Mathematics – Logic
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p11b1214b&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #P11B-1214
Mathematics
Logic
[5421] Planetary Sciences: Solid Surface Planets / Interactions With Particles And Fields, [5435] Planetary Sciences: Solid Surface Planets / Ionospheres, [6225] Planetary Sciences: Solar System Objects / Mars
Scientific paper
Multiple lines of evidence, including geomorphologic features and isotope measurements of the current atmosphere, indicate that at one point Mars sustained a robust atmosphere capable of supporting significant quantities of liquid water. However, the Martian atmosphere is now greatly depleted, implying that atmosphere has been lost to space and the subsurface over time. In addition to other modes of atmospheric loss, bulk escape - the large-scale removal of coherent portions of ionospheric plasma from the upper atmosphere - has likely contributed to depletion. Recent observations of a large Martian flux rope in the process of carrying ionospheric plasma away from Mars indicate that flux ropes could be an important means of bulk escape. Previously, a statistical study of magnetic field data recorded during the elliptical aerobreaking phase of the Mars Global Surveyor (MGS) Mission revealed many relatively small ionospheric flux ropes at a variety of altitudes (Vignes et at., 2003). However, more than seven years of circular mapping data from MGS have not yet been analyzed for the presence of flux ropes, large or small, and hold the potential to inform our understanding of rope characteristics and dynamics. By examining MGS magnetic field data and employing minimum variance analysis of selected time intervals, we identify flux ropes in the MGS mapping data and create a database of their properties. From this database we compute the average values and standard deviations for each of many rope features, which effectively acts as a statistical rope model. Further, relations between rope characteristics (i.e. formation frequency, dimensions, plasma capacity, etc.) and external conditions (i.e. solar zenith angle, altitude, local crustal magnetization, solar wind pressure, etc.) are developed. These data constrain rope formation and termination conditions and mechanisms, modify estimates for particle loss via ropes, and further characterize rope dynamics, thus helping us to evaluate the importance of Martian flux ropes for atmospheric escape.
Brain David Andrew
Briggs J. A.
Eastwood Jonathan P.
Halekas Jasper S.
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