A Three-Dimensional Time-Dependent Model of the Polar Wind

Authors

Robert W. Schunk, Utah State UniversityFollow
Jan Josef Sojka, Utah State UniversityFollow

Document Type

Article

Journal/Book Title/Conference

Journal of Geophysical Research: Space Physics

Volume

94

Issue

A7

Publisher

American Geophysical Union

Publication Date

1989

First Page

8973

Last Page

8991

Abstract

A time-dependent global model of the polar wind was used to study transient polar wind perturbations during changing magnetospheric conditions. The model calculates three-dimensional distributions for the NO⁺, O₂⁺, N₂⁺, N⁺ and O⁺ densities and the ion and electron temperatures from diffusion and heat conduction equations at altitudes between 120 and 800 km. At altitudes above 500 km, the time-dependent nonlinear hydrodynamic equations for O⁺ and H⁺ are solved self-consistently with the ionospheric equations. The model takes account of supersonic ion outflow, shock formation, and ion energization during a plasma expansion event. During the simulation, the magnetic activity level changed from quiet to active and back to quiet again over a 4.5-hour period. The study indicates the following: (1) Plasma pressure changes due to T_e , T_i or electron density variations produce perturbations in the polar wind. In particular, plasma flux tube motion through the auroral oval and high electric field regions produces transient large-scale ion upflows and downflows. At certain times and in certain regions both inside and outside the auroral oval, H⁺ - O⁺ counterstreaming can occur, (2) The density structure in the polar wind is considerably more complicated than in the ionosphere because of both horizontal plasma convection and changing vertical propagation speeds due to spatially varying ionospheric temperatures, (3) During increasing magnetic activity, there is an overall increase in T_e , T_i and the electron density in the F-region, but there is a time delay in the buildup of the electron density that is as long as five hours at high altitudes, (4) During increasing magnetic activity, there is an overall increase in the polar wind outflow from the ionosphere, while the reverse is true for declining activity, (5) In certain regions, however, localized ionospheric holes can develop during increasing magnetic activity, and in these regions the polar wind outflow rate is reduced, (6) During changing magnetic activity, the temporal evolution of the ion density morphology at high altitudes can be different from, and even opposite to, that at low altitudes.

Comments

Originally published by the American Geophysical Union. Abstract available online through the Journal of Geophysical Research: Space Physics.