These proceedings are based upon in~roductory talks, re search repor~s and discussions at the NATO Advanced Work shop on ELECTROMAGNETIC COUPLING IN THE POLAR CLEFTS AND CAPS, held at Lillehammer, Norway, 20-24th September 1988. By this book we will make the information which was pro vided to the participants of the workshop, accessible to a wider audience. Electromagnetic processes governing particle, momen tum, and energy transfer from the solar wind via the magne tosphere and into the earth's upper atmosphere are the main topics of solar-terrestrial research. Due to the peculiar magnetic field configuration in the magnetosphere, result ing from the interaction with the shocked solar wind, the sunward-side boundary is mapped along magnetic field lines in~o a thin, arc-like band of the days ide polar ionosphere at the boundary of the polar cap; i.e. ~he ionospheric cleft region. The polar cusp is a separate, more limited region near magnetic noon, as defined by electron and proton precipitation detected from polar orbiting satel lites. The basic physics of the different coupling modes at the dayside magnetopause is a matter of great controversy. This is an important problem to solve, also because similar boundaries exist in stellar objects throughout the Uni verse. It is expected that ground-based remote sensing tech niques, with their ability to continuously monitoring the temporal and spatial variations of the ionospheric signa tures, will have a great impact on this problem, in parti cular when combined with in situ measurements.

Inhalt
Preface.- Participants.- Electrodynamics of the ionosphere/magnetosphere/ solar wind system at high latitudes.- The formation of isolated magnetic flux tubes on the dayside magnetopause.- Impulsive penetration of solar wind plasma irregularities into the magnetosphere: Relevant laboratory experiments.- Polar rain and the question of direct particle access.- Auroral oval configuration during the quiet condition.- On quantifying the distinctions between the cusp and the cleft/LLBL.- Heating of thermal ions near the equatorward boundary of the mid-altitude polar cleft.- Two-dimensional mapping of dayside convection.- Ionospheric convection in the polar cap as seen by optical imaging.- Balloon observations of electric field over South Pole: Convection patterns.- Ground magnetic perturbations in the polar cap and cleft: Structure and dynamics of ionospheric currents.- ULF pulsations in the polar cusp and cap.- Studies of PclPc3 geomagnetic pulsations at high southern latitudes: Implications for origin and transmission.- Transmission of solar wind hydromagnetic energy into the high latitude magnetosphere.- ELF and VLF waves in the polar clefts and caps.- Pc 15 geomagnetic pulsations and 750 Hz ELF activity at ground level in the northern and southern hemispheres.- Ground magnetic perturbations in the polar cap and cleft: Relationship with the IMF.- Relationships between auroral and magnetic activity in the polar cusp/cleft.- Electrodynamics of auroral and polar cap arcs at very high latitudes.- Simultaneous radar and satellite observations of the polar cusp/cleft at Søndre Strømfjord.- The electrodynamic signature of short scale field aligned currents, and associated turbulence in the cusp and dayside auroral zone.- Polar cleft structure at 09 MLT: Coordinatedsatellite- and ground-based observations.- 6300-A auroral emissions at South Pole: Dayside poleward motion and sun aligned arcs.- Plasma transport through the dayside cleft: A source of ionization patches in the polar cap.- Geomagnetic response of the polar thermosphere and ionosphere.- F-region storms and thermospheric circulation.- Thermospheric dynamics in the polar E- and F-region: Results of a nonlinear, spectral model.- Gravity wave studies at polar latitudes.- 50 MHz backscatter observations in the polar cap ionospheric E region.- The middle and high latitude ionosphere at ? 550 km altitude.- Summary.