Magnetic signatures of ionospheric instabilities

Details Magnetic signatures of ionospheric instabilities Magnetic signatures of ionospheric instabilities

May 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agusmsa42a..01l&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #SA42A-01

Physics

2409 Current Systems (2721), 2415 Equatorial Ionosphere, 2471 Plasma Waves And Instabilities (2772), 2481 Topside Ionosphere

Scientific paper

On its low polar orbit the CHAMP satellite samples equatorial and low latitudes on average 31 times per day. Quite frequently it passes through regions of strongly depleted plasma densities. The associated instability called equatorial spread-F (ESF) develops in the post-sunset local time sector. The highly accurate magnetic instrumentation on board CHAMP enables the observation of the tiny magnetic signatures of ESF. The electric currents causing the magnetic deflections are primarily driven by the plasma pressure gradients existing across the walls. To first approximation, the missing plasma pressure in the depleted fluxtube is compensated by an enhanced magnetic field. In addition, also field-aligned currents are observed. We suggest an F region generator in the equatorial plane communicating with the fluxtubes in both hemispheres. The generated electric fields launch Alfven waves which are reflected at the instabilities. The investigation of this topic is, however, still ongoing. Based on four years of CHAMP magnetic data we will show the statistical properties of ESF magnetic signatures, its distribution in longitude, its variation with season and local time, and discuss its dependence on solar flux and magnetic activity. The results are well in agreement with those obtained from plasma density measurements, but our large database allows for a better differentiation of the effects. We have further investigated the small-scale structures of the instability by taking advantage of the high-resolution (50Hz) CHAMP magnetic field vector data.

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