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Georgoulis M.K.,Research Center for Astronomy and Applied Mathematics of the Academy of Athens | Titov V.S.,Predictive Science Inc. | Mikic Z.,Predictive Science Inc.
Astrophysical Journal | Year: 2012

Using solar vector magnetograms of the highest available spatial resolution and signal-to-noise ratio, we perform a detailed study of electric current patterns in two solar active regions (ARs): a flaring/eruptive and a flare-quiet one. We aim to determine whether ARs inject non-neutralized (net) electric currents in the solar atmosphere, responding to a debate initiated nearly two decades ago that remains inconclusive. We find that well-formed, intense magnetic polarity inversion lines (PILs) within ARs are the only photospheric magnetic structures that support significant net current. More intense PILs seem to imply stronger non-neutralized current patterns per polarity. This finding revises previous works that claim frequent injections of intense non-neutralized currents by most ARs appearing in the solar disk but also works that altogether rule out injection of non-neutralized currents. In agreement with previous studies, we also find that magnetically isolated ARs remain globally current-balanced. In addition, we confirm and quantify the preference of a given magnetic polarity to follow a given sense of electric currents, indicating a dominant sense of twist in ARs. This coherence effect is more pronounced in more compact ARs with stronger PILs and must be of sub-photospheric origin. Our results yield a natural explanation of the Lorentz force, invariably generating velocity and magnetic shear along strong PILs, thus setting a physical context for the observed pre-eruption evolution in solar ARs. © 2012. The American Astronomical Society. All rights reserved.

Leake J.E.,George Mason University | Linton M.G.,U.S. Navy | Torok T.,Predictive Science Inc
Astrophysical Journal | Year: 2013

We present results from three-dimensional visco-resistive magnetohydrodynamic simulations of the emergence of a convection zone magnetic flux tube into a solar atmosphere containing a pre-existing dipole coronal field, which is orientated to minimize reconnection with the emerging field. We observe that the emergence process is capable of producing a coronal flux rope by the transfer of twist from the convection zone, as found in previous simulations. We find that this flux rope is stable, with no evidence of a fast rise, and that its ultimate height in the corona is determined by the strength of the pre-existing dipole field. We also find that although the electric currents in the initial convection zone flux tube are almost perfectly neutralized, the resultant coronal flux rope carries a significant net current. These results suggest that flux tube emergence is capable of creating non-current-neutralized stable flux ropes in the corona, tethered by overlying potential fields, a magnetic configuration that is believed to be the source of coronal mass ejections. © 2013. The American Astronomical Society. All rights reserved..

Roussev I.I.,CAS Yunnan Astronomical Observatory | Roussev I.I.,University of Hawaii at Manoa | Galsgaard K.,Niels Bohr Institute | Downs C.,Predictive Science Inc. | And 4 more authors.
Nature Physics | Year: 2012

Coronal mass ejections (CMEs) are the most energetic events in the solar system and can make near-Earth space a hazardous place. However, there is still no consensus as to what physical mechanisms are responsible for these solar eruptions. Here we demonstrate a fundamental connection between the emergence of magnetic flux into the solar atmosphere and the formation of solar eruptions. We present a model of the dynamics of the solar atmosphere and inner solar wind region using a realistic representation of the electric field at the photosphere, calculated from flux-emergence computer simulations, as the boundary conditions. From this, we show how magnetic flux and helicity injection leads to the reorganization of the solar corona. We show evidence for the in situ formation of a CME plasmoid, which is independent of the emerging flux tube, and we conclusively connect this process to the formation of a hot X-ray structure. © 2012 Macmillan Publishers Limited. All rights reserved.

Agency: National Aeronautics and Space Administration | Branch: | Program: STTR | Phase: Phase II | Award Amount: 741.59K | Year: 2016

Solar Particle Events (SPEs) represent a major hazard for extravehicular maneuvers by astronauts in Earth orbit, and for eventual manned interplanetary space travel. They can also harm aircraft avionics, communication and navigation. We propose to develop a system to aid forecasters in the prediction of such events, and in the identification/lengthening of "all clear" time periods when there is a low probability of such events occurring. The system leverages three recently developed technologies: physics-based models of the solar corona and inner heliosphere, robust CME modeling techniques, and empirical/physics-based assessments of energetic particle fluxes using the Earth-Moon-Mars Radiation Environment Module (EMMREM, University of New Hampshire). When completed, the proposed SPE Threat Assessment Tool, or STAT, will represent a significant step forward in our ability to assess the possible impact of SPE events.

Raymond J.C.,Harvard - Smithsonian Center for Astrophysics | McCauley P.I.,Harvard - Smithsonian Center for Astrophysics | Cranmer S.R.,Harvard - Smithsonian Center for Astrophysics | Downs C.,Predictive science Inc.
Astrophysical Journal | Year: 2014

Extreme-ultraviolet images of Comet Lovejoy (C/2011 W3) from the Atmospheric Imaging Assembly show striations related to the magnetic field structure in both open and closed magnetic regions. The brightness contrast implies coronal density contrasts of at least a factor of six between neighboring flux tubes over scales of a few thousand kilometers. These density structures imply variations in the Alfvén speed on a similar scale. They will drastically affect the propagation and dissipation of Alfvén waves, and that should be taken into account in models of coronal heating and solar wind acceleration. In each striation, the cometary emission moves along the magnetic field and broadens with time. The speed and the rate of broadening are related to the parallel and perpendicular components of the velocities of the cometary neutrals when they become ionized. We use a magnetohydrodynamic model of the coronal magnetic field and the theory of pickup ions to compare the measurements with theoretical predictions, in particular with the energy lost to Alfvén waves as the cometary ions isotropize. © 2014. The American Astronomical Society. All rights reserved..

Mikic Z.,Predictive Science Inc. | Lionello R.,Predictive Science Inc. | Mok Y.,University of California at Irvine | Linker J.A.,Predictive Science Inc. | Winebarger A.R.,NASA
Astrophysical Journal | Year: 2013

We systematically investigate the effects of geometrical assumptions in one-dimensional (1D) models of coronal loops. Many investigations of coronal loops have been based on restrictive assumptions, including symmetry in the loop shape and heating profile, and a uniform cross-sectional area. Starting with a solution for a symmetric uniform-area loop with uniform heating, we gradually relax these restrictive assumptions to consider the effects of nonuniform area, nonuniform heating, a nonsymmetric loop shape, and nonsymmetric heating, to show that the character of the solutions can change in important ways. We find that loops with nonuniform cross-sectional area are more likely to experience thermal nonequilibrium, and that they produce significantly enhanced coronal emission, compared with their uniform-area counterparts. We identify a process of incomplete condensation in loops experiencing thermal nonequilibrium during which the coronal parts of loops never fully cool to chromospheric temperatures. These solutions are characterized by persistent siphon flows. Their properties agree with observations (Lionello et al.) and may not suffer from the drawbacks that led Klimchuk et al. to conclude that thermal nonequilibrium is not consistent with observations. We show that our 1D results are qualitatively similar to those seen in a three-dimensional model of an active region. Our results suggest that thermal nonequilibrium may play an important role in the behavior of coronal loops, and that its dismissal by Klimchuk et al., whose model suffered from some of the restrictive assumptions we described, may have been premature. © 2013. The American Astronomical Society. All rights reserved.

Riley P.,Predictive Science Inc. | Luhmann J.G.,University of California at Berkeley
Solar Physics | Year: 2012

Unipolar streamers (also known as pseudo-streamers) are coronal structures that, at least in coronagraph images, and when viewed at the correct orientation, are often indistinguishable from dipolar (or "standard") streamers. When interpreted with the aid of a coronal magnetic field model, however, they are shown to consist of a pair of loop arcades. Whereas dipolar streamers separate coronal holes of the opposite polarity and whose cusp is the origin of the heliospheric current sheet, unipolar streamers separate coronal holes of the same polarity and are therefore not associated with a current sheet. In this study, we investigate the interplanetary signatures of unipolar streamers. Using a global MHD model of the solar corona driven by the observed photospheric magnetic field for Carrington rotation 2060, we map the ACE trajectory back to the Sun. The results suggest that ACE fortuitously traversed through a large and well-defined unipolar streamer. We also compare heliospheric model results at 1 AU with ACE in-situ measurements for Carrington rotation 2060. The results strongly suggest that the solar wind associated with unipolar streamers is slow. We also compare predictions using the original Wang-Sheeley (WS) empirically determined inverse relationship between solar wind speed and expansion factor. Because of the very low expansion factors associated with unipolar streamers, the WS model predicts high speeds, in disagreement with the observations. We discuss the implications of these results in terms of theories for the origin of the slow solar wind. Specifically, premises relying on the expansion factor of coronal flux tubes to modulate the properties of the plasma (and speed, in particular) must address the issue that while the coronal expansion factors are significantly different at dipolar and unipolar streamers, the properties of the measured solar wind are, at least qualitatively, very similar. © 2011 Springer Science+Business Media B.V.

Antiochos S.K.,NASA | Mikic Z.,Predictive Science Inc. | Titov V.S.,Predictive Science Inc. | Lionello R.,Predictive Science Inc. | Linker J.A.,Predictive Science Inc.
Astrophysical Journal | Year: 2011

Models for the origin of the slow solar wind must account for two seemingly contradictory observations: the slow wind has the composition of the closed-field corona, implying that it originates from the continuous opening and closing of flux at the boundary between open and closed field. On the other hand, the slow wind also has large angular width, up to 60°, suggesting that its source extends far from the open-closed boundary. We propose a model that can explain both observations. The key idea is that the source of the slow wind at the Sun is a network of narrow (possibly singular) open-field corridors that map to a web of separatrices and quasi-separatrix layers in the heliosphere. We compute analytically the topology of an open-field corridor and show that it produces a quasi-separatrix layer in the heliosphere that extends to angles far from the heliospheric current sheet. We then use an MHD code and MDI/SOHO observations of the photospheric magnetic field to calculate numerically, with high spatial resolution, the quasi-steady solar wind, and magnetic field for a time period preceding the 2008 August 1 total solar eclipse. Our numerical results imply that, at least for this time period, a web of separatrices (which we term an S-web) forms with sufficient density and extent in the heliosphere to account for the observed properties of the slow wind. We discuss the implications of our S-web model for the structure and dynamics of the corona and heliosphere and propose further tests of the model. © 2011. The American Astronomical Society. All rights reserved.

Titov V.S.,Predictive Science Inc. | Mikic Z.,Predictive Science Inc. | Linker J.A.,Predictive Science Inc. | Lionello R.,Predictive Science Inc. | Antiochos S.K.,NASA
Astrophysical Journal | Year: 2011

In recent work, Antiochos and coworkers argued that the boundary between the open and closed field regions on the Sun can be extremely complex with narrow corridors of open flux connecting seemingly disconnected coronal holes from the main polar holes and that these corridors may be the sources of the slow solar wind. We examine, in detail, the topology of such magnetic configurations using an analytical source surface model that allows for analysis of the field with arbitrary resolution. Our analysis reveals three new important results. First, a coronal hole boundary can join stably to the separatrix boundary of a parasitic polarity region. Second, a single parasitic polarity region can produce multiple null points in the corona and, more important, separator lines connecting these points. It is known that such topologies are extremely favorable for magnetic reconnection, because they allow this process to occur over the entire length of the separators rather than being confined to a small region around the nulls. Finally, the coronal holes are not connected by an open-field corridor of finite width, but instead are linked by a singular line that coincides with the separatrix footprint of the parasitic polarity. We investigate how the topological features described above evolve in response to the motion of the parasitic polarity region. The implications of our results for the sources of the slow solar wind and for coronal and heliospheric observations are discussed. © 2011. The American Astronomical Society. All rights reserved.

Predictive Science L.L.C. | Date: 2015-05-11

According to an aspect of an embodiment, a method may include obtaining hierarchal data corresponding to a hierarchy associated with an organization. The method may further include obtaining designation data with respect to one or more target areas and one or more target metrics. Moreover, the method may include generating a data map based on the hierarchal data and the designation data. Additionally, the method may include generating one or more scoring formulas and one or more scores based on one or more of the following: the designation data and the hierarchal data. Furthermore, the method may include generating a digital user interface dashboard based on one or more of the following: the data map, the hierarchal data, and the designation data.

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