Nonlinear model of short-scale electrodynamics in the auroral ionosphere

Details Nonlinear model of short-scale electrodynamics in the auroral ionosphere Nonlinear model of short-scale electrodynamics in the auroral ionosphere

Sep 2000

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000angeo..18.1128n&link_type=abstract

Annales Geophysicae, vol. 18, Issue 9, pp.1128-1144

Physics

13

Ionosphere (Auroral Ionosphere, Ionosphere-, Tmosphere Interactions)

Scientific paper

The optical detection of auroral subarcs a few tens of m wide as well as the direct observation of shears several m/s per m over km to sub km scales by rocket instrumentation both indicate that violent and highly localized electrodynamics can occur at times in the auroral ionosphere over scales 100 m or less in width. These observations as well as the detection of unstable ion-acoustic waves observed by incoherent radars along the geomagnetic field lines has motivated us to develop a detailed time-dependent two-dimensional model of short-scale auroral electrodynamics that uses current continuity, Ohm's law, and 8-moment transport equations for the ions and electrons in the presence of large ambient electric fields to describe wide auroral arcs with sharp edges in response to sharp cut-offs in precipitation (even though it may be possible to describe thin arcs and ultra-thin arcs with our model, we have left such a study for future work). We present the essential elements of this new model and illustrate the model's usefulness with a sample run for which the ambient electric field is 100 mV/m away from the arc and for which electron precipitation cuts off over a region 100 m wide. The sample run demonstrates that parallel current densities of the order of several hundred µA m-2 can be triggered in these circumstances, together with shears several m/s per m in magnitude and parallel electric fields of the order of 0.1 mV/m around 130 km altitude. It also illustrates that the local ionospheric properties like densities, temperature and composition can strongly be affected by the violent localized electrodynamics and vice-versa.

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