Plasma Wave Observations with GEOTAIL Spacecraft.

The main scientific objectives of GEOTAIL Plasma Wave Instrument (PWI) are to investigate the characteristic features of wave phenomena which are generated by a variety of plasma processes occurring within the Earth's magnetosphere. The PWI measures plasma waves in the frequency range from 5.62 Hz to 800 kHz for the electric components and from 5.62 Hz to 12.5 kHz for the magnetic components. The instrument is composed of three distinct sets of receivers: (1) the Sweep Frequency Analyzer (SFA), (2) the Multi-Channel Analyzer (MCA) and (3) the Wave-Form Capture (WFC). The first two receivers are dedicated to wave spectra measurement, while the last one is used to capture actual wave forms of two electric and three magnetic field components for the measured plasma wave emissions. The present paper describes the PWI subsystems and their functions. We also report some results from initial observations made during the traversal of the geomagnetic tail and a skimming pass of the dayside magnetopause. These observational results are useful in providing a good overview of the PWI capabilities as well as elucidating the characteristic features of the wave spectra in these regions.