OBSERVATIONS AND SIMULATIONS OF EQUINOCTIAL ASYMMETRY DURING LOW AND HIGH SOLAR ACTIVITIES

Abstract

Employing a dual frequency GPS receiver and using the SAMI2 ionospheric model at the equatorial stations (Sao Luis(salu) and Arequipa(areq)) and low-latitude stations (Cachoeira Paulista(chpi) and Porto Alegre(poal)), the measurement of the ionospheric total electron content (TEC) have been estimated for March and September equinoxes months during an extremely low solar activity of 2009 and an extremely high solar activity of 2001. The seasonal behavior of the ionosphere have been investigated for several decades but the differences of the ionosphere between the March and September equinoxes are still an open question. The analysis reveals that during low and high solar activities, the equinoctial asymmetry in the ionospheic plasma density is a phenomenon of both the low-latitude and equatorial region and occurs during both solar activities. The SAMI2 model was used to investigate the observed GPS TEC behavior and its reveals that, besides the important effects of the meridional wind and of the electric field effect (ExB drift), the thermospheric temperature and O/N2 also plays an important role in the forming of the observed equinoctial asymmetry particularly around the magnetic equator in the ionosphere.