Magnetic cloud boundary layer of 9 November 2004 and its associated space weather effects
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On 9 November 2004, the WIND spacecraft detected a magnetic cloud boundary layer (MCBL) during the interval from 19:07 UT to 20:30 UT. Within the MCBL, there is intense southward magnetic field and the dynamic pressure is rather high, which makes it much geoeffective. Twenty-three minutes later, the MCBL arrived on the magnetopause. An intense geomagnetic storm main phase was driven by the sustaining strong southward magnetic field within the MCBL. During the passage of the MCBL, a typical magnetospheric substorm was triggered. The substorm onset was synthetically identified by the aurora breakup, magnetic dipolarization, dispersionless particle injection, Pi2 pulsation, and the polar bay onset. The substorm triggering is related to the special magnetic and plasma structure within the MCBL. The MCBL accompanying adjacent sheath region formed a dynamic pressure enhancement region, which strongly compressed the magnetosphere and even pushed the magnetopause into the geosynchronous orbit so that two dayside spacecraft GOES-10 and GOES-12 were directly exposed in the magnetosheath for a long interval during the passage of the MCBL. In terms of Shue et al. (1998) model, the closest subsolar standoff distance even reached 5.1 RE during the passage of the MCBL. It can be inferred that the strong dynamic pressure and the strong discontinuities within the MCBL determine the intense compression effect. In addition, a very intense geomagnetically induced current (GIC) event was directly caused by the MCBL. Similar to this case, majority of MCBLs are dynamic pressure enhancement regions, and there are strong southward magnetic field and several strong discontinuities inside these regions, which can potentially drive large-scale magnetospheric activities. In this paper, we take a case study to discuss the magnetospheric activities and the space weather effects caused by MCBLs.