Electric potential patterns have been obtained from the IZMIRAN electrodynamic model (IZMEM) for the northern and southern polar regions during summer, winter, and equinox. The model is derived from a large quantity of high‐latitude ground‐based geomagnetic data (above ± 57° corrected geomagnetic latitude) at all magnetic local time hours. A linear regression analysis technique has been used to obtain the quantitative response of each magnetic observatory to changes of interplanetary magnetic field (IMF) components. Since no ionospheric conductivity model exists specifically for the southern polar region, the statistical model of Wallis and Budzinski (1981) has been applied in both hemispheres. A cross‐polar “background” potential of ∼35 kV, derived by Reiff et al. (1981), is used to calibrate IZMEM's potential patterns. The model's responses to changes in the IMF By and Bz components are analyzed to obtain a set of “elementary” convection patterns in both polar regions for each season of the year. Asymmetry in the potential pattern geometry in both hemispheres can be attributed either to the influence of the “northern” ionospheric conductivity model which was applied to the southern polar region, or to some natural phenomena. The modeled background cross‐polar potential for the condition when Bz = By = 0 is found to be ∼37 kV. Average values of the modeled potential drop caused by each nanotesla of the IMF are the following: ∼14 kV for southward Bz; ∼ −4 kV for northward Bz; and ∼ ±4.5 kV for By components. The latter is not applicable to the “dawn‐dusk” potential drop; it may be applied across the cusp region only. Nevertheless, a combination of the background and elementary potential patterns in the case studies gives a certain estimation of the cross‐polar potential drop, which may be strongly distorted during time of large By. It is concluded that IZMEM provides realistic convection patterns parameterized by the IMF component directions and magnitudes and may be used to provide routine estimates of convection patterns and electric potentials if IMF data are available.

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Abstract.A numerical solution of the problem on dynamics of shear-mode Alfvén waves in the ionospheric Alfvén resonator (IAR) region at middle latitudes at nighttime is presented for a case when a source emits a single pulse of duration τ into the resonator region. It is obtained that a part of the pulse energy is trapped by the IAR. As a result, there occur Alfvén waves trapped by the resonator which are being damped. It is established that the amplitude of the trapped waves depends essentially on the emitted pulse duration τ and it is maximum at τ =(3/4)T , where T is the IAR fundamental period. The maximum amplitude of these waves does not exceed 30% of the initial pulse even under optimum conditions. Relatively low efficiency of trapping the shear-mode Alfvén waves is caused by a difference between the optimum duration of the pulse and the fundamental period of the resonator. The period of oscillations of the trapped waves is approximately equal to T , irrespective of the pulse duration τ . The characteristic time of damping of the trapped waves τ dec is proportional to T , therefore the resonator Q-factor for such waves is independent of T . For a periodic source the amplitude-frequency characteristic of the IAR has a local minimum at the frequency π/ω=(3/4)T , and the waves of such frequency do not accumulate energy in the resonator region. At the fundamental frequency ω=2π /T the amplitude of the waves coming from the periodic source can be amplified in the resonator region by more than 50%. This alone is a basic difference between efficiencies of pulse and periodic sources of Alfvén waves. Explicit dependences of the IAR characteristics (T , τ dec , Q-factor and eigenfrequencies) on the altitudinal distribution of Alfvén velocity are presented which are analytical approximations of numerical results.

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