Incoherent scatter radar observations of the F-region ionosphere at Arecibo during January 1993

Abstract

Abstract We report incoherent scatter radar observation of the F-region ion drift, plasma density, and electron and ion temperatures during the January 1993 World Day 10-day campaign. Although the observed ion drift during the geomagnetically quiet period agrees with previous observation in the horizontal direction to a large extent for similar geophysical conditions, the vertical ion drift shows a very large downward component throughout the entire day, which averages at about 20m s −1 near the F-region peak. Such a large average downward plasma drift has not been reported before at low latitudes. The downward motion of the F-region plasma comes mainly from the component along the geomagnetic field line, which is chiefly controlled by the meridional wind during the day and ambipolar diffusion during the night. The E × B drift also contributes to the downward motion of the F-region plasma during the nighttime although it is in anti-correlation with the variation introduced by the ion motion along the field line. During the geomagnetically disturbed period on 25 January, the ion drifts showed large departure from the quiet period. The perturbed eastward ion drift was highly correlated with that along the magnetic field, which may be indicative of the presence of field-aligned current. Our observation shows that the daytime electron concentration and electron temperature have contrasting correlations at different altitude ranges in the F-region. They are positively correlated below 180 km, anti-correlated between 220–400 km, not well correlated between 440–620 km, and again positively correlated at 660 km. While the positive correlation at 220–400 km has been observed previously and is well understood, the positive correlations below 180 km and at 660 km are less known and have not been systematically studied. Using the electron energy balance equation, we show that the contrasting relationships between electron concentration and electron temperature depend on the ion composition at lower altitudes; and on how electron heating via photoionization compares with thermal conduction at higher altitudes. Our observation shows that plasma motion, electron concentration and the thermal characteristics of the F-region ionosphere are all interrelated. We also present the day-to-day variability of plasma drift, electron and ion temperatures as well as electron concentration.