Longitudinal variations in the position and magnitude of the poleward wall of the ionospheric trough in the southern hemisphere

Abstract

For the first time, joint variations with longitude in the position of the high-latitude ionosphere structures: equatorward boundary of auroral diffuse precipitation, poleward wall and minimum of subauroral (main) ionization trough were considered. The data from the CHAMP satellite in the southern winter hemisphere in the evening, midnight and morning sectors were used, as well as a model of the auroral diffuse precipitation. The average (for all longitudes) distance between the equatorward boundary of the auroral oval and poleward wall increases from 1° in the evening to 2.5° in the morning, and between the auroral oval and trough minimum from 3.5° to 6.5°, respectively. These values agree well with the estimates obtained using different methods in other experiments. The poleward wall and minimum of the trough experience synchronous variations with longitude, the distance between the auroral oval and trough changes with longitude because of the different character of the longitudinal effect. Unexpectedly stable longitudinal variations in the magnitude of the poleward wall were identified for the first time: magnitude changes 4 times in the evening, 6 times at midnight and 3 times in the morning. Longitudinal variations in the poleward wall magnitude at midnight are completely correlated with the diffuse precipitation flux, in the evening with the electron density at mid-latitudes, and in the morning the poleward wall is clearly associated with electron density variations on the dayside. These results confirm the known assumptions that at midnight the poleward wall is completely formed by diffuse precipitation, and in the morning the poleward wall is evidently determined by the transport of ionization from the dayside. In the evening, the influence of residual solar ionization was probably manifested. In this sector, at America-Atlantic longitudes, an equatorward minimum of electron density is often formed, which prevents accurate determination of the trough position. These cases require a deeper analysis. In the evening at longitudes of America and at midnight at longitudes of 30°-90°, neither the poleward wall nor minimum of the trough is sometimes formed at all. This unexpected result requires clarification of the trough formation mechanism.