2022-05-04T17:01:45.000Z http://sot.lmsal.com Ted Tarbell LMSAL http://lmsal.com 3251 Hanover Rd, O/ADBS, B/252, Palo Alto, CA, 94304 +1-650-424-2400 tarbell@lmsal.com Hinode SOTSP Arai Brooks Tiwari (RCO)->DeWijn (RCO) 422 422 null HOP 422 (GREGOR) on AR 13003 AR AR 13003 Active Region 8 294 -238 0 0 2022-05-05T11:16:00.000Z 2022-05-05T12:05:00.000Z 294 -238 Joint observations of the flare atmosphere Normal map 82"x82", Q65/Q75, 1 side Main Objective: To observe the atmospheric response to flare heating and support allocated observing time at GREGOR (Tenerife, Spain) Scientific Justification: White light flares (WLF) are flares with emissions visible at the optical continuum, and also UV enhancements in some cases. Various mechanisms have been proposed to explain the continuum enhancement. Moreover, each mechanism may dominate at different atmospheric layers and, therefore, specific observations are needed to disentangle the contributions. The presence of hydrogen Paschen continuum, originating at the chromosphere, has been observed in off-limb flare observations from HMI/SDO (Heinzel et al. 2017). The presence of the hydrogen Balmer continuum has been observed in on-disc flares observations from IRIS (Heinzel and Kleint 2014; Kleint et al. 2016; Kowalski et al. 2017; Joshi and Schmieder 2021). Additionally, WLF observations from SP/Hinode showed that the optical continuum enhancement is probably not caused by the temperature increase at the formation height of the photospheric continuum, but instead by a photospheric heating down to log τ ~ 0.5, which results in emission profiles of the Fe I lines (Jurcak et al. 2018). They estimated that the major contribution to the increase of the continuum intensity is originating in the heated chromosphere. With this proposal, we aim to do a follow up study of Jurcak et al. (2018) and Kleint et al. (2017), that is, the study of the stratification of the flare atmosphere by means of space- and ground-based instruments with as high temporal cadence as possible to properly constrain the plasma state of the flaring atmosphere. Meanwhile, we aim to run a complementary study of the temporal evolution of the umbra-penumbra boundary with respect to the properties of the magnetic field. Spectropolarimetric observations of SP/Hinode will allow us to study the photospheric vector magnetic field within the whole observed sunspot, complementing the smaller FOV of the photospheric and chromospheric IFU-GRIS/GREGOR observations. IRIS NUV spectra will allow us to study the Balmer continuum emission and line emissions during flares. Slit-jaw images at Mg II wing (2830 A) will complement the images provided by GREGOR (Hα, Ca II h, and blue continuum at 450 nm), thus extending information of the chromospheric emission. The observed emission in hydrogen, Ca II and Mg II lines and continuum will be compared with non-LTE RHD models constructed specifically for the observed flare (e.g. using FLARIX code, Kasparova et al. 2019; Heinzel et al. 2017). If Fermi or STIX/Solar Orbiter data are available, they will be used to constrain the flare heating input. XRT will provide information about temperature and emission measures of hot flaring loops, allowing us to track the atmosphere response and structure above chromospheric heights.