The magnetosphere of Earth, driven by the turbulent solar wind, exhibits many features of complex systems. The far from equilibrium nature is the origin of its multiscale behavior and requires different approaches to develop a comprehensive model of the magnetosphere. The global dynamics is modeled from the observational data using phase space reconstruction techniques and is used for space weather forecasting. The spatio‐temporal dynamics is studied using the average mutual information functions computed from the data of magnetic field variations at ground stations around the globe, and leads to a model consistent with substorm phenomenology. The multiscale behavior is modeled using approaches of statistical physics to characterize the nonequilibrium behavior. The long range correlations underlying extreme events in the magnetosphere are analyzed using the mutual information function. The distributed ground magnetometer stations provide data for modeling the magnetosphere as a multiscale complex network. This combination of different approaches to yield a comprehensive model of the magnetosphere provides a framework for the understanding of natural and anthropogenic complex driven systems.
The tendency of global MHD models to overestimate the transpolar potential in simulations of strong geomagnetic storms and evidence of an adverse feedback of the ionospheric conductance on the potential suggest that these models lack important physics leading to the conductance enhancement. Farley‐Buneman instability in the auroral ionosphere provides this lacking physics. This instability is believed to cause strong anomalous electron heating which affects the ionospheric conductivity. We use an earlier developed model of anomalous electron heating to estimate the ionospheric conductance disturbance as a function of the local electric field. This result is used to modify the ionospheric conductance in the LFM model to study its effect on the simulated transpolar potential. An idealized and a real‐case simulations are accomplished. In both cases a considerable drop in the simulated transpolar potential is found. The latter is in a good agreement with AMIE model and DMSP data.
Earth's magnetosphere during substorms exhibits a number of characteristic features such as the signatures of low effective dimension, hysteresis, and power-law spectra of fluctuations on different scales. The largest substorm phenomena are in reasonable agreement with low-dimensional magnetospheric models and in particular those of inverse bifurcation. However, deviations from the low-dimensional picture are also quite considerable, making the nonequilibrium phase transition more appropriate as a dynamical analog of the substorm activity. On the other hand, the multiscale magnetospheric dynamics cannot be limited to the features of self-organized criticality (SOC), which is based on a class of mathematical analogs of sandpiles. Like real sandpiles, during substorms the magnetosphere demonstrates features, that are distinct from SOC and are closer to those of conventional phase transitions. While the multiscale substorm activity resembles second-order phase transitions, the largest substorm avalanches are shown to reveal the features of first-order nonequilibrium transitions including hysteresis phenomena and a global structure of the type of a temperature-pressure-density diagram. Moreover, this diagram allows one to find a critical exponent, that reflects the multiscale aspect of the substorm activity, different from the power-law frequency and scale spectra of autonomous systems, although quite consistent with second-order phase transitions. In contrast to SOC exponents, this exponent relates input and output parameters of the magnetosphere. Using an analogy to the dynamical Ising model in the mean-field approximation, we show the connection between the data-derived exponent of nonequilibrium transitions in the magnetosphere and the standard critical exponent beta of equilibrium second-order phase transitions.
Understanding the origin and acceleration of magnetospheric relativistic electrons (MREs) in the Earth's radiation belt during geomagnetic storms is an important subject and yet one of outstanding questions in space physics. It has been statistically suggested that during geomagnetic storms, ultra‐low‐frequency (ULF) Pc‐5 wave activities in the magnetosphere are correlated with order of magnitude increase of MRE fluxes in the outer radiation belt. Yet, physical and observational understandings of resonant interactions between ULF waves and MREs remain minimum. In this paper, we show two events during storms on September 25, 2001 and November 25, 2001, the solar wind speeds in both cases were >500 km s−1 while Cluster observations indicate presence of strong ULF waves in the magnetosphere at noon and dusk, respectively, during a∼3‐hour period. MRE observations by the Los Alamos (LANL) spacecraft show a quadrupling of 1.1–1.5 MeV electron fluxes in the September 25, 2001 event, but only a negligible increase in the November 25, 2001 event. We present a detailed comparison between these two events. Our results suggest that the effectiveness of MRE acceleration during the September 25, 2001 event can be attributed to the compressional wave mode with strong ULF wave activities and the physical origin of MRE acceleration depends more on the distribution of toroidal and poloidal ULF waves in the outer radiation belt.
The working group on magnetospheric research covered a variety of science issues in solar wind - magnetosphere- ionosphere coupling, with emphasis on geospace storms. The papers were presented in three oral sessions and a poster session, and were summarized for other working groups in two plenary sessions, which also served as forums for discussing cross- disciplinary issues. Among the plenary talks at the workshop at least six were on topics directly related to the magnetosphere. The panel discussion on future collaborations also featured many areas involving studies of the magnetosphere.
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