Magnetosphere and Ionosphere as a Coupled System: Theory and Observations


The coupling of the terrestrial magnetosphere and ionosphere is fundamental to understanding the behaviour of each region. Strong coupling is often associated with the closure of intense electrical currents flowing along magnetic fields lines. The Alfven wave is a natural agent for carrying these currents, and is known to modify signatures of coupling such as optical auroral emissions when magnetospheric electrons are precipitated in the ionosphere (in so-called 'upward' current regions) as shown in Figure 1. In 'downward' current regions, cold ionospheric electrons are removed and flow into the magnetosphere [Wright et al, 2008]. The redistribution of plasma by currents is rarely taken into account in models of magnetosphere-ionosphere coupling, and traditionally it is more likely that the enhancement of ionospheric conductivity (associated with energetic electron precipitation) is regarded as the dominant effect.

Radar observations [Aikio, 2004] show that ionospheric plasma depletion in downward current regions can be substantial (by up to 90% over 1 minute). This will cause a significant drop in conductivity and have important implications for current flow and hence magnetosphere-ionosphere coupling. This has received little attention in modelling, except by members of the proposed team [Streltsov and Lotko, 2004; Karlsson et al., 2005; Russell, Wright and Hood, 2010]. Recent optical observations of a downward current region (sitting between two auroral arcs) reveal how it widens in an effort to carry the current required by the magnetosphere [Michell et al., 2008]. This behaviour also extends along field lines into the magnetosphere, where the Cluster spacecraft have seen the spatial width of a strong downward current broaden in time [Marklund et al., 2001].

The proposed team will focus on the self-consistent nonlinear coupling of the magnetosphere and ionosphere through observational signatures and theory. We will bring together several observational techniques: The combined use of radar providing coverage of the ionosphere up to 200 km altitude, the FAST satellite providing coverage through the transition region from 400 km up to 4000 km, and the Cluster spacecraft allowing further coverage out to several RE allows the study of magnetosphere and ionosphere coupling in a holistic manner, rather than through the use of assumed inputs into each component part. We will also develop a physical appreciation of the signatures seen in data through the development of theory and modelling. This will take the form of analytical theory and state of the art multi-fluid numerical simulations and kinetic theory.

The team that will carry out this work comprises leading international scientists from around the world who have specialities covering the complementary aspects of our proposal. The success of our research may lead to a significant re-evaluation of the role of the ionosphere in the global picture of magnetosphere-ionosphere coupling at high latitudes and hence add a significant value to the publicity of research programs performed under the auspices of the International Space Science Institute.