Global and multiscale features of the magnetosphere: data-derived and global MHD modeling

The Earth's magnetosphere exhibits global features such as plasmoid formation and release, and multiscale behavior, e. g. , turbulence, bursty bulk flows, current disruption, etc. It is essential to model these features properly in order to forecast them accurately and efficiently. The global behavior has clear dynamical behavior and can be predicted using dynamical models. The multiscale features on the other hand has a power law behavior and can not be modeled in the dynamical sense and can be described/modeled in terms of statistical properties. These properties of the magnetosphere are modeled using correlated data of the solar wind - magnetosphere coupling and global MHD simulations. The data-derived models yield forecasts of the global behavior from a mean-field model and the statistical limits of predictability from the multiscale features. The disturbances originating at the sun can lead to many hazardous effects in the geospace environment, and the development of predictive models of these is one of the key objectives of the International Living With a Star (ILWS) program. The chain of physical processes at the sun and their coupling to the solar wind, the magnetosphere, the ionosphere and the thermosphere, span a wide range of space and time scales and consequently it is at present a challenge to develop a single comprehensive model in which all these processes are directly represented. The present models, such as MHD (global, two-fluid and Hall), hybrid and particle-in- cell simulations each cover a part of the spectrum of processes and new multiscale simulation approaches are needed to cover the global and multiscale phenomena. The solar wind-magnetosphere coupling has been studied extensively using data from many space missions and modeling approaches. The coupling of the solar wind mass, momentum and energy to the magnetosphere is enhanced when the interplanetary magnetic field (IMF) turns southward, leading to geospace storms and substorms. The magnetosphere is a highly dynamic system under these conditions and its main component, the magnetospheric substorms, are disturbances with a typical time scale of an hour. When the IMF remains southward for an extended interval, the ring current grows under the influence of the solar wind variations, leading to geospace storms with typical time scales of days and are characterized by strong variations in the magnetic field on the ground. Along with the storms and substorms there are a number of processes, e. g. , turbulence, bursty bulk flows, current disruption, etc., that contribute to the multiscale phenomena. The Earth's magnetosphere is a non-autonomous dynamical system, driven by the solar wind. Studies of the magnetospheric dynamics using models derived from the correlated data of the solar wind - magnetosphere system have enhanced our understanding of the complex behavior of the magnetosphere. The advantage of this approach is the ability to yield the dynamical behavior of the system, inherent in observational data, independent of modeling assumptions. There has been considerable progress in the modeling and forecasting of the solar wind-magnetosphere coupling as an input-output system using techniques of nonlinear dynamics and complexity (Sharma et al., 2005). These data-derived models are based on the correlated data of the input time series I(t) (usually the solar wind convective electric field VBz) and the output time series O(t) (the geomagnetic activity index AE or AL for substorms and the Dst index for storms).