent of the mean electron content. The amplitude increased during the day, particularly in winter when periodic components predominated. The cut-off at about 17 min was sharply defined, giving a mean scale height for the neutral atmosphere (at 300 km) of about 43 km in summer, 47 km on winter days and 42 km on winter nights.

From 12 hr to 1 month A0 was about 12 per cent of the mean electron content in both summer and winter at 34°S, and 10 per cent at 42°S. The 24 hr and 27 day peaks were largest just before sunspot maximum, and almost disappeared near sunspot minimum. Variations between 1 and 27 days reflect the random occurrence of ionospheric storms and show no consistent peaks. Day to day and night to night variations were both about 10 per cent of the background content for periods from 2 days to 2 yr, apart from a slight decrease between 1 and 6 months.  相似文献   


20.
Using extensive N-body simulations we estimate redshift space power spectra of clusters of galaxies for different cosmological models (SCDM, TCDM, CHDM, ΛCDM, OCDM, BSI, τCDM) and compare the results with observational data for Abell–ACO clusters. Our mock samples of galaxy clusters have the same geometry and selection functions as the observational sample which contains 417 clusters of galaxies in a double cone of galactic latitude |b|>30° up to a depth of 240 h−1 Mpc. The power spectrum has been estimated for wave numbers k in the range 0.03k0.2 h Mpc−1. For k>kmax0.05 h Mpc−1 the power spectrum of the Abell–ACO clusters has a power-law shape, P(k)∝kn, with n≈−1.9, while it changes sharply to a positive slope at k<kmax. By comparison with the mock catalogues SCDM, TCDM (n=0.9), and also OCDM with Ω0=0.35 are rejected. Better agreement with observation can be found for the ΛCDM model with Ω0=0.35 and h=0.7 and the CHDM model with two degenerate neutrinos and ΩHDM=0.2 as well as for a CDM model with broken scale invariance (BSI) and the τCDM model. As for the peak in the Abell–ACO cluster power spectrum, we find that it does not represent a very unusual finding within the set of mock samples extracted from our simulations.  相似文献   

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