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キーワード:
Mars ionosphere; Mars crustal magnetic fields; advection of magnetic
fields; ionospheric plasma flow; Earth Science
要旨:
The plasma environment of Mars is highly influenced by its crustal magnetic fields. In this work, we investigate whether the crustal magnetic fields can be displaced from their original positions due to advection by ionospheric plasma flow. The ranges of interest are altitudes between 200and1000 km and solar zenith angles between 45°and135°. We examine magnetic field data using measurements from the Magnetometer (MAG) onboard the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft. We conduct statistical analyses (∼5 years of data) in order to investigate if horizontal shifts are observed between the data and the crustal magnetic field model by Langlais et al. (2019), <A href="https://doi.org/10.1029/2018je005854">https://doi.org/10.1029/2018je005854</A>. We also show two case studies of individual measurements within a specific region of Mars. The results show statistical and observational evidence that the crustal magnetic fields are often being advected towards the night-side of the planet. The displacement seems to increase exponentially as a function of altitude, reaching a horizontal shift of 100 km at 650 km altitude. Moreover, we use measurements from the SupraThermal And Thermal Ion Composition (STATIC) instrument in order to compare the dynamic pressure of ionospheric plasma flow to the magnetic pressure of the crustal magnetic fields. There are two possible causes for the displacement: a forcing by external magnetic pressure or an advection of the field to the electron fluid, which follows the ion fluid. In this paper, we argue that by the observed relation between ion fluid and displacement, the latter explanation is more probable.
