Browsing by Author "Martínez-Sykora, J."

Now showing 1 - 4 of 4

Detection of Supersonic Downflows and Associated Heating Events in the Transition Region above Sunspots
(2014-07) Kleint, Lucia; Antolin, P.; Tian, Hui; Judge, P.; Testa, Paola; De Pontieu, Bart; Martínez-Sykora, J.; Reeves, Kathy K.; Wülser, Jean-Pierre; McKillop, Sean; Saar, Steven; Carlsson, Mats; Boerner, P.; Hurlburt, Neal E.; Lemen, James; Tarbell, Ted D.; Title, Alan M.; Golub, Leon; Hansteen, Viggo H.; Jaeggli, Sarah; Kankelborg, Charles
Interface Region Imaging Spectrograph data allow us to study the solar transition region (TR) with an unprecedented spatial resolution of 0.''33. On 2013 August 30, we observed bursts of high Doppler shifts suggesting strong supersonic downflows of up to 200 km s–1 and weaker, slightly slower upflows in the spectral lines Mg II h and k, C II 1336, Si IV 1394 Å, and 1403 Å, that are correlated with brightenings in the slitjaw images (SJIs). The bursty behavior lasts throughout the 2 hr observation, with average burst durations of about 20 s. The locations of these shortlived events appear to be the umbral and penumbral footpoints of EUV loops. Fast apparent downflows are observed along these loops in the SJIs and in the Atmospheric Imaging Assembly, suggesting that the loops are thermally unstable. We interpret the observations as cool material falling from coronal heights, and especially coronal rain produced along the thermally unstable loops, which leads to an increase of intensity at the loop footpoints, probably indicating an increase of density and temperature in the TR. The rain speeds are on the higher end of previously reported speeds for this phenomenon, and possibly higher than the freefall velocity along the loops. On other observing days, similar bright dots are sometimes aligned into ribbons, resembling small flare ribbons. These observations provide a first insight into smallscale heating events in sunspots in the TR.
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.
Homologous Helical Jets: Observations By IRIS, SDO, and Hinode and Magnetic Modeling With Data‐Driven
(2015-03-05) Cheung, Mark C.M.; De Pontieu, B.; Tarbell, Ted D.; Fu, Y.; Tian, Hui; Testa, Paola; Reeves, Kathy K.; Martínez-Sykora, J.; Boerner, B.; Wülser, J.P.; Lemen, James; Title, Alan M.; Hurlburt, Neal E.; Kleint, Lucia; Kankelborg, Charles; Jaeggli, Sarah; Golub, Leon; McKillop, Sean; Saar, Steven; Carlsson, Mats; Hansteen, Viggo H.
We report on observations of recurrent jets by instruments on board the Interface Region Imaging Spectrograph, Solar Dynamics Observatory (SDO), and Hinode spacecraft. Over a 4 hr period on 2013 July 21, recurrent coronal jets were observed to emanate from NOAA Active Region 11793. Far-ultraviolet spectra probing plasma at transition region temperatures show evidence of oppositely directed flows with components reaching Doppler velocities of ±100 km s−1. Raster Doppler maps using a Si iv transition region line show all four jets to have helical motion of the same sense. Simultaneous observations of the region by SDO and Hinode show that the jets emanate from a source region comprising a pore embedded in the interior of a supergranule. The parasitic pore has opposite polarity flux compared to the surrounding network field. This leads to a spine-fan magnetic topology in the coronal field that is amenable to jet formation. Time-dependent data-driven simulations are used to investigate the underlying drivers for the jets. These numerical experiments show that the emergence of current-carrying magnetic field in the vicinity of the pore supplies the magnetic twist needed for recurrent helical jet formation.
The Unresolved Fine Structure Resolved: IRIS Observations of the Solar Transition Region
(2014-10) Hansteen, Viggo H.; De Pontieu, B.; Carlsson, Mats; Lemen, James; Title, Alan M.; Boerner, P.; Hurlburt, Neal E.; Tarbell, Ted D.; Wuelser, Jean-Pierre; Pereira, Tiago M. D.; De Luca, E.E.; Golub, Leon; McKillop, Sean; Reeves, Kathy K.; Saar, Steven; Testa, Paola; Tian, Hui; Kankelborg, Charles; Jaeggli, Sarah; Kleint, Lucia; Martínez-Sykora, J.
The heating of the outer solar atmospheric layers, i.e., the transition region and corona, to high temperatures is a longstanding problem in solar (and stellar) physics. Solutions have been hampered by an incomplete understanding of the magnetically controlled structure of these regions. The high spatial and temporal resolution observations with the Interface Region Imaging Spectrograph (IRIS) at the solar limb reveal a plethora of short, lowlying loops or loop segments at transitionregion temperatures that vary rapidly, on the time scales of minutes. We argue that the existence of these loops solves a longstanding observational mystery. At the same time, based on comparison with numerical models, this detection sheds light on a critical piece of the coronal heating puzzle.