A study of geomagnetic storms



Summary. An attempt is made to find interplanetary magnetic field and solar-wind parameters which control the development of geomagnetic storms. For this purpose, the interplanetary energy flux is estimated in terms of the Poynting flux (E×B/4π), and its time variations are compared with the rate of energy dissipation in terms of the ring-current particle injection ui(t), Joule dissipation in the ionosphere uj(t) and auroral particle injection up(t) for 15 major geomagnetic storms.

It is shown that the growth of geomagnetic storms, namely the time variations of the rate of the total energy dissipation, u(t) =ui(t) +uj(t) +up(t), is closely related to the Poynting flux by the following relation:


where l0≅ 7RE and θ′ is a measure of the angle between the interplanetary magnetic field vector and the magnetospheric field vector at the front of the magnetosphere in the equatorial plane. Further, it is shown that


within a factor of 2 for each storm period.

A large increase of u(t) is associated with substorm activity. Thus, the energy flux ɛ(t) entering the magnetosphere is dissipated through magneto-spheric substorm processes within the magnetosphere, and their accumulated effects can be understood as geomagnetic storm phenomena.