Solar Wind-magnetosphere Interaction Research Articles

Information measures based analysis of complex solar wind—magnetosphere interaction dynamics during geomagnetic storms

By calculating the complexity measures such as approximate entropy, sample entropy, algorithmic complexity and permutation entropy of auroral and polar cap index time series, it can be determined whether or not these show similar regularity of underlying solar wind—magnetosphere interaction dynamics. The complexity profiles of magnetospheric indices and coupling coefficients for 45 geomagnetic storm time events of solar cycle 23 using a correlation-based characterisation in the nonlinear regime are explored. Using a sliding window method, we study the variation in permutation entropy of magnetospheric response, which exhibits a high degree of dynamical complexity associated with different features during calm and storm periods.

Challenges in Measuring External Currents Driven by the Solar Wind-Magnetosphere Interaction

In studying the Earth's geomagnetism, it has always been a challenge to separate magnetic fields from external currents originating from the ionosphere and magnetosphere. While the internal magnetic field changes very slowly in time scales of years and more, the ionospheric and magnetospheric current systems driven by the solar wind -magnetosphere interaction are very dynamic. They are intimately controlled by the ionospheric electrodynamics and ionospheremagnetosphere coupling. Single spacecraft observations are not able to separate their spatial and temporal variations, and thus to accurately describe their configurations. To characterize and understand the external currents, satellite observations require both good spatial and temporal resolutions. This paper reviews our observations of the external currents from two recent LEO satellite missions: Space Technology 5 (ST-5), NASA's first three-satellite constellation mission in LEO polar orbit, and Communications/Navigation Outage Forecasting System (C/NOFS), an equatorial satellite developed by US Air Force Research Laboratory. We present recommendations for future geomagnetism missions based on these observations.

Short-term periodicities in interplanetary, geomagnetic and solar phenomena during solar cycle 24

In this paper we study the quasi-periodic variations of sunspot area/number, 10.7 cm solar radio flux, Average Photospheric Magnetic Flux, interplanetary magnetic field (B z ) and the geomagnetic activity index A p during the ascending phase of the current solar cycle 24. We use both Lomb-Scargle periodogram and wavelet analysis technique and find evidence for a multitude of quasi-periodic oscillations in all the data sets. In high frequency range (10 days to 100 days), both methods yield similar significance periodicities around 20–35 days and 45–60 days in all data sets. In the case of intermediate range, the significant periods were around 100–130 days, 140–170 days and 180–240 days The Morlet wavelet power spectrum shows that all of the above-mentioned periods are intermittent in nature. We find that the well-known “Rieger period” of (150–160 days) and near Rieger periods (130–190 days) were significant in both solar, interplanetary magnetic field and geomagnetic activity data sets during cycle 24. The geomagnetic activity is the result of the solar wind-magnetosphere interaction. Thus the variations in the detected periodicity in variety of solar, interplanetary and geomagnetic indices could be helpful to improve our knowledge of the inter-relationship between various processes in the Sun-Earth-Heliosphere system.

A survey of solar wind conditions at 5 AU: a tool for interpreting solar wind-magnetosphere interactions at Jupiter

We examine Ulysses solar wind and interplanetary magnetic field (IMF) observations at 5 AU for two ~13 month intervals during the rising and declining phases of solar cycle 23 and the predicted response of the Jovian magnetosphere during these times. The declining phase solar wind, composed primarily of corotating interaction regions and high-speed streams, was, on average, faster, hotter, less dense, and more Alfvenic relative to the rising phase solar wind, composed mainly of slow wind and interplanetary coronal mass ejections. Interestingly, none of solar wind and IMF distributions reported here were bimodal, a feature used to explain the bimodal distribution of bow shock and magnetopause standoff distances observed at Jupiter. Instead, many of these distributions had extended, non-Gaussian tails that resulted in large standard deviations and much larger mean over median values. The distribution of predicted Jupiter bow shock and magnetopause standoff distances during these intervals were also not bimodal, the mean/median values being larger during the declining phase by ~1 – 4%. These results provide data-derived solar wind and IMF boundary conditions at 5 AU for models aimed at studying solar wind-magnetosphere interactions at Jupiter and can support the science investigations of upcoming Jupiter system missions. Here, we provide expectations for Juno, which is scheduled to arrive at Jupiter in July 2016. Accounting for the long-term decline in solar wind dynamic pressure reported by McComas et al. (2013), Jupiter’s bow shock and magnetopause is expected to be at least 8 – 12% further from Jupiter, if these trends continue.

A neural network Dst index model driven by input time histories of the solar wind–magnetosphere interaction

A model to forecast 1-hour lead Dst index is proposed. Our approach is based on artificial neural networks (ANN) combined with an analytical model of the solar wind–magnetosphere interaction. Previously, the hourly solar wind parameters have been considered in the analytical model, all of them provided by registration of the ACE satellite. They were the solar wind magnetic field component Bz, velocity V, particle density n and temperature T. The solar wind parameters have been used to compute analytically the discontinuity in magnetic field across the magnetopause, denoted as [Bt]. This quantity has been shown to be important in connection with ground magnetic field variations. The method was published, in which the weighted sum of a sequence of [Bt] was proposed to produce the value of Dst index. The maximum term in the sum, possessing the maximum weight, is the one denoting the contribution of the current state of the near-Earth solar wind. The role of the older states is less important – the weights exponentially decay. Moreover, the terms turn to zero if Bz⪯¡0. In this study, we set up a more comprehensive model on the basis of the ANNs. The model is driven by input time histories of the discontinuity in magnetic field [Bt], which are provided by the analytical model. At the output of such revised model, the Dst index is obtained and compared with the real data records. In this way we replaced those exponential weights in the published method with another set of weights determined by the neural networks. We retrospectively tested our models with real data from solar cycle 23. The ANN approach provided better results than a simple method based on exponentially decaying weights. Moreover, we have shown that our ANN model could be used to predict Dst 1h ahead. We assessed the predictive capability of the model with a set of independent events and found correlation coefficient CC=0.74±0.13 and prediction efficiency PE=0.44±0.15. We also compared our model with the so-called Dst-specification models. In those models, the Dst index was derived directly through an analytic or iterative formula or a neural network-based algorithm. We showed that the performance of our model was comparable to that of Dst-specification models.

Response of magnetic fields at geosynchronous orbit and on the ground to the sudden changes of IMF B Z

The rapid change in the Earth’s magnetosphere caused by solar wind disturbances has been an important part of the solar wind-magnetosphere interaction. However most of the previous studies focused on the perturbation of the Earth’s magnetic field caused by solar wind dynamic pressure changes. In this paper, we studied the response of geosynchronous magnetic field and the magnetic field to the rapid southward turning of interplanetary magnetic field during the interval 1350–1420 UT on 7 May 2007. During this event, BZ component of the interplanetary magnetic field decreased from 15 nT to −10 nT within 3 min (1403–1406 UT). The geosynchronous magnetic field measured by three geosynchronous satellites (GOES 10–12) first increased and then decreased. The variations of magnetic field strength in the morning sector (9–10 LT) were much larger than those in the dawn sector (5 LT). Meanwhile, the H components of geomagnetic field on the ground have similar response features but exhibit latitude and LT dependent variations. Compared with H components, the D components do not have regular variations. Although the solar wind dynamical pressure encounters small variations, the magnetic field both in space and on the ground does not display similar variations. Therefore, the increase of geomagnetic field in the dawn sector is caused by the southward turning of IMF (interplanetary magnetic field) BZ. These results will help to better understand the coupling process of geomagnetic filed and interplanetary magnetic field.

Imaging Earth's plasmasphere at 30.4nm

Extreme Ultraviolet (EUV) imaging has the strong potential to provide the global observations needed to tie together the numerous in situ measurements made by a host of Earth orbiting satellites. First, EUV imaging can capture the dayside solar wind magnetosphere (SWM) interaction that defines the energy input to the system. As the solar wind encounters the dayside magnetopause (see Figure 1), charge exchange between solar wind α particles (He ions) and the neutral exosphere produces a 30.4 nm emission that ranges from 0.25 milliRayleighs (during nominal conditions) to 6 Rayleighs (during disturbed conditions). We know that this solar wind energy input carries field lines over the polar caps to the nightside, where explosive substorms produce an earthward (or sunward) return flow that erodes the plasmasphere, causing the formation of sunward-pointing dayside plumes. These plumes can transport away 30-100 tons of magnetospheric plasma (approximately 20-40% of the initial He distribution) in just a few hours. The Extreme Ultraviolet Imager aboard NASA's Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) captured the erosion process with 10-minute resolution. An improved EUV imager that could capture erosion with 1-minute time resolution would answer many outstanding questions about the mechanics of the removal of so much plasma. Secondly, theoretical models and some observations suggest that the arrival of tons of dense plasma at the magnetopause may reduce or suppress the solar wind energy input; i.e., feedback from the magnetosphere can squelch the SWM interaction. Finally, we know from the IMAGE mission that EUV filtered imaging also captures the Far Ultraviolet (FUV) aurora, which is a measure of the overall time-dependent strength of the SWM interaction.

Global magnetohydrodynamic simulations on multiple GPUs

Global magnetohydrodynamic (MHD) models play the major role in investigating the solar wind–magnetosphere interaction. However, the huge computation requirement in global MHD simulations is also the main problem that needs to be solved. With the recent development of modern graphics processing units (GPUs) and the Compute Unified Device Architecture (CUDA), it is possible to perform global MHD simulations in a more efficient manner. In this paper, we present a global magnetohydrodynamic (MHD) simulator on multiple GPUs using CUDA 4.0 with GPUDirect 2.0. Our implementation is based on the modified leapfrog scheme, which is a combination of the leapfrog scheme and the two-step Lax–Wendroff scheme. GPUDirect 2.0 is used in our implementation to drive multiple GPUs. All data transferring and kernel processing are managed with CUDA 4.0 API instead of using MPI or OpenMP. Performance measurements are made on a multi-GPU system with eight NVIDIA Tesla M2050 (Fermi architecture) graphics cards. These measurements show that our multi-GPU implementation achieves a peak performance of 97.36 GFLOPS in double precision.

ULF wave index as magnetospheric and space-weather parameters

Waves in the Ultra Low Frequency (ULF) band owe their existence to solar wind turbulence and transport momentum and energy from the solar wind to the magnetosphere and farther down. Therefore an index based on ULF wave power could better characterize solar wind–magnetosphere interaction than KP, Dst, AE, etc. indices which described mainly quasi-study state condition of the system. We have shown that the ULF wave index accurately characterize relativistic electron dynamics in the magnetosphere as these waves are closely associated with circulation, diffusion and energization of relativistic electrons in the magnetosphere. High speed solar wind streams also act as a significant driver of activity in the Earth’s magnetosphere co-rotating interaction region and are responsible for geomagnetic activities. In the present paper, we have analyzed various cases related with very weak (quiet) days, weak days, storm days and eclipse events and discussed the utility of the ULF wave index to explain the magnetospheric dynamics and associated properties. We have tried to explain that the ULF wave index can equally be useful as a space weather parameter like the other indices.

Probing IMF using nanodust measurements from inside Saturn's magnetosphere

[1] We present a new concept of monitoring the interplanetary magnetic field (IMF) by using in situ measurements of nanodust stream particles in Saturn's magnetosphere. We show that the nanodust detection pattern obtained inside the magnetosphere resembles those observed in interplanetary space and is associated with the solar wind compression regions. Our dust dynamics model reproduces the observed nanodust dynamical properties as well as the detection pattern, suggesting that the ejected stream particles can reenter Saturn's magnetosphere at certain occasions due to the dynamical influence from the time-varying IMF. This method provides information on the IMF direction and a rough estimation on the solar wind compression arrival time at Saturn. Such information can be useful for studies related to the solar wind-magnetosphere interactions, especially when the solar wind parameters are not directly available.

Features of the interaction of interplanetary coronal mass ejections/magnetic clouds with the Earth's magnetosphere

The interaction of interplanetary coronal mass ejections (ICMEs) and magnetic clouds (MCs) with the Earth's magnetosphere exhibits various interesting features principally due to interplanetary parameters which change slowly and reach extreme values of long duration. These, in turn, allow us to explore the geomagnetic response to continued and extreme driving of the magnetosphere. In this paper we shall discuss elements of the following: (i) anomalous features of the flow in the terrestrial magnetosheath during ICME/MC passage and (ii) large geomagnetic disturbances when total or partial mergers of ICMEs/MCs pass Earth. In (i) we emphasize two roles played by the upstream Alfvén Mach number in solar wind–magnetosphere interactions: (i) It gives rise to wide plasma depletion layers. (ii) It enhances the magnetosheath flow speed on draped magnetic field lines. (By plasma depletion layer we mean a magnetosheath region adjacent to the magnetopause where magnetic forces dominate over hydrodynamic forces.) In (ii) we stress that the ICME mergers elicit geoeffects over and above those of the individual members. In addition, features of the non-linear behavior of the magnetosphere manifest themselves.

Deep Solar Activity Minimum 2007 – 2009: Solar Wind Properties and Major Effects on the Terrestrial Magnetosphere

We discuss the temporal variations and frequency distributions of solar wind and interplanetary magnetic field parameters during the solar minimum of 2007 – 2009 from measurements returned by the IMPACT and PLASTIC instruments on STEREO-A. We find that the density and total field strength were significantly weaker than in the previous minimum. The Alfvén Mach number was higher than typical. This reflects the weakness of magnetohydrodynamic (MHD) forces, and has a direct effect on the solar wind–magnetosphere interactions. We then discuss two major aspects that this weak solar activity had on the magnetosphere, using data from Wind and ground-based observations: i) the dayside contribution to the cross-polar cap potential (CPCP), and ii) the shapes of the magnetopause and bow shock. For i) we find a low interplanetary electric field of 1.3±0.9 mV m−1 and a CPCP of 37.3±20.2 kV. The auroral activity is closely correlated to the prevalent stream–stream interactions. We suggest that the Alfvén wave trains in the fast streams and Kelvin–Helmholtz instability were the predominant agents mediating the transfer of solar wind momentum and energy to the magnetosphere during this three-year period. For ii) we determine 328 magnetopause and 271 bow shock crossings made by Geotail, Cluster 1, and the THEMIS B and C spacecraft during a three-month interval when the daily averages of the magnetic and kinetic energy densities attained their lowest value during the three years under survey. We use the same numerical approach as in Fairfield’s (J. Geophys. Res. 76, 7600, 1971) empirical model and compare our findings with three magnetopause models. The stand-off distance of the subsolar magnetopause and bow shock were 11.8 R E and 14.35 R E, respectively. When comparing with Fairfield’s (1971) classic result, we find that the subsolar magnetosheath is thinner by ∼1 R E. This is mainly due to the low dynamic pressure which results in a sunward shift of the magnetopause. The magnetopause is more flared than in Fairfield’s model. By contrast the bow shock is less flared, and the latter is the result of weaker MHD forces.

An adaptive information technology for the operative diagnostics of the tropical cyclones; solar–terrestrial coupling mechanisms

The tools of sequential analysis and percolation theory are herewith used to study the transition processes in the coupled ocean–atmosphere system. To accomplish this aim the recently proposed instability indicator for the detection of the characteristics of the state for this system, is utilized. In more detail, the case of the transition processes for Baltic Sea assessed by the Beaufort Scale is examined by investigating the efficiency of the afore-mentioned indicator.We show that the crucial parameter is not the energy source, like the solar radiation, but the energy conversion. Numerical experiments conducted herewith showed that such an indicator facilitates the monitoring of the variability and direction of transition processes in the oceans, and is capable to predict a remarkable change of the ocean–atmosphere system states. It is finally shown that the combination of sequential and cluster analysis with the percolation procedure allows for the detection of a tropical hurricane up to three days in advance of its start. The tool presented may also be applied to the development of relevant indicators for the predictions of magnetosphere–ionosphere–thermosphere coupling and the solar wind–magnetosphere interactions. Finally, future problems on the subject are discussed.

Wavelet Analysis on Solar Wind Parameters and Geomagnetic Indices

The geomagnetic activity is the result of the solar wind–magnetosphere interaction. It varies following the basic 11-year solar cycle; yet shorter time-scale variations appear intermittently. We study the quasi-periodic behavior of the characteristics of solar wind (speed, temperature, pressure, density) and the interplanetary magnetic field (B x , B y , B z , β, Alfvén Mach number) and the variations of the geomagnetic activity indices (D ST, AE, A p and K p). In the analysis of the corresponding 14 time series, which span four solar cycles (1966 – 2010), we use both a wavelet expansion and the Lomb/Scargle periodograms. Our results verify intermittent periodicities in our time-series data, which correspond to already known solar activity variations on timescales shorter than the sunspot cycle; some of these are shared between the solar wind parameters and geomagnetic indices.

Auroral forms that extend equatorward from the persistent midday aurora during geomagnetically quiet periods

Auroral forms (“crewcuts”) that extend equatorward from the geomagnetically east–west aligned persistent midday aurora have been characterized based on a survey of Svalbard 630.0-nm all-sky images from eight December solstice seasons. The 630.0-nm forms are directly related to a mix of precipitating magnetosheath and plasma sheet electrons embedded in a population of boundary layer ions, as observed by NOAA 6. The associated midday aurora lies at the equatorward edge of poleward velocity-dispersed cusp ‘ion plumes’ observed by DMSP F7 at 1000 magnetic local time. In this survey, crewcuts are found to occur for Kp≤3. Distinct in many salient ways (including dynamics, orientation and associated IMF polarity) from the poleward-moving auroral forms (PMAFs) associated with transient dayside merging, crewcuts represent a solar wind-magnetosphere interaction that is more characteristic of quiet geomagnetic conditions. Crewcuts are present on 44% of the days for which all-sky images are complete and observing conditions are clear ±1.5h around geomagnetic noon. During these periods, crewcuts are observed during 10.6% of the minutes for which IMF data from ISEE 2 or IMP 8 are available. We derive from the data a simple set of IMF “search criteria” that maximize the likelihood of observing crewcuts around the December solstice. The IMF magnitude range for which crewcuts are most commonly observed is 3.5±0.5nT (36%). The IMF GSM component ranges in which crewcuts are most commonly observed are: Bx=−3.5±0.5nT (27%), By=−1.5±0.5nT (25%), and Bz=0.5±0.5nT (26%). The IMF clock angular ranges for which crewcuts are most commonly observed are −70°±10° and 90°±10° (both 21%). The IMF cone angular range for which crewcuts are most commonly observed is 12.5°±2.5° (28%). Considering these observations in the context of magnetic merging topologies, we suggest crewcuts observed at Svalbard are most likely to lie at the foot of overdraped field lines recently opened by spatially patchy, quasi-steady merging in the southern hemisphere.

Solar wind charge exchange during geomagnetic storms

AbstractOn 2001 March 31 a coronal mass ejection pushed the subsolar magnetopause to the vicinity of geosynchronous orbit at 6.6 RE. The NASA/GSFC Community Coordinated Modeling Center (CCMC) employed a global magnetohydrodynamic (MHD) model to simulate the solar wind‐magnetosphere interaction during the peak of this geomagnetic storm. Robertson et al. then modeled the expected soft X‐ray emission due to solar wind charge exchange with geocoronal neutrals in the dayside cusp and magnetosheath. The locations of the bow shock, magnetopause and cusps were clearly evident in their simulations. Another geomagnetic storm took place on 2000 July 14 (Bastille Day). We again modeled X‐ray emission due to solar wind charge exchange, but this time as observed from a moving spacecraft. This paper discusses the impact of spacecraft location on observed X‐ray emission and the degree to which the locations of the bow shock and magnetopause can be detected in images (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

European Project to Improve Models of Geomagnetically Induced Currents

Geomagnetically induced currents (GICs) from solar storms pose a risk to the operation of power transmission grids in Europe and across the globe. The European Risk from Geomagnetically Induced Currents (EURISGIC) project, which began in March 2011 and is supported by the Seventh Framework Programme of the European Union, seeks to mitigate this natural hazard by developing European capabilities for GIC forecasting and warning. Recent well-recognized GIC events were the province-wide blackout in Quebec, Canada, in March 1989 and the blackout in the city of Malmö, in southern Sweden, during the Halloween storm of October 2003. The progressive integration of interconnected and geographically wide power transmission grids is obviously increasing the GIC risk. Hence, there is a need for greater scientific understanding of phenomena in the solar-terrestrial environment that lead to GICs and for the development of systems that facilitate GIC modeling, forecasting, and mitigation. Within the EURISGIC project the flow of GICs throughout the European grid for hypothetical and real events will be simulated using improved grid network models and conductivity models for the continent. The project will produce the first Europe-wide real-time prototype forecast service of GICs in high-voltage power systems, based on in situ solar wind observations by the Advanced Composition Explorer (ACE) spacecraft, empirical modeling, and comprehensive simulations of Earth's magnetosphere. Moreover, on the basis of long-term geomagnetic recordings, EURISGIC will derive the first map of the statistical risk of large GICs throughout Europe. Of special interest is a search for untapped data sources for the solar storm of September 1859, famously observed by British astronomer Richard Carrington, which is often referred to as the most intense geomagnetic storm ever recorded. The project aims to assist European scientists as they strive for 30- to 60-minute lead time forecasts of GIC events. There is presently only one European magnetohydrodynamic code for global simulations of the solar wind-magnetosphere interaction, namely, Grand Unified Magnetosphere-Ionosphere Coupling Simulation (GUMICS-4), developed at the Finnish Meteorological Institute. During EURISGIC, GUMICS-4 will be upgraded to be able to produce real-time GIC forecasts. For this development, EURISGIC will obtain valuable contributions from the U.S. expertise gained from NASA's Solar Shield project (http://ccmc.gsfc.nasa.gov/Solar_Shield/). The U.S. and European codes will run in parallel to produce GIC forecasts in Europe, and they will also stimulate further improvements in simulations. Calculation of GICs in a given power grid is a straightforward problem, which has been considered in several previous national studies, for example, in Finland, Sweden, and the United Kingdom. The key problem is to determine the geoelectric field that drives GICs in power grids. This electric field can be calculated from the measured magnetic field using models of the Earth's conductivity. A special challenge for EURISGIC is to compile a simplified conductivity map of Europe that enables efficient computation of Europe's electric field. When the geoelectric field is known, calculation of GICs in a power grid is reduced to a simple direct current (DC) mathematical problem. In combination, early warning forecasts, risk maps, and worst-case-scenario assessments provided by EURISGIC will contribute to mitigating the risks that GICs represent, thereby avoiding destruction of transformers and enhancing the protection of critical infrastructure in Europe and elsewhere in the world. The project began in March 2011 and will last until February 2014. The Finnish Meteorological Institute is the coordinator, with Ari Viljanen as the coordinating person. Other European Union partners come from Hungary, Sweden, and the United Kingdom. In addition, Russia and the United States belong to the consortium, ensuring the best global GIC expertise within the team. An external group of advisors representing power engineering, education, and space weather services will provide independent reviewing and suggestions to help the consortium reach its ambitious goals. EURISGIC is funded by the Seventh Framework Programme of the European Union (Project 260330). The EURISGIC Web site is http://www.eurisgic.eu. The following are members of the consortium, with their representatives given in parentheses: Finnish Meteorological Institute, Finland (Ari Viljanen); British Geological Survey/Natural Environment Research Council, United Kingdom (Alan Thomson); NeuroSpace, Sweden (Magnus Wik); Swedish Institute of Space Physics, Sweden (Peter Wintoft); Geodetic and Geophysical Research Institute, Hungary (Viktor Wesztergom); Polar Geophysical Institute, Russia (Yaroslav Sakharov); and Catholic University of America, United States (Antti Pulkkinen). Ari Viljanen is a senior scientist at the Finnish Meteorological Institute, in Helsinki, Finland. E-mail: [email protected]

The role of the bow shock in solar wind-magnetosphere coupling

Abstract. In this paper we examine the role of the bow shock in coupling solar wind energy to the magnetosphere using global magnetohydrodynamic simulations of the solar wind-magnetosphere interaction with southward IMF. During typical solar wind conditions, there are two significant dynamo currents in the magnetospheric system, one in the high-latitude mantle region tailward of the cusp and the other in the bow shock. As the magnitude of the (southward) IMF increases and the solar wind becomes a low Mach number flow, there is a significant change in solar wind-magnetosphere coupling. The high-latitude magnetopause dynamo becomes insignificant compared to the bow shock and a large load appears right outside the magnetopause. This leaves the bow shock current as the only substantial dynamo current in the system, and the only place where a significant amount of mechanical energy is extracted from the solar wind. That energy appears primarily as electromagnetic energy, and the Poynting flux generated at the bow shock feeds energy back into the plasma, reaccelerating it to solar wind speeds. Some small fraction of that Poynting flux is directed into the magnetosphere, supplying the energy needed for magnetospheric dynamics. Thus during periods when the solar wind flow has a low Mach number, the main dynamo in the solar wind-magnetosphere system is the bow shock.

Prediction of magnetic substorms using a state space model

Nonlinear dynamical models of the magnetosphere derived from observational time series data using phase space reconstruction techniques have yielded new advances in the understanding of its dynamics. Considering the solar wind–magnetosphere interaction to be a natural input–output system its dynamical features can be reconstructed on the storm time scale by using the method of time delay embedding. Here, fourteen magnetic storm intervals belonging to low/moderate and high solar activity periods are considered and a suitable state space model has designed by performing training and validation tests, for which dawn to dusk electric field (VBz) is chosen as the input, and the AL time series as the output. The percentage of the output variations that is reproduced by the model is termed as fit_model and a higher number of fit_model means a better model. The number of components m used in the state space model is varied from 1–9 and the best prediction is obtained when m=4. The fit_model values of time series used for validation are 67.96, 67.2, 72.44, and 70.89, with m=4. In the present study most of the storms considered are having Dstmax in between −100 and −300nT, and they can be predicted well with this procedure. To reveal the prediction capability of the proposed state space model the 30 steps ahead outputs for the storm events are generated, which reasonably reproduce the observed values.

Dynamic polarization random walk model and fishbone-like instability for self-organized critical systems

We study the phenomenon of self-organized criticality (SOC) as a transport problem for electrically charged particles. A model for SOC based on the idea of a dynamic polarization response with random walks of the charge carriers gives critical exponents consistent with the results of numerical simulations of the traditional ‘sandpile’ SOC models, and stability properties, associated with the scaling of the control parameter versus distance to criticality. Relaxations of a supercritical system to SOC are stretched-exponential similar to the typically observed properties of non-Debye relaxation in disordered amorphous dielectrics. Overdriving the system near self-organized criticality is shown to have a destabilizing effect on the SOC state. This instability of the critical state constitutes a fascinating nonlinear system in which SOC and nonlocal properties can appear on an equal footing. The instability cycle is qualitatively similar to the internal kink (‘fishbone’) mode in a magnetically confined toroidal plasma where beams of energetic particles are injected at high power, and has serious implications for the functioning of complex systems. Theoretical analyses, presented here, are the basis for addressing the various patterns of self-organized critical behavior in connection with the strength of the driving. The results of this work also suggest a type of mixed behavior in which the typical multi-scale features due to SOC can coexist along with the global or coherent features as a consequence of the instability present. An example of this coexistence is speculated for the solar wind–magnetosphere interaction.