A NEW MECHANISM FOR POLAR PATCH FORMATION

Polar patches are regions within the polar cap where the F-region elec tron concentration and airglow emission at 630 nm are enhanced above a background level. Previous observations have demonstrated that polar patches can be readily identified in Polar Anglo-American Conjugate Ex periment (PACE) data. Here PACE data and those from complementary inst ruments are used to show that some polar patches form in the dayside c usp within a few minutes of the simultaneous occurrence of a flow chan nel event (short-lived plasma jets approximately 2 km s-1) and azimuth al flow changes in the ionospheric convection pattern. The latter are caused by variations of the y-component of the interplanetary magnetic field. The physical processes by which these phenomena cause plasma e nhancements and depletions in the vicinity of the dayside cusp and cle ft are discussed. Subsequently, these features are transported into th e polar cap where they continue to evolve. The spatial scale of patche s when formed is usually 200-1000 km in longitude and 2-degrees-3-degr ees wide in latitude. Their motion after formation and the velocity of the plasma within the patches are the same, indicating that they are drifting under the action of an electric field. Occasionally, patches are observed to occur simultaneously in geomagnetic conjugate regions. Since some of these observations are incompatible with the presently- accepted model for patch formation involving the expansion of the high latitude convection pattern entraining solar-produced plasma, further modeling of the effects of energetic particle precipitation in the cu sp, the consequences of flow channel events on the plasma concentratio ns, and the time dependence of plasma convection as a result of interp lanetary magnetic field By changes is strongly recommended. Such studi es could be used to determine the relative importance of this new mech anism compared with the existing theory for patch formation as a funct ion of universal time and season.