Структура и динамика полярных токовых систем : материалы международного симпозиума «Полярные геомагнитные явления», 25-31 мая, Суздаль, СССР / Акад. наук СССР, Кол. фил. им. С. М. Кирова, Поляр. геофиз. ин-т. – Апатиты : [б. и.], 1988.

the field-aligned current density at the upper ionospheric boundary must exceed a critical value determined by the problem geometry, by the iono spheric conductivity, and by the hot ion temperature. If in the ionospheric region with d„ A) (Pig.4) the wave- line potential disturbance U^(x) appeared, then in the regions of the maximum the downward disturbances of 3|t » and in the regions of the minimum the upward disturbances of i (| v/ill arise. At the same time, aa a result of the effective scattering at high altitudes, the ion pressure Fig.4. Scheme illustrating the occurence of the instability reaultlng in the occurenoe of auroral arcs. Fig.3. Pressure disturbance-to- potential disturbance ratio versus the Larmor radius Х,ц to the disturbance wavelength я ratio. near the potential minimum rises and the hot plasma-generated field-aligned current enhances, while the pressure and the generated current near the maximum get decreased. If the initial field-aligned current is earthward its disturbances in the ionosphere and the magnetosphere are directed oppositely and cancel each other (Fig.4a). If, however, the current outflows from the ionosphere the two effects are composed and an instability may arise. In the case of у-extended disturbances the kernel in (5) may be integra ted over Y" and by going to the ionospheric coordinates we obtain p' = - en(U(x,y>—J U(x,|/)K(x,X,j)fl(x')= -en(U- LU ) (6) - O 0 where L is the linear operator; the kernel Кis symmetric with respect to x, x ’. Auroras are localized within a narrow region of a ~ 200 km width where, as a first approximation, W may be considered to be a constant vector and the curvature of the field-aligned band may be disregarded. By selecting the у-axis in the direction of the constant V/ lines, treating the band with у-independent field-aligned current 3°(x), i.e. p=pQ (x)+ y-yp^x), consider ing the ion temperature to vary little within the band, i.e. n=nQ (x)+ + |-yn1(x), e t ! p , Z H =const and U j - U ^ U , from (1) and (6) It follows that 41