Modification of conductivity due to acceleration of the ionospheric medium

Abstract

Abstract.A quantitative division of the ionosphere into dynamo and motor regions is performed on the base of empirical models of space distributions of ionospheric parameters. Pedersen and Hall conductivities are modified to represent an impact of acceleration of the medium because of Ampére's force. It is shown that the currents in the F 2 layer are greatly reduced for processes of a few hours duration. This reduction is in particular important for the night-side low-latitude ionosphere. The International Reference Ionosphere model is used to analyze the effect quantitatively. This model gives a second high conducting layer in the night-side low-latitude ionosphere that reduces the electric field and equatorial electrojets, but intensifies night-side currents during the shortterm events. These currents occupy regions which are much wider than those of equatorial electrojets.It is demonstrated that the parameter σ d =σ P +σ H H / P that involves the integral Pedersen and Hall conductances P , H ought to be used instead of the local Cowling conductivity σ C in calculations of the electric current density in the equatorial ionosphere. We may note that Gurevich et al. (1976) derived a parameter similar to σ d for more general conditions as those which we discuss in this paper; a more detailed description of this point is given in Sect. 6. Both, σ d and σ C , appear when a magnetic field line is near a nonconducting domain which means zero current through the boundary of this domain. The main difference between σ d and σ C is that σ d definition includes the possibility for the electric current to flow along a magnetic field line in order to close all currents which go to this line from neighboring ones. The local Cowling conductivity σ C corresponds to the current closure at each point of a magnetic field line. It is adequate only for a magnetic field line with constant local conductivity at the whole line when field-aligned currents do not exist because of symmetry, but σ C =σ d in this case. So, Correspondence to: H. K. Biernat (helfried.biernat@oeaw.ac.at) there is no reason to use the local Cowling conductivity while the Cowling conductance C = P + 2 H / P is a useful and well defined parameter.

Mathematical Simulation of the Ionospheric Electric Field as a Part of the Global Electric Circuit

“…Then Ohm's law (3) in a gyrotropic medium takes the form with Hall ( H ) Pedersen ( P ) and field-aligned ( ∥ ) conductivities (Kelley 2009). We have created the model (Denisenko et al 2008) to calculate the components P , H , ∥ of the conductivity tensor ̂ above h = 90 km, that is based on the empirical models IRI, MSISE, IGRF. In that model, the ionospheric conductivity is calculated up to an altitude of 2000 km.…”

“…The model (Denisenko et al 2008) permits us to calculate conductivities in the ionosphere only above h = 80 km since the model IRI is not applicable below this height. These calculations show that all components of the conductivity tensor are defined by electrons below h = 90 km and all ions give negligible contributions.…”

The energy method for calculating quasi-stationary atmospheric electric fields

“…As Σ P in (14) there should be placed the sum of the integral conductivities of the northern and southern hemispheres. If we take into account the asymmetry of the hemispheres then the tensor in (12) becomes more sophisticated [6]. The presence of conjugated points is typical for the middle latitudes; whereas the magnetic field lines go away from the polar caps to the distant tail of the magnetosphere, where σ P and σ H are negligible.…”

“…This approximation of the equipotential magnetic field lines is widely used in the modeling of the large-scale electric fields in the ionosphere [8]. Our version of this model in the general case of the potential geomagnetic field is constructed with the empirical model IGRF-10 [7] and described in detail in [6]. Here we need a simplified version of the model for the vertical magnetic field.…”

“…To calculate the values of the components of the conductivity tensor, we created a model in [6]. As the elements, we used the freely available empirical models giving the spatial distributions of the electron and ion concentrations (IRI), the gas composition and temperature (MSISE), and the geomagnetic field (IGRF-10).…”