Browsing by Author "Brannon, Sean R."

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Instrument Calibration of the Interface Region Imaging Spectrograph (IRIS) Mission
(2018-11) Wulser, J. P.; Jaeggli, Sarah A.; De Pontieu, Bart; Tarbell, Ted D.; Boerner, P.; Freeland, S.; Liu, W.; Timmons, R.; Brannon, Sean R.; Kankelborg, Charles; Madsen, C.; McKillop, Sean; Prchlik, J.; Saar, Steven; Schanche, N.; Bryans, P.; Wiesmann, M.
The Interface Region Imaging Spectrograph (IRIS) is a NASA small explorer mission that provides high-resolution spectra and images of the Sun in the 133-141nm and 278-283nm wavelength bands. The IRIS data are archived in calibrated form and made available to the public within seven days of observing. The calibrations applied to the data include dark correction, scattered light and background correction, flat fielding, geometric distortion correction, and wavelength calibration. In addition, the IRIS team has calibrated the IRIS absolute throughput as a function of wavelength and has been tracking throughput changes over the course of the mission. As a resource for the IRIS data user, this article describes the details of these calibrations as they have evolved over the first few years of the mission. References to online documentation provide access to additional information and future updates.
Modeling properties of chromospheric evaporation driven by thermal conduction fronts from reconnection shocks
(2014-09) Brannon, Sean R.; Longcope, Dana
Magnetic reconnection in the corona results in contracting flare loops, releasing energy into plasma heating and shocks. The hydrodynamic shocks produced in this manner drive thermal conduction fronts (TCFs) which transport energy into the chromosphere and drive upflows (evaporation) and downflows (condensation) in the cooler, denser footpoint plasma. Observations have revealed that certain properties of the transition point between evaporation and condensation (the “flow reversal point” or FRP), such as temperature and velocity-temperature derivative at the FRP, vary between different flares. These properties may provide a diagnostic tool to determine parameters of the coronal energy release mechanism and the loop atmosphere. In this study, we develop a one-dimensional hydrodynamical flare loop model with a simplified three-region atmosphere (chromosphere/transition region/corona), with TCFs initiated by shocks introduced in the corona. We investigate the effect of two different flare loop parameters (post-shock temperature and transition region temperature ratio) on the FRP properties. We find that both of the evaporation characteristics have scaling-law relationships to the varied flare parameters, and we report the scaling exponents for our model. This provides a means of using spectroscopic observations of the chromosphere as quantitative diagnostics of flare energy release in the corona.
OBSERVATION AND ANALYSIS OF BALLISTIC DOWNFLOWS IN AN M-CLASS FLARE WITH THE INTERFACE REGION IMAGING SPECTROGRAPH
(2016-12) Brannon, Sean R.
Despite significant advances in instrumentation, there remain no studies that analyze observations of on-disk flare loop plasma flows covering the entire evolution from chromospheric evaporation, through plasma cooling, to draining downflows. We present results from an imaging and spectroscopic observation from the Interface Region Imaging Spectrograph (IRIS) of the SOL2015-03-12T11:50:00 M-class flare, at high spatial resolution and time cadence. Our analysis of this event reveals initial plasma evaporation at flare temperatures indicated by 100-200 km s(-1) blueshifts in the Fe XXI line. We subsequently observe plasma cooling into chromospheric lines (Si IV and O IV) with similar to 11 minute delay, followed by loop draining at similar to 40 km s(-1) as indicated by a \C\"-shaped redshift structure and significant (similar to 60 km s(-1)) non-thermal broadening. We use density-sensitive lines to calculate a plasma density for the flare loops, and estimate a theoretical cooling time approximately equal to the observed delay. Finally, we use a simple elliptical free-fall draining model to construct synthetic spectra, and perform what we believe to be the first direct comparison of such synthetic spectra to observations of draining downflows in flare loops."