Equatorial F-region plasma drifts: A study using OI 630 nm emission all-sky images

Abstract

The equatorial ionospheric plasma bubbles that occur at the low-latitude F-region of the ionosphere and the irregularities associated with them are responsible for severe interference and sudden disruption of transionospheric radio propagation up to Giga Hertz frequency range, interfering with the communication systems, including the GPS. A CCD-based all-sky imager with 180° field-of-view has been operating at a low-latitude station, Kolhapur (16.8°N, 74.2°E, dip lat. 10.6°N) in India on clear, moonless nights, to study the F-region dynamics through the imaging of OI 630.0 nm oxygen emission line. The imager has the capability of permitting observations over regions covering several million square kilometres from a single observing station. The ionospheric plasma bubbles manifest in all-sky imaging observations as nearly north-south aligned intensity-depleted regions. The all-sky images permitted the determination of the eastward plasma drift velocities, depth and width of the plasma bubbles. Also, the observed zonal plasma bubble drift velocities are compared with the thermospheric zonal neutral wind velocities obtained from the HWM-93 model. It reveals good agreement during some nights. The rate of change of zonal wind velocities has been modelled and is found to be consistent in terms of pressure variation computed from the MSIS-E 90 model.