Results from in situ measurements of ionospheric currents in the equatorial region. I.

Abstract

Several rocket borne magnetometer experiments have been conducted from Thumba to measure the equatorial electrojet currents under different solar and geophysical conditions. The data from these experiments have been used to study the vertical structure of the electrojet, the relation between strength of the jet and the magnetic field variation at the ground and the causes of large day-to-day variability of the amplitude of H variation. The results show that the experimentally measured current density peaks at a significantly different altitude compared to the altitude of the peak of Cowling conductivity calculated using model values of Ionospheric parameters. The analysis indicates that given the magnetogram from a station under the electrojet, it is possible to predict the vertical distribution of current density in the electrojet on a quiet day. The mechanism of stabilisation of two stream instability suggested by the theoretical workers ro explain the back scatter radar echoes from type I irregularities on high jet days does not become operative atleast upto jet strengths equivalent to 4H<140nT.

Local time and longitude dependence of the equatorial electrojet magnetic effects

“…1). The EEJ has been considered as a thin current ribbon owing parallel to the dip-equator at a ÿxed altitude (h = 105 km), which was estimated from in situ rocket measurements in the equatorial ionosphere (Maynard, 1967;Sampath and Sastry, 1979). For the models that describe only the latitude dependence of the EEJ, the involved parameters are the latitude of the center (c), the peak current intensity (I0) at the center and the half-width (a) of the EEJ.…”

Equatorial electrojet at African longitudes: first results from magnetic measurements

“…Rocket experiments have been used to provide estimates of the current density along vertical pro®les (Maynard and Cahill, 1965;Maynard, 1967;Sampath and Sastry, 1979), which happened to be very similar. For example, Sampath and Sastry (1979) observed a maximum of the current density at the altitude of 106 km with a vertical half width of 12 km. Furthermore, they showed that the vertical structure remained constant during daytime and from one day to another.…”

“…This phenomenon has been studied through dierent types of experiments: its vertical structure has been investigated using instruments inside rockets (Sastry, 1970, Sampath andSastry, 1979); its magnetic eects have been monitored with the help of meridian chains of magnetometers crossing the geomagnetic equator (Chapman, 1951, Forbush and Casaverde, 1961, Fambitakoye and Mayaud, 1976a, b, c, Hesse, 1982. Ionospheric soundings have allowed studies on the associated ionospheric electric ®elds as well as on electron densities and on ionospheric plasma instabilities (Balsley, 1973).…”

Depth of non-conducting layer in the Indian Ocean region around Thumba, derived from in situ investigations of equatorial electrojet. II.

“…But a rocket magnetometer measures the actual total magnetic field due to the jet as it passes through the current layer. SAMPATH and SASTRY (1979) have shown that the lower and upper boundaries of the electrojet layer are located at 90 and 130 km respectively and that the height of the center of the electrojet h is 106 km. If 4F is the magnitude of total field discontinuity due to the electrojet measured by the rocket magnetometer while crossing the region between 90 and 130 km, since the electrojet has been considered as a uniform current band, the field due to the electrojet just below the current layer where h-0 will be 4F/2.…”