Ionospheric conductance distribution and MHD wave structure: observation and model
نویسندگان
چکیده
The ionosphere in ̄uences magnetohydrodynamic waves in the magnetosphere by damping because of Joule heating and by varying the wave structure itself. There are dierent eigenvalues and eigensolutions of the three dimensional toroidal wave equation if the height integrated Pedersen conductivity exceeds a critical value, namely the wave conductance of the magnetosphere. As a result a jump in frequency can be observed in ULF pulsation records. This eect mainly occurs in regions with gradients in the Pedersen conductances, as in the auroral oval or the dawn and dusk areas. A pulsation event recorded by the geostationary GOES-6 satellite is presented. We explain the observed change in frequency as a change in the wave structure while crossing the terminator. Furthermore, selected results of numerical simulations in a dipole magnetosphere with realistic ionospheric conditions are discussed. These are in good agreement with the observational data.
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