Langmuir waves observed near a solar wind current sheet on 2020 June 07. A series of Langmuir waves are observed with variable frequencies above the electron plasma frequency predicted from n_e, SC. (a) B. (b) n_e, SC. The red crosses indicate the TDS snapshots with Langmuir waves and the number density estimated from f_pk. The three red shaded regions correspond to the three Langmuir wave examples in panels c–h. Panels c,e, and g: three Langmuir waveforms in field-aligned coordinates E_∥ (black) and E_⊥ (red). Panels d, f, and g: power spectra of E_∥ (black) and E_⊥ (red) associated with the Langmuir waveforms in panels c, e, and g, respectively.