Effect of crustal magnetic fields on the near terminator ionosphere at Mars: Comparison of in situ magnetic field measurements with the data of radio science experiments on board Mars Global Surveyor

Abstract

[1] Electron density profiles of the ionosphere of Mars derived from radio occultation data obtained by the radio science Mars Global Surveyor (MGS) experiment have been compared with the crustal magnetic fields measured by the MGS Magnetometer/Electron Reflectometer (MAG/ER) experiment. In the northern hemisphere the crustal fields are rather weak and usually do not prevent direct interaction between the solar wind (SW) and the Martian ionosphere/atmosphere. Exceptions do occur in the isolated minimagnetospheres formed by the crustal anomalies. Much stronger crustal fields are located in limited regions in the southern hemisphere and lead to the formation of large-scale mini-magnetospheres. A study of the electron density profiles obtained when the minimagnetosphere regions are near the terminator has been conducted using the magnetic field measurements at altitudes 170-180 km and 400 km. The magnitude of the electron density peak and the effective scale-height of the electron density for two altitude ranges, 145-165 km and 165-185 km, have been derived for each of the 326 selected profiles studied. In each hemisphere, the longitudinal variations of these derived parameters have been studied. A significant difference between the large-scale minimagnetospheres and regions outside of them has been found. The neutral atmosphere is cooler inside the large-scale mini-magnetospheres. The variations of the magnitude of the electron density peak indicate that the electrons are usually ''hotter'' inside a largescale mini-magnetosphere than outside. It appears that the mini-magnetospheres formed by strong crustal magnetic fields prevent additional heating of the neutral atmosphere due to direct interaction of the SW and also confine the hotter electrons created by photo ionization.

Solar System Ionospheres

“…2004); and Saturn , and recently at Mars (Bertaux et al 2005), unambiguous ionospheric disturbances associated with those patterns have yet to be documented. At Mars, characteristics of the ionosphere in the vicinity of crustal magnetic fields have been shown to be different from those at non-magnetized locations (Krymskii et al 2003;), yet there has been no observational evidence that such patterns are due to auroral processes, as opposed to local plasma instability effects. Thus, the study of solar-planetary relationships continues to look mainly at the Earth for studies of processes initiated by changes in the solar wind at a planet (Prölss 2004).…”

Excitation of plasma waves by unstable photoelectron and thermal electron populations on closed magnetic field lines in the Martian ionosphere

“…First, according to Krymskii et al (2003), the electrons inside such loops are hotter than outside. It can be caused, at least partly, by the interaction with waves.…”

“…Our estimates are based on the available experimental data concerning the distribution of plasma concentration and magnetic fields in the ionosphere of Mars (see Acuña et al, 1998;Krymskii et al 2003;Mitchell et al, 2001;Shinagawa, 2004). Unfortunately, these data are not sufficient for detailed analysis.…”

“…The properties of the ionospheric plasma within closed magnetic flux tubes, therefore, deviate significantly from the surrounding plasma. According to Krymskii et al (2003), in the closed tubes neutral particles are cooler and electrons are hotter than outside. One may speculate that electons are heated by some source inside magnetic loops (e.g.…”

Influence of Martian crustal magnetic anomalies on the emission of energetic neutral hydrogen atoms

“…The parameters and/or chemical states of the neutral atmosphere over the magnetic anomalies could be influenced by the varied plasma flux. There are very few observations of this effect, only Krymskii et al [2003Krymskii et al [ , 2004 reported increase of the upper atmosphere temperature above the anomalies. All these modifications on plasma and/or neutral characteristics may affect the ENA emission near magnetic anomalies.…”