Daytime ionospheric absorption features in the polar cap associated with poleward drifting F-region plasma patches
Earth, Planets and Space volume 50, pages 107–117 (1998)
Absorption of radio waves in the polar ionosphere near the magnetic noon was observed on October 8, 1991, by the 30 MHz imaging riometer at Ny-Alesund, Svalbard (invariant latitude 76.1°). These observations showed that the initially widespread absorption features became localized and enhanced in the high-latitude sector of the field of view, and followed a poleward motion. This behavior occurred quasi-periodically and repeated every 10–20 min. Simultaneous observations by EISCAT “Polar” experiments showed that nine discrete plasma patches, with F-region electron density enhanced by an order of 106 el/cm3, drifted poleward from the polar cusp to the cap during the same period. This coincidence suggested that the ionospheric absorption was associated with F-region plasma patches in the polar cap. Theoretical absorption values of 0.14 dB, estimated using the electron densities and the electron-ion collision frequencies from the EISCAT F-region plasma data, are smaller than the observed values (<0.8 dB). This discrepancy may be related to the difference between the theoretically- and experimentally-determined collision frequencies, as indicated by Wang et al. (1994). These localized, enhanced, and poleward drifting absorption features over Ny-Alesund may be explained as F-region plasma patches produced by a magnetosheath-like particle precipitation into the cusp, and as small-scale irregularities caused by density gradients of the patches drifting into the polar cap.
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Nishino, M., Nozawa, S. & Holtet, J.A. Daytime ionospheric absorption features in the polar cap associated with poleward drifting F-region plasma patches. Earth Planet Sp 50, 107–117 (1998). https://doi.org/10.1186/BF03352092