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.

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 Pcl-Pc3 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 1-5 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.