Spatial and temporal characteristics of poloidal waves in the terrestrial plasmasphere : a CLUSTER case study

• Oscillating magnetic field lines are frequently observed by spacecraft in the terrestrial and other planetary magnetospheres. The CLUSTER mission is a very suitable tool to further study these Alfven waves as the four CLUSTER spacecraft provide for an opportunity to separate spatial and temporal structures in the terrestrial magnetosphere. Using a large scaled configuration formed by the four spacecraft we are able to detect a poloidal Ultra-Low-Frequency (ULF) pulsation of the magnetic and electric field in order to analyze its temporal and spatial structures. For this purpose the measurements are transformed into a specific field line related coordinate system to investigate their specific amplitude pattern depending on the path of the CLUSTER spacecraft across oscillating field lines. These measurements are then compared with modeled spacecraft observations across a localized poloidal wave resonator in the dayside plasmasphere. A detailed investigation of theoretically expected poloidal eigenfrequencies allows us to specify the observed 16 mHz pulsation as a third harmonic oscillation. Based on this we perform a case study providing a clear identification of wave properties such as an spatial scale structure of about 0.67 R-E. the azimuthal wave number m approximate to 30, temporal evolution, and energy transport in the detected ULF pulsations.

Nyckelord

magnetospheric physics

MHD waves and instabilities

plasmasphere

space plasma physics

waves and instabilities

standing alfven waves

field line resonances

magnetic-field

geomagnetic-pulsations

hydromagnetic-waves

axisymmetrical magnetosphere

plasmapause formation

earths magnetosphere

ballooning modes

electric-field

Publikations- och innehållstyp

ref (ämneskategori)

art (ämneskategori)