THE MAGNETOGRAM INVERSION TECHNIQUE - APPLICATIONS TO THE PROBLEM OF MAGNETOSPHERIC SUBSTORMS

The magnetogram inversion technique (MIT) is based upon recordings of geomagnetic variations at the worldwide network of ground-based magnetometers. MIT ensures a calculation of a global spatial distribution of the electric field, currents and Joule heating in the ionosphere. Variant MIT-2 provides, additionally, continuous monitoring of the following parameters: Poynting vector flux from the solar wind into the magnetosphere (epsilon'); power, both dissipated and accumulated in the magnetosphere; magnetic flux in the open tail; and the magnetotail length (l(T)) (distance between the dayside and nightside neutral points in the Dungey model). Using MIT-2 and data of direct measurements in the solar wind, an analysis is made of a number of substroms, and a new scenario of substroms is suggested. The scenario includes the convection model, the model with a neutral line and the model of magnetosphere-ionosphere coupling (outside the current sheet), i.e., the three known models. A brief review is given of these and some other substroms models. A new element in the scenario is the strong positive feedback in the primary generator circuit, which ensures growth of the ratio kappa = epsilon'/epsilon-A by an order of magnitude or more during the substroms. Here epsilon-A is the Pointing vector flux in the Akasofu-Perrault approximation, i.e., without the feedback taken into account. The growth of kappa during the substrom is caused only by the feedback effect. It is assumed that the feedback arises due to an elongation of the magnetotail, i.e., a growth of l(T) by a factor of (2: 3) during the substrom. In the active phase of substrom, a part (the first active phase) has been identified, where the principal role in the energetics is played by the feedback mechanism and the external energy source (although the internal source plus reconnection inside the plasma sheet make a marked contribution). In the second active phase ('expansion') the external generator (solar wind) is switched off, and the main role is now played by the internal energy source (the tail magnetic field and ionospheric wind energy). Models of DP-2 reversible DP-1 transitions are also considered, as well as the 'magnetospheric substrom-solar flare' analogy.