A. M. Krymskii

Effects of magnetic anomalies discovered at Mars on the structure of the Martian ionosphere and solar wind interaction as follows from radio occultation experiments

The slopes of the electron density profiles obtained by radio occultation experiments at Mars revealed different variations with solar zenith angle in comparison with behavior of the electron density profiles in the magnetic field free ionosphere of Venus. The results obtained by the Mars-Global-Surveyor (MGS) spacecraft show the existence of highly variable and very localized magnetic fields of crustal origin at Mars. Addressing the difference between the ionosphere at Venus and Mars, the scale heights of electron density profiles obtained by radio occultation methods onboard Mariner 9 and Viking 1 are analyzed at altitudes higher than the topside boundary of the photoequlibrium region in the magnetic field-free ionosphere. The local increase of the mean scale height in the altitude region 180–250 km is assumed to be either an effect of a nonhorizontal magnetic field associated with the magnetic anomalies or diffusive equilibrium in the magnetic field free ionosphere. The areas where the scale height of electron density profile is increased in comparison with average one have been selected. The angle between the magnetic field measured by MGS MAG/ER at altitudes 120–250 km and local zenith direction is investigated throughout these selected areas.

Structure of the magnetic field fluxes connected with crustal magnetization and topside ionosphere at Mars

[1] The magnetic fluxes associated with the Martian crustal remanent magnetization have been studied in order to investigate the global structure of the magnetic field in and above the level of the Martian ionosphere. The intensely and nonuniformly magnetized crustal sources generate an effective large-scale magnetic field. Reconnection with the interplanetary magnetic field can possibly take place in many localized regions. This will permit solar wind (SW) and more energetic particles to precipitate into and heat the neutral atmosphere by impact ionization. This may occur not only in cusp-like field structures above nearly vertical field anomalies but also in halos extending several hundreds of kilometers from these sources. Numerous cusp-like regions may exist above the many crustal anomalies in the southern hemisphere. The large-scale horizontal magnetic fields due to the crustal sources and induced by the SW interaction are responsible for controlling the detailed structure of the Martian ionosphere. Radio occultation observations in the southern hemisphere show relatively constant and low average values of the electron density scale height and zero dependence on zenith angle in contrast to that of nonmagnetic Venus. INDEX TERMS: 2459 Ionosphere: Planetary ionospheres (5435, 5729, 6026, 6027, 6028); 6225 Planetology: Solar System Objects: Mars; 5443 Planetology: Solid Surface Planets: Magnetospheres (2756); 5440 Planetology: Solid Surface Planets: Magnetic fields and magnetism; 2784 Magnetospheric Physics: Solar wind/magnetosphere interactions; KEYWORDS: Mars, ionosphere, paleomagnetism, magnetosphere

The solar wind interaction with Mars: Consideration of Phobos 2 mission observations of an ion composition boundary on the dayside

This paper describes the features of the boundary in the plasma ion composition near Mars which separates the region dominated by the solar wind protons from the plasma of planetary origin. This boundary was detected by the ASPERA experiment on Phobos 2. It is argued that the features of this boundary seem to be similar to those of other composition boundaries detected elsewhere: the cometopause near comet Halley, and a boundary in the ion composition which appears near Venus during periods of high solar wind dynamic pressure. Numerical modeling of the solar wind interaction with Mars supports the idea that during solar maximum the interaction of the Martian neutral atmosphere with the solar wind can result in a composition transition from solar wind to planetary ions in the low-altitude magnetosheath. This transition occurs because of charge exchange of solar wind protons with the neutral atmosphere and photoionization.

Conditions in the Martian ionosphere/atmosphere from a comparison of a thermospheric model with radio occultation data

Abstract In this paper a possibility to find out some effect of dipole-like intrinsic magnetic field on the plasma scale height at altitudes 180–240 km in the Martian ionosphere, that is above the topside boundary of the chemically controlled region predicted by existing models of the magnetic field-free ionosphere, is examined. It is assumed that the effect could be detected if the relationship between plasma and neutral atmosphere scale heights which is expected under the photochemical equilibrium conditions in the multicomponent atmosphere remains valid at altitude region 180–240 km. The plasma scale heights assessed from the data collected during the Mariner 9 and Viking 1 sessions are statistically analyzed and its trends with the solar zenith angle and F 10.7 flux are evaluated. A half of statistically averaged scale height presented as a function of the solar zenith angle (SZA) and F 10.7 flux is compared with the neutral atmosphere scale heights, calculated from the model of Izakov and Roste (1996) for the corresponding SZA and F 10.7 fluxes. Since the conditions for the radio occultation experiments during the Mariner 9 and Viking 1 sessions are different a ratio of assessed plasma scale height to the appropriate neutral atmosphere scale height suits better for comparison than the average scale heights itself does. Employing such ratios the effect of dust content within the lower atmosphere on the thermal balance within the topside atmosphere at altitude 180–200 km is estimated.

Turbulent pick-up of new-born ions near Venus and Mars and problems of numerical modelling of the solar wind interaction with these planets—II. Two-fluid HD model

Abstract A two-fluid hydrodynamic (HD) model with anomalous friction between ion species (protons and O+ ions) due to turbulence in the magnetosheath is suggested for solar wind (SW) interactions with Venus and Mars. The method of calculation and results are given for both planets. The results are compared with experimental data from the Pioneer-Venus and PHO BOS-2 spacecraft and also with the results of the one-fluid HD model with mass-loading. The results of the two-fluid HD model are in better agreement with the experimental data than those obtained earlier.

Interaction of mass-loaded solar wind flow with blunt body

Abstract The aim of this paper is the numerical modeling of the solar wind interaction with Venus taking into account the mass loading effect due to the photoionization of the Venus neutral oxygen corona. The analysis has shown that this effect unambiguously explains the number of peculiarities of the SW-Venus interaction pattern that could not be quantitatively explained before, namely the shock front position, and the characteristics of the SW flow and magnetic field in the Venus ionosheath observed from experiments onboard of Venera−9 and −10 and Pioneer-Venus spacecraft.

Remnant magnetic fields of Mars and their interaction with the solar wind

This work presents a review of studies of the Martian magnetic fields during the early Soviet missions to Mars in 1971–1974, which never approached Mars by closer than 1000 km before the experiment with the Magnetometer/Electronic Reflectometer (MAG/ER) on board the Mars Global Surveyor spacecraft, which could descend to altitudes of 80–100 km. At present, the experiment with the magnetometer (MAG) onboard the American MAVEN spacecraft adds new data, but the map of distribution of remnant magnetic fields of Mars and the picture of their interaction with the solar wind are already formed and, at its core, obviously, will not be revised. Thus, it would be very instructive to consider the following in detail: (a) what is already known regarding the features and distribution of remnant magnetic fields on Mars; (b) how they control the interaction of solar wind with a weakly magnetized planet (Mars); and (c) what is its distinction from another nonmagnetized planet (Venus).

Comparative study of numerical simulations of the solar wind interaction with Venus

Abstract The assumptions and peculiarities of the numerical codes, as well as the spatial resolution of the gas-dynamical and hybrid simulations which are available at present are discussed. As found the present day estimates of O+ ion production rates which can effect the bow shock geometry as intensively as observed by Pioneer-Venus-Orbiter are controversial. The disagreement of the gas-dynamical simulations by Breus et al. (Planet. Space Sci. 40, 131–138, 1992) and Stahara and Spreiter (Venus and Mars: Atmospheres, Ionospheres and Solar Wind Interactions, Geophysical Monograph 66, p. 345. AGU, 1992) is a result of different numerical implementation of the flow tangency condition which does not permit the specification of the equation of state p = p(ϱ) at the impenetrable obstacle. The numerical code by Breus et al. uses the reflection procedure for the implementation of the flow tangency condition and is insensitive to the equation of state at the obstacle surface. The reflection procedure does not employ explicitly the boundary conditions at the obstacle which the Stahara and Spreiter code does. As a result Stahara and Spreiters (Venus and Mars: Atmoshheres, Ionospheres and Solar Wind Interactions, Geophysical Monograph 66, p. 345. AGU, 1992) simulation is in agreement with observations only in the case of an unreasonable value of the electron impact ionization: in several times of the photoionization within the magnetic barrier at Venus. Breus et al. (Planet. Space Sci. 40, 131–138, 1992) agree well with observations if the electron impact ionization is 60–70% of the photoionization there. Brecht and Ferrante (J. geophys. Res. 96, 11209–11220, 1991) simulated an insignificant effect of the magnetic barrier on the shock geometry. However this simulation is unable to estimate the O+ ionization rate to fit the hybrid model with observations. The cells employed by Moore et al. (J. geophys. Res. 96, 7779–7791, 1991) are larger than the thickness of the magnetic barrier region estimated from the magnetometer data by Zhang et al. (J. geophys. Res. 96, 11145–11153, 1991). Thus Moore et al. cannot simulate the magnetic barrier region properly and their prediction of an insignificant effect of the mass-loading under any expectable O+ ion production rate should be revised.