271 research outputs found
Nonlinear force-free field modelling of solar coronal jets in theoretical configurations
Coronal jets occur frequently on the Sun, and may contribute significantly to the solar wind. With the suite of instruments available now, we can observe these phenomena in greater detail than ever before. Modeling and simulations can assist further in understanding the dynamic processes involved, but previous studies tend to consider only one mechanism (e.g. emergence or rotation) for the origin of the jet. In this study we model a series of idealised archetypal jet configurations and follow the evolution of the coronal magnetic field. This is a step towards understanding these idealised situations before considering their observational counterparts. Several simple situations are set up for the evolution of the photospheric magnetic field: a single parasitic polarity rotating or moving in a circular path; as well as opposite polarity pairs involved in flyby (shearing), cancellation or emergence; all in the presence of a uniform, open background magnetic field. The coronal magnetic field is evolved in time using a magnetofrictional relaxation method. While magnetofriction cannot accurately reproduce the dynamics of an eruptive phase, the structure of the coronal magnetic field, as well as the build up of electric currents and free magnetic energy are instructive. Certain configurations and motions produce a flux rope and allow the significant build up of free energy, reminiscent of the progenitors of so-called blowout jets, whereas other, simpler configurations are more comparable to the standard jet model. The next stage is a comparison with observed coronal jet structures and their corresponding photospheric evolution
The evolution of solar sigmoidal active regions
Thesis (Ph.D.)--Boston UniversityThe formation, evolution and eruption of solar active regions is a main theme in solar physics. Ultimately the goal is predicting when, where and how an eruption will occur, which will greatly aid space weather forecasting. Special kinds of S-shaped active regions (sigmoids) facilitate this line of research, since they provide conditions that are easier to disentangle and have a high probability for erupting as flares and/or coronal mass ejections (CME). Several theories have been proposed for the formation, evolution, and eruption of solar active regions. Testing these against detailed models of sigmoidal regions can provide insight into the dominant mechanisms and conditions required for eruption. This thesis explores the behavior of solar sigmoids via both observational and magnetic modeling studies. Data from the most modern space-based solar observatories are utilized in addition to state-of-the-art three-dimensional data-driven magnetic field modeling to gain insight into the physical processes controlling the evolution and eruption of solar sigmoids. We use X-ray observations and the magnetic field models to introduce the reader to the underlying magnetic and plasma structure defining these regions. By means of a large comprehensive observational study we investigate the formation and evolution mechanism. Specifically, we show that flux cancellation is a major mechanism for building the underlying magnetic structure associated with sigmoids, namely magnetic flux ropes. We make use of topological analysis to describe the complicated magnetic field structure of the sigmoids. We show that when data-driven models are used in sync with MHD simulations and observations we can arrive at a consistent picture of the scenario for CME onset, namely the positive feedback between reconnection at a generalized X-line and the torus instability. In addition we show that topological analysis is of great use in analyzing the post-eruption flare- and CME-associated observational features. Such analysis is used to extend the standard 2D flare/CME models to 3D and to find potentially large implications of topology to understanding 3D reconnection and the seed populations of energetic particles in CMEs
Comparing User Responses to Limited and Flexible Interaction in a Conversational Interface
The principles governing written communication have been well studied, and well incorporated in interactive computer systems. However, the role of spoken language and in human-computer interaction, while an increasingly popular modality, still needs to be explored further [3]. Evidence suggests that this technology must further evolve in order to support more "natural" conversations [2], and that the use of speech interfaces is correlated with a high cognitive demand and attention [4]. In the context of spoken dialogue systems, a continuum has long been identified between "systeminitiative" interactions, where the system is in complete control of the overall interaction and the user answers a series of prescribed questions, and "user-initiative" interactions, where the user is free to say anything and the system must respond [5]. However, much of the work in this area predates the recent explosive growth of conversational interfaces
The Relation between Solar Eruption Topologies and Observed Flare Features I: Flare Ribbons
In this paper we present a topological magnetic field investigation of seven
two-ribbon flares in sigmoidal active regions observed with Hinode, STEREO, and
SDO. We first derive the 3D coronal magnetic field structure of all regions
using marginally unstable 3D coronal magnetic field models created with the
flux rope insertion method. The unstable models have been shown to be a good
model of the flaring magnetic field configurations. Regions are selected based
on their pre-flare configurations along with the appearance and observational
coverage of flare ribbons, and the model is constrained using pre-flare
features observed in extreme ultraviolet and X-ray passbands. We perform a
topology analysis of the models by computing the squashing factor, Q, in order
to determine the locations of prominent quasi-separatrix layers (QSLs). QSLs
from these maps are compared to flare ribbons at their full extents. We show
that in all cases the straight segments of the two J-shaped ribbons are matched
very well by the flux-rope-related QSLs, and the matches to the hooked segments
are less consistent but still good for most cases. In addition, we show that
these QSLs overlay ridges in the electric current density maps. This study is
the largest sample of regions with QSLs derived from 3D coronal magnetic field
models, and it shows that the magnetofrictional modeling technique that we
employ gives a very good representation of flaring regions, with the power to
predict flare ribbon locations in the event of a flare following the time of
the model
EMOTIONAL INTELLIGENCE AND PSYCHOLOGICAL CHARACTERISTICS OF ATHLETES OF DIFFERENT SPORTS
A number of studies in psychology and the field of sports focus on the topic of the relationship between
emotional intelligence and personality characteristics as well as their influence on sports performance.
PURPOSE: The aim of this study was to examine the connections and interrelations among personality traits:
extraversion, conscientiousness, agreeableness, emotional stability and openness to experience, and
emotional intelligence in relation to successful performance in sport.
METHODS: The research was done among 88 athletes practicing different sports (46 women and 42 men,
aged between 12 and 59 years old), divided into groups according to their age, gender, qualification, sports
experience, and level of education. RESULTS: There were statistically significant differences in the appraisal
of othersâ emotions (U=602; p=.017) along the factor âeducationâ (Secondary or High). Athletes with high
education are more adept at determining the emotions of others than those with secondary education. We
revealed statistically significant differences according to gender in agreeableness (U=706; p=.029) and
appraisal of othersâ emotions (U=714; p=.034). CONCLUSIONS: The female athletes showed higher results
than the male ones on the agreeableness scale and were better at appraising othersâ emotions
Data-Optimized Coronal Field Model: I. Proof of Concept
Deriving the strength and direction of the three-dimensional (3D) magnetic
field in the solar atmosphere is fundamental for understanding its dynamics.
Volume information on the magnetic field mostly relies on coupling 3D
reconstruction methods with photospheric and/or chromospheric surface vector
magnetic fields. Infrared coronal polarimetry could provide additional
information to better constrain magnetic field reconstructions. However,
combining such data with reconstruction methods is challenging, e.g., because
of the optical-thinness of the solar corona and the lack and limitations of
stereoscopic polarimetry. To address these issues, we introduce the
Data-Optimized Coronal Field Model (DOCFM) framework, a model-data fitting
approach that combines a parametrized 3D generative model, e.g., a magnetic
field extrapolation or a magnetohydrodynamic model, with forward modeling of
coronal data. We test it with a parametrized flux rope insertion method and
infrared coronal polarimetry where synthetic observations are created from a
known "ground truth" physical state. We show that this framework allows us to
accurately retrieve the ground truth 3D magnetic field of a set of force-free
field solutions from the flux rope insertion method. In observational studies,
the DOCFM will provide a means to force the solutions derived with different
reconstruction methods to satisfy additional, common, coronal constraints. The
DOCFM framework therefore opens new perspectives for the exploitation of
coronal polarimetry in magnetic field reconstructions and for developing new
techniques to more reliably infer the 3D magnetic fields that trigger solar
flares and coronal mass ejections.Comment: 14 pages, 6 figures; Accepted for publication in Ap
Multi-wavelength spectroscopic observation of EUV jet in AR 10960
We have studied the relationship between the velocity and temperature of a
solar EUV jet. The highly accelerated jet occurred in the active region NOAA
10960 on 2007 June 5. Multi-wavelength spectral observations with EIS/Hinode
allow us to investigate Doppler velocities at the wide temperature range. We
analyzed the three-dimensional angle of the jet from the stereoscopic analysis
with STEREO. Using this angle and Doppler velocity, we derived the true
velocity of the jet. As a result, we found that the cool jet observed with
\ion{He}{2} 256 \AA is accelerated to around which is over the upper limit of the chromospheric evaporation. The
velocities observed with the other lines are under the upper limit of the
chromospheric evaporation while most of the velocities of hot lines are higher
than that of cool lines. We interpret that the chromospheric evaporation and
magnetic acceleration occur simultaneously. A morphological interpretation of
this event based on the reconnection model is given by utilizing the
multi-instrumental observations.Comment: Accepted for publication in Ap
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