Ion-acoustic solitary waves and spectrally uniform scattering cross section enhancements

Abstract. Spectra measured by incoherent scatter radars are formed predominantly by scattering of the incident signal off ion-acoustic and Langmuir waves in the ionosphere. Occasionally, the upshifted and/or downshifted lines produced by the ion-acoustic waves are enhanced well above thermal levels and referred to as naturally enhanced ion-acoustic lines. In this paper, we study another kind of enhancement, which is spectrally uniform over the whole ion-line, i.e. the up- and downshifted shoulder and the spectral valley in between. Based on observations made with the EISCAT Svalbard radar (ESR) facility, we investigate the transient and spectrally uniform power enhancements, which can be explained by ion-acoustic solitary waves. We use a theory of nonlinear waves in a magnetized plasma to determine the properties of such waves and evaluate their effects on scattered signals measured by ESR. We suggest a new mechanism that can explain backscattered power enhancements by one order of magnitude above the thermal level and show that it is consistent with observations.