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Chifu I.,Max Planck Institute for Solar System Research | Chifu I.,Astronomical Institute of Romanian Academy | Wiegelmann T.,Max Planck Institute for Solar System Research | Inhester B.,Max Planck Institute for Solar System Research
Astrophysical Journal | Year: 2017

Insights into the 3D structure of the solar coronal magnetic field have been obtained in the past by two completely different approaches. The first approach are nonlinear force-free field (NLFFF) extrapolations, which use photospheric vector magnetograms as boundary condition. The second approach uses stereoscopy of coronal magnetic loops observed in EUV coronal images from different vantage points. Both approaches have their strengths and weaknesses. Extrapolation methods are sensitive to noise and inconsistencies in the boundary data, and the accuracy of stereoscopy is affected by the ability of identifying the same structure in different images and by the separation angle between the view directions. As a consequence, for the same observational data, the 3D coronal magnetic fields computed with the two methods do not necessarily coincide. In an earlier work (Paper I) we extended our NLFFF optimization code by including stereoscopic constrains. The method was successfully tested with synthetic data, and within this work, we apply the newly developed code to a combined data set from SDO/HMI, SDO/AIA, and the two STEREO spacecraft. The extended method (called S-NLFFF) contains an additional term that monitors and minimizes the angle between the local magnetic field direction and the orientation of the 3D coronal loops reconstructed by stereoscopy. We find that when we prescribe the shape of the 3D stereoscopically reconstructed loops, the S-NLFFF method leads to a much better agreement between the modeled field and the stereoscopically reconstructed loops. We also find an appreciable decrease by a factor of two in the angle between the current and the magnetic field. This indicates the improved quality of the force-free solution obtained by S-NLFFF. © 2017. The American Astronomical Society. All rights reserved.


Chifu I.,Max Planck Institute for Solar System Research | Chifu I.,TU Braunschweig | Chifu I.,Astronomical Institute of Romanian Academy | Inhester B.,Max Planck Institute for Solar System Research | And 4 more authors.
Solar Physics | Year: 2012

Data from the STEREO (Solar Terrestrial Relations Observatory) mission are intensively used for 3D reconstruction of solar coronal structures. After the launch of the SDO (Solar Dynamic Observatory) satellite, its additional observations give the possibility to have a third eye for more accurate 3D reconstruction in the very low corona (< 1. 5 R ⊙). With our reconstruction code MBSR (Multi-view B-spline Stereoscopic Reconstruction), we use three view directions (STEREO A, B, and SDO) to perform the 3D reconstruction and evolution of a prominence which triggered a CME on 1 August 2010. In the paper we present the reconstruction of this prominence from the moment it starts to erupt until it leaves the field of view of the coronagraph. We also determine the evolution of the leading edge of the CME. Based on the temporal evolution, we analyze some of its properties, such as velocity, acceleration, opening and rotation angles and evolution of the cavity. © 2012 Springer Science+Business Media B.V.


Dumitrache C.,Astronomical Institute of Romanian Academy | Mierla M.,Astronomical Institute of Romanian Academy
EAS Publications Series | Year: 2010

Our paper intends to estimate the EUV dimming appearing in a prominence eruption into a coronal mass ejection from the observationally point of few and so well from a numerical model. We have performed a numerical MHD simulation on a solar radius and obtained a CME originating from a prominence. The mass dimming was revealed clearly and we compared the mass evolution of the CME to that of an event observed on 14 January 2001 by SOHO. © EAS, EDP Sciences 2011.


Roman R.,Astronomical Institute of Romanian Academy | Szucs-Csillik I.,Astronomical Institute of Romanian Academy
Astrophysics and Space Science | Year: 2012

The regularization of a new problem, namely the three-body problem, using 'similar' coordinate system is proposed. For this purpose we use the relation of 'similarity', which has been introduced as an equivalence relation in a previous paper (see Roman in Astrophys. Space Sci. doi:10.1007/s10509-011-0747-1, 2011). First we write the Hamiltonian function, the equations of motion in canonical form, and then using a generating function, we obtain the transformed equations of motion. After the coordinates transformations, we introduce the fictitious time, to regularize the equations of motion. Explicit formulas are given for the regularization in the coordinate systems centered in the more massive and the less massive star of the binary system. The 'similar' polar angle's definition is introduced, in order to analyze the regularization's geometrical transformation. The effect of Levi-Civita's transformation is described in a geometrical manner. Using the resulted regularized equations, we analyze and compare these canonical equations numerically, for the Earth-Moon binary system. © 2011 Springer Science+Business Media B.V.


Chifu I.,Max Planck Institute for Solar System Research | Chifu I.,Astronomical Institute of Romanian Academy | Chifu I.,TU Braunschweig | Inhester B.,Max Planck Institute for Solar System Research | Wiegelmann T.,Max Planck Institute for Solar System Research
Astronomy and Astrophysics | Year: 2015

Aims. Nonlinear force-free field (NLFFF) extrapolation has been used extensively in the past to extrapolate solar surface magnetograms to stationary coronal field models. In theoretical tests with known boundary conditions, the nonlinear boundary value problem can be solved reliably. However, if the magnetogram is measured with errors, the extrapolation often yields field lines that disagree with the shapes of simultaneously observed and stereoscopically reconstructed coronal loops. We here propose an extension to an NLFFF extrapolation scheme that remedies this deficiency in that it incorporates the loop information in the extrapolation procedure. Methods. We extended the variational formulation of the NLFFF optimization code by an additional term that monitors and minimizes the difference of the local magnetic field direction and the orientation of 3D plasma loops. We tested the performance of the new code with a previously reported semi-analytical force-free solution. Results. We demonstrate that there is a range of force-free and divergence-free solutions that comply with the boundary measurements within some error bound. With our new approach we can obtain the solution out of this set the coronal fields which is well aligned with given loops. Conclusions. We conclude that the shape of coronal loops reconstructed by stereoscopy may lead to an important stabilization of coronal NLFFF field solutions when, as is typically the case, magnetic surface measurements with limited precision do not allow determining the solution solely from photospheric field measurements. © ESO, 2015.


Dumitrache C.,Astronomical Institute of Romanian Academy | Popescu N.A.,Astronomical Institute of Romanian Academy
Romanian Journal of Physics | Year: 2013

We present here an overview of an important solar phenomenon with major im-plications for space weather and planetary life. The coronal mass ejections (CMEs) come from the Sun and expand in the heliosphere, becoming interplanetary coronal mass ejections (ICMEs). They represent huge clouds of plasma and magnetic fields that travel with velocities reaching even 2000 km/s and perturbing the planetary and interplanetary field. The magnetic clouds (MC) are a special class of ICMEs. We sum-marize some aspects as the ICMEs identification, propagation and track back to the Sun, where the solar source could be found. Each event has its own peculiarity. Much more, the ICMEs moving in the ecliptic plane are different from that travelling out of the Sun-Earth plane. Their study gives us an idea about the three dimension manifest of the heliosphere. We notice here few known catalogues of the ICMEs and magnetic clouds, useful for the general studies of the ICMEs. We also summarize some results of the authors previous work.


Dumitrache C.,Astronomical Institute of Romanian Academy | Popescu N.A.,Astronomical Institute of Romanian Academy | Oncica A.,Astronomical Institute of Romanian Academy
Solar Physics | Year: 2011

High-latitude interplanetary mass ejections (ICMEs) observed beyond 1 AU are not studied very often. They are useful for improving our understanding of the 3D heliosphere. As there are only few such events registered by the Ulysses spacecraft, the task of detecting their solar counterparts is a challenge, especially during high solar activity periods, because there are dozens coronal mass ejections (CMEs) registered by SOHO that might be chosen as candidates. We analyzed a high-latitude ICME registered by the Ulysses spacecraft on 18 January 2002. Our investigation focused on the correlation between various plasma parameters that allow the identification to be made of the ICME and its components such as the forward shock, the magnetic cloud and the reverse shock. Using a linear approach and a graphical method we have been able to track the ICME event back to the Sun and to compute the day of the occurrence of the solar CME. In order to decide among several CME candidates which one is the right solar counterpart of our event, we have performed a follow-up computation of these CMEs from the Sun to Ulysses, by using two different speed formulas. First, the computation was simply based on the initial CME velocity, while the other was based on the ICME velocity estimated from the CME initial speed (Lindsay et al. 1999). Differences of hours have been obtained between the arrival time predicted in these two ways, but the second one gave the best results. Both methods indicated the same two CMEs as the solar counterparts. We have found the solar source of these CMEs as being a huge polar filament that erupted in several steps. This ICME event displayed a double magnetic cloud configuration. A minimum variance analysis helped us to detect the smooth rotation of the clouds and their helicity. Both magnetic clouds show the same helicity as the filament that erupted and released them. A cylinder-shape model of both clouds gives the same helicity sign. © 2011 Springer Science+Business Media B.V.


Roman R.,Astronomical Institute of Romanian Academy
Astrophysics and Space Science | Year: 2011

A new equivalence relation, named relation of 'similarity' is defined and applied in the restricted three-body problem. Using this relation, a new class of trajectories (named 'similar' trajectories) are obtained; they have the theoretical role to give us new details in the restricted three-body problem. The 'similar' coordinate systems allow us in addition to obtain a unitary and an elegant demonstration of some analytical relations in the Roche geometry. As an example, some analytical relations published by Seidov (in Astrophys. J. 603:283, 2004) are demonstrated. © 2011 Springer Science+Business Media B.V.


Roman R.,Astronomical Institute of Romanian Academy | Szucs-Csillik I.,Astronomical Institute of Romanian Academy
Astrophysics and Space Science | Year: 2014

A family of polynomial coupled function of n degree is proposed, in order to generalize the Levi-Civita regularization method, in the restricted three-body problem. Analytical relationship between polar radii in the physical plane and in the regularized plane are established; similar for polar angles. As a numerical application, trajectories of the test particle using polynomial functions of 2,3,...,8 degree are obtained. For the polynomial of second degree, the Levi-Civita regularization method is found. © 2013 Springer Science+Business Media Dordrecht.


Roman R.,Astronomical Institute of Romanian Academy | Szucs-Csillik I.,Astronomical Institute of Romanian Academy
Astrophysics and Space Science | Year: 2014

The equilibrium points and the curves of zero-velocity (Roche varieties) are analyzed in the frame of the regularized circular restricted three-body problem. The coordinate transformation is done with Levi-Civita generalized method, using polynomial functions of n degree. In the parametric plane, five families of equilibrium points are identified: L1 i, L2 i,..., Ln i i ∈ {1,2,...,5 \}, n ∈ ℕ*. These families of points correspond to the five equilibrium points in the physical plane L 1,L 2,...,L 5. The zero-velocity curves from the physical plane are transformed in Roche varieties in the parametric plane. The properties of these varieties are analyzed and the Roche varieties for n∈{1,2,...,6} are plotted. The equation of the asymptotic variety is obtained and its shape is analyzed. The slope of the Roche variety in L1 1 point is obtained. For n=1 the slope obtained by Plavec and Kratochvil (1964) in the physical plane was found. © 2014 Springer Science+Business Media Dordrecht.

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