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Panasenco O.,Advanced Heliophysics | Martin S.F.,Helio Research | Velli M.,Jet Propulsion Laboratory
Solar Physics | Year: 2014

Recent high-resolution observations from the Solar Dynamics Observatory (SDO) have reawakened interest in the old and fascinating phenomenon of solar tornado-like prominences. This class of prominences was first introduced by Pettit (Astrophys. J. 76, 9, 1932), who studied them over many years. Observations of tornado prominences similar to the ones seen by SDO had already been documented by Secchi (Le Soleil, 1877). High-resolution and high-cadence multiwavelength data obtained by SDO reveal that the tornado-like appearance of these prominences is mainly an illusion due to projection effects. We discuss two different cases where prominences on the limb might appear to have a tornado-like behavior. One case of apparent vortical motions in prominence spines and barbs arises from the (mostly) 2D counterstreaming plasma motion along the prominence spine and barbs together with oscillations along individual threads. The other case of apparent rotational motion is observed in a prominence cavity and results from the 3D plasma motion along the writhed magnetic fields inside and along the prominence cavity as seen projected on the limb. Thus, the "tornado" impression results either from counterstreaming and oscillations or from the projection on the plane of the sky of plasma motion along magnetic-field lines, rather than from a true vortical motion around an (apparent) vertical or horizontal axis. We discuss the link between tornado-like prominences, filament barbs, and photospheric vortices at their base. © 2013 Springer Science+Business Media Dordrecht.


Due to the very broad range of the scales available for the development of turbulence in space and astrophysical plasmas, the energy at the resonant scales of wave-particle interaction often constitutes only a tiny fraction of the total magnetic turbulent energy. Despite the high efficiency of resonant wave-particle interaction, one may therefore question whether resonant interaction really is the determining interaction process between particles and turbulent fields. By evaluating and comparing resonant and nonresonant effects in the frame of a quasilinear calculation, the dominance of resonance is here put to the test. By doing so, a basic test of the classical resonant quasilinear diffusive result for the pitch-angle scattering of charged energetic particles is also performed.


Ragot B.R.,Helio Research
Astrophysical Journal | Year: 2011

A new method for the full nonlinear computation of sets of turbulent field lines has recently been introduced that allows inclusion of the equivalent of more than four decades of turbulent scales with a fully three-dimensional distribution of wavevectors. The integration scheme is here detailed, which, through transformation of the set of differential equations into mappings, compounds the efficiency and accuracy of the method. The potential of the method is then demonstrated with multiscale simulations of magnetic flux tubes ranging over nearly four decades of length scales both along and across the background field. Magnetic flux tubes of various sizes are computed for a turbulence spectrum typical of the quiet slow solar wind near 1 AU. Implications of the simulation results for the transport of energetic particles, and in particular, for the interpretation of impulsive solar-energetic-particle and upstream ion-event observations are discussed. © 2011. The American Astronomical Society. All rights reserved.


Ragot B.R.,Helio Research
Astrophysical Journal | Year: 2011

A study of the statistics of field-line dispersal recently showed that beyond its expected ballistic and diffusive regimes, the mean separation logarithm of simulated turbulent field lines displays supradiffusive behavior. The reason for this unexpected supradiffusion is investigated. The approach taken in this new study is to try to better characterize the statistics of the field-line separations in terms of random walk. © 2011. The American Astronomical Society. All rights reserved. Printedin the U.S.A.


Ragot B.R.,Helio Research
Astrophysical Journal | Year: 2010

A new method for the full nonlinear computation of sets of turbulent field lines is introduced that extends the sums of random numbers distribution method previously applied to the computation of individual field lines. With a multiscale variation of the phases consistent with in situ observations of intermittent solar wind (SW) turbulence, the new method allows inclusion of the equivalent of more than four decades of turbulent scales with a fully three-dimensional distribution of wavevectors. As a first application, pairs of magnetic field lines are computed in independent realizations of the turbulence, for spectra typical of the quiet slow SW near 1 AU. The statistics of field-line dispersal are then studied from the simulated pairs of magnetic field lines and compared to earlier theoretical predictions. It appears that while the earlier theoretical picture remains relatively accurate as long as the mean variation of separation logarithm Λ is less than one, the qualitative picture is quickly altered as Λ grows past one. © 2010. The American Astronomical Society.


The probability distribution functions (PDFs) of magnetic field variations display strong scale-dependent non-Gaussianity in the turbulent solar wind. This is a typical signature of intermittent turbulence. Physical modeling of the turbulent field variations based on the characteristics of the observed turbulence, including the variability of its power level, produces, free of parameter adjustment and over a broad range of inertial scales, accurate fits of the non-Gaussian PDFs. The effects of phase randomization and time resolution of the Fourier power spectra are further tested to determine which of the phase correlation or the spectral variability is responsible for the strong non-Gaussianity of the observed PDFs of field variations. The periods of enhanced power level are found to be responsible for the non-Gaussian tails of the PDFs. © 2013. The American Astronomical Society. All rights reserved..


Ragot B.R.,Air Force Research Lab | Ragot B.R.,Helio Research
Astrophysical Journal | Year: 2010

A new method for the full nonlinear computation of turbulent field lines is presented that extends the Sums of Random Numbers Distribution method previously applied to the computation of generalized quasilinear (GQL) field lines. A study of the mean cross-field displacement confirms the theoretical prediction of a nonlinear diffusion regime, on the large scales where the mean cross-field displacement exceeds twice the perpendicular correlation length. The simulation results duplicate at all length scales the variations of the mean cross-field displacement predicted by the theoretical calculations, including the transitions from GQL supradiffusion to nonlinear diffusion. Both GQL and full nonlinear computations also reproduce, accurately, the predicted variations with turbulence level of the large-scale GQL and nonlinear diffusion coefficients, respectively. © 2010. The American Astronomical Society.


A new method for simulating the three-dimensional dynamics of charged energetic particles in very broadband noncompressive magnetic turbulence is introduced. All scales within the primary inertial range of the turbulence observed in the solar wind near 1AU are now included for the independent computations of both the particle dynamics and the turbulent magnetic field lines (MFLs). While previous theories of resonant particle pitch-angle (PA) scattering and transport in interplanetary magnetic fields had favored interpreting the observed depletions in the electron PA distributions (PADs) around 90° PA as evidence of poor scattering at low PA cosines, the computed particle dynamics reveal a very different reality. The MFL directions now vary on many scales, and the PADs are depleted around 90° PA due to nonresonant filtering of the particles that propagate at too large an angle to the local magnetic field. Rather than being too weak, the scattering through 90° PA is actually so strong that the particles (electrons and protons/ions) are reflected and trapped in the turbulent magnetic fields. While the low-frequency nonresonant turbulence produces ubiquitous magnetic traps that only let through particles with the most field-aligned velocities, higher-frequency near-gyroscale turbulence, when present, enhances particle transport by allowing the particles to navigate between magnetic traps. Finally, visualizing both particle trajectories and MFLs in the very same turbulence reveals a powerful tool for understanding the effects of the turbulent fields on the particle dynamics and cross-field transport. Some cross-field-line scattering, strongly amplified by MFL dispersal, results in a strong cross-field scattering of the particles. From this visualization, it also appears that near-gyroscale turbulence, previously known as gyroresonant turbulence, does not resonantly interact with the particles. The interaction between particles and fields at or near the gyroscale, though potentially strong, does not actually involve the periodic driving of a true resonance. © 2012. The American Astronomical Society. All rights reserved.


Martin S.F.,Helio Research
Solar Physics | Year: 2015

The first section of this memoir queries my formative years. Indirectly I address the question, did my childhood and early years make a difference in my choice of career? Why and how did I begin my journey to becoming a scientist? Did I choose the field of solar astronomy or did circumstances dictate it for me? In the second section, I travel through my work environments and experiences, talking about interactions and aspects of being a scientist that do not appear in our research papers. What parts of my research were happenstances and what parts did I plan? What does it feel like to be on scientific quests? Using examples in my journey, I also turn to questions that have intrigued me throughout my sojourn as a solar astronomer. How do scientific discoveries come about? What factors lead to little discoveries? And what factors lead to major exciting discoveries? Are there timely questions we do not think to ask? How can small, seemingly scattered pieces of knowledge suddenly coalesce into a deeper understanding – what is called the “Aha!” experience – the times when our mental light switches on, and with child-like wonder we behold a “big picture”? © 2015, The Author(s).


Grant
Agency: NSF | Branch: Standard Grant | Program: | Phase: | Award Amount: 125.00K | Year: 2010

The Principal Investigators (PIs) intend to take advantage of a unique opportunity for complete access to the Dutch Open Telescope (DOT) on La Palma in the Canary Islands, which specializes in high-resolution solar imaging. For this project, this science team is being offered the entire 2010 observing season which runs from April to October at La Palma. This effort is extremely timely, given the delayed rise of activity in solar cycle 24 that has followed the deepest solar minimum in over a century. The year 2010 provides the only opportunity in this decade for scientists to study the rise of a new solar cycle after such a deep minimum of activity.

The DOT is a superior facility for high-resolution ground-based solar imaging, taking advantage of advanced on-site optical speckle processing. The DOT exploits excellent daytime seeing conditions on La Palma which minimize turbulence and cloud obscuration. The DOT is also capable of tomographic observations of the Sun using filters set at nine wavelengths, with each optical wavelength sampling a different height in the solar atmosphere.

This international research effort will directly contribute to improved space weather forecasts of coronal mass ejections and solar flares. The lead PI is from a small woman-owned company and this effort will directly involve four female scientists, as well as one additional female scientist as an external collaborator. This project therefore will contribute to diversity and increased participation of under-represented groups in the physical sciences.

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