Browsing by Author "Cheung, M."

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High‐resolution Observations of the Shock Wave Behavior for Sunspot Oscillations with the Interface Region Imaging Spectrograph
(2014-05) Tian, Hui; DeLuca, E.E.; Reeves, Kathy K.; McKillop, Sean; De Pontieu, Bart; Martínez-Sykora, J.; Carlsson, Mats; Hansteen, Viggo H.; Kleint, Lucia; Cheung, M.; Golub, Leon; Saar, Steven; Testa, Paola; Weber, Mark A.; Lemen, James; Title, Alan M.; Boerner, P.; Hurlburt, Neal E.; Tarbell, Ted D.; Wülser, Jean-Pierre; Kankelborg, Charles; Jaeggli, Sarah; McIntosh, Scott W.
We present the first results of sunspot oscillations from observations by the Interface Region Imaging Spectrograph. The strongly nonlinear oscillation is identified in both the slitjaw images and the spectra of several emission lines formed in the transition region and chromosphere. We first apply a single Gaussian fit to the profiles of the Mg II 2796.35 Å, C II 1335.71 Å, and Si IV 1393.76 Å lines in the sunspot. The intensity change is ~30%. The Doppler shift oscillation reveals a sawtooth pattern with an amplitude of ~10 km s1 in Si IV. The Si IV oscillation lags those of C II and Mg II by ~3 and ~12 s, respectively. The line width suddenly increases as the Doppler shift changes from redshift to blueshift. However, we demonstrate that this increase is caused by the superposition of two emission components. We then perform detailed analysis of the line profiles at a few selected locations on the slit. The temporal evolution of the line core is dominated by the following behavior: a rapid excursion to the blue side, accompanied by an intensity increase, followed by a linear decrease of the velocity to the red side. The maximum intensity slightly lags the maximum blueshift in Si IV, whereas the intensity enhancement slightly precedes the maximum blueshift in Mg II. We find a positive correlation between the maximum velocity and deceleration, a result that is consistent with numerical simulations of upward propagating magnetoacoustic shock waves.
The Interface Region Imaging Spectrograph (IRIS)
(2014-02) De Pontieu, Bart; Title, Alan M.; Lemen, James; Kushner, G.D.; Akin, D.J.; Allard, A.; Berger, T.; Boerner, P.; Cheung, M.; Chou, C.; Drake, J.F.; Duncan, D.W.; Freeland, S.; Heyman, G.F.; Hoffman, C.; Hurlburt, Neal E.; Lindgren, R.W.; Mathur, D.; Rehse, R.; Sabolish, D.; Seguin, R.; Schrijver, C.J.; Tarbell, Ted D.; Wülser, J.P.; Wolfson, C.J.; Yanari, C.; Mudge, J.; Nguyen-Phuc, N.; Timmons, R.; van Bezooijen, R.; Weingrod, I.; Brookner, R.; Butcher, G.; Dougherty, B.; Eder, J.; Knagenhjelm, V.; Larsen, S.; Mansir, D.; Phan, L.; Boyle, P.; Cheimets, P.N.; DeLuca, E.E.; Golub, Leon; Gates, R.; Hertz, E.; McKillop, Sean; Park, Saehan; Perry, T.; Podgorski, W.A.; Reeves, Kathy K.; Saar, Steven; Testa, Paola; Tian, Hui; Weber, Mark A.; Dunn, C.; Eccles, S.; Jaeggli, Sarah; Kankelborg, Charles; Mashburn, K.; Pust, Nathan J.; Springer, Larry
The Interface Region Imaging Spectrograph (IRIS) small explorer spacecraft provides simultaneous spectra and images of the photosphere, chromosphere, transition region, and corona with 0.33 0.4 arcsec spatial resolution, twosecond temporal resolution, and 1 km s1 velocity resolution over a fieldofview of up to 175 arcsec × 175 arcsec. IRIS was launched into a Sunsynchronous orbit on 27 June 2013 using a PegasusXL rocket and consists of a 19cm UV telescope that feeds a slitbased dualbandpass imaging spectrograph. IRIS obtains spectra in passbands from 1332 1358 Å, 1389 1407 Å, and 2783 2834 Å, including bright spectral lines formed in the chromosphere (Mg ii h 2803 Å and Mg ii k 2796 Å) and transition region (C ii 1334/1335 Å and Si iv 1394/1403 Å). Slitjaw images in four different passbands (C ii 1330, Si iv 1400, Mg ii k 2796, and Mg ii wing 2830 Å) can be taken simultaneously with spectral rasters that sample regions up to 130 arcsec × 175 arcsec at a variety of spatial samplings (from 0.33 arcsec and up). IRIS is sensitive to emission from plasma at temperatures between 5000 K and 10 MK and will advance our understanding of the flow of mass and energy through an interface region, formed by the chromosphere and transition region, between the photosphere and corona. This highly structured and dynamic region not only acts as the conduit of all mass and energy feeding into the corona and solar wind, it also requires an order of magnitude more energy to heat than the corona and solar wind combined. The IRIS investigation includes a strong numerical modeling component based on advanced radiativeMHD codes to facilitate interpretation of observations of this complex region. Approximately eight Gbytes of data (after compression) are acquired by IRIS each day and made available for unrestricted use within a few days of the observation.