192 research outputs found
Deriving the radial distances of wide coronal mass ejections from elongation measurements in the heliosphere - Application to CME-CME interaction
We present general considerations regarding the derivation of the radial
distances of coronal mass ejections (CMEs) from elongation angle measurements
such as those provided by SECCHI and SMEI, focusing on measurements in the
Heliospheric Imager 2 (HI-2) field of view (i.e. past 0.3 AU). This study is
based on a three-dimensional (3-D) magneto-hydrodynamics (MHD) simulation of
two CMEs observed by SECCHI on January 24-27, 2007. Having a 3-D simulation
with synthetic HI images, we are able to compare the two basic methods used to
derive CME positions from elongation angles, the so-called "Point-P" and
"Fixed-Phi" approximations.
We confirm, following similar works, that both methods, while valid in the
most inner heliosphere, yield increasingly large errors in HI-2 field of view
for fast and wide CMEs. Using a simple model of a CME as an expanding
self-similar sphere, we derive an analytical relationship between elongation
angles and radial distances for wide CMEs. This relationship is simply the
harmonic mean of the "Point-P" and "Fixed-Phi'' approximations and it is aimed
at complementing 3-D fitting of CMEs by cone models or flux rope shapes. It
proves better at getting the kinematics of the simulated CME right when we
compare the results of our line-of-sights to the MHD simulation. Based on this
approximation, we re-analyze the J-maps (time-elongation maps) in January
26-27, 2007 and present the first observational evidence that the merging of
CMEs is associated with a momentum exchange from the faster ejection to the
slower one due to the propagation of the shock wave associated with the fast
eruption through the slow eruption.Comment: 10 pages, 4 figures, accepted in Annales Geophysicae (Special Issue:
Three eyes on the Sun - multi-spacecraft studies of the corona and impacts on
the heliosphere
Solar-Terrestrial Simulations of CMEs with a Realistic Initiation Mechanism: Case Study for Active Region 10069
Most simulations of coronal mass ejections (CMEs) to date either focus on the
interplanetary propagation of a giant plasma "blob" without paying too much
attention to its origin and to the formation process or they focus on the
complex evolution of the coronal magnetic field due to (sub-)photospheric
motions which result in an eruption. Here, we present global simulations of
CMEs where coronal motions are used to produce a realistic evolution of the
coronal magnetic field and cause an eruption. We focus on active region 10069,
which produced a number of eruptions in late August 2002, including the August
24, 2002 CME - a fast (~2000 km/s) eruption originating from W81-, as well as a
slower eruption on August 22, 2002 (originating from W62). Using a
three-dimensional magneto-hydrodynamic (MHD) simulation of these ejections with
the Space Weather Modeling Framework (SWMF), we show how a realistic initiation
mechanism enables us to study the deflection of the CME in the corona and in
the heliosphere. Reconnection of the erupting magnetic field with that of
neighboring streamers and active regions modify the solar connectivity of the
field lines connecting to Earth and change the expected solar energetic
particle fluxes. Comparing the results at 1 AU of our simulations with in situ
observations by the ACE spacecraft, we propose an alternate solar origin for
the shock wave observed at L1 on August 26.Comment: 4 pages, 2 figures, refereed proceedings for Solar Wind 1
Towards a Realistic, Data-Driven Thermodynamic MHD Model of the Global Solar Corona
In this work we describe our implementation of a thermodynamic energy
equation into the global corona model of the Space Weather Modeling Framework
(SWMF), and its development into the new Lower Corona (LC) model. This work
includes the integration of the additional energy transport terms of coronal
heating, electron heat conduction, and optically thin radiative cooling into
the governing magnetohydrodynamic (MHD) energy equation. We examine two
different boundary conditions using this model; one set in the upper transition
region (the Radiative Energy Balance model), as well as a uniform chromospheric
condition where the transition region can be modeled in its entirety. Via
observation synthesis from model results and the subsequent comparison to full
sun extreme ultraviolet (EUV) and soft X-Ray observations of Carrington
Rotation (CR) 1913 centered on Aug 27, 1996, we demonstrate the need for these
additional considerations when using global MHD models to describe the unique
conditions in the low corona. Through multiple simulations we examine ability
of the LC model to asses and discriminate between coronal heating models, and
find that a relative simple empirical heating model is adequate in reproducing
structures observed in the low corona. We show that the interplay between
coronal heating and electron heat conduction provides significant feedback onto
the 3D magnetic topology in the low corona as compared to a potential field
extrapolation, and that this feedback is largely dependent on the amount of
mechanical energy introduced into the corona.Comment: 17 pages, 11 figures, Submitted to ApJ on 12/08/200
Cognitive Problems, Metacognition, and Philosophy of Language
In this paper I argue that many of the cognitive problems (such as low self-esteem, permanent anxiety, bad learning strategies, student-teacher conflict of values, or motivational deficit ) that interfere with problem solving are rooted in individuals\u27 philosophically naive views of how their own intelligence works and can be overcome through development of an adequate philosophical competence. Accordingly, I attempt a delineation of the scientific prescription for overcoming these problems, metacognition, in terms of concepts of contemporary\u27 philosophy\u27 of language. Four scientific concepts were examined, including M. V. Covington\u27s concept of strategic thinking, J. Lochhead\u27s concept of the role of verbalization in thinking, R. Paul\u27s concept of conceptualization and elements of thought, and M. Lipman\u27s concept of the role of philosophy, in children\u27s early cognitive development, which all consider overcoming of cognitive problems. Four philosophical concepts were examined, including L. Wittgenstein\u27s early concept of the correct use of language, his later concept of language games, J. Searle\u27s concept of speech acts, and R. Rorty\u27s concept of the speech acts, and R. Rorty\u27s concept of the political answer to philosophical questions, which all consider overcoming of traditional philosophical problems. In the scientific views, cognitive problems are explained by individuals\u27 inadequate personal epistemology and overcome through the mind\u27s activity, metacognition, which involves knowledge of how one\u27s intelligence works, or a concept of cognition and a utilization of this knowledge in any new problematic situation. Similarly, in the philosophical views, philosophical problems are generally explained by misuse of the logic of language and overcome by mediation of what I called the philosophical methodology of dissolution, which I interpreted as involving both an appropriate concept of cognition and a permanent utilization of this concept. Thus, the delineation of the concept of metacognition in philosophical terms becomes possible, given that cognitive problems qualify better for the competence of philosophy than for the expertise of science. By means of J. Habermas\u27 concept of philosophy as a mediating interpreter I conceptualized both philosophical and cognitive problems as problems of mediation which come into being in the exchange of expertise on two presupposed levels of discourse and activity, respectively, expert culture and everyday communication. Since the problems of mediation are conceived of as remaining out of the scope of the expert fields but in the scope of philosophy as an non-expert field, the latter was used to provide with its competence the problem solving practices which deal with such problems on the level of everyday communication. Then, I illustrate an overcoming of cognitive problems by mediation of the philosophical methodology of dissolution which I examine and represent in the form of the scientific concept of metacognition as a sequence of explanation and application of a philosophical concept of cognition which in this case is a compositional philosophical concept of language
The August 24, 2002 Coronal Mass Ejection: When a Western Limb Event Connects to Earth
We discuss how some coronal mass ejections (CMEs) originating from the
western limb of the Sun are associated with space weather effects such as solar
energetic particles (SEPs), shock or geo-effective ejecta at Earth. We focus on
the August 24, 2002 coronal mass ejection, a fast (~ 2000 km/s) eruption
originating from W81. Using a three-dimensional magneto-hydrodynamic simulation
of this ejection with the Space Weather Modeling Framework (SWMF), we show how
a realistic initiation mechanism enables us to study the deflection of the CME
in the corona and the heliosphere. Reconnection of the erupting magnetic field
with that of neighboring streamers and active regions modify the solar
connectivity of the field lines connecting to Earth and can also partly explain
the deflection of the eruption during the first tens of minutes. Comparing the
results at 1 AU of our simulation with observations by the ACE spacecraft, we
find that the simulated shock does not reach Earth, but has a maximum angular
span of about 120, and reaches 35 West of Earth in 58 hours. We
find no significant deflection of the CME and its associated shock wave in the
heliosphere, and we discuss the consequences for the shock angular span.Comment: 7 pages, 4 figures, IAU 257 Symposium Proceeding
The Brightness of Density Structures at Large Solar Elongation Angles: What is Being Observed by STEREO/SECCHI?
We discuss features of coronal mass ejections (CMEs) that are specific to
heliospheric observations at large elongation angles. Our analysis is focused
on a series of two eruptions that occurred on 2007 January 24-25, which were
tracked by the Heliospheric Imagers (HIs) onboard STEREO. Using a
three-dimensional (3-D) magneto-hydrodynamic simulation of these ejections with
the Space Weather Modeling Framework (SWMF), we illustrate how the combination
of the 3-D nature of CMEs, solar rotation, and geometry associated with the
Thomson sphere results in complex effects in the brightness observed by the
HIs. Our results demonstrate that these effects make any in-depth analysis of
CME observations without 3-D simulations challenging. In particular, the
association of bright features seen by the HIs with fronts of CME-driven shocks
is far from trivial. In this Letter, we argue that, on 2007 January 26, the HIs
observed not only two CMEs, but also a dense corotating stream compressed by
the CME-driven shocks.Comment: 5 pages, 2 figures, accepted for ApJ Lette
The Deflection of the Two Interacting Coronal Mass Ejections of 2010 May 23-24 as Revealed by Combined In situ Measurements and Heliospheric Imaging
In 2010 May 23-24, SDO observed the launch of two successive coronal mass
ejections (CMEs), which were subsequently tracked by the SECCHI suite onboard
STEREO. Using the COR2 coronagraphs and the heliospheric imagers (HIs), the
initial direction of both CMEs is determined to be slightly west of the
Sun-Earth line. We derive the CME kinematics, including the evolution of the
CME expansion until 0.4 AU. We find that, during the interaction, the second
CME decelerates from a speed above 500 km/s to 380 km/s the speed of the
leading edge of the first CME. STEREO observes a complex structure composed of
two different bright tracks in HI2-A but only one bright track in HI2-B. In
situ measurements from Wind show an "isolated" ICME, with the geometry of a
flux rope preceded by a shock. Measurements in the sheath are consistent with
draping around the transient. By combining remote-sensing and in situ
measurements, we determine that this event shows a clear instance of deflection
of two CMEs after their collision, and we estimate the deflection of the first
CME to be about 10 degrees towards the Sun-Earth line. The arrival time,
arrival speed and radius at Earth of the first CME are best predicted from
remote-sensing observations taken before the collision of the CMEs. Due to the
over-expansion of the CME after the collision, there are few, if any, signs of
interaction in in situ measurements. This study illustrates that complex
interactions during the Sun-to-Earth propagation may not be revealed by in situ
measurements alone.Comment: 14 pages, 8 figures, 1 table, accepted to the Astrophysical Journa
Numerical Investigation of a Coronal Mass Ejection from an Anemone Active Region: Reconnection and Deflection of the 2005 August 22 Eruption
We present a numerical investigation of the coronal evolution of a coronal
mass ejection (CME) on 2005 August 22 using a 3-D thermodynamics
magnetohydrodynamic model, the SWMF. The source region of the eruption was
anemone active region (AR) 10798, which emerged inside a coronal hole. We
validate our modeled corona by producing synthetic extreme ultraviolet (EUV)
images, which we compare to EIT images. We initiate the CME with an
out-of-equilibrium flux rope with an orientation and chirality chosen in
agreement with observations of a H-alpha filament. During the eruption, one
footpoint of the flux rope reconnects with streamer magnetic field lines and
with open field lines from the adjacent coronal hole. It yields an eruption
which has a mix of closed and open twisted field lines due to interchange
reconnection and only one footpoint line-tied to the source region. Even with
the large-scale reconnection, we find no evidence of strong rotation of the CME
as it propagates. We study the CME deflection and find that the effect of the
Lorentz force is a deflection of the CME by about 3 deg/Rsun towards the East
during the first 30 minutes of the propagation. We also produce coronagraphic
and EUV images of the CME, which we compare with real images, identifying a
dimming region associated with the reconnection process. We discuss the
implication of our results for the arrival at Earth of CMEs originating from
the limb and for models to explain the presence of open field lines in magnetic
clouds.Comment: 14 pages, 8 Figures, accepted to Astrophysical Journa
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