磁暴期间极光椭圆与极盖区电离层效应比较研究——F区负暴

联合利用EISCAT和E-Svalbard非相干散射雷达数据,研究l997年5月强磁暴期间向阳侧极盖与极光椭圆区电离层F区负暴.发现在磁暴主相和恢复相初期,极光椭圆和极盖区电离层都在大约l90km高度出现类似F1的峰,F2主峰完全消失,F区电子密度大幅度下降.但离子温度的变化在两个区域很不相同,在极光椭圆区大幅度升高,而在极盖区没有显著变化,反映出引起F区负暴的主要机制在两个区域不尽相同.强对流电场引起大气焦耳加热与离子增温而使O+离子消失的化学反应速率增大所导致的电离损失,对极光椭圆区负暴起主要作用;而输运过程,特别是持续长达数小时的沿场上行离子流,对极盖区负暴起重要作用.磁暴主相期间,当EISCAT雷达位于等离子体对流涡旋转换区下方时,在无焦耳加热与离子摩擦增温的情况下,观测到由顶部电离层O+离子沿场高速外流引起的F区电子密度耗空.

A COMPARATIVE STUDY OF MAGNETIC STORM EFFECTS ON THE IONOSPHERE IN THE POLAR CAP AND AUROAL OVAL-F-REGION NEGATIVE STORM

With coordinated EISCAT and ESR radar data, ionospheric storm in both the dayside polar cap and the auroral oval during the major magnetic storm of May 15, 1997 is studied, focusing on the F region negative storm. It is found that in both the polar cap and the auroral zone a F1 like peak of ionization appeared at 190km height during the main and recovery phases of the storm; while the normal F2 peak disappeared and great depletions of electron density occurred. In contrast, variations of ion temperature are very different in the two regions, with little change in polar cap while strong enhancement in auroral oval, implying a difference in key mechanisms for the negative storms in the two regions. The increase of O + ion loss rate through chemical reaction due to Joule heating and enhancement of ion temperature resulted from strong electric field played a crucial role in the auroral zone. The plasma transport process, however, especially the long lasting large ion upflow, is of great importance in the polar cap. In addition, large F region electron density depletion associated with null Joule heating and ion temperature enhancement is observed by EISCAT radar in the transient region of the two cells of plasma convection, which is caused by strong field aligned O + ion outflow when the radar passing through probably under the polar cleft ion fountain region.