These proceedings are based on the invited talks and selected research reports presented at the NATO Advanced Study Institute (ASI) on "POLAR CAP BOUNDARY PHENOMENA" held at Longyearbyen, Svalbard, June 4 - 13, 1997. The role of the polar cap and its boundary is very substantial in solar-terrestrial physics. At this NATO AS! a major change in thinking on the "cusp" precipitation region in the high-latitude days ide upper atmosphere was reflected, at least for intervals when the interplanetary magnetic field (IMF) is directed southward. It is likely that this has implications for northward IMF as well. The change comes from the now almost complete acceptance of the concept of magnetosheath particle entry along open magnetic field lines and the evolution of the precipitation into the upper atmosphere with time elapsed since magnetic reconnection which opened the field line. A key prediction of this view is that the low-latitude boundary layer (LLBL) is on open field lines.

Table of Contents:
Recent work on the Kelvin-Helmholtz instability at the dayside magnetopause and boundary layer.- Magnetopause motions in a Newton-Busemann approach.- Comparison of gasdynamics and MHD predictions for magnetosheath flow.- Time-varying reconnection. Quantitative reconnection.- An empirical model of the magnetopause for broad ranges of solar wind pressure and BZ IMF.- Solar wind He2+ and H+ distributions in the cusp for southward IMF.- Identifying the open-closed field line boundary.- Open and closed low latitude boundary layer.- The dynamic magnetosphere.- Ionospheric signatures of magnetopause processes.- Excitation of flow in the Earth’s magnetosphere-ionosphere system: observations by incoherent-scatter radar.- Large-scale electric fields in the dayside magnetosphere.- Polar observations of cusp electrodynamics: evolution from 2- to 4-cell convection patterns.- Relationship between large-, meso-, and small-scale field-aligned currents and their current carriers.- The dayside aurora and its regulation by the interplanetary magnetic field.- Auroral and geomagnetic signatures of flux transfer events and associated current systems for positive and negative IMF BY.- Coherent-scatter radar studies of the dayside cusp.- Ionospheric radiowave absorption processes in the dayside polar cap boundary regions.- Response of the polar cap ionosphere to changes in (solar wind) IMF.- Polar cap phenomena and their relation to boundary layers and the IMF.- Polar patches - outstanding issues.- Conjugate features of auroras observed by TV cameras and imaging riometers at auroral zone and polar cap conjugate-pair stations.- HF radars as a tool for conjugate studies of magnetospheric phenomena.- Conjugate ground observations and possible source regions of two types of PC 1–2 pulsationsat very high latitudes.- Studies of geomagnetic conjugacy at very high latitudes.- A model for the high latitude isotropic boundary.- Particle boundaries during a solar electron event.- Structure analysis of geosynchronous substorm oscillations.- Substorms and the inner magnetosphere: onset and initial expansion.- Observations of tailward sreaming ions in the near-earth tail during a magnetospheric substorm.- Space weather - the practice of space physics.- A summary of the NATO ASI on polar cap boundary phenomena.