Response of the Polar Cap Ionosphere to Changes in (Solar Wind) IMF

Abstract

The character of the polar cap ionosphere is dominated by the component of the solar wind IMF (Interplanetary Magnetic Field) that is parallel/anti-parallel to earth’s magnetic field. Changes in the polar cap ionosphere properties, driven by changes in the IMF, necessarily drive changes in both the polar thermosphere and in growth rates of plasma instabilities and polar plasma structuring over a range of scale sizes exceeding 104. The physical processes determining this character are mutually interactive. Selected interactive physical processes are reviewed, to help clarify what is known, and suggest where important new findings may be found, particularly at Svalbard. The ionosphere/ thermosphere transient response to IMF reversals should clarify magnetospheric topology for northward IMF. The cusp thermosphere should exhibit transient upwelling and molecular enrichments. Certain cusp aurora should be excited by thermal electrons; their greater altitude may impact understanding of polar ionospheric convection. Polar ionospheric patch research requires more rigor in specific areas. A number of clear signatures are suggested for polar cap arcs, cusp reconnection events, and related phenomena. The thermosphere, as the rest frame for plasma response to electric fields (currents, heating, chemical loss, instabilities), can have transpolar winds order a km/s, which require measurement.