References of "Bisikalo, D. V"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailUVIS observations of the FUV OI and CO 4P Venus dayglow during the Cassini flyby
Hubert, Benoît ULg; Gérard, Jean-Claude ULg; Gustin, Jacques ULg et al

in Icarus (2010), 207

We analyze FUV spatially-resolved dayglow spectra obtained at 0.37 nm resolution by the UVIS instrument during the Cassini flyby of Venus. We use a least-squares fit method to determine the brightness of ... [more ▼]

We analyze FUV spatially-resolved dayglow spectra obtained at 0.37 nm resolution by the UVIS instrument during the Cassini flyby of Venus. We use a least-squares fit method to determine the brightness of the OI emissions at 130.4 and OI 135.6 nm, and of the bands of the CO fourth positive system which are dominated by fluorescence scattering. We compare the brightness observed along the UVIS foot track of the two OI multiplets with that deduced from a model of the excitation of these emissions by photoelectron impact on O atoms and resonance scattering of the solar 130.4 nm emission. The large optical thickness 130.4 nm emission is accounted for using a radiative transfer model. The airglow intensities are calculated along the foot track and found to agree with the observed 130.4 nm brightness within ˜10%. The modeled OI 135.6 nm brightness is also well reproduced by the model. The oxygen density profile of the VTS3 model is found to be consistent with the observations. We find that self-absorption of the (0, v″) bands of the fourth positive emission of CO is important and we derive a CO vertical column of about 6.4 × 10[SUP]15[/SUP] cm[SUP]‑2[/SUP] in close agreement with the value provided by the VTS3 empirical atmospheric model. [less ▲]

Detailed reference viewed: 26 (5 ULg)
Full Text
Peer Reviewed
See detailThe Venus ultraviolet oxygen dayglow and aurora: Model comparison with observations
Gérard, Jean-Claude ULg; Hubert, Benoît ULg; Shematovich, V. I. et al

in Planetary and Space Science (2008), 56

We compare the intensity of the OI 130.4 and 135.6 nm emissions calculated using the soft electron precipitation measured on board the Pioneer Venus (PV) Orbiter with the auroral brightness observed with ... [more ▼]

We compare the intensity of the OI 130.4 and 135.6 nm emissions calculated using the soft electron precipitation measured on board the Pioneer Venus (PV) Orbiter with the auroral brightness observed with the ultraviolet spectrometer (OUVS) on board the PV. For this purpose, we use a new electron transport model based on a Monte Carlo implementation of the Boltzmann equation and a multi-stream radiative transfer model to calculate the effects of multiple scattering on the intensity field of the 130.4-nm triplet. We show that the consideration of the enhancement of the emergent 130.4-nm to the 135.6-nm intensity by multiple scattering in the optically thick Venus atmosphere increases the auroral 130.4/135.6 ratio by a factor of about 3. We find agreement with the mean 130.4/135.6 ratio observed with PV-OUVS using the typical suprathermal electron energy spectrum reported from PV in situ measurements showing a characteristic energy of about 14 eV. To account for the average OI auroral emissions, the required precipitated energy flux is 2×10[SUP]-3[/SUP] mW m[SUP]-2[/SUP], that is about 30% of the measured suprathermal night-side soft electron spectrum used as a reference. The calculated brightness of the CO Cameron bands is about twice as large as the weak observed emission, but within the error bars of the observations and the uncertainties of the dissociative excitation cross-section of CO[SUB]2[/SUB]. The electron transport model, coupled with calculations of excitation processes is also applied to an analysis of the FUV oxygen day airglow observations made with PV-OUVS and the Hopkins Ultraviolet Telescope (HUT) spectrograph. Comparisons indicate that the model accounts for both the disc-averaged intensities observed with the HUT spectrograph, the limb scans and the 130.4-nm images obtained with PV-OUVS. The relative contribution of resonance scattering of the solar line and photoelectron impact to the excitation of the 130.4-nm triplet depends on the altitude, but is globally dominated by resonance scattering. The intensity of the 130.4-nm dayglow emission does not vary proportionally with the O density in the lower thermosphere, but provides nevertheless a useful tool to remotely probe the atomic oxygen density and its variations. [less ▲]

Detailed reference viewed: 22 (5 ULg)
Full Text
Peer Reviewed
See detailMonte Carlo model of electron transport for the calculation of Mars dayglow emissions
Shematovich, V. I.; Bisikalo, D. V.; Gérard, Jean-Claude ULg et al

in Journal of Geophysical Research. Planets (2008), 113

A model of the photoelectron collision-induced component of the Mars dayglow using recent cross sections and solar flux is described. The calculation of the photoelectron source of excitation is based on ... [more ▼]

A model of the photoelectron collision-induced component of the Mars dayglow using recent cross sections and solar flux is described. The calculation of the photoelectron source of excitation is based on a stochastic solution of the Boltzmann equation using the direct simulation Monte Carlo method. The neutral atmosphere is taken from outputs of a global circulation model, and recent inelastic collision cross sections are adopted. The calculated vertical profiles of the CO Cameron bands and CO[SUB]2[/SUB] [SUP]+[/SUP] doublet emissions integrated along the line of sight compare well with the Spectroscopy for the Investigation of the Characteristics of the Atmosphere of Mars (SPICAM) limb profiles observed with the SPICAM spectrograph on board Mars Express made at Ls = 166° during the summer season at northern midlatitudes. The comparison shows agreement to within the uncertainties of the excitation cross sections. Seasonal changes in the brightness and the altitude of the emission peaks are predicted with intensity variations in the range 15-20%. [less ▲]

Detailed reference viewed: 16 (10 ULg)
Full Text
Peer Reviewed
See detailEnergetic oxygen atoms in the polar geocorona
Shematovich, V. I.; Bisikalo, D. V.; Gérard, Jean-Claude ULg

in Journal of Geophysical Research. Space Physics (2006), 111

The role of the auroral sources induced by the electron and proton precipitation in the formation of the hot oxygen corona in the polar upper atmosphere is studied. It is found that both electron ... [more ▼]

The role of the auroral sources induced by the electron and proton precipitation in the formation of the hot oxygen corona in the polar upper atmosphere is studied. It is found that both electron precipitation through exothermic chemistry and proton precipitation through atmospheric sputtering significantly contribute to the population of the hot oxygen geocorona. It is also found that only atmospheric sputtering results in the formation of the escape flux of energetic oxygen atoms, providing an important source of heavy atoms for the magnetosphere. The exothermic chemistry induced by the electron precipitation and/or by the absorption of the solar UV radiation is operating continuously in the polar upper atmosphere and results in a steady population of the very near-Earth environment by suprathermal oxygen atoms with energies below a few eV. By contrast, atmospheric sputtering by magnetospheric protons provides a more variable contribution, strongly coupled with the cusp region. It produces the more energetic oxygen atoms that populate the external regions of the hot oxygen geocorona. The results of calculations are in a good agreement with the analysis of the low-latitude perigee Low Energy Neutral Atom (LENA) images showing that the instrument signal consists of low to medium energy (5-30 eV) oxygen atoms produced in and near the cusp region. The more energetic (>30 eV) fraction of energetic oxygen atoms produced by the ion-induced atmospheric sputtering could be responsible for the energetic neutrals observed by the instrument far away from the cusp or oval regions. The total escape flux of oxygen atoms associated with atmospheric sputtering by protons is found about 8 × 10[SUP]23[/SUP] s[SUP]-1[/SUP] therefore this mechanism may provide a substantial contribution to the magnetospheric oxygen population. [less ▲]

Detailed reference viewed: 21 (7 ULg)
See detailVenus' ultraviolet airglow and aurora: Monte Carlo simulations and comparison with observations
Gérard, Jean-Claude ULg; Shematovich, V. I.; Bisikalo, D. V. et al

in European Planetary Science Congress 2006 (2006)

The Venus airglow has been observed from spectrometers on board rockets probes and satellites such as OUVS on Pioneer Venus Venera Galileo HUT on the Space Shuttle and quite recently SPICAV on Venus ... [more ▼]

The Venus airglow has been observed from spectrometers on board rockets probes and satellites such as OUVS on Pioneer Venus Venera Galileo HUT on the Space Shuttle and quite recently SPICAV on Venus Express The spectrum is dominated by emissions from helium hydrogen oxygen and carbon lines and CO bands Localized emissions of OI at 1304 and 1356 A have been sporadically observed on the nightside and are likely caused by precipitation of auroral electrons in the wake of the planet We have developed a Monte Carlo code solving the Boltzmann equation for energetic electrons to calculate the energy distribution function and fluxes of primary and secondary auroral electrons and for photoelectrons The model is used to calculate the vertical distribution of the excitation rate of various excited states For optically thick transitions such as the 3P-3S triplet at 1304 A a radiative transfert code is used to calculate the emergent emission rate We find that the relative intensity of the oxygen and CO Cameron band emissions is a sensitive indicator of the energy of auroral electrons The observed values indicate that the mean energy is on the order of 10-50 eV Dayglow intensity and distributions are also compared with observed characteristics [less ▲]

Detailed reference viewed: 31 (4 ULg)
Full Text
Peer Reviewed
See detailA Monte Carlo model of auroral hydrogen emission line profiles
Gérard, Jean-Claude ULg; Shematovich, V. I.; Bisikalo, D. V. et al

in Annales Geophysicae [= ANGEO] (2005), 23

Hydrogen line profiles measured from space-borne or ground-based instruments provide useful information to study the physical processes occurring in the proton aurora and to estimate the proton flux ... [more ▼]

Hydrogen line profiles measured from space-borne or ground-based instruments provide useful information to study the physical processes occurring in the proton aurora and to estimate the proton flux characteristics. The line shape of the hydrogen lines is determined by the velocity distribution of H atoms along the line-of-sight of the instrument. Calculations of line profiles of auroral hydrogen emissions were obtained using a Monte Carlo kinetic model of proton precipitation into the auroral atmosphere. In this model both processes of energy degradation and scattering angle redistribution in momentum and charge transfer collisions of the high-energy proton/hydrogen flux with the ambient atmospheric gas are considered at the microphysical level. The model is based on measured cross sections and scattering angle distributions and on a stochastic interpretation of such collisions. Calculations show that collisional angular redistribution of the precipitating proton/hydrogen beam is the dominant process leading to the formation of extended wings and peak shifts in the hydrogen line profiles. All simulations produce a peak shift from the rest line wavelength decreasing with increasing proton energy. These model predictions are confirmed by analysis of ground-based H-beta line observations from Poker Flat, showing an anti-correlation between the magnitude of the peak shift and the extent of the blue wing of the line. Our results also strongly suggest that the relative extension of the blue and red wings provides a much better indicator of the auroral proton characteristic energy than the position of the peak wavelength. [less ▲]

Detailed reference viewed: 18 (3 ULg)
Full Text
Peer Reviewed
See detailAn auroral source of hot oxygen in the geocorona
Shematovich, V. I.; Bisikalo, D. V.; Gérard, Jean-Claude ULg

in Geophysical Research Letters (2005), 32

The high-energy proton-hydrogen (H[SUP]+[/SUP]/H) beam associated with proton auroral precipitation transfers momentum in elastic and inelastic collisions with ambient thermal atomic oxygen in the high ... [more ▼]

The high-energy proton-hydrogen (H[SUP]+[/SUP]/H) beam associated with proton auroral precipitation transfers momentum in elastic and inelastic collisions with ambient thermal atomic oxygen in the high latitude thermosphere. This process provides a localized novel source of hot oxygen atoms in addition to exothermic photochemistry, charge exchange and momentum transfer from O[SUP]+[/SUP] ion precipitation and charge exchange with accelerated ionospheric O[SUP]+[/SUP] ions. We suggest that this source contributes to the population of the hot oxygen geocorona and to the flux of escaping oxygen atoms. For an incident proton energy flux of 1 mW m[SUP]-2[/SUP] and a mean energy E[SUB]mean[/SUB] ~ 5 keV, we calculate a density of hot oxygen atoms with energy above 1 eV of 2.0 × 10[SUP]3[/SUP] cm[SUP]-3[/SUP] and a mean kinetic energy of about 3.5 eV at 700 km. The total upward flux of hot oxygen atoms with energies higher 1 eV is estimated as 3.5 × 10[SUP]8[/SUP] cm[SUP]-2[/SUP] s[SUP]-1[/SUP]. [less ▲]

Detailed reference viewed: 6 (1 ULg)
Full Text
Peer Reviewed
See detailRemote sensing of the proton aurora characteristics from IMAGE-FUV
Bisikalo, D. V.; Shematovich, V. I.; Gérard, Jean-Claude ULg et al

in Annales Geophysicae [= ANGEO] (2003), 21

The combination of simultaneous global images of the north polar region obtained with the IMAGE-FUV imaging system makes it possible to globally map the properties of the electron and proton auroral ... [more ▼]

The combination of simultaneous global images of the north polar region obtained with the IMAGE-FUV imaging system makes it possible to globally map the properties of the electron and proton auroral precipitation. The SI12 imager, which observes the Doppler-shifted Lyman-a [less ▲]

Detailed reference viewed: 14 (1 ULg)
Full Text
Peer Reviewed
See detailSummary of quantitative interpretation of IMAGE far ultraviolet auroral data
Frey, H. U.; Mende, S. B.; Immel, T. J. et al

in Space Science Reviews (2003), 109

Direct imaging of the magnetosphere by instruments on the IMAGE spacecraft is supplemented by simultaneous observations of the global aurora in three far ultraviolet (FUV) wavelength bands. The purpose of ... [more ▼]

Direct imaging of the magnetosphere by instruments on the IMAGE spacecraft is supplemented by simultaneous observations of the global aurora in three far ultraviolet (FUV) wavelength bands. The purpose of the multi-wavelength imaging is to study the global auroral particle and energy input from the magnetosphere into the atmosphere. This paper describes the method for quantitative interpretation of FUV measurements. The Wide-Band Imaging Camera (WIC) provides broad band ultraviolet images of the aurora with maximum spatial resolution by imaging the nitrogen lines and bands between 140 and 180 nm wavelength. The Spectrographic Imager (SI), a dual wavelength monochromatic instrument, images both Doppler-shifted Lyman-alpha emissions produced by precipitating protons, in the SI-12 channel and OI 135.6 nm emissions in the SI-13 channel. From the SI-12 Doppler shifted Lyman-alpha images it is possible to obtain the precipitating proton flux provided assumptions are made regarding the mean energy of the protons. Knowledge of the proton (flux and energy) component allows the calculation of the contribution produced by protons in the WIC and SI-13 instruments. Comparison of the corrected WIC and SI-13 signals provides a measure of the electron mean energy, which can then be used to determine the electron energy flux. To accomplish this, reliable emission modeling and instrument calibrations are required. In-flight calibration using early-type stars was used to validate the pre-flight laboratory calibrations and determine long-term trends in sensitivity. In general, very reasonable agreement is found between in-situ measurements and remote quantitative determinations. [less ▲]

Detailed reference viewed: 24 (1 ULg)
See detailIonospheric Conductances Due To Auroral Proton and Electron Precipitation Deduced From Image-fuv Observations.
Coumans, Valérie ULg; Hubert, Benoît ULg; Meurant, M. et al

in EGS XXVII General Assembly, Nice, 21-26 April 2002 (2002)

The FUV instrument on the IMAGE (Imager for Magnetopause-to-Aurora Global Ex- ploration) satellite monitors the aurora in three different spectral regions. The Wide- band Imaging Camera (WIC) observes the ... [more ▼]

The FUV instrument on the IMAGE (Imager for Magnetopause-to-Aurora Global Ex- ploration) satellite monitors the aurora in three different spectral regions. The Wide- band Imaging Camera (WIC) observes the molecular N2 LBH and the atomic NI emissions at 140-180 nm. The two channels of the Spectrographic Imager (SI) ob- serve the Doppler shifted Lyman- emission at 121.8 nm due to precipitating protons (SI12) and the electron auroral emission of OI at 135.6 nm (SI13). We calculate the Pedersen and Hall ionospheric conductances due to auroral particles based on FUV observations separately for the proton and electron precipitation. We first estimate the electron and proton energy fluxes from the FUV data, relying on energy degradation and auroral emission models. A two-stream model is used for the electron aurora while the proton aurora modeling is based on the direct Monte Carlo method, which gives a stochastic solution to the Boltzmann equations for the H+ - H beam. The electron energy is evaluated by combining observations from the three FUV instruments. For the proton energy, we use a statistical model based on in-situ particle measurements. Second, the particle energy and energy flux are used to estimate the ionization rates separately for protons and electrons, consistently with the energy degradation models. Finally, the electron and ion densities are estimated from ionization profiles, and the Pedersen and Hall conductances are calculated from fundamental equations. Appli- cations of the method to the distribution of the conductance at winter solstice in the course of substorm development over the north polar region will be illustrated. [less ▲]

Detailed reference viewed: 6 (1 ULg)
Peer Reviewed
See detailThe role of proton precipitation in the excitation of auroral FUV emissions
Hubert, Benoît ULg; Gérard, Jean-Claude ULg; Bisikalo, D. V. et al

in Journal of Geophysical Research (2001), 106

Far ultraviolet remote sensing from a high-altitude satellite is extensively used to image the global aurora, derive its energetics, and follow its dynamical morphology. It is generally assumed that the ... [more ▼]

Far ultraviolet remote sensing from a high-altitude satellite is extensively used to image the global aurora, derive its energetics, and follow its dynamical morphology. It is generally assumed that the observed emissions are dominated by the interaction of the precipitated electrons with the thermospheric constituents. A model to calculate far ultraviolet emissions excited by auroral electrons and protons and the secondary electrons they generate has been used to calculate the volume excitation rate of the H I Ly-alpha, O I 1304 and 1356 Å, N I 1493 Å multiplets, and the N[SUB]2[/SUB] Lyman-Birge-Hopfield (LBH) bands. The characteristic energy and the energy flux are derived from the observed statistical distribution of precipitated protons and electrons. This model is applied to the midnight aurora, the noon cusp, and a proton-dominated aurora for moderately disturbed conditions. We show that in the first two cases, direct electron impact dominates the vertically integrated emission rate over the proton component, although proton excitation plays an important role at some altitudes in the daytime cusp. In afternoon regions of the auroral zone near the auroral boundary, secondary electrons due to proton ionization are the main source of FUV emissions. The energy dependence of the efficiency of LBH band emission viewed from high altitude is calculated for electron and proton precipitations. Maps of the N[SUB]2[/SUB] LBH emission excited by both components are obtained, and regions of proton-dominated auroral emission are identified. It is found that the distribution of the ratio of proton-induced to electron-induced brightness resembles maps of the ratio of the respective precipitated energy fluxes. Proton-dominated FUV emissions are thus located in a C-shaped sector extending from prenoon to midnight magnetic local times with a maximum proton contribution near the equatorward boundary of the statistical electron oval. The distribution of the Ly-alpha/LBH intensity ratio is found to mimic the ratio of the proton flux/total energy flux, although it is insufficient by itself to accurately determine the relative fraction of auroral energy carried by the protons. [less ▲]

Detailed reference viewed: 6 (0 ULg)
See detailDetermination of electron and proton auroral energy inputs from FUV-IMAGE
Gérard, Jean-Claude ULg; Hubert, Benoît ULg; Meurant, M. et al

Conference (2001, May 01)

The FUV experiment onboard the IMAGE spacecraft offers the unique possibility to obtain simultaneous snapshots of the global north aurora every 2 minutes in three different spectral channels. The WIC ... [more ▼]

The FUV experiment onboard the IMAGE spacecraft offers the unique possibility to obtain simultaneous snapshots of the global north aurora every 2 minutes in three different spectral channels. The WIC camera has a broadband channel covering the 135-190 nm interval including the N[SUB]2[/SUB] LBH bands, part of which may be absorbed by O[SUB]2[/SUB]. The SI13 channel is centered on the OI 135.6 nm line which is optically thin and includes a ~ 40% LBH contribution. Finally, the SI12 camera images the Doppler-shifted Ly-α emission excited by the proton aurora. This set of instrumentation is combined with auroral models to determine the electron and the proton energy fluxes from the magnetosphere. Examples will be presented and compared with the values deduced from the NOAA satellites. Simultaneous in-situ measurements of the particle characteristic energy have been combined with the data extracted from the FUV images to validate the models and derive empirical relationships between the particle flux measured by the detectors and the brightness observed by FUV-IMAGE at the footprint of the same magnetic field line. Finally, we will assess the ability to deduce the characteristic energy of the auroral particles from the ratio of co-registered images in the WIC and SI13 cameras. This method is based on the difference of vertical distribution of the LBH and the OI 135.6 nm emissions. It offers the potential to globally remotely sense not only the energy flux from the magnetosphere but also the main features of the electron characteristic energy. [less ▲]

Detailed reference viewed: 17 (5 ULg)
Peer Reviewed
See detailEffect of hot oxygen on thermospheric O I UV airglow
Hubert, Benoît ULg; Gérard, Jean-Claude ULg; Cotton, D. M. et al

in Journal of Geophysical Research (1999), 104

The role of nonthermal oxygen atoms in the vertical distribution of the O I 989 Å EUV multiplet intensity is investigated using a thermospheric radiative transfer code. The superthermal oxygen ... [more ▼]

The role of nonthermal oxygen atoms in the vertical distribution of the O I 989 Å EUV multiplet intensity is investigated using a thermospheric radiative transfer code. The superthermal oxygen concentration and temperatures are derived from the energy distribution functions of the O([SUP]3[/SUP]P) atoms calculated by a Monte Carlo stochastic model, and their effect on UV radiative transfer is compared to sounding rocket observations. The calculated intensity increase associated with the perturbation of the Doppler profile by the presence of hot O([SUP]3[/SUP]P) atoms is shown to be insufficient to account for the set of sounding rocket EUV intensity data. [less ▲]

Detailed reference viewed: 13 (0 ULg)
Peer Reviewed
See detailAn updated model of the hot nitrogen atom kinetics and thermospheric nitric oxide
Gérard, Jean-Claude ULg; Bisikalo, D. V.; Shematovich, V. I. et al

in Journal of Geophysical Research (1997), 102

New observations and reanalysis of previous measurements suggest an upward revision of the measured thermospheric nitric oxide density. Our previous model of NO production by fast N([SUP]4[/SUP]S) atom ... [more ▼]

New observations and reanalysis of previous measurements suggest an upward revision of the measured thermospheric nitric oxide density. Our previous model of NO production by fast N([SUP]4[/SUP]S) atom collisions with O[SUB]2[/SUB] has been updated. It includes the effect of soft solar X rays, Auger electrons, and a detailed treatment of N[SUB]2[/SUB] dissociative ionization channels. In addition, new calculations indicate that the transfer of translational energy in N+N[SUB]2[/SUB] collisions is less efficient than in the hard sphere approximation. This result leads to reevaluation of the energy dependent relaxation cross section and to an upward revision of the reacting efficiency of collisions of N with O[SUB]2[/SUB] to form nitric oxide. The calculated peak NO density increases by a factor of ~2 when the effect of superthermal nitrogen atoms is included. The model response of the N([SUP]4[/SUP]S) energy distribution function and NO density to solar cycle variations is presented. The NO density at 110 km changes from 5.4×10[SUP]7[/SUP] to 1.3×10[SUP]8[/SUP]cm[SUP]-3[/SUP] when the solar F[SUB]10.7[/SUB] index varies from 70 to 245, but its response depends on the magnitude of the soft X ray increase with solar activity. [less ▲]

Detailed reference viewed: 12 (0 ULg)
Peer Reviewed
See detailThe distribution of hot hydrogen atoms produced by electron and proton precipitation in the Jovian aurora
Bisikalo, D. V.; Shematovich, V. I.; Gérard, Jean-Claude ULg et al

in Journal of Geophysical Research (1996), 101

The energy distribution functions of nonthermal thermospheric hydrogen atoms are calculated for electron and proton precipitation in the Jovian aurora. A numerical model taking into account the production ... [more ▼]

The energy distribution functions of nonthermal thermospheric hydrogen atoms are calculated for electron and proton precipitation in the Jovian aurora. A numerical model taking into account the production, elastic and inelastic relaxation and transport processes for hot H atoms is developed. This model is based on a Monte Carlo solution of the nonlinear Boltzmann equation for hot H atoms produced by electron and proton impact on H and H[SUB]2[/SUB] and exothermic chemical reactions. The distribution functions show a much higher energy tail for proton than electron precipitation. It is shown that the steady state flux of hot atoms (E>=2 eV) is essentially isotropic. The peak and column hot H densities are about 3×10[SUP]5[/SUP] cm[SUP]-3[/SUP] and 1×10[SUP]14[/SUP] cm[SUP]-3[/SUP] for a 100 erg cm[SUP]-2[/SUP]s[SUP]-1[/SUP] precipitation combining hard (22 keV) and soft (0.2 keV) electrons mixed with a 10 erg cm[SUP]-2[/SUP]s[SUP]-1[/SUP] flux of soft (0.3 keV) protons. These column densities, coupled with the wide range of hot H atom energies, may play an important role in the formation of the Lyman alpha line profile. Multiple scattering in the wings of the Ly alpha line by the fast H atoms is shown to partly account for the broad Ly alpha profile observed in the Jovian aurora with the Hubble space telescope. [less ▲]

Detailed reference viewed: 13 (0 ULg)
Peer Reviewed
See detailA kinetic model of the formation of the hot oxygen geocorona. 2: Influence of O(+) ion precipitation
Bisikalo, D. V.; Shematovich, V. I.; Gérard, Jean-Claude ULg

in Journal of Geophysical Research (1995), 100

A model for the oxygen geocorona near the exobase solving the nonlinear Boltzmann equation with a Monte Carlo method is used to calculate the distribution of the hot oxygen atoms during geomagnetically ... [more ▼]

A model for the oxygen geocorona near the exobase solving the nonlinear Boltzmann equation with a Monte Carlo method is used to calculate the distribution of the hot oxygen atoms during geomagnetically disturbed nighttime conditions. The precipitation of energetic O(+) ions and the subsequent enhancement of the hot O corona at high latitudes is simulated for the September 17, 1971, storm conditions. It is found that in such circumstances, the O(+) precipitation is a significant source of superthermal O atoms leading to important perturbations of the velocity distribution of the bulk oxygen population. The effective gas temperature near the exobase is similar to that in the undisturbed atmosphere, but the hot O density rises considerably over the quiet condition values. [less ▲]

Detailed reference viewed: 3 (0 ULg)
Peer Reviewed
See detailThe importance of new chemical sources for the hot oxygen geocorona
Gérard, Jean-Claude ULg; Richards, P. G.; Shematovich, V. I. et al

in Geophysical Research Letters (1995), 22

Exothermic reactions involving metastable neutrals and ions were recently proposed as sources of hot oxygen atoms in addition to the classical O2(+) and NO(+) dissociative recombination. The Boltzmann ... [more ▼]

Exothermic reactions involving metastable neutrals and ions were recently proposed as sources of hot oxygen atoms in addition to the classical O2(+) and NO(+) dissociative recombination. The Boltzmann equations for thermal and nonthermal populations of O atoms are solved with Monte Carlo stochastic simulation method. It is shown that the calculated energy distribution functions of O atoms are significantly in nonequilibrium in the transition region between the thermosphere and the exosphere. It is found that the inclusion of additional sources leads to stronger disturbances of the energy distribution function and, as a consequence, increases the nonthermal fraction of hot O atoms. The variation of the vertical distribution of hot O between solar maximum and minimum conditions is also evaluated and shows good agreement with the available experimental evidence. [less ▲]

Detailed reference viewed: 7 (0 ULg)
Peer Reviewed
See detailA kinetic model of the formation of the hot oxygen geocorona. 1: Quiet geomagnetic conditions
Shematovich, V. I.; Bisikalo, D. V.; Gérard, Jean-Claude ULg

in Journal of Geophysical Research (1994), 99

A model of the hot oxygen geocorona in the transition region near the exobase is described. It is based on a Monte Carlo solution of the nonlinear Boltzmann equation for hot oxygen atoms produced by ... [more ▼]

A model of the hot oxygen geocorona in the transition region near the exobase is described. It is based on a Monte Carlo solution of the nonlinear Boltzmann equation for hot oxygen atoms produced by chemical processes usually considered as a source of hot oxygen (photodissociation of O2 and dissociative recombination of O2(+) and NO(+) ions). The evolution of the system is described stochastically as a series of random Markovian processes. The energy distribution function of the thermal and non-thermal O(3P) atoms and of the nonthermal O(1D) atoms is calculated from the thermospheric collision-dominated region to the exosphere where the gas flow is virtually collisionless. The model is applied to equatorial latitudes for conditions of low solar and geomagnetic activity. Numerical simulations show that the distribution function of thermal oxygen is increasingly perturbed by collisions with the hot oxygen population at high altitudes and departs significantly from a Maxwellian distribution at all altitudues. The number density and temperature of the nonthermal oxygen atoms are derived from their microscopic distribution function and found tobe in qualitative agreement with previous theoretical and experimental estimates. [less ▲]

Detailed reference viewed: 8 (0 ULg)