Radar Observations of Equatorial Ionospheric Irregularities

Abstract

Long-term data set of radar observations using coherent and incoherent scatter radar sources during 1996-2008 were used to study the trend of low-latitude ionospheric irregularities, also referred to as equatorial spread F (ESF), near geomagnetic equator over Jicamarca, Peru (12°S, 76.9°W, geomagnetic latitude 1°N). Radar signatures are classified on the basis of their structures. The occurrences of radar signatures of the F-region plasma irregularities are highly seasonal and solar cycle dependence. Irregularities are more dominant during December solstice with ~88% of the total night of observations, while the irregularities occurrences are minimum during June solstice with~29% of the total nights of observations. Using incoherent scatter radar observations, the relationships of vertical drift velocities of plasma with the onset of ESF have been studied. Generally, the strong spread F develops for the early night higher upward drift velocity, while the weak spread F is most often generated for the small upward drift velocity in the early evening hours. Radar plumes or broad spread F are not developed for the early night downward drifts of plasma during the equinox season, while during the December solstice such early night downward drift inhibits the development of ESF. However, in June solstice, small upward or downward drift velocities also lead to the development of weak spread F.