Quasi-periodic Counter-propagating Fast Magnetosonic Wave Trains from Neighboring Flares: SDO/AIA Observations and 3D MHD Modeling |
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Leon Ofman Submitted: 2018-05-01 22:50
Since their discovery by SDO/AIA in EUV, rapid (phase speeds of ~1000 km s-1), quasi-periodic, fast-mode propagating wave trains (QFPs) have been observed accompanying many solar flares. They typically propagate in funnel-like structures associated with the expanding magnetic field topology of the active regions (ARs). The waves provide information on the associated flare pulsations and the magnetic structure through coronal seismology. The reported waves usually originate from a single localized source associated with the flare. Here, we report the first detection of counter-propagating QFPs associated with two neighboring flares on 2013 May 22, apparently connected by large-scale, trans-equatorial coronal loops. We present the first results of 3D MHD model of counter-propagating QFPs an idealized bi-polar AR. We investigate the excitation, propagation, nonlinearity, and interaction of the counter-propagating waves for a range of key model parameters, such as the properties of the sources and the background magnetic structure. In addition to QFPs, we also find evidence of trapped fast (kink) and slow mode waves associated with the event. We apply coronal seismology to determine the magnetic field strength in an oscillating loop during the event. Our model results are in qualitative agreement with the AIA-observed counter propagating waves and are used to identify the various MHD wave modes associated with the observed event providing insights into their linear and nonlinear interactions. Our observations provide the first direct evidence of counter-propagating fast magnetosonic waves that can potentially lead to turbulent cascade and carry significant energy flux for coronal heating in low-corona magnetic structures.
Authors: Leon Ofman; Wei Liu
Projects: SDO-AIA
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Publication Status: ApJ, in press
Last Modified: 2018-05-02 12:06
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Three dimensional MHD Modeling of Vertical Kink Oscillations in an Active Region Plasma Curtain |
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Leon Ofman Submitted: 2015-05-21 08:03
Observations on 2011 August 9 of an X6.9-class flare in active region (AR) 11263 by the Atmospheric Imaging Assembly (AIA) on-board the Solar Dynamics Observatory (SDO), were followed by a rare detection of vertical kink oscillations in a large-scale coronal active region plasma curtain in EUV coronal lines. The damped oscillations with periods in the range 8.8-14.9 min were detected and analyzed recently. Our aim is to study the generation and propagation of the MHD oscillations in the plasma curtain taking into account realistic 3D magnetic and density structure of the curtain. We also aim at testing and improving coronal seismology for more accurate determination of the magnetic field than with standard method. We use the observed morphological and dynamical conditions, as well as plasma properties of the coronal curtain based on Differential Emission Measure (DEM) analysis to initialize a 3D MHD model of its vertical and transverse oscillations by implementing the impulsively excited velocity pulse mimicking the flare generated nonlinear fast magnetosonic propagating disturbance interacting with the curtain obliquely. The model is simplified by utilizing initial dipole magnetic field, isothermal energy equation, and gravitationally stratified density guided by observational parameters. Using the 3D MHD model, we are able to reproduce the details of the vertical oscillations and study the process of their excitation by nonlinear fast magnetosonic pulse, propagation, and damping, finding agreement with the observations. We estimate the accuracy of simplified slab-based coronal seismology by comparing the determined magnetic field strength to actual values from the 3D MHD modeling results and demonstrate the importance of taking into account more realistic magnetic geometry and density for improving coronal seismology.
Authors: L. Ofman, M. Parisi, A.K. Srivastava
Projects: SDO-AIA
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Publication Status: Submitted to Astronomy and Astrophysics
Last Modified: 2015-05-25 09:29
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Relative drifts and temperature anisotropies of protons and α particles in the expanding solar wind - 2.5D hybrid simulations |
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Leon Ofman Submitted: 2015-01-24 09:50
We perform 2.5D hybrid simulations to investigate the origin and evolution of relative drift speeds between protons and α particles in the collisionless turbulent low-β solar wind plasma. We study the generation of differential streaming by wave-particle interactions and absorption of turbulent wave spectra. Next we focus on the role of the relative drifts for the turbulent heating and acceleration of ions in the collisionless fast solar wind streams. The energy source is given by an initial broad-band spectrum of parallel propagating Alfvén-cyclotron waves, which co-exists with the plasma and is self-consistently coupled to the perpendicular ion bulk velocities. We include the effect of a gradual solar wind expansion, which cools and decelerates the minor ions. This paper for the first time considers the combined effect of self-consistently initialized dispersive turbulent Alfvénic spectra with differentially streaming protons and α particles in the expanding solar wind outflows within a 2.5D hybrid simulation study. In the non-expanding wind, we find a threshold value of the differential streaming V α p = 0.5 VA, for which the relative drift speed remains nearly steady. For ions, streaming below the threshold value, the waves act to increase the magnitude of the relative drift speed. Ions, which stream faster than the threshold value become subject to nonlinear streaming instability and as the system evolves their bulk velocities decrease. We find that the solar wind expansion strongly affects the relative drift speeds and significantly slows down both ion species for all values of the relative drift speeds considered in this study.
Authors: Maneva, Y., Ofman, L., Vinas, A.-F.
Projects: None
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Publication Status: A&A, submitted
Last Modified: 2015-01-26 10:04
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Ion Heating in Inhomogeneous Expanding Solar Wind Plasma: The Role of Parallel and Oblique Ion-Cyclotron Waves |
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Leon Ofman Submitted: 2015-01-13 03:32
Remote sensing observations of coronal holes show that heavy ions are hotter than protons and their temperature is anisotropic. In-situ observations of fast solar wind streams provide direct evidence for turbulent Alfvén wave spectrum, left-hand polarized ion-cyclotron waves, and He^++ - proton drift in the solar wind plasma, which can produce temperature anisotropies by resonant absorption and perpendicular heating of the ions. Furthermore, the solar wind is expected to be inhomogeneous on decreasing scales approaching the Sun. We study the heating of solar wind ions in inhomogeneous plasma with a 2.5D hybrid code. We include the expansion of the solar wind in an inhomogeneous plasma background, combined with the effects of a turbulent wave spectrum of Alfvénic fluctuations and initial ion-proton drifts. We study the influence of these effects on the perpendicular ion heating and cooling and on the spectrum of the magnetic fluctuations in the inhomogeneous background wind. We find that inhomogeneities in the plasma lead to enhanced heating compared to the homogenous solar wind, and the generation of significant power of oblique waves in the solar wind plasma. The cooling effect due to the expansion is not significant for super-Alfvénic drifts, and is diminished further when we include an inhomogenous background density. We reproduce the ion temperature anisotropy seen in observations and previous models, which is present regardless of the perpendicular cooling due to solar wind expansion. We conclude that small scale inhomogeneities in the inner heliosphere can significantly affect resonant wave ion heating.
Authors: Ozak, N.; Ofman, L.; Vi?as, A.-F.
Projects: None
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Publication Status: Accepted for publication
Last Modified: 2015-01-13 14:06
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Three-dimensional multi-fluid model of a coronal streamer belt with a tilted magnetic dipole |
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Leon Ofman Submitted: 2015-01-13 03:28
Observations of streamers in EUV emission with SOHO/UVCS show dramatic differences in line profiles and latitudinal variations of heavy ions emission compared to hydrogen Ly α emission. In order to use ion emission observations of streamers as the diagnostics of the slow solar wind properties, an adequate model of a streamer including heavy ions is required. We extended previous 2.5D multi-species MHD model of a coronal streamer to 3D spherical geometry, and as the first approach we consider a tilted dipole configuration of the solar magnetic field. The aim of the present study is to test the 3D results by comparing to previous 2.5D model result for a 3D case with moderate departure from azimuthal symmetry. The model includes O^5+ ions with preferential empirical heating and allows calculating their density, velocity and temperature in coronal streamers. We present the first results of our 3D multi-fluid model showing the parameters of protons, electrons and heavy ions (O^5+) at the steady-state solar corona with tilted steamer belt. We find that the 3D results are in qualitative agreement with our previous 2.5D model, and show longitudinal variation in the variables in accordance with the titled streamer belt structure. Properties of heavy coronal ions obtained from the 3D model together with EUV spectroscopic observations of streamers will help understanding the 3D structures of streamers reducing line-of-sight integration ambiguities, and the physics of the slow solar wind, identifying the locations of its sources in the corona.
Authors: L. Ofman, E. Provornikova, L. Abbo, and S. Giordano
Projects: None
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Publication Status: Published
Last Modified: 2015-01-13 14:06
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Observations and models of slow solar wind with Mg9+ ions in quiescent streamers |
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Leon Ofman Submitted: 2012-11-09 07:08
Quiescent streamers are characterized by a peculiar UV signature as pointed out by the results from the observations of the Ultraviolet and Coronograph Spectrometer (UVCS) on board SOHO: the intensity of heavy ion emission lines (such as OVI) show dimmer core relative to the edges. Previous models show that the structure of the heavy ion streamer emission relates to the acceleration regions of the slow solar wind at streamer legs and to gravitational settling processes in the streamer core. Observations of Mg9+ ion EUV emission in coronal streamers at solar minimum were first reported by the UVCS instrument. The Mg X 625A emission is an order of magnitude smaller than the OVI 1032A emission, requiring longer exposures to obtain statistically significant results. Here, MgX coronal observations are analyzed and compared, for the first time, with the solar minimum streamer structure in hydrogen and OVI emissions. We employ the 2.5D three-fluid model, developed previously to study the properties of O5+ ions in streamers, and calculate for the first time the density, temperature, and outflow structure of Mg9+ ions in the solar minimum streamer. The Mg9+ ions are heated by an empirical radial heating function constrained by observations of the kinetic ion temperature obtained from MgX emission line profiles. The detailed structure of Mg9+ density, temperature, and outflow speed determined by the Coulomb momentum and energy exchange as well as electromagnetic interactions with electrons and protons in the three-fluid model of the streamer. The results of the model are in good qualitative agreement with observations, and provide insights on the possible link between the magnetic structure of the streamer, slow solar wind sources, and relative abundances of heavy ions.
Authors: Leon Ofman; Lucia Abbo; Silvio Giordano
Projects:
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Publication Status: The Astrophysical Journal, accepted for publication
Last Modified: 2012-11-27 15:07
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Interaction of EIT Waves with Coronal Active Regions |
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Leon Ofman Submitted: 2001-11-12 10:10
Large scale coronal waves associated with flares were first
observed by the Solar and Heliospheric Observatory (SOHO) Extreme
ultraviolet Imaging Telescope (EIT). We present the first 3D MHD
modeling of this phenomena in order to investigate the interaction
of the EIT waves with active regions, and the possibility of
destabilization of an active region by these waves. The active
region is modeled by an initially force-free, bipolar magnetic
configuration with gravitationally stratified density. We include
finite thermal pressure, and resistive dissipation in our model.
The EIT wave is launched at the boundary of the region, as short
time velocity pulse that travels with the local fast magnetosonic
speed towards the active region. We find that the EIT wave
induces transient currents in the active region, and the resulting
Lorentz force lead to the dynamic distortion of the magnetic
field, and to the generation of secondary waves. The resulting
magnetic compression of the plasma induces flows in the active
region, which are particularly strong in the current-carrying
active region. We investigate the effect of the magnetic field
configuration, and find that current carrying configuration is
destabilized by the impact of the wave. Analysis of the 3D
interaction between EIT waves and active regions can serve as a
diagnostic of the active region coronal magnetic structure and
stability.
Authors: L. Ofman, B.J. Thompson
Projects: Soho-EIT
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Publication Status: ApJ, submitted
Last Modified: 2004-07-14 08:23
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