An analysis of interplanetary sources of geomagnetic storm during November 7-8, 1998
【摘要】：We analyzed the properties of the solar wind appeared during November 7–8, 1998. Results show that the spaceship ACE spotted a shock (hereinafter referred to as the first shock) at 07:33 UT, November 7. The sheath appeared from the first shock to 22:00 UT November 7. A magnetic cloud-like (MCL) was observed during the period from 22:00 UT November 7 to 11:50 UT, November 8. Another shock was observed at 04:19 UT, November 8 (the second shock). It is apparent that the second shock has entered the rear part of the MCL (MCL_2), though the former part of the MCL (MCL_1) was not affected by the second shock. The main phase of the geomagnetic storm is split into three steps for the convenience of SYM-H index analysis. Step 1 covers the period from the sudden storm commence (SSC) at 08:15 UT, November 7 to the moment of 22:44 UT, November 7. Step 2 starts from 22:44 UT, November 7 and ends at 04:51 UT, November 8. The last step runs from 04:51 UT, November 8 to 06:21 UT, November 8. Step 2 has played a key role in the main development phase of the geomagnetic storm. Analysis of the solar wind properties associated with the main phase shows that the three steps in the main phase have sheath, MCL_1, and MCL_2 as their respective interplanetary source. Specifically, the sheath is covered by the solar wind data from 07:33 UT to 22:00 UT, November 7, MCL1 by the solar wind data from 22:00 UT, November 7 to 04:19 UT November 8, and MCL_2 by the solar wind data from 04:19 UT to 05:57 UT, November 8. MCL_1 had a strong and long lasting so UTh directed magnetic field, allowing it to play a key role in the development of the main phase. MCL_2 made a much smaller contribution to the main development phase, compared with MCL_1.