Wind/WAVES observations of high-frequency plasma waves in solar wind reconnection exhausts

摘要

This paper studies high-frequency plasma waves during 28 encounters of the Wind spacecraft with solar wind reconnection exhausts. We use measurements by the Thermal Noise Receiver (TNR) and Time Domain Sampler (TDS) experiments on Wind/WAVES to survey characteristics of electron plasma waves and the most common regions where they are found. TNR spectrograms showed intense emission bursts ～4 kHz (corresponding to the ion acoustic range) during 79% of the events while around the local electron plasma frequency intense emission bursts were recorded for 39% of the events. The TDS instrument, operating at 120,000 samples per second, detected three kinds of electric waveforms: Langmuir waves, electron solitary waves (ESW), and wave packets with frequencies between ion and electron plasma frequencies typically interpreted as Doppler-shifted ion acoustic waves. Except for one very intense ESW event, the average amplitudes for all these three waveform types were similar, below 1 mV/m. We found an increased probability to observe intense plasma wave activity when the reconnection X-line region was approached. Wave activity may be present anywhere in the reconnection exhaust, although the boundary region of the exhaust appears to be the most dynamic region for wave activity. In particular, the majority of the captured ESW occurred near the exhaust boundaries.