Space-relevant observational signatures, such as frequency spectra, phase velocities, excitation thresholds, and ion heating, associated with electrostatic ion-cyclotron waves excited by the inhomogeneous energy-density driven (IEDD) instability in a laboratory experiment are presented. A comparison is made between these waves and the broadband ELF waves recently observed in the auroral ionosphere with sounding rockets and satellites. The measurements of broadband spectra, electron-Landau-resonant phase velocities, low excitation threshold value of parallel electron drift speed, and significant perpendicular ion heating suggest that attributing the broadband ELF waves to the IEDD instability mechanism is justified. ¿ 1999 American Geophysical Union