Rocket and ground-based electron density soundings versus IRI representation

Abstract

Monthly averages of F-region cut-off frequency foF2 and peak height hmF2 data obtained during the solar maximum years 1978 and 2000 through the use of ionosondes located at equatorial and low latitude regions in Brazil are compared with the IRI representations. The equatorial stations are Fortaleza (3°53'S, 38°25'W), and São Luís (2°20'S, 44°12'W), and the low latitude station was Cachoeira Paulista (22°41'S, 45°00'W). The ionosonde data analyzed here were taken at each 15 minutes, in the months of February, May, August and November, of 1978 and 2000. In a second part of this study, electron density profiles obtained by three rocket flights in the Brazilian equatorial region are also compared with the IRI representations. The rocket experiments were carried out on July 7, 1984, December 11, 1985 and October 14, 1994. The first and the second experiments were performed at the sub-equatorial station Natal (35°14'W, 5°55'S) and the third one at the equatorial station Alcântara (2°19'S, 44°22W). The results clearly show that IRI significantly underestimates the equatorial hmF2 during the pre-midnight period. On the other hand, the IRI representation for hmF2 over off-equatorial station Cachoeira Paulista is in rather better agreement with the experimental density profile. The IRI representation of the foF2 parameter is in reasonable agreement with the data for both the equatorial region and Cachoeira Paulista, although the model appears to systematically overestimate foF2 in August for both 1978 and 2000. The rocket electron density profiles show that the highly variable height distribution of the electron density during ionospheric plasma bubble events may always prevent the correct representation of electron density profiles in the equatorial region during the occurrence of those events.