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Vertical kink oscillations of coronal loops triggered by recurrent jets

Author(s): Wang, Tongjiang (1,2), Ofman, Leon (1,2), Davila, Joseph M. (2)

Institution(s): (1) The Catholic University of America, USA, (2) NASA's GSFC, USA

Abstract:

Transverse coronal loop oscillations were first observed by TRACE in EUV images, and have been interpreted as global standing kink modes. These loop oscillations are thought to be excited by a blast wave in the form of a shock or a fast-mode wave produced by a flare or CME. In this presentation, we report simultaneous imaging and spectroscopic observations with SDO/AIA and Hinode/EIS of a vertical loop oscillations triggered by recurrent jets at the footpoints. These oscillations start with a fast disturbance traveling along the loop with the propagating speed more than 500 km/s, much faster than the apparent EUV jets. The vertical loop oscillations are associated with quasi-periodic outwardly propagating features with the speeds 30-300 km/s, suggestive of loop expansions. In addition, we perform 3D MHD modeling of a typical such event to understand the excitation of kink oscillations by impulsive flows.




Sharp Acceleration of Sunspot Rotation Associated with Flares in NOAA AR 11158

Author(s): Shuo Wang, Chang Liu, Na Deng, Haimin Wang

Institution(s): NJIT

Abstract:

The NOAA AR 11158 produced several major flares and showed spiral penumbra that indicates rotation of sunspots. The Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory provides both 45 seconds and 720 seconds cadence white-light images from two cameras. These unprecedented high-cadence and high-resolution data give us a unique opportunity to study the change of sunspot rotation associated with flares. We calculated vorticity of selected spots derived using the Differential Affine Velocity Estimator method. The results of vorticity evolution from two different cameras match each other, and are consistent with previous studies on spot rotation. We find that some spots show sharp acceleration of rotation at the time of the rising phase of GOES soft X-ray flux, and the faster-than-normal spot rotation could last for about 5-60 minutes.




Computing the Solar EUV Irradiance at Wavelengths Below 450 Å

Author(s): Harry Warren

Institution(s): NRL

Abstract:

The solar EUV irradiance plays a central role in determining the state of the Earth’s upper atmosphere. The EUV irradiance at the shortest wavelengths, which is highly variable over time scales from seconds to decades, is particularly important for many aspects of space weather. Systematic spectrally resolved observations at the shortest EUV wavelengths, however, have been rare and there is a need to develop a methodology for estimating and forecasting the solar irradiance at all EUV wavelengths from sparse data sets. The AIA on SDO provides full Sun solar images in 7 narrow EUV wavelength ranges. These channels were selected to provide complete thermal coverage of the corona and allow for calculation of the differential emission measure distribution. In this presentation we report on our efforts to use AIA DEM calculations to estimate the solar EUV irradiance at wavelength below 450 Å, where the emission is predominately optically thin. To validate our AIA DEM calculations we have performed extensive comparisons with simultaneous observations from the EIS instrument on Hinode and find that with the proper constraints we can generally reproduce the results obtained with detailed spectroscopic observations using AIA. We also present comparisons with existing time series of QEUV, the integrated solar irradiance at wavelengths below 450 Å.




The SDO Social Media Program: Walking the cat back into the bag

Author(s): Wawro, Martha (1,2); Van Norden, Wendy (1,2); Young, C. Alex (1); Durscher, Romeo (3)

Institution(s): 1) NASA GSFC; 2) ADNET Systems Inc. 3) Stanford University

Abstract:

As social media continues to grow as a way to communicate with the public about science missions, data and other STEM related topics, there has become a need for more organized and regimented Social Media programs and plans. In the Heliophysics science division at Goddard Space Flight Center we have been working on creating a template for social media programs which incorporates not just the goals for the program, as well as identifying an audience, but also deals with concerns about messaging, collaboration with other organizations, controversial topics, and evaluation. We hope that through creating a more unified approach we can develop a social media program that not only meets the needs of the audience but incorporates the needs of all of the different entities including the scientists, EPO Professionals and Office of Communications.




Solar Cycle Variation of Coronal Mass Ejections

Author(s): David Webb

Institution(s): ISR, Boston College

Abstract:

The frequency of occurrence of CMEs observed in white light (WL) tends to track the solar cycle in both phase and amplitude, which varies by an order of magnitude over the cycle. Since WL CMEs have been counted since Skylab, we now have observations extending over the last four solar cycles. LASCO has now observed the entire Solar Cycle 23 and continues to observe through the current rise phase of Cycle 24. It has detected CMEs at a rate slightly higher than earlier observations, varying from around 1/day around solar minimum to ~5/day at maximum. Running averages of the CME rate vs. sunspot number shows that both have double cycle peaks, with the CME peak lagging sunspots by many months. This lag is likely related to observations that high latitude CMEs arise from polar crown filaments which have a “rush to the poles”' near maximum and disappear (erupt) with a frequency that slightly lags sunspot numbers at low latitudes. Cycle 23 had an unusually long decline and flat minimum. During this period we have been able to image and count CMEs in the heliosphere, and can determine rates from both LASCO and STEREO coronagraphs and from the Solar Mass Ejection Imager (SMEI) and the SECCHI Heliospheric Imagers in the heliosphere. Manual rates estimated by observers are now supplemented by counts from identifications made by automatic programs, such as contained in the SEEDS, CACTus and ARTEMIS catalogs. Despite differences in amplitude, the CME rate continues to track the sunspot number through its minimum and rise of Cycle 24. We will discuss these rate estimates, both for the Cycle 23-24 period and over the last four cycles for which we have WL CME observations.




Photospheric Drivers of Coronal Evolution

Author(s): B.T. Welsch(1), M. Kazachenko(1), G. H. Fisher(1), M. C. M. Cheung(2), M. L. DeRosa(2), and the CGEM Team(1,2,3)

Institution(s): (1) Space Sciences Lab, UC-Berkeley; (2) Lockheed Martin Solar & Astrophysics Lab; (3) Stanford University

Abstract:

Flares and coronal mass ejections (CMEs) are driven by the release of free magnetic energy stored in the coronal magnetic field. While this energy is stored in the corona, photospheric driving must play a central role in its injection, storage, and release, since magnetic fields present in the corona originated within the solar interior, and are anchored at the photosphere. Also, the corona's low diffusivity and high Alfven speed (compared to that at the photosphere) imply that the large-scale coronal field essentially maintains equilibrium (outside of episodic flares and CMEs!), and therefore only evolves due to forcing from photospheric evolution. But fundamental questions about each stage of this "storage and release" paradigm remain open: How does free magnetic energy build up in the corona? How is this energy stored? And what triggers its release? The unprecedented combination of high cadence, resolution, and duty cycle of the HMI vector magnetograph enables modeling coronal magnetic evolution in response to photospheric driving, a powerful approach to addressing these questions. I will discuss our efforts to use HMI vector magneotgrams of AR 11158 to derive time-dependent boundary conditions for a data-driven coronal magnetic field model. These efforts will play a key role in the planned Coronal Global Evolutionary Model (CGEM), a data-driven, time-dependent model of the global coronal field. This work is supported by NASA's Living With a Star program and NSF's Division of Atmospheric and Geospace Sciences.




Quasi-Periodic Pulsations during the onset of solar flares: multi-instrumental comparison

Author(s): M. J. West (1), L. Dolla (1), C. Marque (1), D. B. Seaton (1), T. Van Doorsselaere (2), M. Dominique (1), D. Berghmans (1), C. Cabanas (1), A. De Groof (1, 3), W. Schmutz (4), A. Verdini (1), J. Zender (3), A. N. Zhukov (1,5)

Institution(s): (1) Solar-Terrestrial Center of Excellence, Royal Observatory of Belgium, Brussels, Belgium; (2) Centrum voor Plasma-Astrofysica, Department of Mathematics, KULeuven, Leuven, Belgium; (3) European Space Agency, ESTEC, Noordwijk, The Netherlands; (4) Physikalisch-Meteorologisches Observatorium Davos, World Radiation Center, Davos Dorf, Switzerland; (5) Skobeltsyn Institute of Nuclear Physics, Moscow State University, Moscow, Russia

Abstract:

Quasi-periodic pulsations have been observed in the rising phase of solar flares for many years. Observations have been made over a wide spectral range, extending from X-rays to radio wavelengths. The current generation of spacebourne instruments, especially SDO, EVE and ESP, have exceptionally high sampling rates and allow us to make more detailed observations of this phenomena. In this work, we compare short-period oscillations (around 10 s) observed in flare events by multiple instruments: the radiometer channels of SDO/EVE-ESP (soft X-ray, coronal and chromospheric passbands), the EUV channels of the radiometer PROBA2/LYRA, the RHESSI passbands and short-wavelength radio observations.




A comparison of SOHO/SEM zeroth-order (0.1-50 nm) and SDO/EVE integrated spectral irradiances

Author(s): Seth Wieman, Leonid Didkovsky, Darrell Judge

Institution(s): University of Southern California

Abstract:

The SOHO/CELIAS Solar EUV Monitor (SEM), which has measured absolute extreme ultraviolet (EUV) solar irradiance nearly continuously over a 17 year period covering two solar minima, includes a zero-order channel with an approximate bandpass of 0.1-50 nm. We present a comparison of SDO/EVE 6-50 nm integrated spectral irradiance with the SOHO/SEM zeroth-order band irradiances for the period of overlap between the SOHO and SDO missions. Also included in this comparison are absolute measurements from the Neon Rare Gas Ionization Cell (RGIC), an instrument with similar bandpass (~5-57 nm as limited by the photionization threshold of neon), that is flown periodically on the SOHO/SEM sounding rocket calibration underflights, the most recent of which launched on July 24, 2012 providing a measurement that is concurrent with both SDO/EVE and SOHO/SEM. A reference spectrum is required in order to calculate irradiance values based on the SEM raw data as well as to correct for the small differences in bandpass when intercomparing EVE, SEM and RGIC measurements. Before the SDO/EVE spectra were available, the SOLERS22 model reference spectrum was used. In this work, the effect of using composite spectra based on SDO/EVE spectra in place of SOLERS22 for the period during which SDO has been in operation is discussed.




Fe I Spectra of Core-Halo Structures in a White-Light Flare

Author(s): Yan Xu, Ju Jing & Haimin Wang

Institution(s): New Jersey Institute of Technology

Abstract:

In this study, we present the imaging spectroscopy of an X-class flare with white-light emission on September 06, 2011, observed with Helioseismic Magnetic Imager (HMI) on board Solar Dynamics Observatory (SDO). The HMI provides seeing-free images at 6173 \AA continuum with a 45s cadence and six-point spectrograms centered at 6173.34 \AA with 0.172 \AA steps. Taking advantage of the 0.5\arcsecond image scale, the flare kernels are fully resolved and fine structures, including the core and halo, are able to be identified. We analyzed the line-profile, constructed from six spectral positions, of the flare core and halo pixels, respectively. We studied the morphology of the continuum flare kernel comparing with previous white-light observations. The resemblance and the discrepancy of the two kinds of spectra, which could be related to different heating mechanisms, are then discussed.




SDO and Hinode observations of coronal heating at a flare kernel site

Author(s): Young, P.R. (1), Doschek, G.A. (2), Warren, H.P. (2), Hara, H. (3)

Institution(s): (1) George Mason University, VA, USA, (2) Naval Research Laboratory, DC, USA, (3) NAOJ, Tokyo, Japan

Abstract:

Flare kernels are compact features located in the chromosphere that are the sites of rapid heating and plasma upflow during the rise phase of flares. They provide an excellent opportunity for testing models of energy transport and dissipation in the solar atmosphere as they are very bright and emit over a wide temperature range. A M1.1 class flare that peaked at 07:44 UT on 2011 February 16 was observed simultaneously by SDO and Hinode, and one flare kernel observed prior to the flare peak is highlighted. It is found to emit at all temperatures from the chromosphere through to 30 MK, with all AIA channels brightening simultaneously and rise times of only 1 minute. The kernel is located on a ridge of strong magnetic field close to a neutral line in the active region. The kernel is at the resolution limit of AIA, suggesting a size of < 0.6 arcsec. Hinode/EIS allows velocity patterns in the kernel to be tracked over a wide temperature range and reveals a dominant high speed upflow of 400 km/s at temperatures of 10-30 MK, with both down and upflows measured at cooler temperatures of 1.5-3.0 MK, suggesting unresolved structures. All emission lines show evidence of significant non-thermal broadening, and the electron density of the plasma is 3.4 x 10^10 cm-3. The observations are compared to models of chromospheric evaporation and similarities and differences are highlighted.





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Last Updated on Tuesday, 29 March 2011 09:36