Seminars

Lecturer: Dr Masatoshi Yamauchi (IRF-K)
Date: 2004-10-21 00:00
Place:

Concentration of Aurora Arc from viewpoint of Alfvén wave reflection at Ionosphere.



[past observation]: While it is well known that the aurora activity is strongly controlled by the solar wind input, not all the controlling factors of actual aurora intensity, even the statistical one, is not well known. One obvious controlling factor is the ionospheric conductivity. High conductance (summer) favors large potential drop over the polar cap and total current intensity [e.g., Fujii et al., 1981; Fujii and Iijima, 1987; Yamauchi and Araki, 1989; Lu et al., 1994] and subsequent joule dissipation. However, peak density of the field-aligned current is higher during low conductance in winter [Newell and Meng, 1996].

[my model #1]: Using simple wave reflection model [Sato and Iijima, 1980; Kan and Sun, 1985], I have simulated the effect of local conductivity enhancement due to the field-aligned current (this represents the precipitation). Just including the conductivity enhancement into the linear wave reflection system, we can include the positive feedback of the enhancement of ionospheric conductivity and intensification of field-aligned current through the conductivity gradient. The simulation shows larger localization of the field-aligned current for low background conductivity because the ratio between the enhanced conductance and the background conductance is larger for low background conductance.

[my model #2]: In addition I made a simple calculation to examine the seasonal (ionospheric conductivity) effect on the ionospheric joule dissipation. Since the decay time of the magnetospheric energy is counter proportional to the total dissipation by the both hemispheres, this has clear semi-annual peak. Since input energy to a given point is proportional this decay time multiplied by the local conductivity, we can easily predict the famous semi-annual variation of nightside geomagnetic activities (in Kp and AL indices) and annual variation of dayside activity even if we ignore the semi-annual variation of energy input from the solar wind by the geometrical effect (Russell-McPerron effect).

Created 2004-12-06 16:25:52 by Rick McGregor
Last changed 2004-12-06 16:25:52 by Rick McGregor