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We study wave emissions, in the frequency range from above thelower  hybrid frequency up to the plasma frequency, observedduring one of the Cluster crossings of a high-beta exterior cuspregion on 4 March 2003. Waves are localized near narrow currentsheets with a thickness a few  times the ion inertial length;currents are strong, of the order of 0.1-0.5μA/m<sup>2</sup>(0.1-0.5mA/m<sup>2</sup>when mapped to ionosphere). The high frequencypart of the waves, frequencies above the electron-cyclotronfrequency, is analyzed in more detail. These high frequency wavescan  be broad-band, can have spectral peaks at the plasma frequencyor spectral peaks at frequencies below the plasma frequency. Thestrongest wave emissions  usually have a spectral peak near theplasma frequency. The wave emission intensity and spectralcharacter change on a very short time scale, of the order of 1s.The wave emissions with strong spectral peaks near the plasmafrequency are usually seen on the edges of the narrow currentsheets. The most probable generation mechanism of high frequencywaves are electron  beams via bump-on-tail or electron two-streaminstability. Buneman and ion-acoustic instability can be excludedas a possible generation  mechanism of waves. We suggest that highfrequency waves are generated by  electron beams propagating alongthe separatrices of the reconnection region

Cluster observations of high-frequency waves in the exterior cusp