A model of the magnetospheric substorm
IT is generally recognised that the Earth's magnetic tail and the plasma sheet play a vital role in the processes responsible for the observational phenomenon known as the magnetospheric substorm. Many different models1–5 of substorm behaviour have been described with differing degrees of success, and to propose another requires some justification. A new model, if it is to be useful, must do two things. It must be specific enough to make quantitative theoretical analysis possible, and it must fit the morphological features more completely or in a more elegant way than other models. In addition, it should be distinctive enough from other models to be separated from them by observational tests. I believe the model presented here has those properties.
Tail of the magnetosphere
The Chapman and Ferraro [e.g., Beard, 1960] model of the magnetosphere is entirely dissipationless and, as a consequence, contains no tangential stress at the magnetosphere boundary. It has been suggested that either viscous interaction [Axford and Hines, 1961; Piddington, 1963] or reconnection of field lines [Dungey, 1961; Levy, Petschek, and Siscoe, 1963] can give rise to tangential stresses which produce internal convection within the magnetosphere. A number of auroral and ionospheric observations appear to be consistent with such a convection pattern. It was also suggested [Piddington, 1960] that tangential stresses might stretch the magnetosphere tail and thus account for the main phase of magnetic storms.
Geomagnetic storm theory
A discussion of the two-gas theory of the transmission of geomagnetic disturbances through the atmosphere (to several earth radii) is extended, with the following results: (i) The central problem concerning the main phase of a geomagnetic storm is the mechanism of penetration of solar ions into the geomagnetic field. An explanation is given depending on a combination of a uniform electric space-charge field and a system of irregular fields. (ii) A model of the main phase of a geomagnetic storm is given, the principal feature of which is a ‘magnetic tail’ extending from the earth on the dark side. (iii) The model may help to explain some other effects: the Gegenschein, electrons with auroral energies, the location of the Van Allen zones, and diurnal cosmic-ray variations, (iv) All observed geomagnetic disturbances have their sources initially in current systems in the lower ionosphere. Some are subsequently maintained by current systems in the earth itself and in the region of interaction between the solar and terrestrial plasmas. Others, mainly polar and equatorial, are maintained by ionospheric currents driven by space-charge electric fields, (v) Any ring current outside the geomagnetic field could cause an increase in the horizontal component. A westward-flowing ring current embedded in the field could cause either an increase or a decrease in the horizontal component. The basic effect is not the current but a sustained inward or outward mechanical force on the material in which the current flows.