Physics
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufm.p21b0368n&link_type=abstract
American Geophysical Union, Fall Meeting 2002, abstract #P21B-0368
Physics
2459 Planetary Ionospheres (5435, 5729, 6026, 6027, 6028), 5407 Atmospheres: Evolution, 5421 Interactions With Particles And Fields, 5440 Magnetic Fields And Magnetism, 6225 Mars
Scientific paper
The magnetic fluxes associated with the Martian crustal remnant magnetization have been studied in order to investigate the global structure of the magnetic field in and above the level of Martian ionosphere. The intensely and nonuniformly magnetized crustal sources generate an effective large-scale magnetic field. Re-connection 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. This may occur not only in cusp-like structures above nearly vertical field anomalies but also in halos extending several hundreds of kilometers from these sources. In the Northern hemisphere, the crustal fields are rather weak and usually do not prevent direct interaction between the SW and the Martian ionosphere/atmosphere. Exceptions occur in the isolated mini-magnetospheres formed by the crustal anomalies. Much stronger crustal fields are located in certain regions in the Southern hemisphere and lead to the formation of large-scale mini-magnetospheres. Numerous cusp-like regions may exist above the many crustal anomalies in the Southern hemisphere. 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. A study of the electron density profiles obtained when the mini-magnetosphere regions are near the terminator has been conducted using the magnetic field measurements at altitudes 170-180 km and 400ñ34 km. The altitude and magnitude of the electron density peak, the effective scale-height of the electron density and the normalized standard deviation for two altitude ranges, 145-165 km and 165-185 km, have been derived for each of the 326 selected profiles. In each hemisphere, the longitudinal variations of these derived parameters have been studied. A significant difference between the large-scale mini-magnetospheres and regions outside of them has been found. The variations of the magnitude of the electron density peak indicate that the electrons are usually "hotter" inside a large-scale mini-magnetosphere than outside. Comparison with the MGS in-situ Accelerometer data also indicates that the neutral atmosphere is persistently cooler inside the large-scale mini-magnetospheres. It appears that the strong crustal magnetic fields prevent additional heating of the neutral atmosphere by direct interaction of the SW as well as confine the hotter electrons created by photo ionization.
Acuña Mario Humberto
Bauer Siegfried J.
Breus Tamara K.
Connerney J. E.
Crider Dana Hurley
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