Evidence of standing waves during a Pi2 pulsation event observed on Cluster

A. B. Collier (1, 2) , A. R. W. Hughes (1) , L. G. Blomberg (2) , P. R. Sutcliffe (3)

1 School of Physics
2 SPP - Division of Space and Plasma Physics [Stockholm]
3 Hermanus Magnetic Observatory

Observations of Pi2 pulsations at middle and low latitudes have been explained in terms of cavity mode resonances, whereas transients associated with field-aligned currents appear to be responsible for the high latitude Pi2 signature.

Data from Cluster are used to study a Pi2 event observed at 18:09 UTC on 21 January 2003, when three of the satellites were within the plasmasphere (L=4.7, 4.5 and 4.6) while the fourth was on the plasmapause or in the plasmatrough (L=6.6). Simultaneous pulsations at ground observatories and the injection of particles at geosynchronous orbit corroborate the occurrence of a substorm.

Evidence of a cavity mode resonance is established by considering the phase relationship between the orthogonal electric and magnetic field components associated with radial and field-aligned standing waves. The relative phase between satellites located on either side of the geomagnetic equator indicates that the field-aligned oscillation is an odd harmonic. Finite azimuthal Poynting flux suggests that the cavity is effectively open ended and the azimuthal wave number is estimated as m~13.5.

Domaines: Océan, Atmosphère; Sciences de la Terre

A. B. Collier, A. R. W. Hughes, L. G. Blomberg, P. R. Sutcliffe. Evidence of standing waves during a Pi2 pulsation event observed on Cluster. Annales Geophysicae, 2006, 24 (10), pp.2719-2733. ⟨hal-00318191⟩