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 15 毫秒
1.
Rates of production of O(1 D) atoms in the upper atmosphere by photodissociation of O2, dissociative recombination of O2 +, NO+ and electron impact excitation of O(3 P) have been calculated for low, medium and high levels of solar activity. Variations with solar activity, of neutral and ionic composition, electron and neutral temperatures of the upper atmosphere and solar extreme ultraviolet fluxes incident on it have been taken into consideration.Emission rates ofOi red line (6300Å) have been computed taking into account the deactivation both by molecular oxygen and nitrogen. It has been shown that the integrated intensity from low to high activity period varies by approximately an order of magnitude in agreement with the results of experimental observations.  相似文献   

2.
Measurements of the twilight enhancement of airglow emission from O+(2P) near 7325 Å reveal major changes which accompany geomagnetic activity, no significant distance between evening and morning and an increase in brightness paralleling the approach to solar maximum. The principal source for O+(2P) is direct photoionization from O(3P) but at low solar activity there appears to be a contribution from another source in early twilight which may be local photoelectron ionization into O+(2P). The geomagnetic and solar effects appear to reflect changes in the O and N2 density in the thermosphere; ground based twilight measurements of O+ emissions thus provide a simple means for monitoring thermospheric structure from 300 km to ～ 500 km at solar minimum and to ～600 km at solar maximum.  相似文献   

3.
A comparison of ion and neutral composition measurements at Venus for periods of greatly different solar activity provides qualitative evidence of solar control of the day-to-night transport of light ion and neutral species. Concentrations of H+ and He in the predawn bulge near solar maximum in November, 1979, exhibit a depletion signature correlated with a pronounced modulation in the solar F10.7 and EUV fluxes. This perturbation, not observed in the predawn region during an earlier period of relative quiet solar conditions, is interpreted as resulting from pronounced changes in solar heating and photoionization on the dayside, which in turn modulate the transport of ions and neutrals into the bulge region.  相似文献   

4.
W-H. IP  D.A. Mendis 《Icarus》1976,28(3):389-400
  相似文献   

5.
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   

6.
The dynamics of parameters of the near-Earth solar wind (SW) and the effect of solar activity on the parameters of three SW components (fast SW from large-scale coronal holes (CHs); slow SW from active regions, streamers, and other sources; and transient flows related to sporadic solar activity) at the beginning of the 24th solar cycle (2009–2011) are analyzed. It is demonstrated that temperaturedependent parameters of ionic composition (C+6/C+5 and O+7/O+6) of the transient SW component in the profound minimum of solar activity in 2009 were correlated with the variation of the rate of weak (type C and weaker) flares. This verifies the presence of a hot component associated with these flares in the SW. The variations in the velocity and the kinetic temperature of fast SW from CHs with an increase in activity are more pronounced in the bulk of the high-speed stream, and the variations of O+7/O+6 and Fe/O ratios and the magnitude of the interplanetary magnetic field are the most prominent in the region of interaction between fast and slow SW streams. The analysis reveals that a value of O+7/O+6 = 0.1 serves as the criterion to distinguish between fast SW streams and interplanetary coronal mass ejections in the 2009 activity minimum. This value is lower than the one (0.145) determined earlier based on the data on the 23rd cycle (Zhao et al., 2009). Therefore, the distinguishing criterion is not an absolute one and depends on the solar activity level.  相似文献   

7.
The observation of ions created by ionization of cometary gas, either by ground-based observations or byin situmeasurements can give us useful information about the gas production and composition of comets. However, due to the interaction of ions with the magnetized solar wind and their high chemical reactivity, it is not possible to relate measured ion densities (or column densities) directly to the parent gas densities. In order to quantitatively analyze measured ion abundances in cometary comae it is necessary to understand their dynamics and chemistry. We have developed a detailed ion–chemical network of cometary atmospheres. We include production of ions by photo- and electron impact-ionization of a background neutral atmosphere, charge exchange of solar wind ions with cometary atoms/molecules, reactions between ions and molecules, and dissociative recombination of molecular ions with thermal electrons. By combining the ion–chemical network with the three-dimensional plasma flow as computed by a new fully three-dimensional MHD model of cometary plasma environments (Gombosiet al.1996) we are able to compute the density of the major cometary ions everywhere in the coma. The input parameters for our model are the solar wind conditions (density, speed, temperature, magnetic field) and the composition and production rate of the gas. We applied our model to Comet P/Halley in early March 1986, for which the input parameters are reasonably well known. We compare the resulting column density of H2O+with ground-based observations of H2O+from DiSantiet al.(1990). The results of our model are in good agreement with both the spatial distribution and the absolute abundance of H2O+and with their variations with the changing overall water production rate between two days. The results are encouraging that it will be possible to obtain production rates of neutral cometary constituents from observations of their ion products.  相似文献   

8.
The thickness of the peak of the ionosphere depends primarily on the temperature T n of the neutral gas, and corresponds approximately to an α-Chapman layer at a temperature of 0.87T n. The overall slab thickness, as given by Faraday rotation measurements, is then τ =0.22 n + 7km. Expansion of the topside ionosphere, and changes in the E-andFl-regions increase τ by about 20 km during the day in summer. Near solar minimum τ is increased by a lowering of the O +/H + transition height; if the neutral temperature T n is estimated, this height can be obtained from observed values of τ.Hourly values of slab thickness were determined over a period of 6 yr at 34°S and 42°S. Near solar maximum the night-time values were about 260 km in all seasons. The corresponding neutral temperatures agree with satellite drag values; they show a semiannual variation of 14 per cent and a seasonal change of 5 per cent. Daytime values of τ were about 230 km in winter and 320 km in summer, implying a seasonal change of 30 per cent in T n. Temperatures increase steadily throughout the day in all seasons, with a rapid post-sunset cooling in summer. Downwards movements produce a large peak in τ at 0600 hr in winter. A large upwards flux, equal to about 40 per cent of the maximum (limiting) value, reduces τ for several hours after sunrise in winter. The slab thickness increases near solar minimum showing a reduction of the O +/H + transition height to about 700 km in summer and 500 km in winter.  相似文献   

9.
In this study we analyze the non-thermal loss rates of O+, O2+ and CO2+ ions over the last 4.5 billion years (Gyr) in the Martian history by using a 3D hybrid model. For this reason we derived the past solar wind conditions in detail. We take into account the intensified particle flux of the early Sun as well as an Martian atmosphere, which was exposed to a sun's extreme ultraviolet (EUV) radiation flux 4.5 Gyr ago that was 100 times stronger than today. Furthermore, we model the evolution of the interplanetary magnetic field by a Weber & Davis solar wind model. The ‘external’ influences of the Sun's radiation flux and solar wind flux lead to the formation of an ionospheric obstacle by photoionization, charge exchange and electron impact. For the early Martian conditions we could show that charge exchange was the dominant ionization mechanism. Several hybrid simulations for different stages in the evolution of the Martian atmosphere, at 1, 2, 5, 10, 30 and 100 EUV, were performed to analyze the non-thermal escape processes by ion pick-up, momentum transfer from the solar wind to the ionosphere and detached ionospheric plasma clouds. Our results show a non-linear evolution of the loss rates. Using mean solar wind parameters the simulations result in an oxygen loss equivalent to the depth of a global Martian ocean of about 2.6 m over the last 4.5 Gyr. The induced magnetic field strength could be increased up to about 2000 nT. A simulation run with high solar wind density results in an oxygen loss of a Martian ocean up to 205 m depth during 150 million years after the sun reached the zero age mean sequence (ZAMS).  相似文献   

10.
The rates of momentum and energy transfer have been obtained for charge exchange collisions between ion and neutral gases having arbitrary Maxwellian temperatures Ti and Tn and bulk transport velocities ci and cn. The results are directly applicable to the F-region of the ionosphere where O+ - O charge is the dominant mechanism affecting ion momentum and energy transfer.  相似文献   

11.
The structural differences of the ion and neutral composition in the thermospheric region are studied by solving a system of basic ionospheric and atmospheric equations. The study shows that the compositional changes during a magnetic storm arise largely as a result of changes in the neutral composition at the turbopause. A decrease in [O]/[N2] in the lower atmosphere triggers a complex chain of events which results in an increase of the neutral gas temperature, depletion of the O+ layer and enhancement of NO+. The relative changes in these layers occasionally produce a sequence of electron density profiles giving rise to the so-called G condition. It is shown that, compared to the neutral atmosphere, the ionosphere is much more sensitive to the changes in [O]/[N2] in the lower thernaospheric region. Since the ionospheric parameters can be measured much more accurately than the atmospheric parameters, it is argued that they should form an integral part of the observational data required to construct the atmospheric models.  相似文献   

12.
A mathematical model has been developed to calculate consistent values for the O+ and H+ concentrations and field-aligned velocities and for the O+, H+ and electron temperatures in the night-time equatorial topside ionosphere. Using the results of the model calculations a study is made to establish the ability of F-region neutral air winds to produce observed ion temperature distributions and to investigate the characteristics of ion temperature troughs as functions of altitude, latitude and ionospheric composition. Solar activity conditions that give exospheric neutral gas temperatures 600 K, 800 K and 1000 K are considered.It is shown that the O+-H+ transition height represents an altitude limit above which ion cooling due to adiabatic expansion of the plasma is extremely small. The neutral atmosphere imposes a lower altitude limit since the neutral atmosphere quenches any ion cooling which field-aligned transport tends to produce. The northern and southern edges of the ion temperature troughs are shown to be restricted to a range of dip latitudes, the limiting dip latitudes being determined by the magnetic field line geometry and by the functional form of the F-region neutral air wind velocity. Both these parameters considerably influence the interaction between the neutral air and the plasma within magnetic flux tubes.  相似文献   

13.
An analysis is made of the photodissociation and photoionization processes in the mesosphere due to the solar H Lyman-alpha line. The irradiance of the line and its variation with solar activity are considered in the determination of the photodissociation of CH4, CO2, H2O and O2, and of the photoionization of NO. Lyman-alpha contributes directly to these processes in the mesosphere after its absorption, which depends on wavelength and temperature, by molecular oxygen. The H Lyman-alpha radiation considered for mesospheric processes is characterized by a profile of an emission line with a central reversal, and wings extending to about ± 1.75 A where the intensity reaches about 1% of that of the peak. Simple formulae are deduced for the photodissociation optical depths and frequencies and these take into account the various solar activity conditions and the different spectral characteristics of each molecule.  相似文献   

14.
We present an updated model for the photochemistry of Io's atmosphere and ionosphere and use this model to investigate the sensitivity of the chemical structure to vertical transport rates. SO2is assumed to be the dominant atmospheric gas, with minor molecular sodium species such as Na2S or Na2O released by sputtering or venting from the surface. Photochemical products include SO, O2, S, O, Na, NaO, NaS, and Na2. We consider both “thick” and “thin” SO2atmospheres that encompass the range allowed by recent HST and millimeter-wave observations, and evaluate the possibility that O2and/or SO may be significant minor dayside constituents and therefore likely dominant nightside gases. The fast reaction between S and O2limits the column abundance of O2to ∼104less than that calculated by Kumar (J. Geophys. Res.87, 1677–1684, 1982; 89(A9), 7399–7406, 1984) for a pure sulfur/oxygen atmosphere. If a significant source of NaO2or Na2O were supplied by the surface and mixed rapidly upward, then oxygen liberated in the chemical reactions which also liberate free Na would provide an additional source of O2. Fast eddy mixing will enhance the transport of molecular sodium species to the exobase, in addition to increasing the vertical transport rate of ions. Ions produced in the atmosphere will be accelerated by the reduced corotation electric field penetrating the atmosphere. These ions experience collisions with the neutral gas, leading to enhanced vertical ion diffusion. The dominant ion, Na+, is lost primarily by charge exchange with Na2O and/or Na2S in the lower atmosphere and by diffusion through the ionopause in the upper atmosphere. The atmospheric column abundance of SO, O2, and the upper atmosphere escape rates of Na, S, O, and molecular sodium species are all strong functions of the eddy mixing rate. Most atmospheric escape, including that of molecular sodium species, probably occurs from the low density “background” SO2atmosphere, while a localized high density “volcanic” SO2atmosphere can yield an ionosphere consistent with that detected by the Pioneer 10 spacecraft.  相似文献   

15.
A two-dimensional kinetic model calculation for the water group species (H2O, H2, O2, OH, O, H) in Europa's atmosphere is undertaken to determine its basic compositional structure, gas escape rates, and velocity distribution information to initialize neutral cloud model calculations for the most important gas tori. The dominant atmospheric species is O2 at low altitudes and H2 at higher altitudes with average day-night column densities of 4.5×1014 and 7.7×1013 cm−2, respectively. H2 forms the most important gas torus with an escape rate of ∼2×1027 s−1 followed by O with an escape rate of ∼5×1026 s−1, created primarily as exothermic O products from O2 dissociation by magnetospheric electrons. The circumplanetary distributions of H2 and O are highly peaked about the satellite location and asymmetrically distributed near Europa's orbit about Jupiter, have substantial forward clouds extending radially inward to Io's orbit, and have spatially integrated cloud populations of 4.2×1033 molecules for H2 and 4.0×1032 atoms for O that are larger than their corresponding populations in Europa's local atmosphere by a factor of ∼200 and ∼1000, respectively. The cloud population for H2 is a factor of ∼3 times larger than that for the combined cloud population of Io's O and S neutral clouds and provides the dominant neutral population beyond the so-called ramp region at 7.4-7.8 RJ in the plasma torus. The calculated brightness of Europa's O cloud on the sky plane is very dim at the sub-Rayleigh level. The H2 and O tori provide a new source of europagenic molecular and atomic pickup ions for the thermal plasma and introduce a neutral barrier in which new plasma sinks are created for the cooler iogenic plasma as it is transported radially outward and in which new sinks are created to alter the population and pitch angle distribution of the energetic plasma as it is transported radially inward. The europagenic instantaneous pickup ion rates are peaked at Europa's orbit, dominate the iogenic pickup ion rates beyond the ramp region, and introduce new secondary plasma source peaks in the solution of the plasma transport problem. The H2 torus is identified as the unknown Europa gas torus that creates both the observed loss of energetic H+ ions at Europa's orbit and the corresponding measured ENA production rate for H.  相似文献   

16.
The evolution of the martian atmosphere with regard to its H2O inventory is influenced by thermal loss processes of H, H2, nonthermal atmospheric loss processes of H+, H2+, O, O+, CO2, and O2+ into space, as well as by chemical weathering of the surface soil. The evolution of thermal and nonthermal escape processes depend on the history of the intensity of the solar XUV radiation and the solar wind density. Thus, we use actual data from the observation of solar proxies with different ages from the Sun in Time program for reconstructing the Sun's radiation and particle environment from the present to 3.5 Gyr ago. The correlation between mass loss and X-ray surface flux of solar proxies follows a power law relationship, which indicates a solar wind density up to 1000 times higher at the beginning of the Sun's main sequence lifetime. For the study of various atmospheric escape processes we used a gas dynamic test particle model for the estimation of the pick up ion loss rates and considered pick up ion sputtering, as well as dissociative recombination. The loss of H2O from Mars over the last 3.5 Gyr was estimated to be equivalent to a global martian H2O ocean with a depth of about 12 m, which is smaller than the values reported by previous studies. If ion momentum transport, a process studied in detail by Mars Express is significant on Mars, the water loss may be enhanced by a factor of about 2. In our investigation we found that the sum of thermal and nonthermal atmospheric loss rates of H and all nonthermal escape processes of O to space are not compatible with a ratio of 2:1, and is currently close to about 20:1. Escape to space cannot therefore be the only sink for oxygen on Mars. Our results suggest that the missing oxygen (needed for the validation of the 2:1 ratio between H and O) can be explained by the incorporation into the martian surface by chemical weathering processes since the onset of intense oxidation about 2 Gyr ago. Based on the evolution of the atmosphere-surface-interaction on Mars, an overall global surface sink of about 2×1042 oxygen particles in the regolith can be expected. Because of the intense oxidation of inorganic matter, this process may have led to the formation of considerable amounts of sulfates and ferric oxides on Mars. To model this effect we consider several factors: (1) the amount of incorporated oxygen, (2) the inorganic composition of the martian soil and (3) meteoritic gardening. We show that the oxygen incorporation has also implications for the oxidant extinction depth, which is an important parameter to determine required sampling depths on Mars aimed at finding putative organic material. We found that the oxidant extinction depth is expected to lie in a range between 2 and 5 m for global mean values.  相似文献   

17.
《Planetary and Space Science》1987,35(10):1317-1321
In this study a method is outlined which is capable of giving neutral temperatures and height changes in the aurora when the molecular emissions originate from the E-region.Absolute spectrometric measurements of N2+ 1NG and O2+ 1NG bands and the auroral green line are performed in a nightside aurora. Rotational temperatures and band intensities are deduced by a least-squares fit of synthetic spectra to observations. There is a close correlation between the variations in rotational temperatures and the relative intensity ratio of N2+ 1NG(0,3) and O2+ 1NG(1,0) bands. The change in the relative intensity ratio is similar to the intensity variation predicted by the changing N2 and O2 densities from 120 to 150 km, obtained from the MSIS 83 model atmosphere, and the derived neutral temperature variations are consistent with a similar change in emission height of the aurora. Therefore the changing temperature is most likely due to a changing emission height of the aurora, and no local heating can be inferred.  相似文献   

18.
An analysis of ion data from 390 Venus Express, VEX, orbits demonstrates that the flow of solar wind- and ionospheric ions near Venus is characterized by a marked asymmetry. The flow asymmetry of solar wind H+ and ionospheric O+ points steadily in the opposite direction to the planet’s orbital motion, and is most pronounced near the Pole and in the tail/nightside region. The flow asymmetry is consistent with aberration forcing, here defined as lateral forcing induced by the planet’s orbital motion. In addition to solar wind forcing by the radial solar wind expansion, Venus is also subject a lateral/aberration forcing induced by the planet’s orbital motion transverse to the solar wind flow.The ionospheric response to lateral solar wind forcing is analyzed from altitude profiles of the ion density, ion velocity and ion mass-flux. The close connection between decreasing solar wind H+ mass-flux and increasing ionospheric O+ mass-flux, is suggestive of a direct/local solar wind energy and momentum transfer to ionospheric plasma. The bulk O+ ion flow is accelerated to velocities less than 10 km/s inside the dayside/flank Ionopause, and up to 6000 km in the tail. Consequently, the bulk O+ outflow does not escape, but remains near Venus as a fast (km/s) O+ zonal wind in the Venus polar and nightside upper ionosphere. Furthermore, the total O+ mass-flux in the Venus induced magnetosphere, increases steadily downward to a maximum of 2 × 10−14 kg/(m2 s) at ≈400 km altitude, suggesting a downward transport of energy and momentum. The O+, and total mass-flux, decay rapidly below 400 km. With no other plasma mass-flux as replacement, we argue that the reduction of ion mass-flux is caused by ion-neutral drag, a transfer of ion energy and momentum to neutrals, implying that the O+ plasma wind is converted to a neutral (thermosphere) wind at Venus. Incidentally, such a neutral wind would go in the same direction as the Venus atmosphere superrotation.  相似文献   

19.
W.-L. Tseng  W.-H. Ip  T.A. Cassidy 《Icarus》2010,206(2):382-389
The saturnian system is subject to constant bombardment by interplanetary meteoroids and irradiation by solar UV photons. Both effects release neutral molecules from the icy ring particles either in the form of impact water vapor or gas emission in the form of H2O, O2 and H2. The observations of the Cassini spacecraft during its orbit insertion have shown the existence of molecular and atomic oxygen ions. Subsequent modeling efforts have led to the picture that an exospheric population of neutral oxygen molecules is probably maintained in the vicinity of the rings via photolytic-decomposition of ice and surface reactions. At the same time, ionized products O+ and ions move along the magnetic field lines and, depending on the optical local thickness rings, can thread through the ring plane or impact a ring particle, the ion principal sink. In addition, collisional interactions between the ions and neutrals will change the scale height of the ions and produce a scattered component of O2 molecules and O atoms which can be injected into Saturn’s upper atmosphere or the inner magnetosphere. The ring atmosphere, therefore, serves as a source of ions throughout Saturn’s magnetosphere. If photolysis of ice is the dominant source of O2, then the complex structure of the ring atmosphere/ionosphere and the injection rate of neutral O2 will be subject to modulation by the seasonal variation of Saturn along its orbit. In this work, we show how the physical properties of the ring oxygen atmosphere, the scattered component, and the magnetospheric ion source rate vary as the ring system goes through the cycle of solar insolation. In particular, it is shown that the magnetopheric ions should be nearly depleted at Saturn’s equinox if O2 is produced mainly by photolysis of the ring material.  相似文献   

20.
Abstract— The outer layers of the Sun are thought to preserve the average isotopic and chemical composition of the solar system. The solar O-isotopic composition is essentially unmeasured, though models based on variations in meteoritic materials yield several predictions. These predictions are reviewed and possible variations on these predictions are explored. In particular, the two-component mixing model of Clayton and Mayeda (1984) (slightly revised here) predicts solar compositions to lie along an extension of the calcium-aluminum-rich inclusion (CAI) 16O line between (δ18O, δ17O) = (16.4, 11.4)%0 and (12.3, 7.5)%0. Consideration of data from ordinary chondrites suggests that the range of predicted solar composition should extend to slightly lower δ18O values. The predicted solar composition is critically sensitive to the solid/gas ratio in the meteorite-forming region, which is often considered to be significantly enriched over solar composition. A factor of two solid/gas enrichment raises the predicted solar (δ18O, δ17O) values along an extension of the CAI 16O line to (33, 28)%0. The model is also sensitive to the nebular O gas phase. If conversion of most of the gaseous O from CO to H2O occurred at relatively low temperatures and was incomplete at the time of CM aqueous alteration, the predicted nebular gas composition (and hence the solar composition) would be isotopically heavier along a slope 1/2 line. The likelihood of having a single solid nebular O component is discussed. A distribution of initial solid compositions along the CAI 16O line (rather than simply as an end-member) would not significantly change the predictions above in at least one scenario. Even considering these variations within the mixing model, the predicted range of solar compositions is distinct from that expected if the meteoritic variations are due to non-mass-dependent fractionation. Thus, a measurement of the solar O composition to a precision of several permil would clearly distinguish between these theories and should clarify a number of other important issues regarding solar system formation.  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