Study of plasma turbulence in the central plasma sheet using high and low orbiting satellites.

The consequences that the turbulence in the plasma sheet has for the physics of the magnetosphere are not clear at this time. Particle and field measurements in situ made by high-latitude satellites crossing the plasma sheet can shed light to the main aspects of this turbulence. Fluctuations of the plasma bulk velocity across the plasma sheet were studied using the Interball/Tail satellite measurements for different levels of geomagnetic activity. It was found that the values of Eddy diffusion coefficients increase significantly during substorm growth and expansion phases and decreases slowly to the initial level during the recovery phase. A relationship between these coefficients and the geomagnetic field also varies depending on the phase of substorm, indicating possible change in the turbulence regimen. However, even multipoint high-latitude satellite measurements always will be affected by the necessity of a correct discrimination between spatial and temporal variations of plasma parameters. Fast movement of a low-latitude spacecraft across the auroral zone (minutes) makes it possible to observe the "frozen in" picture of global plasma behavior. So analysis of electric field and particle precipitating flux data measured by the low-altitude Intercosmos-Bulgaria-1300 satellite allowed to reconstruct large-scale features of the magnetospheric electric field spectra, what can be considered as a good complementation of direct measurements of the plasma sheet turbulence.