On the deviations of measured electron density profiles from IRI predictions for low latitudes

Abstract

In situ electron density profiles obtained from the equatorial stations in Brazil using conventional Langmuir probes and High Frequency Capacitance probes are compared with the IRI predictions in the light of the spectral distribution of the plasma density irregularities observed. Plasma instability mechanisms, especially the Rayleigh-Taylor and the Cross-Field instability mechanisms are considered responsible for the generation of the plasma irregularities observed at different height regions along the electron density profile, in the post sunset ionosphere. A comparative study of the observed characteristics of the plasma irregularities with those expected from the theories can give us information on the reliability of the observed profiles. This reliability estimate is all the more important because of the fact that the techniques used for the measurement of electron density are known to be associated with some inherent problems. The presence or absence of plasma irregularities in a given height region can, therefore, give us information as to whether the deviations of the observed electron density profiles from the IRI predictions are genuine or not. From this comparative study one can also obtain information as to what are the physical parameters responsible for the observed deviations in the profiles and thereby suggest some possible improvements in the methods used for IRI predictions for low latitudes.