Confined and Ejective Eruptions of Kink-unstable Flux Ropes

The Astrophysical Journal (Impact Factor: 5.99). 07/2005; 630(1). DOI: 10.1086/462412
Source: arXiv


The ideal helical kink instability of a force-free coronal magnetic flux rope, anchored in the photosphere, is studied as a model for solar eruptions. Using the flux rope model of Titov & Demoulin (1999} as the initial condition in MHD simulations, both the development of helical shape and the rise profile of a confined (or failed) filament eruption (on 2002 May 27) are reproduced in very good agreement with the observations. By modifying the model such that the magnetic field decreases more rapidly with height above the flux rope, a full (or ejective) eruption of the rope is obtained in very good agreement with the developing helical shape and the exponential-to-linear rise profile of a fast coronal mass ejection (CME) (on 2001 May 15). This confirms that the helical kink instability of a twisted magnetic flux rope can be the mechanism of the initiation and the initial driver of solar eruptions. The agreement of the simulations with properties that are characteristic of many eruptions suggests that they are often triggered by the kink instability. The decrease of the overlying field with height is a main factor in deciding whether the instability leads to a confined event or to a CME. Comment: minor update to conform to printed version; typo in table corrected

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    • "As described in the previous section, the helical deformation of a flux rope's axis that may ultimately produce a kinked shape is generally referred to as writhe (Török, Berger, and Kliem, 2010). The kink instability is one of the principal mechanisms thought to drive prominence eruptions (see Section 5 and the review by Fan 2015), and numerical simulations of kink-unstable flux ropes have been very successful in reproducing characteristics of observed events (Török and Kliem, 2005), suggesting that coronal flux ropes exist prior to eruption (Gibson and Fan, 2006). An overview of how the kink instability manifests in solar observations is given by Gilbert, Alexander, and Liu (2007), a recent effort to quantify the twist in a likely kink-unstable event is presented by Yan et al. (2014), and recent numerical simulations addressing whether or not the amount of pre-eruptive twist can be estimated from the measurements of writhe are presented by Török et al. (2014). "
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    ABSTRACT: We present a statistical study of prominence and filament eruptions observed by the Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics Observatory (SDO). Several properties are recorded for 904 events that were culled from the Heliophysics Event Knowledgebase (HEK) and incorporated into an online catalog for general use. These characteristics include the filament and eruption type, eruption symmetry and direction, apparent twisting and writhing motions, and the presence of vertical threads and coronal cavities. Associated flares and white-light coronal mass ejections (CME) are also recorded. Total rates are given for each property along with how they differ among filament types. We also examine the kinematics of 106 limb events to characterize the distinct slow- and fast-rise phases often exhibited by filament eruptions. The average fast-rise onset height, slow-rise duration, slow-rise velocity, maximum field-of-view (FOV) velocity, and maximum FOV acceleration are 83 Mm, 4.4 hours, 2.1 km/s, 106 km/s, and 111 m/s^2, respectively. All parameters exhibit lognormal probability distributions similar to that of CME speeds. A positive correlation between latitude and fast-rise onset height is found, which we attribute to a corresponding negative correlation in the average vertical magnetic field gradient, or decay index, estimated from potential field source surface (PFSS) extrapolations. We also find the decay index at the fast-rise onset point to be 1.1 on average, consistent with the critical instability threshold theorized for straight current channels. Finally, we explore relationships between the derived kinematics properties and apparent twisting motions. We find that events with evident twist have significantly faster CME speeds and significantly lower fast-rise onset heights, suggesting relationships between these values and flux rope helicity.
    Solar Physics 05/2015; 290(6). DOI:10.1007/s11207-015-0699-7 · 4.04 Impact Factor
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    • "Daily Xb10 (lower panel) and hourly Xhf (upper panel) indices produced by SET from GOES XRS data. 2002; Török and Kliem, 2005; NASA/TM—2006–214137, 2006, and Chen and Kunkel, 2010] "
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    ABSTRACT: This paper describes new capabilities for operational geomagnetic Disturbance storm time (Dst) index forecasts. We present a data‐driven, deterministic algorithm called Anemomilos for forecasting Dst out to a maximum of 6 days for large, medium, and small storms, depending upon transit time to the Earth. This capability is used for operational satellite management and debris avoidance in Low Earth Orbit (LEO). Anemomilos has a 15 min cadence, 1 h time granularity, 144 h prediction window (+6 days), and up to 1 h latency. A new finding is that nearly all flare events above a certain irradiance threshold, occurring within a defined solar longitude/latitude region and having sufficient estimated liftoff velocity of ejected material, will produce a geoeffective Dst perturbation. Three solar observables are used for operational Dst forecasting: flare magnitude, integrated flare irradiance through time, and event location. Magnitude is a proxy for ejecta quantity or mass and, combined with speed derived from the integrated flare irradiance, represents the kinetic energy. Speed is estimated as the line‐of‐sight velocity for events within 45° radial of solar disk center. Storms resulting from high‐speed streams emanating from coronal holes are not modeled or predicted. A new result is that solar disk, not limb, observable features are used for predictive techniques. Comparisons between Anemomilos predicted and measured Dst for every hour over 25 months in three continuous time frames between 2001 (high solar activity), 2005 (low solar activity), and 2012 (rising solar activity) are shown. The Anemomilos operational algorithm was developed for a specific customer use related to thermospheric mass density forecasting. It is an operational space weather technology breakthrough using solar disk observables to predict geomagnetically effective Dst up to several days at 1 h time granularity. Real‐time forecasts are presented at
    Space Weather 09/2013; 11(9). DOI:10.1002/swe.20094 · 2.15 Impact Factor
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    • "The emergence of such twisted and unstable magnetic flux tubes, or their activation and interactions in the active regions, may also trigger the flare energy release and associated eruptions as studied recently by ,e.g., Kumar, Manoharan, and Uddin (2010a), Kumar et al. (2010c), Kumar et al. (2010b), Srivastava et al., 2010. On the modelling side, most of the numerical simulations have used magnetic flux emergence and sunspot rotation caused by photospheric plasma flows to increase the magnetic helicity leading to the final eruption (e.g., Amari et al., 2000, Török and Kliem, 2003, 2005). Shen, Liu, and Liu (2011) have reported the dynamics of a filament that failed in the eruption several times, and finally succeeded to erupt with the triggering of a C-class flare process and associated CME on 8 February 2010 from active region (AR) NOAA 11045. "
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    ABSTRACT: We present the multiwavelength observations of a flux rope that was trying to erupt from NOAA AR 11045 and the associated M-class solar flare on 12 February 2010 using space-based and ground-based observations from TRACE, STEREO, SOHO/MDI, Hinode/XRT, and BBSO. While the flux rope was rising from the active region, an M1.1/2F class flare was triggered near one of its footpoints. We suggest that the flare triggering was due to the reconnection of a rising flux rope with the surrounding low-lying magnetic loops. The flux rope reached a projected height of ≈0.15R ⊙ with a speed of ≈90 km s−1 while the soft X-ray flux enhanced gradually during its rise. The flux rope was suppressed by an overlying field, and the filled plasma moved towards the negative polarity field to the west of its activation site. We found the first observational evidence of the initial suppression of a flux rope due to a remnant filament visible both at chromospheric and coronal temperatures that evolved a couple of days earlier at the same location in the active region. SOHO/MDI magnetograms show the emergence of a bipole ≈12 h prior to the flare initiation. The emerged negative polarity moved towards the flux rope activation site, and flare triggering near the photospheric polarity inversion line (PIL) took place. The motion of the negative polarity region towards the PIL helped in the build-up of magnetic energy at the flare and flux rope activation site. This study provides unique observational evidence of a rising flux rope that failed to erupt due to a remnant filament and overlying magnetic field, as well as associated triggering of an M-class flare. KeywordsFlux rope–Magnetic field–Magnetic reconnection–Solar flare – coronal loops
    Solar Physics 09/2011; 272(2):301-317. DOI:10.1007/s11207-011-9829-z · 4.04 Impact Factor
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