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1.
Two extreme ultraviolet (EUV) spectrophotometers flown in December 1978 on Venera 11 and Venera 12 measured the hydrogen Lyman α emission resonantly scattered in the atmosphere of Venus. Measurements were obtained across the dayside of the disk, and in the exosphere up to 50,000 km. They were analyzed with spherically symmetric models for which the radiative transfer equation was solved. The H content of the Venus atmosphere varies from optically thin to moderately thick regions. A shape fit at the bright limb allows one to determine the exospheric temperature Tc and the number density nc independently of the calibration of the instrument or the exact value of the solar flux. The dayside exospheric temperature was measured for the first time in the polar regions, with Tc = 300 ± 25°K for Venera 11 (79°S) and Tc = 275 ± 25°K (59°S) for Venera 12. At the same place, the density is nc = 4?2+3 × 104 atom.cm?3, and the integrated number density Nt from 250 to 110 km (the level of CO2 absorption) is 2.1 × 1012 atom.cm?2, a factor of 3 to 6 lower than that predicted in aeronomical models. This probably indicates that the models should be revised in the content of H-bearing molecules and should include the effect of dynamics. Across the disk the value of Nt decreases smoothly with a total variation of two from the morning side to the afternoon side. Alternately it could be a latitude effect, with less hydrogen in the polar regions. The nonthermal component if clearly seen up to 40,000 km of altitude. It is twice as abundant as at the time of Mariner 10 (solar minimum). Its radial distribution above 4000 km can be simulated by an exospheric distribution with T = 1030K and n = 103 atom.cm?3 at the exobase level. However, there are less hot atoms between 2000 and 4000 km than predicted by an ionospheric source. A by-product of the analysis is a determination of a very high solar Lyman α flux of 7.6 × 1011 photons (cm2 sec Å)?1 at line center (1 AU) in December 1978.  相似文献   

2.
The orbit of Explorer 19 (1963-53A) has been determined at 60 epochs between February 1976 and October 1976 from over 3000 observations. Using values of the orbital decay rate corrected for the effects of solar radiation pressure, 58 values of air density at a height of 900 km have been evaluated. After correcting for solar and geomagnetic activity and seasonal-latitudinal and diurnal variations in the exospheric temperature, the residual variation exhibited modulations associated with the ‘winter helium bulge’.An examination of three different models of the helium variation has indicated a procedure, which combines distinct features of the CIRA (1972) and Jacchia (1977) model atmospheres, for determining the atmospheric drag effect on Explorer 19. It is proposed that this technique may be equally applicable to any satellite in near-polar orbit at an equivalent height.  相似文献   

3.
The Agena B upper-stage rocket 1963-27A was launched into a near-circular orbit, inclined at 82.3° to the Equator, on 29 June 1963. Its orbit is determined at 52 epochs over the 16 month interval prior to its decay on 26 October 1969. The resulting orbital elements are used to obtain 95 atmospheric density values, at heights near 400km. Corrected to fixed heights, and normalised to a common exospheric temperature, these values reveal the semi-annual variation in density. A comparison between the observed variation and that of a recent model atmosphere is made. Although agreement between the two is generally good, their principal differences are discussed.  相似文献   

4.
Using key dates associated with solar interaction regions (SIR), a superposed epoch analysis is performed on the zonal and meridional kinetic energy density and square of the vorticity (enstrophy) of the main motion at 500 mb height. No relationships are found between SIR and these atmospheric dynamical parameters irrespective of the polarity (North or South) of the enhanced interplanetary magnetic fields (IMF) within the SIR, or with latitude and season. This investigation and other available results suggest that the short term solar variations do not influence large volumes of the troposphere but only localized regions.The average atmospheric kinetic energy density during active solar conditions is higher than during quiet solar condition, with no significant differences in enstrophy. This confirms an earlier result.It is also shown that SIR with enhanced southward directed IMF correspond to higher level of geomagnetic index (Ap > 10, Kp > 3) than randomly selected days.  相似文献   

5.
High latitude geomagnetic field lines differ significantly from a dipole geometry. Time of flight calculations using the Mead-Fairfield (1975) model of the geomagnetic field are presented for different tilt angles and Kp conditions. Typical standing wave periods of geomagnetic pulsations are estimated for three different magnetospheric cold plasma regions, corresponding to waves guided in (i) the plasmatrough, (ii) the extended plasmasphere and (iii) regions of enhanced proton density (detached plasma) within the plasmatrough.Pc4/5 pulsation studies at high latitudes are briefly reviewed and some new results from Tromso are given. Many of the observations reveal hydromagnetic waves whose location and period are consistent with ducting in a region of enhanced plasma density within the plasmatrough.  相似文献   

6.
The Ultraviolet Spectrometer Experiment on the MARINER 10 spacecraft measured the hydrogen Lyman α emmission resonantly scattered in the Venus exosphere at several viewing aspects during the encounter period. Venus encounter occurred at 17:01 GMT on 5 February 1974. Exospheric emissions above the planet's limb were measured and were analyzed with a spherically symmetric, single scattering, two-temperature model. On the sunlit hemisphere the emission profile was represented by an exospheric hydrogen atmosphere with Tc = 275±50 K and nc = 1.5 × 105 cm?3 and a non-thermal contribution represented by TH = 1250±100 K with nH = 500±100 cm?3. The observations of the dark limb showed that the spherically symmetric model used for the sunlit hemisphere was inappropriate for the analysis of the antisolar hemisphere. The density of the non-thermal component had increased at low altitudes, < 12,000 km, and decreased at high altitudes, > 20,000 km, by comparison. We conclude that the non-thermal source is on the sunward side of the planet. Analysis of the dark limb crossing suggests that the exospheric temperature on the dark side is <125 K if the exospheric density remains constant over the planet; upper limits are discussed. An additional source of Lyman α emission, 70 ± 15 R, was detected on the dark side of the planet and is believed to be a planetary albedo in contrast to multiple scattering from the sunlit side. Our analysis of the MARINER 10 data is consistent when applied to the MARINER 5 data.  相似文献   

7.
China 2 rocket, 1971-18B, was launched on 3rd March 1971 into an orbit inclined at 69.9° to the Equator, with an initial perigee height of 265 km. Analysis of its orbit has yielded values of air density at average intervals of 6 days between July 1971 and January 1972. When corrected to a fixed height, the density exhibits a correlation with the geomagnetic index Ap and the solar 10.7-cm radiation. With values of density extending over seven months it is possible to examine a complete cycle of the semi-annual variation at a height near 300 km. The values of density, corrected for the day-to-night variation and for solar and geomagnetic activity, reveal minima in mid-August and late January; at the intervening maximum, in early November, the density is almost 40% higher than at the minima.  相似文献   

8.
Coronal density, temperature, and heat-flux distributions for the equatorial and polar corona have been deduced from Saito’s model of averaged coronal white-light (WL) brightness and polarization observations. These distributions are compared with those determined from a kinetic collisionless/exospheric model of the solar corona. This comparison indicates similar distributions at large radial distances (>?7 R⊙) in the collisionless region. However, rather important differences are found close to the Sun in the acceleration region of the solar wind. The exospheric heat flux is directed away from the Sun, while that inferred from all WL coronal observations is in the opposite direction, i.e. conducting heat from the inner corona toward the chromosphere. This could indicate that the source of coronal heating extends up into the inner corona, where it maximizes at r>1.5 R⊙, well above the transition region.  相似文献   

9.
Long-term MGS drag density observations at 390 km reveal variations of the density with season LS (by a factor of 2) and solar activity index F10.7 (by a factor of 3 for F10.7 = 40-100). According to Forbes et al. (Forbes, J.M., Lemoine, F.G., Bruinsma, S.L., Smith, M.D., Zhang, X. [2008]. Geophys. Res. Lett. 35, L01201, doi:10.1029/2007GL031904), the variation with F10.7 reflects variations of the exospheric temperature from 192 to 284 K. However, the derived temperature range corresponds to variation of the density at 390 km by a factor of 8, far above the observed factor of 3. The recent thermospheric GCMs agree with the derived temperatures but do not prove their adequacy to the MGS densities at 390 km. A model used by Forbes et al. neglects effects of eddy diffusion, chemistry and escape on species densities above 138 km. We have made a 1D-model of neutral and ion composition at 80-400 km that treats selfconsistently chemistry and transport of species with F10.7, T∞, and [CO2]80 km as input parameters. Applying this model to the MGS densities at 390 km, we find variation of T∞ from 240 to 280 K for F10.7 = 40 and 100, respectively. The results are compared with other observations and models. Temperatures from some observations and the latest models disagree with the MGS densities at low and mean solar activity. Linear fits to the exospheric temperatures are T∞ = 122 + 2.17F10.7 for the observations, T∞ = 131 + 1.46F10.7 for the latest models, and T∞ = 233 + 0.54F10.7 for the MGS densities at 390 km. Maybe the observed MGS densities are overestimated near solar minimum when they are low and difficult to measure. Seasonal variations of Mars’ thermosphere corrected for the varying heliocentric distance are mostly due to the density variations in the lower and middle atmosphere and weakly affect thermospheric temperature. Nonthermal escape processes for H, D, H2, HD, and He are calculated for the solar minimum and maximum conditions.Another problem considered here refers to Mars global photochemistry in the lower and middle atmosphere. The models gave too low abundances of CO, smaller by an order of magnitude than those observed. Our current work shows that modifications in the boundary conditions proposed by Zahnle et al. (Zahnle, K., Haberle, R.M., Catling, D.C., Kasting, J.F. [2008]. J. Geophys. Res. 113, E11004, doi:10.1029/2008JE003160) are reasonable but do not help to solve the problem.  相似文献   

10.
During the period October to December 1981, the Dynamics Explorer-2 (DE-2) spacecraft successively observed the South polar and the North polar regions, and recorded the temperature, composition and dynamical structure of the upper thermosphere. In October 1981, perigee was about 310 km altitude, in the vicinity of the South Pole, with the satellite orbit in the 09.00–21.00 L.T. plane. During late November and December, the perigee had precessed to the region of the North Pole, with the spacecraft sampling the upper thermosphere in the 06.00 18.00 L.T. plane. DE-2 observed the meridional wind with a Fabry-Perot interferometer (FPI), the zonal wind with the wind and temperature spectrometer (WATS), the neutral temperature with the FPI, and the neutral atmosphere composition and density with the neutral atmosphere composition spectrometer (NACS). A comparison between the South (summer) Pole and the North (winter) Pole data shows considerable seasonal differences in all neutral atmosphere parameters. The region of the summer pole, under similar geomagnetic and solar activity conditions, and at a level of about 300 km, is about 300 K warmer than that of the winter pole, and the density of atomic oxygen is strongly depleted (and nitrogen enhanced) around the summer pole (compared with the winter pole). Only part of the differences in temperature and composition structure can be related to the seasonal variation of solar insolation, however, and both polar regions display structural variations (with latitude and Universal Time) which are unmistakeable characteristics of strong magnetospheric forcing. The magnitude of the neutral atmosphere perturbations in winds, temperature, density and composition within both summer and winter polar regions all increase with increasing levels of geomagnetic activity.The UCL 3-dimensional time dependent global model has been used to simulate the diurnal, seasonal and geomagnetic response of the neutral thermosphere, attempting to follow the major features of the solar and geomagnetic inputs to the thermosphere which were present during the late 1981 period.In the UCL model, geomagnetic forcing is characterized by semi-empirical models of the polar electric field which show a dependence on the Y component of the Interplanetary Magnetic Field, due to Heppner and Maynard (1983), It is possible to obtain an overall agreement, in both summer and winter hemispheres, with the thermospheric wind structure at high latitudes, and to explain the geomagnetic control of the combined thermal and compositional structure both qualitatively and quantitatively. To obtain such agreement, however, it is essential to enhance the polar ionosphere as a consequence of magnetospheric particle precipitation, reflecting both widespread auroral (kilovolt) electrons, and “soft” cusp and polar cap sources. Geomagnetic forcing of the high latitude thermosphere cannot be explained purely by a polar convective electric field, and the thermal as well as ionising properties of these polar and auroral electron sources are crucial components of the total geomagnetic input.  相似文献   

11.
A superposed-epoch method is used to investigate the occurrence of spread-F at Huancayo relative to days of high sunspot activity and also relative to days of high geomagnetic activity. A good correlation is found between days of high Ap index and high spread-F occurrence for a pre-sunrise interval of a few hours. When 3-hourly kp indices are used they show a peak value approximately 6 hr prior to an above-average occurrence of spread-F. It is suggested that this pre-sunrise spread-F is associated with ionospheric height rises which are produced by travelling disturbances, initiated in polar regions at times of high geomagnetic activity.  相似文献   

12.
A superposed-epoch method is used to investigate the occurrence of spread-F at Huancayo relative to days of high sunspot activity and also relative to days of high geomagnetic activity. A good correlation is found between days of high Ap, index and high spread-F occurrence for a pre-sunrise interval of a few hours. When 3-hourly Kp indices are used they show a peak value approximately 6 hr prior to an above-average occurrence of spread-F. It is suggested that this pre-sunrise spread-F is associated with ionospheric height rises which are produced by travelling disturbances, initiated in polar regions at times of high geomagnetic activity.  相似文献   

13.
Thomson (incoherent) scatter radar measurements of F-region electron densities and temperatures were made approximately twice per month throughout 1966 and 1967 at Millstone Hill for periods of 24 hr. Owing to the increase in sunspot activity the results display a rich variety of different types of behaviour. Geomagnetically quiet days tended to follow patterns observed near sunspot minimum. Thus in winter there is typically a marked diurnal variation in electron density with a peak near noon and often a smaller secondary maximum between 02 and 04 EST. In summer there is less day-to-night variation and the peak density is encountered near ground sunset. Usually hmaxF2 is higher in summer than winter and the layer thickness is larger also.Some magnetically disturbed days follow a distinct pattern in which Nmax and hmax are normal during the first day of the storm until afternoon when they both increase to very high values. There is then a corresponding decrease in electron temperature. During the night the electron temperature often reaches abnormally high values, providing evidence of nocturnal heating. On the following day Nmax and hmax are abnormally low.During 1967 instances in which the trough of low electron density moved south to occupy a position over Millstone became frequent. The electron temperature rose to particularly high values on these occasions. These morphological features are discussed in terms of current theoretical ideas. The results are also employed to derive seasonal variations of electron temperature and protonospheric heat flux. It is shown that since 1964 the protonospheric heat flux has been larger in winter than summer and displays a clear sunspot cycle variation.  相似文献   

14.
The velocity distribution of hydrogen atoms in the terrestrial exosphere was measured as a function of radial distance (up to 7 Earth radii, ER) with the help of a Lyman-α hydrogen absorption cell, flown in 1968 on board the OGO-5 satellite. This paper contains the final analysis of the measurements. As a basis of comparison, the theory for the calculation of projected velocity distribution along a line of sight is established for the theoretical exospheric model of Chamberlain (1963). Self-absorption of Lyman-α photons along a line of sight is included to derive Lyman-α line profiles emerging from the geocorona. The effect of the hydrogen absorption cell, measured by the reduction factor R(p) is predicted as a function of impact parameter p of the line of sight, for various values of the parameters of a Chamberlain's model, nc (density of exobase level), Tc (temperature at the exobase level), and rcs (satellite critical radius). This predicted reduction factor R(p) is compared to the measured Rm(p), with the following findings: the Ly-α line width decreases with radial distance, as expected from the “evaporation and escape” theory of Chamberlain; the measured temperature Tc = 1080 K is in very good agreement with the exospheric temperature prediction from satellite drag data. An upper limit of 8 × 104at. cm?3 is imposed on nc, regardless of photometric absolute calibration. A good fit to data requires the presence of atoms in satellite orbits, distributed in a different fashion than that described by the concept of satellite critical radius. Lyman-alpha radiation pressure is thought to be the cause of this departure from the exospheric theory of Chamberlain (1963), otherwise perfectly confirmed.The same scientific rationale will be applied to exospheric hydrogen of the planets Mars and Venus in subsequent papers.  相似文献   

15.
Temperature data collected over several years from rocket grenade and other experiments at Point Barrow (Alaska), Fort Churchill (Canada) and Wallops Island (Virginia) have been analysed to determine the effect of geomagnetic activity on the neutral temperature in the mesosphere and to study the latitudinal variation of this effect. An analysis carried out has revealed almost certainly significant correlations between the temperature and the geomagnetic indicies Kp and Ap at Fort Churchill and marginally significant correlations at Barrow and Wallops. This has also been substantiated by a linear regression analysis.The results indicate two types of interdependence between mesospheric temperature and geomagnetic field variations. The first type is the direct heating effect, during a geomagnetic disturbance, which has been observed in the present analysis with a time lag of 3–15 hr at the high latitudes and 36 hr at the middle latitudes. The magnitude of this heating effect has been found to decrease at the lower altitudes. The second type of interrelation which has been observed is temperature perturbations preceding geomagnetic field variations, both presumably caused by a disturbance in atmospheric circulation at these levels.  相似文献   

16.
Using an exosphere model which includes the effects of rotation and temperature and density variations at the exobase, we determine kinetic temperature and density distributions for planetary exospheres in general and terrestrial O, He and H in particular, the latter being based on empirical models for density and temperature variations at exobase altitudes. We examine the effects of energy flow and confirm Fahr's suggestion that the lateral energy flow at the exobase should be important for the temperature distributions above the base. Considering uniform density and sinusoidal temperature variations at the base, we find that temperatures decrease with altitude above the diurnal temperature maximum Tmax at the base. On the other hand, above the diurnal temperature minimum Tmin at the base, the temperatures increase from the base to peak values (except for low values of mMG/kT0) and then decrease above the peaks, tending to approach the values above Tmax. The corresponding densities near the base, above Tmin, decrease with altitude more rapidly than above Tmax but exhibit considerable increases in their scale heights in the vicinity of their temperature peaks, at which points the densities begin to approach those above Tmax. In the converse case, with uniform base temperature and sinusoidal base density variations, the exospheric density and temperature distributions above the diurnal density maximum Nmax and minimum Nmin at the base result in similar characteristics to those above Tmax and Tmin, respectively. Applying the model to terrestrial O, He and H, we find that multiple exospheric temperatures should occur wherein temperatures above Tmax decrease less rapidly with altitude for increasing species mass. On the other hand, O and He temperatures increase with altitude above Tmin to peak values near 5000 km and then decrease above the peaks while H temperatures decrease with altitude throughout. We also examine the effects of the terrestrial exospheric H temperature distribution on optical depths for Lyman alpha absorption and find that such temperature variation may be important for radiative transfer calculations when the depths are greater than unity and satellite orbits are unimportant.  相似文献   

17.
Density measurements at 140, 160, 180 and 200km from the AE-C accelerometer experiment during 1974 are analyzed by least-squares multiple linear regression. The resulting empirical model is compared to the widely-used Jacchia (1971) model which is primarily based on satellite orbital decay data above 200 km. The semiannual and geomagnetic (Kp) variations derived from the AE-C data set are in good agreement with Jacchia's predictions. However, individual magnetic storm responses often exceed such average representations of the geomagnetic effect by more than a factor of two. The density is more variable with respect to the daily 10.7cm solar flux than Jacchia's model predicts. The regression analysis reveals a positive correlation with the absolute value of the geographic latitude. The statistical weakness of this latter effect reflects the transient, aperiodic nature of high-latitude heating events related to magnetic activity, which can only be properly analyzed on an individual basis. Finally, the sub-solar bulge effect enters the regression equation with about half the amplitude predicted by the Jacchia model at these heights.  相似文献   

18.
P. Hedelt  Y. Ito  L. Esposito 《Icarus》2010,210(1):424-435
Based on measurements performed by the Hydrogen Deuterium Absorption Cell (HDAC) aboard the Cassini orbiter, Titan’s atomic hydrogen exosphere is investigated. Data obtained during the T9 encounter are used to infer the distribution of atomic hydrogen throughout Titan’s exosphere, as well as the exospheric temperature.The measurements performed during the flyby are modeled by performing Monte Carlo radiative transfer calculations of solar Lyman-α radiation, which is resonantly scattered on atomic hydrogen in Titan’s exosphere. Two different atomic hydrogen distribution models are applied to determine the best fitting density profile. One model is a static model that uses the Chamberlain formalism to calculate the distribution of atomic hydrogen throughout the exosphere, whereas the second model is a Particle model, which can also be applied to non-Maxwellian velocity distributions.The density distributions provided by both models are able to fit the measurements although both models differ at the exobase: best fitting exobase atomic hydrogen densities of nH = (1.5 ± 0.5) × 104 cm−3 and nH = (7 ± 1) × 104 cm−3 were found using the density distribution provided by both models, respectively. This is based on the fact that during the encounter, HDAC was sensitive to altitudes above about 3000 km, hence well above the exobase at about 1500 km. Above 3000 km, both models produce densities which are comparable, when taking into account the measurement uncertainty.The inferred exobase density using the Chamberlain profile is a factor of about 2.6 lower than the density obtained from Voyager 1 measurements and much lower than the values inferred from current photochemical models. However, when taking into account the higher solar activity during the Voyager flyby, this is consistent with the Voyager measurements. When using the density profile provided by the particle model, the best fitting exobase density is in perfect agreement with the densities inferred by current photochemical models.Furthermore, a best fitting exospheric temperature of atomic hydrogen in the range of TH = (150-175) ± 25 K was obtained when assuming an isothermal exosphere for the calculations. The required exospheric temperature depends on the density distribution chosen. This result is within the temperature range determined by different instruments aboard Cassini. The inferred temperature is close to the critical temperature for atomic hydrogen, above which it can escape hydrodynamically after it diffused through the heavier background gas.  相似文献   

19.
This paper presents a correlative study between the peak values of geomagnetic activity indices (Dst, Kp, ap and AE) and the peak values of various interplanetary field (Bt, Bz, E and σB) and plasma (T, D, V, P and β) parameters along with their various products (BV, BzV and B2V) during intense geomagnetic storms (GMSs) for rising, maximum and decay phases as well as for complete solar cycle 23. The study leads to the conclusion that the peak values of different geomagnetic activity indices are in good correlation with Bt, Bz, σB, V, E, BV, BzV and B2V, therefore these parameters are most useful for predicting GMSs and substorms. These parameters are also reliable indicators of the strength of GMSs. We have also presented the lag/lead time analysis between the maximum of Dst and peak values of geomagnetic activity indices, various interplanetary field/plasma parameters for all GMSs. We have found that the average of peak values of geomagnetic activity indices and various field/plasma parameters are larger in decay phase compare to rising and maximum phases of cycle 23. Our analyses show that average values of lag/lead time lie in the ≈?4.00 h interval for Kp, ap and AE indices as well as for Bt, Bz, σB, E, D and P. For a more meaningful analysis we have also presented the above study for two different groups G1 (CME-driven GMSs) and G2 (CIR-driven GMSs) separately. Correlation coefficients between various interplanetary field/plasma parameters, their various products and geomagnetic activity indices for G1 and G2 groups show different nature. Three GMSs and associated solar sources observed during three different phases of this solar cycle have also been studied and it is found that GMSs are associated with large flares, halo CMEs and their active regions are close to the solar equator.  相似文献   

20.
The temporal response of ion and neutral densities to a geomagnetic storm has been investigated on a global scale with data from consecutive orbits of OGO-6 (>400km) for 4 days covering both magnetically quiet and disturbed conditions. The first response of the neutral atmosphere to the storm takes place in the H and He densities which start to decrease near the time of the storm sudden commencement. The maximum decreases in H and He were more than 40% of the normal density at high latitudes. A subsequent increase in O and N2 densities occurs about 8 hours later than the change in H and He densities, while the relative O and N2 density changes indicate a depletion of atomic oxygen in the lower thermosphere by more than a factor of two. The overall features of the change in the neutral atmosphere, especially the patterns of change for individual species, strongly support the physical picture that energy is deposited primarily at high latitudes during the storm, and the thermosphere structure changes through (1) heating of the lower thermosphere and (2) generation of large scale circulation in the atmosphere with upwelling at high latitudes and subsidence at the equator. The storm-time response of H+ occurs in two distinct regions separated by the low latitude boundary of the light ion trough. While on the poleward side of the boundary the H+ density decreases in a similar manner to the decrease in H density, on the equatorward side of the boundary the H+ decrease occurs about half a day later. It is shown that the decrease of H+ density is principally caused by the decrease in H density for both regions. The difference in H+ response between the two regions is interpreted as the difference in H+ dynamics outside and inside the plasmasphere. The O+ density shows an increase, the pattern of which is rather similar to that for O. Two possibilities for explaining the observed change in O+ density are suggested. One attributes the observed increase in O+ density to an increase in the plasma temperature during the storm. The other possibility is that the increase in the production rate of O+ due to an increase in O density exceeds the increase in the loss rate of O+ due to an increase in N2 density, especially around the time of sunrise. Hence the change in O+ density in the F-region may actually be controlled by the change in O density.  相似文献   

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