极光吸收的日变化与季变化

麦阔里岛和戴维斯站分别位于极光带中心和极光带极向边缘区内.这两处的极光吸收次数在晚间多些,其中突然性吸收主要出现在午夜(当地地磁时间)前,缓变性吸收在午夜后.极光吸收与太阳的活动性密切相关.太阳风高能粒子主要沉降在极光中心带磁午夜区,然后向东西与南北方向扩散,以向西的电射流为主,向东的为辅.但向西的弱些、速度慢些;向东的强些、速度快些.太阳活动增强后,尤其是强的X耀斑事件后,向西的电射流增多增强.另外,在较高磁纬地区的戴维斯站,冬季时极光吸收增多增强.但在极光中心区的麦阔里岛观测站,基本上无此种季节效应.这可能是由于冬季(对南半球而言)极光卵向南偏移造成的.

THE DIURNAL AND SEASONAL VARIATIONS OF THE AURORAL ABSORPTIONS

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) .