A comparison of the temperature and density structure in high and low speed thermal proton flows |
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| Authors: | WJ Raitt RW Schunk PM Banks |
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| Institution: | Department of Applied Physics and Information Science, University of California, San Diego, La Jolla, California 92037, U.S.A. |
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| Abstract: | The continuity, momentum and energy hydrodynamic equations for an H+-O+ topside ionosphere have been solved self-consistently for steady state conditions similar to those found outside the plasmasphere. Results are given for undisturbed and trough conditions with a range of H+ outflow velocities yielding subsonic and supersonic flow. In the formulation of the equations, account was taken of the velocity dependence of ion-neutral, ion-ion and ion-electron collision frequencies. In addition, parallel stress and the nonlinear acceleration term were retained in the H+ momentum equation. Results computed from this model show that, as a result of Joule (frictional) heating, the H+ temperature rises with increasing outflow velocity in the subsonic flow regime, reaching a maximum value of about 4000 K. For supersonic flow other terms in the H+ momentum equation become important and alter the H+ velocity profile such that convection becomes a heat sink in the 1000–1500 km altitude range. This, together with the reduced Joule heating resulting from the high-speed velocity dependence of the H+ collision frequencies, results in a decrease in the H+ temperature as the outflow velocity increases. However, for all outward flows the H+ temperature remains substantially greater than the O+ temperature. With identical upper boundary velocities, the H+ flow velocity is higher at low altitudes for trough conditions compared with non-trough conditions, but the H+ temperature in the trough is lower. The form of the H+ density profiles for supersonic flow does not in general differ greatly from those obtained with wholly subsonic flow conditions. |
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