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1.
A model of auroral electron deposition processes has been developed using Monte Carlo techniques to simulate electron transport and energy loss. The computed differential electron flux and pitch angle were compared with in situ auroral observations to provide a check on the accuracy of the model. As part of the energy loss process, a tally was kept of electronic excitation and ionization of the important atomic and molecular states. The optical emission rates from these excited states were computed and compared with auroral observations of (3914 Å), (5577 Å), (7620 Å) and (N2VK). In particular, the roles played by energy transfer from N2(A3+u) and by other processes in the excitation of O(1S) and O2(b1+g) were investigated in detail. It is concluded that the N2(A3+u) mechanism is dominant for the production of OI(5577 Å) in the peak emission region of normal aurora, although the production efficiency is much smaller than the measured laboratory value; above 150 km electron impact on atomic oxygen is dominant. Atomic oxygen densities in the range of 0.75±0.25 MSIS-86 [O] were derived from the optical comparisons for auroral latitudes in mid-winter for various levels of solar and magnetic activity.  相似文献   

2.
A model of auroral precipitation (AP) developed on the basis of statistical processing of DMSP F6 and F7 satellite data (Vorobjev and Yagodkina, 2005, 2007) was used for the calculation of the global distribution of the auroral luminosity in different spectral ranges. The algorithm for the calculation of the integral intensity in bands N2 LBH (170.0 nm), ING N 2 + (391.4 nm), 1PG N2 (669.0 nm), and (OI) 557.7-nm emission is shown in detail. The processes of formation of electronically excited atoms O(1S) as a result of the transport of excitation energy from metastable state N2(A3Σ u + ), excitation of O(3P) by primary and secondary electrons, and dissociative recombination were taken into account to calculate the intensity of emission at 557.7 nm. A high correlation between the model distribution of the auroral luminosity in the UV spectral range and the observations of the Polar satellite is demonstrated.  相似文献   

3.
A mathematical model of the middle and high latitude ionosphere   总被引：5，自引：0，他引：5  
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4.
It is now well known that there is a substantial outflow of ionospheric plasma from the terrestrial ionosphere at high latitudes. The outflow consists of light thermal ions (H+, He+) as well as both light and heavy energized ions (H+, He+, O+, N+, NO+, O2+, N2+). The thermal ion outflows tend to be associated with the classical polar wind, while the energized ions are probably associated with either auroral energization processes or nonclassical polar wind processes. Part of the problem with identifying the exact cause of a given outflow relates to the fact that the ionosphere continuously convects into and out of the various high-latitude regions (sunlight, cusp, polar cap, nocturnal oval) and the time-constant for outflow is comparable to the convection time. Therefore, it is difficult to separate and quantify the possible outflow mechanisms. Some of these mechanisms are as follows. In sunlit regions, the photoelectrons can heat the thermal electrons and the elevated electron temperature acts to increase the polar wind outflow rate. At high altitudes, the escaping photoelectrons can also accelerate the polar wind as they drag the thermal ions with them. In the cusp and auroral oval, the precipitating magnetospheric electrons can heat the thermal electrons in a manner similar to the photoelectrons. Also, energized ions, in the form of beams and conics, can be created in association with field-aligned auroral currents and potential structures. The cusp ion beams and conics that have been convected into the polar cap can destabilize the polar wind when they pass through it at high altitudes, thereby transferring energy to the thermal ions. Additional energization mechanisms in the polar cap include Joule heating, hot magnetospheric electrons and ions, electromagnetic wave turbulence, and centrifugal acceleration.Some of these causes of ionospheric outflow will be briefly reviewed, with the emphasis on the recent simulations of polar wind dynamics in convecting flux tubes of plasma.  相似文献   

5.
Ionospheric heating experiments were done by the EISCAT Heater in Tromsø on 15–19 November, 1993. A low-light TV camera was installed at the VLF receiving station at Porojärvi about 100 km to the south-east of Tromsø. The spectral analysis of the auroral luminosity variations showed that the brightness of the aurora varied at the modulation frequency of the heating wave. The results of this analysis and the numerical simulations of the auroral luminosity variations caused by the HF heating are shown. The variations of the optical emission intensity at the heating frequency occur during the auroral ionosphere modification. The observed intensity variation of the auroral green line during the interval of enhanced electron temperature is explained by a decreasing rate of the O2+ ion dissociative recombination when the electron temperature increases. The brightness variation depends on the characteristic energy and the intensity of the auroral electron flux and the heating wave parameters. The artificial luminosity pulsations caused by HF heating are estimated.  相似文献   

6.
Millstone Hill ionospheric storm time measurements of the electron density and temperature during the ionospheric storms (15-16 June 1965; 29–30 September 1969 and 17–18 August 1970) are compared with model results. The model of the Earth’s ionosphere and plasmasphere includes interhemispheric coupling, the H+, O+(4S), O+(2D), O+(2P), NO+, O+2 and N+2 ions, electrons, photoelectrons, the electron and ion temperature, vibrationally excited N2 and the components of thermospheric wind.In order to model the electron temperature at the time of the 16 June 1965 negative storm, the heating rate of the electron gas by photoelectrons in the energy balance equation was multiplied by the factors 5–30 at he altitude above 700 km for the period 4.50-12.00 LT, 16 June 1965. The [O]/[N2] MSIS-86 decrease and vibrationally excited N2 effects are enough to account for the electron density depressions at Millstone Hill during the three storms. The factor of 2 (for 27–30 September 1969 magnetic storm) and the & actor 2.7 (for 16–18 August 1970 magnetic storm) reduction in the daytime peak density due to enhanced vibrationally excited N2 is brought about by the increase in the O++N2 rate factor.  相似文献   

7.
This study compares the Isis II satellite measurements of the electron density and temperature, the integral airglow intensity and volume emission rate at 630 nm in the SAR arc region, observed at dusk on 4 August, 1972, in the Southern Hemisphere, during the main phase of the geomagnetic storm. The model results were obtained using the time dependent one-dimensional mathematical model of the Earth’s ionosphere and plasmasphere (the IZMIRAN model). The major enhancement to the IZMIRAN model developed in this study to explain the two component 630 nm emission observed is the analytical yield spectrum approach to calculate the fluxes of precipitating electrons and the additional production rates of N+2, O+2, O+(4S), O+(2D), O−(2P), and O+(2P) ions, and O(1D) in the SAR arc regions in the Northern and Southern Hemispheres. In order to bring the measured and modelled electron temperatures into agreement, the additional heating electron rate of 1.05 eV cm−3 s−1 was added in the energy balance equation of electrons at altitudes above 5000 km during the main phase of the geomagnetic storm. This additional heating electron rate determines the thermally excited 630 nm emission observed. The IZMIRAN model calculates a 630 nm integral intensity above 350 km of 4.1 kR and a total 630 nm integral intensity of 8.1 kR, values which are slightly lower compared to the observed 4.7 kR and 10.6 kR. We conclude that the 630 nm emission observed can be explained considering both the soft energy electron excited component and the thermally excited component. It is found that the inclusion of N2(v > 0) and O2(v > 0) in the calculations of the O+(4S) loss rate improves the agreement between the calculated Ne and the data on 4 August, 1972. The N2(v > 0) and O2(v > 0) effects are enough to explain the electron density depression in the SAR arc F-region and above F2 peak altitude. Our calculations show that the increase in the O+ + N2 rate factor due to the vibrationally excited nitrogen produces the 5–19% reductions in the calculated quiet daytime peak density and the 16–24% decrease in NmF2 in the SAR arc region. The increase in the O+ + N2 loss rate due to vibrationally excited O2 produces the 7–26% decrease in the calculated quiet daytime peak density and the 12–26% decrease in NmF2 in the SAR arc region. We evaluated the role of the electron cooling rates by low-lying electronic excitation of O2(a1δg) and O2(b1σg+), and rotational excitation of O2, and found that the effect of these cooling rates on Te can be considered negligible during the quiet and geomagnetic storm period 3–4 August, 1972. The energy exchange between electron and ion gases, the cooling rate in collisions of O(3P) with thermal electrons with excitation of O(1D), and the electron cooling rates by vibrational excitation of O2 and N2 are the largest cooling rates above 200 km in the SAR arc region on 4 August, 1972. The enhanced IZMIRAN model calculates also number densities of N2(B3πg+), N2(C3πu), and N2(A3σu+) at several vibrational levels, O(1S), and the volume emission rate and integral intensity at 557.7 nm in the region between 120 and 1000 km. We found from the model that the integral integral intensity at 557.7 nm is much less than the integral intensity at 630 nm.  相似文献   

8.
The occurrence of anomalous (nonthermal) profiles of green emission of oxygen atoms detected with a Fabry-Perot spectrometer in auroras with the effect of a rapid decrease in the intensity of the wings of their dissociative component has been investigated. Based on an analysis of these measured profiles, it has been found that the characteristic time of recombination of a molecular oxygen ion at altitudes of 200–400 km is about 5–7 s. It appears that these molecular ions occur in a horizontally limited region of the auroral ionosphere as a result of ionization by a space localized flux of soft electrons with energies of 0.2–0.4 keV penetrating up to altitudes of 200 km. The estimation of the electron flux produces a value of 1010–1013 electrons cm?2 s?1. They generate the excess concentration n(O 2 + ) ~ 5.6 × 105 cm?3.  相似文献   

9.
The energy of precipitating particles that cause auroras can be characterized by the ratio of different atom and molecule emissions in the upper atmospheric layers. It is known that the spectrum of precipitating electrons becomes harder when substorms develop. The ratio of the I 6300 red line to the I 5577 green line was used to determine the precipitating-electron spectrum hardness. The I 6300/I 5577 parameter was used to roughly estimate the electron energy in auroral arcs observed in different zones of the auroral bulge at the bulge poleward edge and within this bulge. The variations in the emission red and green lines in auroral arcs during substorms that occurred in the winter season 2007–2008 and in January 2006 were analyzed based on the zenith photometer and all-sky camera data at the Barentsburg and Longyearbyen (LYR) high-latitude observatories. It has been indicated that the average value of the I 6300/I 5577 emission ratio for arcs within the auroral bulge is larger than this value at the bulge poleward edge. This means that the highest-energy electron precipitation is observed in arcs at the poleward edge of the substorm auroral bulge.  相似文献   

10.
The high-latitude ionospheric response to a major magnetic storm on May 15, 1997 is studied and different responses in the polar cap and the auroral oval are highlighted. Depletion of the F2 region electron density occurred in both the polar cap and the auroral zone, but due to different physical processes. The increased recombination rate of O+ ions caused by a strong electric field played a crucial role in the auroral zone. The transport effect, however, especially the strong upward ion flow was also of great importance in the dayside polar cap. During the main phase and the beginning of the recovery phase soft particle precipitation in the polar cap showed a clear relation to the dynamic pressure of the solar wind, with a maximum cross-correlation coefficient of 0.63 at a time lag of 5 min.  相似文献   

11.
Multi-instrument experimental data are analyzed to determine the main processes forming a deep trough in the electron density at F-peak altitudes during a strong magnetic storm (Kp⩾5). Previous attempts to explain the observations were not successful. The model we use to interpret the data includes production of vibrationally excited N2 in the region poleward of the trough and its transport into the trough region by a southward wind. The main source of the vibrationally excited N2 is secondary electrons created by precipitating electrons. Joule heating and dissipation of precipitating electron energy create a pressure gradient and induce the southward wind. According to the model calculations, such a system of processes can cause the very strong electron density depletion observed by the Millstone Hill incoherent scatter radar on April 20, 1985. An important additional condition for such a deep trough is a decrease in the [O]/[N2] ratio. The total energy flux and average energy of precipitating electrons just poleward of the trough is also a factor.  相似文献   

12.
A fully time-dependent mathematical model, SUPIM, of the Earth’s plasmasphere is used in this investigation. The model solves coupled time-dependent equations of continuity, momentum and energy balance for the O+, H+, He+, N+2, O+2, NO+ ions and electrons; in the present study, the geomagnetic field is represented by an axial-centred dipole. Calculation of vibrationally excited nitrogen molecules, which has been incorporated into the model, is presented here. The enhanced model is then used to investigate the behaviour of vibrationally excited nitrogen molecules with F10.7 and solar EUV flux, during summer, winter and equinox conditions. The presence of vibrational nitrogen causes a reduction in the electron content. The diurnal peak in electron content increases linearly up to a certain value of F10.7, and above this value increases at a lesser rate, in agreement with previous observations and modelling work. The value of F10.7 at which this change in gradient occurs is reduced by the presence of vibrational nitrogen. Vibrational nitrogen is most effective at F-region altitudes during summer daytime conditions when a reduction in the electron density is seen. A lesser effect is seen at equinox, and in winter the effect is negligible. The summer reduction in electron density due to vibrational nitrogen therefore reinforces the seasonal anomaly.  相似文献   

13.
This study compares the OV1-10 satellite measurements of the integral airglow intensities at 630 nm in the SAR arc regions observed in the northern and southern hemisphere as a conjugate phenomenon, with the model results obtained using the time-dependent one-dimensional mathematical model of the Earth ionosphere and plasmasphere (the IZMIRAN model) during the geomagnetic storm of the period 15–17 February 1967. The major enhancements to the IZMIRAN model developed in this study are the inclusion of He+ ions (three major ions: O+ H+ and He+ and three ion temperatures), the updated photochemistry and energy balance equations for ions and electrons, the diffusion of NO+ and O+2 ions and O(1D) and the revised electron cooling rates arising from their collisions with unexcited N2, O2 molecules and N2 molecules at the first vibrational level. The updated model includes the option to use the models of the Boltzmann or non-Boltzmann distributions of vibrationally excited molecular nitrogen. Deviations from the Boltzmann distribution for the first five vibrational levels of N2 were calculated. The calculated distribution is highly non-Boltzmann at vibrational levels v > 2 and leads to a decrease in the calculated electron density and integral intensity at 630 nm in the northern and southern hemispheres in comparison with the electron density and integral intensity calculated using the Boltzmann vibrational distribution of N2. It is found that the intensity at 630 nm is very sensitive to the oxygen number densities. Good agreement between the modeled and measured intensities is obtained provided that at all altitudes of the southern hemisphere a reduction of about factor 1.35 in MSIS-86 atomic oxygen densities is included in the IZMIRAN model with the non-Boltzm-ann vibrational distribution of N2. The effect of using of the O(1D) diffusion results in the decrease of 4–6% in the calculated integral intensity of the northern hemisphere and 7–13% in the calculated integral intensity of the southern hemisphere. It is found that the modeled intensities of the southern hemisphere are more sensitive to the assumed values of the rate coefficients of O+(4S) ions with vibrationally excited nitrogen molecules and quenching of O+(2D) by atomic oxygen than the modeled intensities of the northern hemisphere.  相似文献   

14.
In this paper the formulation of the problem and preliminary numerical computation results of the thermosphere-ionosphere-protonosphere system parameters are discussed.The model constructed describes time-dependent distributions of the multicomponent near-earth space plasma parameters by means of numerical integration of the appropriate three-dimensional plasma hydrodynamic equations. In the thermospheric block of the model, global distribution of neutral gas temperature and N2, O2, O concentrations, as well as three-dimensional circulation of the neutral gas are calculated in the range of height from 80 km to 520 km. In the ionospheric section of the model, global time-dependent distribution of ion and electron temperatures, as well as molecular and atomic O+, H+ ion concentrations are calculated. Global two-dimensional distribution of electric potential is calculated taking into account computed thermosphere and ionosphere parameters.The inputs needed for our global model are the solar EUV spectrum; the auroral precipitation pattern; the distribution of the field-aligned currents and the model of the geomagnetic field.Preliminary results are obtained without regard to electromagnetic plasma drift for the solar minimum, low geomagnetic activity and spring equinox conditions. Global distributions of the calculated parameters in the magnetic dipole latitude-longitude frame are presented for 1200 UT. In the summary ignored processes and future direction are discussed.  相似文献   

15.
Basic properties of the mid-latitude traveling ionospheric disturbances (TIDs) during the maximum phase of a major magnetic storm of 6–8 April 2000 are shown. Total electron content (TEC) variations were studied by using data from GPS receivers located in Russia and Central Asia. The nightglow response to this storm at mesopause and termospheric altitudes was also measured by optical instruments FENIX located at the observatory of the Institute of Solar-Terrestrial Physics (51.9°N,103.0°E), and MORTI located at the observatory of the Institute of Ionosphere (43.2°N, 77.0°E). Observations of the O (557.7 and 630.0 nm) emissions originating from atmospheric layers centered at altitudes of 90 and 250 km were carried out at Irkutsk and of the O2(b1∑g+−X3∑g−) (0-1) emission originating from an atmospheric layer centered at altitude of 94 km was carried out at Almaty. Our radio and optical measurement network observed a storm-induced solitary large-scale wave with duration of 1 h and a wave front width of no less than 5000 km, while it traveled equatorward with a velocity of 200 m/s from 62°N to 38°N geographic latitude. The TEC disturbance, basically displaying an electron content depression in the maximum of the F2 region, reveals a good correlation with growing nightglow emission, the temporal shift between the TEC and emission variation maxima being different for different altitudes. A comparison of the auroral oval parameters with dynamic spectra of TEC variations and optical 630 nm emissions in the frequency range 0.4–4 mHz (250–2500 s periods) showed that as the auroral oval expands into mid-latitudes, also does the region with a developed medium-sale and small-scale TEC structure.  相似文献   

16.
In this research, an integrated simulation–optimization modeling approach (ISOMA) was developed for supporting agricultural N2O emission mitigation at the watershed scale. This approach can successfully combine soil N2O emission simulation and the consequential mitigation management within a general modeling framework. Also, uncertainties associated with the key soil parameter can be effectively reflected and addressed through adoption of Monte Carlo analysis for the simulation results. The Monte Carlo simulated results were then used to generate fuzzy membership functions that can be consequentially used for emission mitigation management, reflecting the combined uncertainties for N2O emission simulation and mitigation management. The developed ISOMA was then applied to a reservoir watershed in Miyun county of Beijing municipality. In the studying watershed, the simulation model was calibrated and verified. Then, N2O emission from multiple agricultural land-use patterns were predicted. The amounts of N2O emission of four land use patterns (i.e., cash tree, orchard, cropland, and natural forest) were (536.9, 590.8, 653.1), (237.7, 254.4, 275.9), (79.5, 100.7, 105.1), (33.0, 47.3, 61.1) kg CO2 eq ha?1 year?1, respectively. Two scenarios (i.e., G1 and G2) were set up according to development priorities of local economy and society. Meanwhile, multiple credibility levels were considered according to the risk of N2O emission. The land use patterns could be adjusted according to solutions of ISOMA. The developed methods could help regional manager choose various production patterns with cost-effective agriculture N2O emission management schemes in the Miyun reservoir watershed. The manager also can obtain deeply insights into the tradeoffs between agricultural benefits and system reliabilities.  相似文献   

17.
Energetic particle precipitation couples the solar wind to the Earth's atmosphere and indirectly to Earth's climate. Ionisation and dissociation increases, due to particle precipitation, create odd nitrogen (NOx) and odd hydrogen (HOX) in the upper atmosphere, which can affect ozone chemistry. The long-lived NOx can be transported downwards into the stratosphere, particularly during the polar winter. Thus, the impact of NOx is determined by both the initial ionisation production, which is a function of the particle flux and energy spectrum, as well as transport rates. In this paper, we use the Sodankylä Ion and Neurtal Chemistry (SIC) model to simulate the production of NOx from examples of the most representative particle flux and energy spectra available today of solar proton events (SPE), auroral energy electrons, and relativistic electron precipitation (REP). Large SPEs are found to produce higher initial NOx concentrations than long-lived REP events, which themselves produce higher initial NOx levels than auroral electron precipitation. Only REP microburst events were found to be insignificant in terms of generating NOx. We show that the Global Ozone Monitoring by Occultation of Stars (GOMOS) observations from the Arctic winter 2003–2004 are consistent with NOx generation by a combination of SPE, auroral altitude precipitation, and long-lived REP events.  相似文献   

18.
Increase in the nighttime high-latitude nonthermal emissions in the mesosphere and lower thermosphere in the 4.3 and 15 μm CO2 bands during solar proton events has been estimated for the first time. The estimations have been performed for protons with energies not lower than 1 MeV precipitating into the atmosphere. A strong increase in the 4.3 μm emission can be anticipated during the above events; however, a substantial increase in the 15 μm emission is improbable. The 4.3 μm emission can increase only above approximately 80 km regardless of the energy of precipitating protons. The excitation of CO2 vibrational states, transitions from which generate the 4.3 μm emission, is caused by the vibrational excitation of N2 molecules due to collisions with secondary electrons, produced during solar proton events, and the following transfer of this excitation to CO2(0001) molecules during N2-CO2 collisions. Original Russian Text ? V.P. Ogibalov, S.N. Khvorostovskii, G.M. Shved, 2006, published in Geomagnetizm i Aeronomiya, 2006, Vol. 46, No. 2, pp. 159–167.  相似文献   

19.
We compare measurements of the ionospheric F region at Millstone Hillduring the severe geomagnetic disturbances of 5–11 June 1991 with results from the IZMIRANand FLIP time-dependent mathematical models of the Earths ionosphere and plasmasphere. Somecomparisons are also made with the Millstone Hill semi-empirical model which was previouslyused to model this storm. New rate coefficients from recent laboratory measurements of the O++N2 and O++O2 loss rates are included in theIZMIRAN and Millstone Hill models. The laboratory measurements show that vibrationallyexcited N2 and O2 (N2(v) and O2(v)) are both important at high temperatures such as found in the thermosphere during disturbedconditions at summer solar maximum. Increases in the O++N2 loss ratedue to N2(v) result in a factor ∼2 reduction in the daytime F2 peak electron density. On some days inclusion of N2(v) improves theagreement between the models and the data, and on other days it worsens it. In the present workwe show for the first time the significant effect that the increase in the O+recombination rate due to O2(v) may have on the calculated NmF2. There are considerable uncertainties in the model calculations during the unusual,extremely disturbed conditions found during the daytime on 6 June. The results illustratedifficulties involved and the current state of the art in modelling severe disturbances, and thusprovide a benchmark against which future progress can be gauged.  相似文献   

20.
Interpretation and measurement of redox intensity in natural waters   总被引：2，自引：0，他引：2  
Frevert deserves credit for proposing—for equilibrium systems—a distinction between a conceptually defined redox intensity, pε, and an operationally defined redox condition under stationary states, pe, as given by the response of a sensor electrode, and for pointing out that pε need not relate to pe. We would like to re-emphasize (1, 2, 3) that in defining a redox intensity, pε=−log{e}, we have treated the electron conceptually as a basic redox component which, as a species in aqueous solution, does not have an existence of its own. Morel (4) has elaborated on the use of the electron as a (phase rule) component in redox reactions. As he shows, it obviously can be treated equivalent to O2, i.e. O2=(H+)−4(e−)−4(H2O)2. We define (3) pε as “the hypothetical electron activity at equilibrium which measures the relative tendency of a solution to accept or transfer electrons”. This free energy change ΔG can be expressed as a redox potential (electrode potential) in volts (i.e., as a free energy change per mole of electrons associated with a given reduction). Electron activities may be defined in any equilibrium systems where the free activities of reductants {Red}, and oxidants {Ox}, are defined. Thus, pε (like pH) is a derivative form of free energy. Using electrons in redox reactions and as components does not at all imply that such electrons exist as species in waters. In the compilation of “Stability Constants” of the Chemical Society (London), Sillén and Martell (1964) treat the electron as an inorganic ligand and establish an electron activity scale that corresponds to the definition given.  相似文献   

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