Rocket measurements of ionospheric electron density from Brazil in the last two decades

Several rockets carrying plasma diagnostic experiments were launched from the Brazilian rocket launching stations in Natal (5.9°S, 35.2°W Geog. Lat.) and Alcantara (2.31°S, 44.4°W Geog. Lat.). Langmuir Probes (LP) were used to measure the height profiles of electron density (ne) and electron temperature (Te) and high frequency capacitance (HFC) probes were used to measure ne. The main objectives of the studies reported here are: (1) to compare the observed ne profiles with the Model predictions and (2) to look into the possible reasons for the deviations of the observed ne profiles from the model predictions. An attempt is made to obtain information as to what are the physical parameters responsible for the observed deviations in the profiles and thereby to suggest some possible improvements in the methods used for model predictions for low latitudes. The electron density profiles estimated from the Langmuir and the HFC probe measurements, qualitatively, match with the IRI-95 model profiles especially during daytime or during nighttime when the F-region base is rather at a low level. However, quantitatively, the model profiles deviate considerably from the observations. These deviations can be attributed to one or more of the following: (a) inadequacy of the IRI-95 model to represent the equatorial ionosphere over Brazilian region which is not adequately represented in the data base used in the IRI model formulation; (b) the non-inclusion of the effects of electrodynamic forces in the IRI model. These processes are extremely important in the low latitude ionosphere; (c) non-inclusion of the effect of electron temperature variation on the saturation electron current and thereby on the proportionality constant that relates the sensor current collected with the electron number density, that can result in an overestimation of the electron density in regions of lower electron temperature; (d) non-inclusion of the negative plasma sheath effect in the sensor current electron density relationship.