SPRG Seminars - Archive

October 4, 2005:

The Role of Magnetic Clouds and Interplanetary Shocks in Driving Magnetospheric Activity
Emilia Huttunen, UCB/SSL

Interplanetary counterparts of coronal mass ejections (ICME) are the primary causes of intense magnetospheric storms. An ICME consists of two regions, sheath and ejecta that are both potential drivers of magnetic activity at the Earth. The ejecta is composed of plasma and magnetic field from the eruption and the sheath is a region of compressed and heated solar wind plasma ahead of the ejecta. Magnetic clouds form a subset of ejecta that are particularly geoeffective due to high magnetic field magnitudes and organized rotation of the field direction on the timescale of a day. I will discuss about different topologies of magnetic clouds and show statistical results of the solar cycle variations in the stucture of magnetic clouds during the solar cycle 23.Sheath regions were statistically the most important drivers of intense magnetic storms (defined by the 1-hour Dst index below -100 nT). The significance of magnetic clouds was highlighted in the declining phase of the solar activity when they caused the largest storms of the cycle 23.

For predictive purposes it is important to distinguish between the sheath and the magnetic cloud. The magnetic fields in these structures are fundamentally different origin and the solar wind parameters that control the solar wind-magnetosphere coupling have different behavior. The analysis of magnetic indices (Dst, Kp and auroral indices) indicates that sheath regions are inclined to induce intense activity at high latitudes and rapid changes in ionospheric currents and electric fields. Furthermore, high solar wind dynamic pressure during sheath regions can push the magnetopause inside geostationary orbit for several hours. I will show examples of the different magnetospheric response to magnetic clouds and sheath regions.

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