Ambient plasma conditions in the wave occurrence region. Panel a shows MAVEN spacecraft altitude and panel e shows local time as a function of universal time (UT). The occurrences of high-frequency waves are marked with red “x” (b) Ion and electron density; (c) magnetic field strength; (d) angle between magnetic field and solar wind velocity vectors; (f) bulk solar wind speed; (g) ion and electron temperatures; (h) the peak frequency as seen in the spectra of observed electric field, , (red) and upper-hybrid wave frequency estimated from ambient plasma parameters, f_uh ≈ f_pe, (blue) as a function of altitude. The above quantities are shown for all 19 high-frequency wave events considered in the present study.