On Atmospheric Loss of Oxygen Ions from Earth Through Magnetospheric Processes

Details On Atmospheric Loss of Oxygen Ions from Earth Through Magnetospheric Processes On Atmospheric Loss of Oxygen Ions from Earth Through Magnetospheric Processes

May 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agusm..sm51a05s&link_type=abstract

American Geophysical Union, Spring Meeting 2001, abstract #SM51A-05

Other

0325 Evolution Of The Atmosphere, 2736 Magnetosphere/Ionosphere Interactions, 2760 Plasma Convection, 2784 Solar Wind/Magnetosphere Interactions, 5407 Atmospheres--Evolution

Scientific paper

Earth's intrinsic magnetic field shields the upper atmosphere from direct interaction with the solar wind, and the direct escape of neutral oxygen through thermal and non-thermal processes, which is important for unmagnetized planets such as Venus and Mars, is small compared to the ion loss through magnetospheric processes. The intrinsic magnetic field facilitates a number of different plasma acceleration mechanisms at high latitudes. These acceleration mechanisms result in an observed outflow rate of ~7.2x1025 O+ ions/s with speeds above gravitational escape velocity averaged over the solar cycle [Yau et al., 1988]. However, the same global magnetic field that facilitates the ion acceleration processes may also mitigate this loss by trapping the ions and returning them to the atmosphere. In this paper, we examine loss rate of terrestrial atmospheric oxygen through magnetospheric processes by examining loss rates of four escape routes with high-altitude spacecraft observations. The estimated O+ loss rate is almost one order of magnitude smaller than the polar O+ outflow rate. This disagreement suggests that there is either a significant return flux from the magnetosphere to the low-latitude ionosphere or unknown loss process(es) of oxygen ions. In the former case, the gap in the O+ escape rates may indicate that the existence of a substantial intrinsic magnetic field can help a planet to keep its atmosphere. Alternatively in the latter case, a candidate of the unknown loss mechanism(s) may be escape of cold O+ ions at energies below 50 eV either to the magnetosheath or through the plasma sheet, which are difficult to observe in the magnetosphere without spacecraft potential control. Another candidate is the charge exchange loss of ring current ions that become dominated by O+ during magnetic storm periods. For further understanding, systematic ion-composition measurements in the magnetosheath and the plasma sheet as well as quantitative investigation of ring current loss mechanisms are needed.

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