Abstract
In order to efficiently and self-consistently describe the transport of high-latitude ionospheric plasma into the magnetosphere, we have developed a Dynamic coupled Fluid-Kinetic (DyFK) model for describing plasma flow along a magnetic flux tube. The collision-dominated ionospheric plasma is treated with a low-speed fluid approach for altitudes between 120-1100 km, while a generalized semikinetic approach is used for the topside and higher altitudes, starting at 800 km. This paper presents a description of the new DyFK model, along with illustrative results obtained from modeling the effects of soft (100 eV) auroral electron precipitation using the new model. The results demonstrate the accuracy and efficiency of the new DyFK model and illustrate how soft electron precipitation provides a mechanism to drive observed upflows of high-latitude ionospheric plasma along geomagnetic field lines.
Highlights
More than thirty years ago, Dessler and Michel (1966) predicted a "gentle" loss of H+ ions from the p-0lar ionosphere due to an evaporation of lighter ions which they called the "polar breeze". Axford (1968) later considered the effect of ions being accelerated by an ambipolar electric field associated with the dominant Q+ ions and the thermal electrons, and suggested that the flow would become supersonic, in analogy with solar wind models of that period
The new Dynamic coupled Fluid-Kinetic (DyFK) model is used to investigate the response of a high-latitude flux tube to time dependent changes in the fluid zone induced by ionization and heating by soft electron precipitation
Once a steady state has been achieved, soft electron precipitation is turned on with an average energy of 100 eV and energy flux at 800 km of 3 ergs cm-2 s-1 The precipitation is allowed to continue for one hour geophysical time
Summary
More than thirty years ago, Dessler and Michel (1966) predicted a "gentle" loss of H+ ions from the p-0lar ionosphere due to an evaporation of lighter ions which they called the "polar breeze". Axford (1968) later considered the effect of ions being accelerated by an ambipolar electric field associated with the dominant Q+ ions and the thermal electrons, and suggested that the flow would become supersonic, in analogy with solar wind models of that period. In the mid 1980's, time-dependent hydrodynamic (Gombosi et al, 1985) and 16 moment (Ganguli et al, 1987) models were developed to simulate the dynamic polar plasma outflow Kinetic models, such as that by Lemaire and Scherer (1971), utilized a guiding center approximation, Liouville mapping and quasi neutrality conditions to construct steady state models of the high-altitude collisionless polar wind. The only available comparison between hydrodynamic and semikinetic models which included time-dependent effects was that of Ho et al (1993), which compared both steady-state and time-dependent versions of transport and semikinetic collisionless mod els of the evolving polar wind expansion into a vacuum These limited comparisons suggested that for steady-state conditions, moment-based generalized transport models adequately ap proximate kinetic results. How ever, we first describe the salient features of this steady-state version
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