Abstract:

Macquarie Island and Davis Station is located at the centre and the edge of auroral oval respectively. The auroral absorptions over these stations freqently occur in the night. Among them most of sudden ionospheric absorption events occur in pre-midnight (MLT) and most of slow ionospheric absorption events occur in post-midnight. The auroral absorptions are related to the solar activity. Energetic particles of solar wind precipitate mainly in the centre of auroral oval near magnetic midnight, then they spread in all directions, mainly in form of westward jet and less in form of eastward jet .The westward jet is weaker and its spreading velocity is slower, but the eastward jet is stronger and the velocity is higher. With the increasing solar activity, especially after large X flare, the westward jet increases and strengthens. Moreover, at higher latitudes, as over the Davis Station, the auroral absorption increases and strengthens in winter. But at the centre of auroral oval, as over the Macquarie Island, there is not such a seasonal effect. It is possible that the auroral oval shifts southerly and hence produces this effect in winter (for Southern Hemisphere) .