Miguel Angel Hidalgo

PLASMA AND MAGNETIC FIELD INSIDE MAGNETIC CLOUDS: A GLOBAL STUDY

Data observed during spacecraft encounters with magnetic clouds have been extensively analyzed in the literature. Moreover, several models have been proposed for the magnetic topology of these events, and fitted to the observations. Although these interplanetary events present well-defined plasma features, none of those models have included a simultaneous analysis of magnetic field and plasma data. Using as a starting point a non-force-free model that we have developed previously, we present a global study of MCs that include both the magnetic field topology and the plasma pressure. In this paper we obtain the governing equations for both magnitudes inside a MC. The expressions deduced are fitted simultaneously to the measurements of plasma pressure and magnetic field vector. We perform an analysis of magnetic field and plasma WIND observations within several MCs from 1995 to 1998. The analysis is confined to four of these events that have high-quality data. Only in one fitting procedure we obtain the orientation of the magnetic cloud relative to the ecliptic plane and the current density of the plasma inside the cloud. We find that the equations proposed reproduce the experimental data quite well.

Magnetic Field Configuration Models and Reconstruction Methods for Interplanetary Coronal Mass Ejections

This study aims to provide a reference for different magnetic field models and reconstruction methods for interplanetary coronal mass ejections (ICMEs). To understand the differences in the outputs of these models and codes, we analyzed 59 events from the Coordinated Data Analysis Workshop (CDAW) list, using four different magnetic field models and reconstruction techniques; force-free fitting, magnetostatic reconstruction using a numerical solution to the Grad–Shafranov equation, fitting to a self-similarly expanding cylindrical configuration and elliptical, non-force-free fitting. The resulting parameters of the reconstructions for the 59 events are compared statistically and in selected case studies. The ability of a method to fit or reconstruct an event is found to vary greatly; this depends on whether the event is a magnetic cloud or not. We find that the magnitude of the axial field is relatively consistent across models, but that the axis orientation of the ejecta is not. We also find that there are a few cases with different signs of the magnetic helicity for the same event when we leave the boundaries free to vary, which illustrates that this simplest of parameters is not necessarily always clearly constrained by fitting and reconstruction models. Finally, we examine three unique cases in depth to provide a comprehensive idea of the different aspects of how the fitting and reconstruction codes work.

A Global Magnetic Topology Model for Magnetic Clouds. I.

In two previous papers, we presented a global model for the analysis of magnetic clouds (MCs), where the three components of the magnetic field were fitted to the corresponding Geocentric Solar Ecliptic experimental data, obtaining reliable information, for example, about the orientation of these events in the interplanetary medium. That model, due to its non-force-free character, (∇p ≠ 0), could be extended to determine the plasma behavior. In the present work, we develop that extension, now including the plasma behavior inside the cloud through the analysis of the plasma pressure, and define a fitting procedure where the pressure and the magnetic field components are fitted simultaneously. After deducing the magnetic field topology and the current density components of the model, we calculate the expression of the pressure tensor and, in particular, its trace. In light of the results, we conclude that incorporating the plasma behavior in the analysis of the MCs can give us a better scenario in which to understand the physical mechanisms involved in the evolution of such magnetic structures in the interplanetary medium.

A CIRCULAR-CYLINDRICAL FLUX-ROPE ANALYTICAL MODEL FOR MAGNETIC CLOUDS

We present an analytical model to describe magnetic flux-rope topologies. When these structures are observed embedded in Interplanetary Coronal Mass Ejections (ICMEs) with a depressed proton temperature, they are called Magnetic Clouds (MCs). Our model extends the circular-cylindrical concept of Hidalgo et al. by introducing a general form for the radial dependence of the current density. This generalization provides information on the force distribution inside the flux rope in addition to the usual parameters of MC geometrical information and orientation. The generalized model provides flexibility for implementation in 3D MHD simulations. Here, we evaluate its performance in the reconstruction of MCs in in situ observations. Four Earth-directed ICME events, observed by the Wind spacecraft, are used to validate the technique. The events are selected from the ICME Wind list with the magnetic obstacle boundaries chosen consistently with the magnetic field and plasma in situ observations and with a new parameter (EPP, the Electron Pitch angle distribution Parameter) which quantifies the bidirectionally of the plasma electrons. The goodness of the fit is evaluated with a single correlation parameter to enable comparative analysis of the events. In general, at first glance, the model fits the selected events very well. However, a detailed analysis of events with signatures of significant compression indicates the need to explore geometries other than the circular-cylindrical. An extension of our current modeling framework to account for such non-circular CMEs will be presented in a forthcoming publication.

Injection of solar energetic particles into both loop legs of a magnetic cloud

Each of the two STEREO spacecraft carries a SEPT Instrument which measures electrons and protons. Anisotropy observations are provided in four viewing directions. The SEP event on 7 Nov 2013 was observed by both STEREO spacecraft, which were longitudinally separated by 68{\deg} at that time. While STEREO A observed the expected characteristics of an SEP event at a well-connected position, STEREO B detected a very anisotropic bi-directional distribution of near-relativistic electrons and was situated inside a magnetic-cloud-like structure during the early phase of the event. We examine the source of the bi-directional SEP distribution at STEREO B. On the one hand this distribution could be caused by a double injection into both loop legs of the MC. On the other hand, a mirroring scenario where the incident beam is reflected in the opposite loop leg could be the reason. Furthermore, the energetic electron observations are used to probe the magnetic structure inside the magnetic cloud. We show that STEREO B was embedded in an MC-like structure ejected three days earlier. We apply a GCS model to the coronagraph observations from three viewpoints as well as the Global Magnetic Cloud model to the in situ measurements at STEREO B to determine the orientation and topology of the MC close to the Sun and at 1 AU. We also estimate the path lengths of the electrons propagating through the MC to estimate the amount of magnetic field line winding inside the structure. The relative intensity and timing of the energetic electron increases in the different SEPT telescopes at STEREO B strongly suggest that the bi-directional electron distribution is formed by SEP injections in both loop legs of the MC separately instead of by mirroring farther away beyond the STEREO orbit. Observations by the Nancay Radioheliograph of two distinct radio sources during the SEP injection further support the above scenario.

Energetic-particle-flux decreases related to magnetic cloud passages as observed by the Helios 1 and 2 spacecraft

It has been observed that a magnetic cloud (MC) can affect the propagation conditions of solar energetic particles and low-energy cosmic rays. This effect is commonly observed as a decrease in the energetic-particle fluxes, which are partially excluded from the interior of the cloud. The twin spacecraft Helios 1 and Helios 2 explored the inner heliosphere between 0.29 AU and 1 AU from the mid 1970s to early 1980s. The E6 Experiment onboard Helios is the energetic-particle detector able to measure electrons, protons and alphas in the range of 300 keV/n to >50 MeV/n. It has been shown previously that, in absence of strong solar-particle events, the single detector rates of the E6 anti-coincidence and saphire Cherenkov detectors are sensitive to cosmic rays with rigidities above GV. Because their statistical precision is in the order of hundreds of counts per second, both detectors are very well suited for studying the short-term decreases observed in their count rates during magnetic cloud passages. A total of 35 magnetic clouds have been identified at the Helios locations. Nineteen of them were free of solar energetic-particle contamination. This subset led us to investigate the effect of magnetic clouds on the galactic cosmic ray (GCR) flux. The depth of the decreases are studied in terms of the solar wind and magnetic field properties of the magnetic cloud. We found dependences with the MC magnetic field strength, magnetic rigidity and with the MC time of flight, with the latter supporting the idea of magnetically closed MCs, i.e. with the two legs rooted in the Sun. We also studied MC properties and found evidence of MC expansion during its journey through the inner heliosphere.

Evidence of Magnetic Flux Ropes in the Solar Wind From Sigmoidal and non-Sigmoidal Active Regions

We have examined WIND magnetic field and plasma data during the first half of 1998 in order to find encounters of this spacecraft with magnetic clouds. From the events obtained through this search, we have selected four of them taking into account their solar origin. The four magnetic clouds are related to halo or partial halo CMEs, but the morphology of the active region before the eruption is sigmoidal for three of them and non-sigmoidal for the other one. We have analyzed these events in the solar wind by fitting the experimental data to a non-force-free flux-rope model. We conclude that both kinds of active regions develop in the solar wind an ejection with a flux-rope topology.

Spin magnetotransport in a two-dimensional electron system confined in a quantum well

We show a simple model that computes the magnetoconduction in a two-dimensional electron system (2DES) where the spin is another degree of freedom in the system. The 2DES is confined in a quantum well (QW) immersed in a heterostructure, where the Rashba spin–orbit interaction is present. When an external magnetic field is applied to the system, the competition between the spin–orbit interaction and the Zeeman effect on the magnetoconduction of the 2DES is analysed, in the cases where one or two sub-bands are occupied in the QW. In the model different spin-oriented 2DES can be treated independently, with a spin current associated with each system. The model has been tested with experimental results obtained from a 2DES formed in an InGaAs layer.

Cosmic rays below 15 GeV and the current rising solar activity phase

The cosmic ray component in the range of energies below 15 GeV is strongly affected by transient phenomena related to solar activity. Cosmic rays and solar particles with energies between 0.5 and 15 GeV can be observed by neutron monitors at ground level. In absence of solar activity, the background counting rate registered by neutron monitors is dominated by the galactic cosmic ray component, showing only long-term variations correlated with the solar cycle. During active periods, short-term temporal variations can be observed in close association with solar activity phenomena such as flares and coronal mass ejections. Most of these transients can produce a strong response in the magnetosphere. The aim of this work is to study the relationship between neutron monitor measurements and the magnetospheric response observed in Dst index, paying special attention to their connection with solar transient phenomena during the current rising solar activity phase.

The Geoeffectiveness of Magnetic Clouds as a Function of Their Orientation

Trying to get light into the paradigm of forecasting geomagnetic activity, we have looked for a relationship between geoeffectiveness and the orientation and helicity of magnetic clouds. During the years 1995–2000, we have selected all the geomagnetic storms with Dst index less than −70 nT. Then, we have inspected WIND data looking for a possible magnetic cloud related to every storm event. When a magnetic cloud is encountered, we have fitted to experimental data a model that we have developed for the magnetic cloud topology in order to obtain the attitude of the magnetic cloud and its helicity. On the basis of the results obtained, a close relationship is observed between the orientation of the magnetic cloud and its helicity, and the geomagnetic activity.