DIRECT DETERMINATION OF THE LOCAL IONOSPHERIC HALL CONDUCTANCE DISTRIBUTION FROM 2-DIMENSIONAL ELECTRIC AND MAGNETIC-FIELD DATA - APPLICATION OF THE METHOD USING MODELS OF TYPICAL IONOSPHERIC ELECTRODYNAMIC SITUATIONS

The applicability of a method to directly deduce the ionospheric Hall conductance distribution Sigma(H) from ground magnetic and ionospheric electric field observations, here called ''method of characteristics,'' is tested by using input data from models of some typical. ionospheric electrodynamic situations. We shall show that the method in the form of a fully automatical computer algorithm is able to reproduce well the Sigma(H) distributions of all modeled situations, i.e. a two-dimensional eastward electrojet, a Harang discontinuity, an omega band, and a westward traveling surge. Furthermore, we will show quantitatively that the ambiguity implied by the necessary assumption of the distribution of the Hall to Pedersen conductance ratio has only a small effect on the results obtained. We also prove quantitatively that the assumption of vertical, straight geomagnetic field lines made in the derivation of the method leads only to very small errors if the case of oblique, but straight geomagnetic field lines is taken to be realistic. Moreover, we review the general theory of the method and discuss some additional theoretical aspects. In particular, we will show that isolated points with (E) over right arrow E = 0, but nonvanishing del(h) .(E) over right arrow E are associated with extrema or saddle points of the Sigma(H) distribution, and calculate the magnetic field disturbance of an ionospheric current system with oblique, but straight field-aligned currents directly below the ionospheric plane. The method does not require an electrostatic situation; i.e., del(h)x (E) over right arrow E not equal 0 is allowed.