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The time domain sampler (TDS) experiment onWIND measures electric and magnetic wave forms with a sampling rate whichreaches 120 000 points per second. We analyse here observations made in thesolar wind near the Lagrange point L1. In the range of frequencies abovethe proton plasma frequency fpi and smaller than or of theorder of the electron plasma frequency fpe, TDS observed threekinds of electrostatic (e.s.) waves: coherent wave packets of Langmuir waveswith frequencies f ~ fpe, coherent wave packetswith frequencies in the ion acoustic range fpi <f < fpe, and more or less isolated non-sinusoidalspikes lasting less than 1 ms. We confirm that the observed frequency of the lowfrequency (LF) ion acoustic wave packets is dominated by the Doppler effect: thewavelengths are short, 10 to 50 electron Debye lengths λD.The electric field in the isolated electrostatic structures (IES) and in the LFwave packets is more or less aligned with the solar wind magnetic field. Acrossthe IES, which have a spatial width of the order of ~ 25λD,there is a small but finite electric potential drop, implying an averageelectric field generally directed away from the Sun. The IES wave forms, whichhave not been previously reported in the solar wind, are similar, although witha smaller amplitude, to the weak double layers observed in the auroral regions,and to the electrostatic solitary waves observed in other regions in themagnetosphere. We have also studied the solar wind conditions which favour theoccurrence of the three kinds of waves: all these e.s. waves are observed moreor less continuously in the whole solar wind (except in the densest regionswhere a parasite prevents the TDS observations). The type (wave packet or IES)of the observed LF waves is mainly determined by the proton temperature and bythe direction of the magnetic field, which themselves depend on the latitude ofWIND with respect to the heliospheric current sheet. Key words. Interplanetary physics (plasma waves andturbulence; solar wind plasma). Space plasma physics (electrostatic structures)

WIND observations of coherent electrostatic waves in the solar wind