PLASMA-WAVES IN THE DAYSIDE POLAR-CAP BOUNDARY-LAYER - BIPOLAR AND MONOPOLAR ELECTRIC PULSES AND WHISTLER-MODE WAVES

We report four different types of plasma waves detected in and near th e dayside polar cap boundary layer (PCBL) region at high altitudes (> 6 R-E) One wave type is narrowband whistler-mode emission at frequenci es just below f(ce) (5.5 kHz). These emissions could be locally genera ted by resonant wave-particle interactions involving an electron beam of similar to 100 eV energy. A second type is a low frequency (200-300 Hx) whistler mode wave, which may be locally generated by similar to 25 keV electrons or similar to 45 keV ions. It is also possible that t hese latter waves are generated at low altitudes near the ionosphere a nd then converted from the ion cyclotron mode into whistler-mode durin g propagation from the generation region to the spacecraft. Two furthe r types of waves are large-amplitude bipolar and monopolar solitary '' electrostatic'' waves. The bipolar wave structures are possibly genera ted all along the magnetic field lines in the field-aligned current re gions (at all local times). The monopolar structures could be evolved bipolar solitary waves. A one-d schematic is presented to explain the paired monopolar structures as a result of splitting of an electron ho le into two parts.