Computer Science – Sound
Scientific paper
May 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agusmsm33a..04k&link_type=abstract
American Geophysical Union, Spring Meeting 2008, abstract #SM33A-04
Computer Science
Sound
7845 Particle Acceleration
Scientific paper
There is a growing consensus that heavy ions in the magnetosphere affect geomagnetic activity, convection, and reconnection. The O+ fraction in the ring current is known to grow during magnetic activity and dominates during geomagnetic storms. During substantial magnetic activity molecular ions are also observed in the topside ionosphere and magnetosphere with fluxes the order of 0.10 of the O+ fluxes. Despite these observations how heavy ions escape the ionosphere is not clear. For example O+ charge exchanges with H and molecular ions exist only in the E-region and lower F-region. There are a limited number of mechanisms producing upward fluxes of heavy ions in the topside ionosphere. In the F-region soft electron precipitation can increase the temperature and scale height of the electron gas leading to expansion, an ambipolar electric field and upflowing ions (Type II). Likewise increased convection can heat the ion gas leading to an increase in scale height and upflowing ions (Type I). In both cases when the heat source is removed, ions flow downward. At overlapping and somewhat higher altitudes upward heavy ion fluxes are also associated with transverse ion acceleration (TIA) which in turn is primarily associated with an observation called BBELF (broad band extra low frequency) waves. How these three mechanisms interact is not yet quantified. For example a two step process of heat generated upflow followed by TIA to generate outflow is one model. There are reasons to suggest that this two-step and altitude dependent model may be misleading. For example if BBELF is generated by a current driven instability, it is more likely to occur in low density regions and moving more plasma density to higher altitudes is irrelevant. If the BBELF is driven by the phase mixing of dispersive Alfven waves on steep horizontal density gradients, then the Type I or Type II uplift of the ionosphere would tend to remove the gradients through thermal inertia. On the other hand for O+ to not charge exchange with H, the BBELF process may need to work at higher altitudes and lower thermospheric H densities and would be benefit from ionospheric uplift. Combining rocket and radar observations can help address how these heavy ion fluxes are transported to higher altitudes or escape velocities. For example the ISR radar observations yield large data bases at low altitudes while sounding rockets probe the space detailed fine-scale kinetic environment above the fluid regime. One goal of this combination is to provide the lower boundary conditions for multiple-fluid ionospheric- magnetospheric coupling models.
Kintner Paul M.
Lynch Kennda
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