August Kink mode oscillation of the current sheet Oscillations by dahntayjones

VIEWS: 15 PAGES: 1

									August 22, 2001: Kink mode oscillation of the current sheet
Oscillations of the current sheet observed by the Cluster spacecraft are investigated,
using the special ability of Cluster to separate between spatial and temporal variations.
We find that before substorm onset, as defined by the AE index and ground based
magnetometers, a thin current sheet moves with a velocity of 10 km/s mainly in the
vertical direction; after substorm onset the current sheet thickens and moves with greater
velocity, ~25 km/s.
                                     20                                                      I
                     B x (nT )




                                         0

                                    20


                                     20                                                      II
                     B x,lp (nT )




                                         0

                                     20


                                     20                                                      III
                     B y,lp (nT )




                                         0

                                     20


                                     20                                                      IV
                     B z,lp (nT )




                                         0

                                     20

                                     20                                                      V
                     B x (nT )




                                         0

                                     20
                                                   A    B   C      D
                                                                                             VI
                                                                              vz
                                    vns




                                                                              10 km/s
                                                                                        vx

                                     20                                                      V II
                     B C x, J t




                                         0

                                     20

                                         0
                                    10                                                       V III
                    l (R E )




                                             1
                                    10
                                      0930       0945       1000       1015                       1030
                                                             UT




Oscillations of the current sheet observed before and after substorm onset can well be
interpreted and modelled as a driven magnetoacoustic oscillation of the current sheet,
with different values for the (Harris) current sheet half thickness and the current sheet
velocity before and after substorm onset. The damping rate of the wave can be shown
to be related to the thickening rate of the current sheet.

								
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