S. A. Haider

Calculated ionization rates, ion densities, and airglow emission rates due to precipitating electrons in the nightside ionosphere of Mars

The calculations presented in this paper clearly establish that the electron fluxes measured by the HARP instrument, carried on board Phobos 2, could cause significant electron impact ionization and excitation in the nightside atmosphere of Mars, if these electrons actually do precipitate. The calculated peak electron densities were found to be about a factor of 2 larger than the mean observed nightside densities, indicating that if a significant fraction of the measured electrons actually precipitate, they could be the dominant mechanism responsible for maintaining the nightside ionosphere. The calculated zenith column emission rates of the O I 5577-A and 6300-A and CO Cameron band emissions, due to electron impact and dissociative recombination mechanisms, were found to be significant.

Chemistry of the nightside ionosphere of Mars

The chemistry of seven ions, O2+, NO+, CO2+, O+, N2+, CO+, and H+, is studied in the nightside ionosphere of Mars using the analytical yield spectrum approach and coupled continuity equations for the steady state condition. The source and sink processes of these ions are discussed in detail. We have found that the nightside Martian ionosphere produced due to precipitation of magnetotail electrons agrees with the Viking observations rather than other sources of ionization such as the precipitation of plasma sheet electron or horizontal plasma transport from dayside ionosphere to the nightside similar to that operating on Venus, The precipitation of magnetotail electron produces major ion CO2+ which is quickly removed by the reactions (1) CO2+ + O → O2+ + CO, (2) CO2+ + O → O+ + CO2 and (3) O+ + CO2 → O2+ + CO leading to O2+ as a dominant ion in the nightside ionosphere of Mars. The reactions of O+ with N and NO are the major sources of NO+, which is lost entirely by dissociative recombination reaction. The second reaction is the major source of O+ below 190 km. Above this altitude the magnetotail electron impact ionization process is an important source of O+. This process is also important for the production of CO+ and N2+. The ion O+ is destroyed by the third reaction, while CO+ and N2+ are destroyed by charge transfer reaction with CO2. The ion H+ is produced due to charge exchange reaction between O+ and H which is lost by CO2.

Auroral and photoelectron fluxes in cometary ionospheres

Photoelectron and auroral electron fluxes in cometary ionospheres have been studied in detail using the analytical yield spectrum approach. The effects on photoelectron fluxes of cometocentric distance, solar zenith angle (using generalized Chapman function), and solar minimum and maximum conditions, on the assumption of local energy deposition, are determined. Energy loss to ambient electrons is accounted for. Auroral electron fluxes are calculated for monoenergetic and observed primary electron spectra. The results are compared with other theoretical works and good agreement is found. Auroral electrons make a larger contribution to the observed electron spectrum compared with the extreme ultraviolet-generated photoelectrons.

Radial distribution of production rates, loss rates and densities corresponding to ion masses ⩽40 amu in the inner coma of Comet Halley: Composition and chemistry

In this paper we have studied the chemistry of C, H, N, O, and S compounds corresponding to ions of masses ⩽40 amu in the inner coma of the Comet 1P/Halley. The production rates, loss rates, and ion mass densities are calculated using the Analytical Yield Spectrum approach and solving coupled continuity equation controlled by the steady state photochemical equilibrium condition. The primary ionization sources in the model are solar EUV photons, photoelectrons, and auroral electrons of the solar wind origin. The chemical model couples ion–neutral, electron–neutral, photon–neutral and electron–ion reactions among ions, neutrals, electrons, and photons through over 600 chemical reactions. Of the 46 ions considered in the model the chemistry of 24 important ions (viz., CH3OH+2, H3CO+, NH+4, H3S+, H2CN+, H2O+, NH+3, CO+, C3H+3, OH+, H3O+, CH3OH+, C3H+4, C2H+2, C2H+, HCO+, S+, CH+3, H2S+, O+, C+, CH+4, C+2, and O+2) are discussed in this paper. At radial distances 1000 km, the 6 major ions are H3O+, CH3OH+2, H2O+, H3CO+, C2H+2, and NH+4; along with ions CO+, OH+, and HCO+, whose importance increases with further increase in the radial distance. It is found that at radial distances greater than ∼1000 km (±500 km) the major chemical processes that govern the production and loss of several of the important ions in the inner coma are different from those that dominate at distances below this value. The importance of photoelectron impact ionization, and the relative contributions of solar EUV, and auroral and photoelectron ionization sources in the inner coma are clearly revealed by the present study. The calculated ion mass densities are compared with the Giotto Ion Mass Spectrometer (IMS) and Neutral Mass Spectrometer (NMS) data at radial distances 1500, 3500, and 6000 km. There is a reasonable agreement between the model calculation and the Giotto measurements. The nine major peaks in the IMS spectra between masses 10 and 40 amu are reproduced fairly well by the model within a factor of two inside the ionopause. We have presented simple formulae for calculating densities of the nine major ions, which contribute to the nine major peaks in the IMS spectra, throughout the inner coma that will be useful in estimating their densities without running the complex chemical models.

Photoelectron flux and nightglow emissions of 5577 and 6300 Å due to solar wind electron precipitation in Martian atmosphere

[i] The detailed model calculations of photoelectron flux and nightglow emissions of 5577 and 6300 A lines are made using analytical yield spectrum approach based on Monte Carlo method. The calculated photoelectron spectra are compared with electron reflectometer (ER) measurements made by Mars Global Surveyor (MGS) at the energy range 10-1000 eV. This calculation suggests that X-ray ionization is an important process in the dayside ionosphere of Mars at energy greater than 90 eV, and 10- to 90-eV electron population is controlled by photoionization and photoelectron impact ionization. The secondary electron flux, excitation rates, emission rates, and limb intensities of 5577 and 6300 A lines are calculated due to precipitation of solar wind electrons observed by ER experiment at the energy range 10-1000 eV in the nighttime ionosphere of Mars. In the vicinity of the peak altitudes, it is found that excitation/emission of atomic oxygen after the electron impact dissociation of CO 2 is the main source of 5577 A emissions, while dissociative recombination of molecular oxygen ion is the major source of 6300 A emissions after the electron impact excitation of atomic oxygen. The calculated secondary electron spectra are also compared with ER experiment measurements between energies of 10 and 1000 eV. The nightglow limb intensities are compared with the upper limit set by Mars 5 spectroscopic observations.

Calculated densities of H3O+(H2O)n,NO2− (H2O)n, CO3− (H2O)n and electron in the nighttime ionosphere of Mars: Impact of solar wind electron and galactic cosmic rays

We have calculated the densities of positive ions and negative ions in the ionosphere of Mars at solar zenith angle 106° between height interval 0 km and 220 km. This model couples ion-neutral, electron neutral, dissociation of positive and negative ions, electron detachment, ion-ion, ion-electron recombination processes through 117 chemical reactions. Of the 34 ions considered in the model, the chemistry of 17 major ions (O 2 + , NO + , CO 2 + , H 3 O + H 2 O, H 3 O + (H 2 O) 2 , H 3 O + (H 2 O) 3 , H 3 O + (H 2 O) 4 , O 2 + CO 2 , H 3 O + , CO 4 - , CO 3 - , CO 3 - H 2 O, CO 3 - (H 2 O) 2 , NO 2 - H 2 O, NO 2 - (H 2 O) 2 , NO 3 - H 2 O, and NO 3 - (H 2 O) 2 ) are discussed in this paper. At altitude below 70 km, the electron density is mainly controlled by hydrated hydronium ions and water clusters of NO 2 - and CO 3 - . The ions O 2 + and NO + dominate above this altitude. This calculation suggests that the ionosphere of Mars contains F and D peaks at altitude ~130 km and ~30 km due to precipitation of solar wind electron and galactic cosmic rays respectively. F peak is mainly produced by O 2 + after heavy loss of CO 2 + with atomic oxygen. D peak occurs due to high efficiency of electron attachment to Ox molecules, which entails that concentration of negative ions is higher than that of electron below 30 km. These results are compared with radio measurements made by Mars 4 and Mars 5 in the nighttime ionosphere.

Zonal variations of peak ionization rates in upper atmosphere of Mars at high latitude using Mars Global Surveyor accelerometer data

[1] The Accelerometer Experiment onboard Mars Global Surveyor (MGS) measured many density profiles in the upper atmosphere of Mars during aerobraking at many latitudes, longitudes, altitudes, local solar time (LST), and seasons. Here, in this paper, we use the accelerometer data of 57 orbits (P0588-P0648) from 30 September 1998 to 24 October 1998 between latitude ranges (50°-70°N) at LST 1600 hours, under spring equinox and medium solar activity conditions (average F 10.7 ∼ 120). Using these densities, the neutral densities of different gases are derived from their mixing ratio. From these neutral densities the longitudinal distribution of peak photoionization rates, peak photoelectron impact ionization rates, and the total peak ionization rates of CO + 2 , N + 2 and O + are obtained for solar zenith angle 78° at wavelength range 10-1025.7 A due to solar EUV radiation using analytical yield spectrum approach (AYS). These calculations are made at different altitudes and longitudes starting from 115 to 220 km and 0° to 360°E using intervals of 0.1 km and 5°, respectively. These conditions are appropriate for MGS phase 2 aerobraking period from which the accelerometer data are used. The Fourier analysis of the various peak ionization rates of CO + 2 , N + 2 , and O + indicates the presence of two dominant harmonic regions at high latitude in the upper atmosphere of Mars. The first is a class of long planetary-scale waves that may be associated with the fixed topography of Martian surface. The second is a class of rapidly moving transient disturbances that may be associated with baroclinic instability processes.

Chemistry of O(1D) atoms in the coma: implications for cometary missions

Abstract The forbidden red oxygen lines at 6300 and 6364 A, which results due to 1D→3P transition, provide an important diagnostic tool in the study of comets. These lines cannot be produced by resonance fluorescence excitation of the ground-state oxygen atom, and therefore are mainly produced due to dissociation of H2O and other O-containing species in comets (e.g., OH, CO, CO2, H2CO etc.) by photon and electron impact and in other collision reactions. Since the lifetime of 1D state is quite long (∼110 sec) collisional de-excitation processes are important. We have used a coupled chemistry-transport model in conjunction with an efficient emission production code to study the chemistry of O(1D) atoms and the production of OI 6300 A emission in comets. The model calculations are made for comet 46P/Wirtanen: the target of the ROSETTA mission. It is found that in the inner coma the density profile of O(1D) is controlled dominantly by the H2O. The model predicts ∼300 R of OI 6300 A brightness on comet Wirtanen.

Mars Global Surveyor radio science electron density profiles: Some anomalous features in the Martian ionosphere

We have analyzed some 807 Mars Global Surveyor electron density profiles that are confined to the northern high latitudes and thus are relatively free of the effects of crustal magnetic fields. These profiles have shown some anomalous features in the Martian ionosphere, and one of these is the noticeable variability in number density (N m ) and height (h m ) of the primary ionospheric peak on the same day when solar conditions and solar zenith angle have remained the same, a feature not expected from a photochemically controlled layer. We study this feature by generating longitudinal plots of N m and h m for the 807 profiles and by applying a least squares spectral fit consisting of wave number 1, 2, and 3 components to these data sets. We find some significant relationship between the two parameters, with the troughs in N m coinciding with the ridges in h m (and vice versa) on the longitudinal scale. An examination at fixed solar zenith angles shows a significant anticorrelation between the two parameters recorded over a period of about 3 months. However, theoretical considerations would support a positive correlation expected in response to changes in the EUV flux that occurred during this period. Further, we observe a large variability in electron density at 160 and 180 km, altitudes in the topside ionosphere, where photochemistry is expected to dominate. This is an additional anomalous feature. No such variability is observed in the topside ionosphere of Venus. We discuss plausible mechanisms like neutral atmosphere dynamics and solar wind interaction to explain some of the features.

O+ escape in the polar ion exosphere of Mars

Abstract A model for the polar ion exosphere of Mars is developed to calculate the escape fluxes of oxygen ions and electrons through the plasmasheet of Mars at different exospheric temperatures (600K – 2300K) along the magnetic field lines originating from the baropause at latitude 75 degrees and longitude zero degrees. The intensity of the magnetic field lines in the noon-midnight meridian plane at all latitudes are calculated by assuming that Mars has a weak magnetic field of dipolar nature. To calculate the electric potential in the region of magnetic field, the quasi-neutrality condition is satisfied in such a way that escape fluxes of oxygen ions and electrons have to be equal at every point. It has been found that above T∞ = 2300K, the escape flux does not increase and has the maximum flux ∼4.3 × 106cm−2s−1 and escape rate ∼3.5 × 1024 ions s−1. These values show close agreement with the observations taken by the TAUS and ASPERA experiments in the plasmasheet of Mars. The present calculation concludes that O+ ions in the plasmasheet of Mars are mainly due to the escape of oxygen ions from the ionosphere in presence of a charge separation electric field.