Catalogued parameters…• Current sheet normal vector and velocity, derived using a timing analysis. Later used to calculate an accurate measure of current sheet thickness.

• Current density within the current sheet derived using Ampere’s Law.

• Downstream solar wind activity and internal substorm conditions.

• Hi Energy Particle Flux and Electron Density.

Data was obtained primarily from Clusters Flux Gate Magnetometer (FGM) and its high energy particle detectors (RAPID and PEACE).

A coordinated study of the Earth’s magnetotail using observational data from Cluster and Double Star

Oliver NailardUniversity of Birmingham, UK

Introduction

- Cluster and Double Star are unique in that they allow for separate spatial and temporal variations in arbitrary geometry measurements in the near-Earth environment.

- In a region such as the Earth’s magnetotail this method of observation becomes particularly valuable when seeking to understand the dynamical processes involved in substorm mechanics and current sheet motion.

- An extensive cataloguing of Cluster magnetotail crossings followed by a study of the correlations between internal and external parameters was undertaken.

-This was proceeded by an event study which utilised both Cluster and Double Star observations to demonstrate the advantage of coordinated

studies in this region.

nrntV arbsh ˆˆ

rαβ = Separation vector between any spacecraft pair.tαβ = Time difference for this pair at boundary. n = Normal vector to current sheet.Vsh

arb = Velocity of current sheet.

Statistical Survey

The solar wind has two primary effects on the behaviour of the magnetotail:

1) Will demonstrate how the solar wind plays its role in the substorm cycle and how its associated processes influence internal magnetotail structure.

2) Will demonstrate the possible existence of a dynamic link, independent of substorm dynamics, between solar wind activity and motion within the tail and current sheet.

• The timing analysis method used allowed accurate determination of contributing components of current sheet motion (velocity and direction). Consequently it was possible to analyse how these various components effect each other and effect internal magnetotail dynamics associated with substorms. The position of the current sheet and the its direction of motion have no affect on substorm dynamics. Trends exist between sheet velocity and thickness (Top left).

• Substorm onset and expansion activity within the magnetotail, intrinsic of high Dst and current density, is directly related to current sheet thickness and current sheet velocity (Bottom left and top right).

• A simple dynamic link between solar wind intensity and current sheet activity exists. Increased ram pressure (particularly with dominant Y-components of velocity) has an element of control over current sheet velocity (Bottom right).

• A link between solar wind activity and substorm dynamics was not detected, however the statistical nature of this survey implies a connection would not be found.

Cluster / Double Star Event Study: 03 September 2004

• Cluster: Located near apogee, 18 Re down-tail encounters a large magnetic disturbance (C3) between 0130 and 0140. A timing analysis revealed propagation in an Earth-ward direction at approximately 50km/s (Bottom left).

C3 also caused significant activity in the RAPID and PEACE instruments which points to a large physical process taking place. Analysis of current density illustrated similar characteristics.

• TC-1: Located 13 Re down-tail encounters the same disturbance between 0230 and 0240 (Top right). Cluster/TC-1 spatial and temporal intervals allow a second event-speed to be inferred as approximately 8.8 km/s, indicating the event slowing down. Magnetic data also reveals the event to be increasing in magnitude.

• TC-2: Located 3 Re down-tail did not encounter the event. This may indicate the possible presence of a current disruption zone inherent of substorm expansion in the Current Disruption model.

Orbit plots of Cluster, TC-1 and TC-2: 03/09/04

Magnetic field data from Clusters FGM

Magnetic field data from TC-1’s FGM

Magnetic field data from TC-2’s FGM

3D schematic of the Earths magnetosphere

Cluster and Double Star orbital dynamics

Current sheet thickness as a function of current sheet velocity. Current sheet thickness as a function of Dst.

Current density as a function of current sheet thickness. Current sheet velocity as a function of ram pressure (with a dominant y-component).