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There are 146 abstracts


Coupled model for the formation of an active region corona

Author(s): Chen, Feng (1), Bingert, Sven (2), Peter, Hardi (3), Cameron Robert (4), Schüssler, Manfred (5), Cheung, Mark C. M. (6)

Institution(s): (1) Max Planck Institute for Solar System Research, Katlenburg-Lindau, Germany, (2) Lockheed Martin Solar and Astrophysics Laboratory, CA, USA

Abstract:

We will present the first model that couples the formation of an active region corona to a model of the emergence. This allows us to study when, where, and why active region loops form, and how they evolve. For this we use an existing 3D radiation MHD model of the emergence of an active region through the upper convection zone and the photosphere as a lower boundary for a coronal model. Our 3D MHD coronal model accounts for the braiding of the magnetic field lines that induces currents in the corona that is getting filled with the emerging magnetic field. Starting with a basically field-free atmosphere we follow the flux emergence until numerous individually identifiable hot coronal loops have been formed. The temperatures in the coronal loops of well above 1 MK are reached at densities corresponding to actually observed active region loops. The loops develop over a very short time period of the order of several minutes through the evaporation of material from the chromosphere. Because we have full access to the heating rate as a function of time and space in our computational domain we can determine the conditions under which these loops form.




Coordinated Observations of On-Disk Type II Spicules with IBIS and Hinode

Author(s): XIN CHEN (1), NA DENG (1), JU JING (1), ALEXANDRA TRITSCHLER (2), KEVIN REARDON (3,4) and HAIMIN WANG (1)

Institution(s): (1) Space Weather Research Laboratory, New Jersey Institute of Technology (2) National Solar Observatory, Sunspot, NM (3) INAF - Osservatorio Astrofisico di Arcetri, Florence, Italy (4) Astrophysics Research Centre, Queen’s University, Belfast, Northern Ireland, UK

Abstract:

Ubiquitous small-scale spicules/jets in the chromosphere are believed to be an important ingredient contributing to coronal heating and solar wind by supplying energy and mass upwards. In particular, type II spicules discovered at the solar limb (De Pontieu et al. 2007) and their highly probable chromospheric on disk counterpart "Rapid Blueshifted Excursions" (RBEs; Langangen et al. 2008) have drawn much attention in recent years. Their rapid heating, high speed upflow and association with magnetic field indicate that the most possible underlying driving mechanism is magnetic reconnection on small scales. In order to understand the physical properties of these features, we carried out a coordinated high resolution and high cadence observation of chromospheric RBEs using the Interferometric BIdimensional Spectrometer (IBIS) at the Dunn Solar Telescope and photospheric magnetic fields using Hinode SOT/SP and SOT/NFI in October 2011. We identify RBEs based on the IBIS observations, study their properties (velocity, density, temperature etc.) by statistical analysis and show their relationship with signatures of small-scale magnetic reconnection in the Hinode magnetograms. Furthermore, we search for coronal counterpart of RBEs from observations of the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO). References: De Pontieu, B. et al. 2007, PASJ, 59, 655-662 Langangen, O. et al. 2008, ApJ, 679, L167




The Coronal Mass Source for Post-Eruption Arcade Loops

Author(s): Cheung, M. C. M. (1), Title , A. M. (1), Boerner, P. (1)

Institution(s): Lockheed Martin Solar & Astrophysics Laboratory

Abstract:

Dark, sunward propagating features above post-eruption arcades have long been studied using X-ray and EUV data since their first reported discovery in the Yohkoh era. The data suggests that these so-called supra-arcade downflows (SADs, sometimes referred to as tadpoles) may be evacuated field lines retracting from the current sheet beneath a coronal mass ejection. In this study, we focus on the bright material in between tadpoles. AIA observations indicate that this high emission-measure (EM) material is also propagating sunward. From this empirical detection, we argue that a large fraction of retracting field lines is loaded with mass. This plasma, which was initially thrown up into the high coronal during the preceding CME launch, is trapped in the reconnected magnetic field lines. As these field lines retract toward a more force-free configuration, they pump the plasma sunward and compress the plasma to high densities, temperatures (T > 10 MK) and EMs, leading to the fuzzy haze above the post-eruption arcade loops. The fuzzy haze actually precedes the formation of distinct arcade loops, which originate starting from the loop tops (which are near the bottom of the haze) instead of the footpoints. We suggest this occurs because the bottom of the haze is the region that has experienced the most compression (due to pile-up up of retracting field lines) and is thus an ideal location for catastrophic cooling to occur.




“Reconstructing the Subsurface Three-Dimensional Magnetic Structure of A Solar Active Region Using SDO/HMI Observations”

Author(s): Georgios Chintzoglou, Jie Zhang

Institution(s): George Mason University

Abstract:

A solar active region (AR) is a three-dimensional magnetic structure formed in the convection zone, whose property is fundamentally important for determining the coronal structure and solar activity when emerged. However, our knowledge on the detailed 3-D structure prior to its emergence is rather poor, largely limited by the low cadence and sensitivity of previous instruments. Here, using the 45-second high-cadence observations from the Helioseismic and Magnetic Imager (\emph{HMI}) onboard the Solar Dynamics Observatory (\emph{SDO}), we are able for the first time to reconstruct a 3-D Datacube and infer the detailed subsurface magnetic structure of NOAA AR 11158 and to characterize its magnetic connectivity and topology. This task is accomplished with the aid of the image-stacking method and advanced 3-D visualization. We find that the AR consists of two major bipoles, or four major polarities. Each polarity in 3-D shows interesting tree-like structure, i.e. while the root of the polarity appears as a single tree-trunk-like tube, the top of the polarity has multiple branches consisting of smaller and thinner flux-tubes which connect to the branches of the opposite polarity that is similarly fragmented. The roots of the four polarities align well along a straight line, while the top branches are slightly non-coplanar. Our observations suggest that an active region, even appearing most complicated on the surface, may originate from a simple straight flux-tube that undergoes both horizontal and vertical bifurcation processes during its rise through the convection zone.




Progress Report of Korean Data Center for SDO

Author(s): Choi, S., Hwang, E., Baek, J.-H., Kim, Y.-H., Park, Y.-D., and Cho, K.-S.

Institution(s): Korea Astronomy and Space Science Institute

Abstract:

KASI has been constructing Korean Data Center for SDO based on the letter of agreement between KASI and NASA for space weather research. We have installed a data transfer server and a storage system about 1.5 PB. We have successfully installed NetDRMS to synchronize database and JMD to download FITS files with the help of Stanford University and NSO. We will increase its storage capacity more from year to year. In 2013, we will improve network performance and stability through GLORIAD between Stanford University and KASI, and it will be integrated with VSO (Virtual Solar Observatory). In addition, scientists and space weather institutes will be able to access Korean data center through the website (http://sdo.kasi.re.kr) and the visualization tool that is in development and be scheduled to be released in the middle of this year. The Korean Data Center for SDO will contribute space weather researches and applications not only in Korea but also over the world.




Comparison Between Line-Of-Sight Observables And Milne-Eddington Inversion Results From HMI: 24- And 12-hour Period Oscillations

Author(s): Couvidat, Sebastien (1), Liu, Yang (1), Scherrer, Philip H. (1), Schou, Jesper (1), and the HMI Team

Institution(s): (1) Stanford University, CA, USA

Abstract:

Oscillations with 12 and 24 hour periods are visible in sunspots on line-of-sight (LOS) observables and, to a lesser extent, on Milne-Eddington (ME) inversion results from the SDO/HMI instrument.Such oscillations are artifacts produced by the LOS algorithm and ME inversion procedure, and are not of solar origin. For instance, the LOS algorithm depends on an Fe I line profile and on HMI filter transmission profiles to convert the HMI intensities into Doppler velocities and LOS magnetic-field strengths: one of the issues we encountered is that in the presence of strong fields the Fe I profile used is inappropriate and results in errors in the left and right circular polarization velocity estimates. Here we present some properties of these 12- and 24-hour period oscillations, and we discuss their origin and the possibility of improving the LOS algorithm and ME inversion procedure to reduce their amplitudes.




Turbulence as a Unifying Principle in Coronal Heating and Solar Wind Acceleration

Author(s): Steven R. Cranmer

Institution(s): Harvard-Smithsonian Center for Astrophysics

Abstract:

The origins of the hot solar corona and the supersonically expanding solar wind are still the subject of much debate. Far from there being a shortage of ideas, there is in fact a surplus of proposed physical mechanisms, each of which requires testing by comparison with the right observations. Many of the suggested processes are related to the dissipation of solar MHD waves, and many involve multiple steps of energy conversion between waves, turbulence, current sheets, and other nonlinear plasma features. This presentation will give a summary of wave/turbulence models that seem to succeed in explaining the time-steady properties of the corona and the existence of fast and slow solar wind streams. Models employing turbulent heating have been found to reproduce many of the observed features of the fast and slow solar wind without the need for artificial "coronal heating functions" used by earlier models. The newest versions of these models are also being used to simulate the development of corotating stream structures at 1 AU, seeded by small-scale coronal flux tubes resolved at the sub-arcsecond level at the solar surface. This presentation will also summarize the results of time-dependent 3D reduced MHD simulations of turbulence in coronal loops and open field regions. These simulations largely validate the phenomenological turbulent heating terms used in larger-scale models, and they shed light on the apparent inability of slow quasi-static "braiding" to provide sufficient energy to explain coronal heating.




Some Difficulties in Determining Causality of Sympathetic Solar Events

Author(s): M.L. DeRosa(1), C.J. Schrijver(1), A.M. Title(1), A.R. Yeates(2)

Institution(s): (1) Lockheed Martin Solar and Astrophysics Laboratory (2) Department of Mathematical Sciences, Durham University

Abstract:

Much has been made regarding the occurrence of synchronous eruptive events occurring in the solar corona. Determining the frequencies at which they occur and understanding the causal linkages that may connect such events (making them sympathetic in addition to synchronous) are an area of active research. Causal linkages are observed to take the form of (1) disturbances in magnetic fields that connect active regions, (2) disturbances in the magnetic field configuration overlying active regions, and/or (3) triggering by disturbances propagating from one region to another. Here we display two types of synchronous events: those where, using a combination of image sequences from SDO and STEREO as well as coronal-field modeling, evidence for sympathy seems solid, and those where evidence of sympathy is more ambiguous. We use these two types of cases to illustrate some difficulties in establishing whether synchronous events are in fact sympathetic. This has implications for determining the frequency and importance of sympathetic events, and thus for understanding of coronal field evolution and the origins of space weather.




Coronal Post-Flare Dynamics for 14 August 2010 Late Phase of the Coronal Dimming Event

Author(s): Leonid Didkovsky (1), Darrell Judge (1), Seth Wieman (1), Tom Woods (2), Rachel Hock (3), Phillip Chamberlin (4), Kent Tobiska (5), Hugh Hudson (6)

Institution(s): (1) University of Southern California, (2) Laboratory for Atmospheric and Space Physics, (3) US Air Force, (4) Goddard Space Flight Center, (5) Space Environment Technologies, (6) Space Sciences Laboratory

Abstract:

Coronal irradiance dynamics related to the 14 August 2010 C4.4 post-flare event was analyzed using EUV spectral emission lines in the range of logT from 5.8 to 6.4 (0.7 to 2.6 MK). Temporal changes of high-resolution spectral irradiance for different thermal layers of the Corona from the Extreme ultraviolet Variability Experiment (EVE) onboard the Solar Dynamics Observatory (SDO) were compared to study both a decrease and an increase of the spectral irradiance during the late phase of the coronal dimming. We found an irradiance decrease which propagated from the low-temperature layer to the higher temperature layers with much lower speed than the speed of the `horizontal’ dimming wave inside the low-temperature layer. This upward decrease of the irradiance in the coronal layers may represent a `vertical’ spatial perturbation of the plasma within these layers in response to the plasma density and temperature decreases of the dimming wave. The perturbation may cause a redistribution of the coronal loops and trigger the late phase of the flare. The increase of the irradiance detected in the high-temperature coronal layers where the late phase of the flare occurred after 12 UT was propagating in part downward, restoring the pre-dimming plasma conditions in these Coronal layers.




Flare Footpoint Regions Observed by the Extreme-ultraviolet Imaging Spectrometer (EIS) on Hinode

Author(s): G. A. Doschek, H. P. Warren, P. R. Young, & A. Caspi

Institution(s): Naval Research Laboratory

Abstract:

The Extreme-ultraviolet Imaging Spectrometer (EIS) on Hinode has observed flare footpoints using a variety of studies designed to observe various aspects of the solar flare Standard Model. Some of these observations are accompanied by imaging data from RHESSI. We present observations of upflows in flare footpoint regions obtained from picket-fence raster observations of two flares that occurred on 24 and 25 September 2011. The observations consist of upflow and non-thermal speeds at various temperatures (from about 1 MK to 15 MK) at footpoint regions as well as a limited differential emission measure. RHESSI observations provide constraints on the energetic electron precipitation into the footpoints. Electron densities are available from an Fe XIV ratio, and SDO AIA data are also investigated for context. The RHESSI energy input will be assessed in terms of 1D models of the footpoint regions.





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Last Updated on Tuesday, 29 March 2011 09:36