Large-scale oscillations and transport processes generated by multiscale inhomogeneities in the ionospheric field-aligned flows: A 3-D simulation with a dipole magnetic field

摘要

High-resolution observations by the FAST and Freja satellites indicate that multiscale transverse structures in magnetic-field-aligned flows are common features in the auroral ionosphere. A number of multiscale processes, such as broadband low-frequency oscillations, coherent structures, and various cross-field transport effects are well correlated with these inhomogeneities. Previously, these effects were studied using the three-dimensional multifluid model with a uniform magnetic field. In the present study a more realistic model with a dipole magnetic field has been used. Self-consistent generation of the low-frequency modes driven by local transverse gradients in the field-aligned ion flow and associated transport processes have been simulated. In spite of the large variations of the magnetic field with altitude (by several orders of magnitude), the most important features, observed in the previous simulations with a uniform magnetic field, have been reproduced with a new model. For typical polar wind conditions, it has been found that inhomogeneous parallel flow can excite low-frequency oscillations with comparable amplitudes over a wide range of altitudes (several RE). This leads to a significant cross-field transport over the same range of altitudes. It has also been shown that even small-amplitude short-scale modulations of the original large-scale flow profile significantly increases low-frequency mode generation and associated cross-field transport at various altitudes. The relevance of the obtained results to recent observations is discussed. (C) 2007 Elsevier Ltd. All rights reserved.