The phenomenon of plasmasphere refilling, and general considerations of plasmasphere structure and plasmasphere‐ionosphere coupling, have received increased attention in recent years in terms of both observational considerations and modeling investigations. New ideas arising from both observations and modeling efforts are revealing the refilling region to be rich in intriguing physical processes, including hot‐cold plasma interactions through wave‐particle effects and Coulomb collisions, electrostatic shocks, and differences in light and heavy ion behavior during refilling. “Global” observational and modeling studies of the plasmasphere structure are in the process of demonstrating the complex manner in which refilling and the spatial and temporal variations of convection interplay to produce complex structure in the plasmasphere; these studies are particularly timely as they could be extremely helpful for interpreting results from proposed imaging of plasmaspheric He+. This review will serve to highlight the observational and theoretical/modeling progress during the past few years as well as to introduce and place in context the particular contributions contained in this special section.

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Abstract.One of the interesting observations from the FAST satellite is the detection of strong spiky waveforms in the parallel electric field in association with ion cyclotron oscillations in the perpendicular electric fields. We report here an analytical model of the coupled nonlinear ion cyclotron and ion-acoustic waves, which could explain the observations. Using the fluid equations for the plasma consisting of warm electrons and cold ions, a nonlinear wave equation is derived in the rest frame of the propagating wave for any direction of propagation oblique to the ambient magnetic field. The equilibrium bulk flow of ions is also included in the model to mimic the field-aligned current. Depending on the wave Mach number M defined by M = V /C s with V and C s being the wave phase velocity and ion-acoustic speed, respectively, we find a range of solutions varying from a sinusoidal wave form for small amplitudes and low M to sawtooth and highly spiky waveforms for nearly parallel propagation. The results from the model are compared with the satellite observations.

Generating credible climate change and extremes projections remains a high-priority challenge, especially since recent observed emissions are above the worst-case scenario. Bias and uncertainty analyses of ensemble simulations from a global earth systems model show increased warming and more intense heat waves combined with greater uncertainty and large regional variability in the 21st century. Global warming trends are statistically validated across ensembles and investigated at regional scales. Observed heat wave intensities in the current decade are larger than worst-case projections. Model projections are relatively insensitive to initial conditions, while uncertainty bounds obtained by comparison with recent observations are wider than ensemble ranges. Increased trends in temperature and heat waves, concurrent with larger uncertainty and variability, suggest greater urgency and complexity of adaptation or mitigation decisions.climate change ͉ extremes ͉ regional analysis R ecent observations of global-average emissions (1, 2) show higher trajectories than the worst-case A1FI scenario reported in IPCC AR4 (3). Average A1FI temperatures (1, 4) trend higher than the best-case B1 as well as the relatively worse-case A2 scenario (5). Model simulations, validated with observations, have pointed to more intense, longer lasting, and more frequent heat waves in the 21st century (6). However, a rigorous statistical validation of the increased global warming and heat waves, followed by an investigation of the trends at regional scales, is required for decision-makers and end-users. Larger trends in warming and extremes suggest a greater urgency to develop adaptation and mitigation strategies (7,8). On the other hand, a comprehensive assessment of the uncertainties and geographical variability provide an understanding of the tradeoff space for risk-informed decisions (9), which refers to different tactical or strategic options that may be available to a decisionmaker for climate change adaptation and mitigation. Uncertainty of climate model projections has been quantified (10-14) either by comparing model hindcasts with observations or by comparing an ensemble of simulations. However, hindcasts validate models after the fact and hence risk underestimating predictive ability (15), while ensembles may only capture specific aspects of the variability. Hence the reliable and timely analysis of evolving climate model projections, extremes, and uncertainty remains a challenge (16-21). ResultsStatistically Higher Warming Trends. First, we show that the globalaverage temperatures from the middle to end of the 21st century are likely to be higher than previously believed (3). This is suggested by the fact that recent observed emissions trend toward or above A1FI assumptions (1, 2). The fact that observed emissions are at or above the level of A1FI, or any given scenario, in the current decade may not be a compelling reason to support conclusions about temperature in the late 21st century, as the trends could change considerably...