ON THE CURRENT-VOLTAGE RELATIONSHIP IN AURORAL BREAKUPS AND WESTWARDS-TRAVELING SURGES

Auroral precipitating electrons pass through an acceleration region be fore entering the atmosphere. Regardless of what produces it, a parall el electric field is assumed to cause the acceleration. It is well kno wn that from kinetic theory an expression for the corresponding upward field-aligned current can be calculated, which under certain assumpti ons can be linearized to j(parallel to) = KV. The K constant, referred to as the Lions-Evans-Lundin constant, depends on the source density and thermal energy of the magnetospheric electrons; it is an important parameter in magnetosphere-ionosphere coupling models. However, the K parameter is still rather unknown, and values are found in a wide ran ge of 10(-8)-10(-10) S m(-2) In this study, we investigated how the ty pe of auroral structure affects the K values. We look at onset and wes twards-travelling surge(WTS) events and make comparisons with earlier results from observations of more stable auroral arcs. A new analysis technique for studying those magnetospheric parameters using ground-ba sed measurements is introduced. Electron density measurements are take n with the EISCAT radar, and through an inversion technique the flux-e nergy spectra are calculated. Source densities, thermal energies and p otential drops are estimated from fittings of accelerated Maxwellian d istributions. With this radar technique we have the possibility to stu dy the changes of the mentioned parameters during the development of o nsets and the passage of surges over EISCAT. The study indicates that the linearization of the full Knight formulation holds even for the ve ry high potential drops and thermal temperatures found in the dynamic onset and WTS events. The values of K are found to be very low, around 10(-11) S m(-2) in onset cases as well as WTS events. The results may establish a new technique where ionospheric measurements are used for studying the ionosphere-magnetosphere coupling processes.