Interplay of source/seed electrons and wave-particle interactions in producing relativistic electron PSD enhancements in the outer Van Allen belt

We perform a superposed epoch analysis on two groups of selected geospace disturbance events, emerging from single and isolated interplanetary drivers, and resulting in either the enhancement or the depletion of the average relativistic electron Phase Space Density (PSD). We investigate the occurrence of behavioural/temporal patterns of solar wind and geomagnetic parameters, chorus and ULF Pc5 wave activity, and the source/seed electron PSD in the outer Van Allen radiation belt. Our results indicate that the source electron population of μ = 10 MeV/G exhibits a similar behaviour during both event groups, while the μ = 1 MeV/G population can be considered as negligible for the whole process of wave excitation and electron energisation. Moreover, events that result in relativistic electron enhancement are characterised by statistically stronger and prolonged storm, substorm and wave activity, combined with an abundance of seed electrons of μ = 100 MeV/G, mostly at L* = 4–5, the nominal heart of the outer radiation belt.First author draf

Empirical Model of the Inner Magnetosphere H+ Pitch Angle Distributions

An empirical model is presented in order to describe the pitch angle distributions of H+ particles in inner magnetosphere. The data analysis is based on three-year observations made by the AMPTE/CCE/CHEM instrument in the energy range 1-300 keV and in the L-shell range 3-9, using the average proton fluxes with AE < 100 nT. The model consists of a multi-parametric functional form, that depends on pitch angle, energy, L-shell and a few independent factors. The factors are determined for every magnetic local time. This is the first model, able to accurately reproduce the average proton pitch angle distributions in the whole inner magnetosphere, revealing interesting statistical features. Many of these features have been already evidenced by previous studies and can be explained by processes theoretically interpreted. Furthermore, the model outlines some new features never analyzed before

Geomagnetic storm dependence on the solar flare class

Content. Solar flares are often used as precursors of geomagnetic storms. In particular, Howard and Tappin (2005) recently published in A&A a dependence between X-ray class of solar flares and Ap and Dst indexes of geomagnetic storms which contradicts to early published results. Aims. We compare published results on flare-storm dependences and discuss possible sources of the discrepancy. Methods. We analyze following sources of difference: (1) different intervals of observations, (2) different statistics and (3) different methods of event identification and comparison. Results. Our analysis shows that magnitude of geomagnetic storms is likely to be independent on X-ray class of solar flares.Comment: 3 pages, 1 tabl

Complex systems methods characterizing nonlinear processes in the near-Earth electromagnetic environment: recent advances and open challenges

Learning from successful applications of methods originating in statistical mechanics, complex systems science, or information theory in one scientific field (e.g., atmospheric physics or climatology) can provide important insights or conceptual ideas for other areas (e.g., space sciences) or even stimulate new research questions and approaches. For instance, quantification and attribution of dynamical complexity in output time series of nonlinear dynamical systems is a key challenge across scientific disciplines. Especially in the field of space physics, an early and accurate detection of characteristic dissimilarity between normal and abnormal states (e.g., pre-storm activity vs. magnetic storms) has the potential to vastly improve space weather diagnosis and, consequently, the mitigation of space weather hazards. This review provides a systematic overview on existing nonlinear dynamical systems-based methodologies along with key results of their previous applications in a space physics context, which particularly illustrates how complementary modern complex systems approaches have recently shaped our understanding of nonlinear magnetospheric variability. The rising number of corresponding studies demonstrates that the multiplicity of nonlinear time series analysis methods developed during the last decades offers great potentials for uncovering relevant yet complex processes interlinking different geospace subsystems, variables and spatiotemporal scales

The Earth: Plasma Sources, Losses, and Transport Processes

This paper reviews the state of knowledge concerning the source of magnetospheric plasma at Earth. Source of plasma, its acceleration and transport throughout the system, its consequences on system dynamics, and its loss are all discussed. Both observational and modeling advances since the last time this subject was covered in detail (Hultqvist et al., Magnetospheric Plasma Sources and Losses, 1999) are addressed

On the Statistics of Acceleration and Loss of Relativistic Electrons in the Outer Radiation Belt: A Superposed Epoch Analysis

We investigate the response of the outer Van Allen belt electrons to various types of solar wind and magnetospheric disturbances. We use electron phase space density calculations as well as concurrent Pc5 and chorus wave activity observations in the outer belt during the Van Allen Probes era to compare 20 electron enhancement and 8 depletion events. Results indicate that the combined effect of magnetopause shadowing and outward diffusion driven by Pc5 waves is present in both groups of events. Furthermore, in the case of enhancement events, the synergy of enhanced seed population levels and chorus activity—due to the enhanced substorm activity—can effectively replenish the losses of relativistic electrons, while inward diffusion can further accelerate them. ©2019. American Geophysical Union. All Rights Reserved

Development of an operational modeling system for urban heat islands: An application to Athens, Greece

The urban heat island (UHI) effect is one prominent form of localized anthropogenic climate modification. It represents a significant urban climate problem since it occurs in the layer of the atmosphere where almost all daily human activities take place. This paper presents the development of a high-resolution modeling system that could be used for simulating the UHI effect in the context of operational weather forecasting activities. The modeling system is built around a state-of-the-art numerical weather prediction model, properly modified to allow for the better representation of the urban climate. The model performance in terms of simulating the near-surface air temperature and thermal comfort conditions over the complex urban area of Athens, Greece, is evaluated during a 1.5-month operational implementation in the summer of 2010. Results from this case study reveal an overall satisfactory performance of the modeling system. The discussion of the results highlights the important role that, given the necessary modifications, a meteorological model can play as a supporting tool for developing successful heat island mitigation strategies. This is further underlined through the operational character of the presented modeling system. © Author(s) 2014

Modeling of ion dynamics in the inner geospace during enhanced magnetospheric activity

We investigate the effect of magnetic disturbances on the ring current buildup and the dynamics of the current systems in the inner geospace by means of numerical simulations of ion orbits during enhanced magnetospheric activity. For this purpose, we developed a particle-tracing model that solves for the ion motion in a dynamic geomagnetic field and an electric field due to convection, corotation and Faraday induction and which mimics reconfigurations typical to such events. The kinematic data of the test particles is used for analyzing the dependence of the system on the initial conditions, as well as for mapping the different ion species to the magnetospheric currents. Furthermore, an estimation of Dst is given in terms of the ensemble-averaged ring and tail currents. The presented model may serve as a tool in a Sun-to-Earth modeling chain of major solar eruptions, providing an estimation of the inner geospace response. © 2016 Author(s)