Cluster observations of sudden impulses in the magnetotail caused by interplanetary shocks and pressure increases

Abstract

Abstract. Sudden impulses (SI) in the tail lobe magnetic field associated with solar wind pressure enhancements are investigated using measurements from Cluster. The magnetic field components during the SIs change in a manner consistent with the assumption that an antisunward moving lateral pressure enhancement compresses the magnetotail axisymmetrically. We found that the maximum variance SI unit vectors were nearly aligned with the associated interplanetary shock normals. For two of the tail lobe SI events during which Cluster was located close to the tail boundary, Cluster observed the inward moving magnetopause. During both events, the spacecraft location changed from the lobe to the magnetospheric boundary layer. During the event on 6 November 2001 the magnetopause was compressed past Cluster. We applied the 2-D Cartesian model developed by Collier et al. (1998) in which a vacuum uniform tail lobe magnetic field is compressed by a step-like pressure increase. The model underestimates the compression of the magnetic field, but it fits the magnetic field maximum variance component well. For events for which we could determine the shock normal orientation, the differences between the observed and calculated shock propagation times from the location of WIND/Geotail to the location of Cluster were small. The propagation speeds of the SIs between the Cluster spacecraft were comparable to the solar wind speed. Our results suggest that the observed tail lobe SIs are due to lateral increases in solar wind dynamic pressure outside the magnetotail boundary.

The asymmetric geospace as displayed during the geomagnetic storm on August 17, 2001

“…As is apparent from the time-shifted ACE data to the bow-shock a large pressure pulse was 15 observed about 35 hours later: 17 Aug, 2001 at∼ 11 UT ( Figure 2F) and immediately showed up in the SYM/H index ( Figure 2H) as a huge increase of the magnetopause currents as a result of a dramatic compression of the magnetosphere. The arrival of this interplanetary shock and its effect on the magnetosphere at the initial phase of the storm has been reported by others (Huttunen et al, 2005;Echer et al, 2008). ).…”

The interaction of ultra-low-frequency pc3-5 waves with charged particles in Earth’s magnetosphere

“…IP shock-induced vortex-like flow has been observed by Huttunen et al (2005), Keika et al (2008), Tian et al (2012), and in the tail plasma sheet. The vortex-like plasma flow structure can excite Alfvén waves at certain frequencies depending on its azimuthal phase velocity.…”

Propagation of a shock-related disturbance in the Earth's magnetosphere

“…There are different approaches to study how the IP shock propagates through the magnetosphere, whether it is by the IP shock driven at the magnetopause or a wave launched by the interaction of the magnetopause with the IP shock, which is already discussed by Huttunen et al [2005] and Collier et al [1998]. After interaction with the fast forward shock, the bow shock starts to move earthward [Šafránková et al, 2007].…”