Necessary Conditions for a Hot Quiet Sun Atmosphere: Chromospheric Flares and Low Corona Twisted Flux Rope Eruptions

International audienceThe issue of relevant scales involved in the heating of the solar atmosphere is an important one. Since the temperature already reaches 1 MK a few megameters above the photosphere, observations made by Parker Solar Probe will be able to explore those at larger heights but only indirectly at those lower heights, where small scale coupling between sub-photospheric, chromospheric and coronal structure and dynamics occurs. While Solar Orbiter will be able to bring such observations, modeling appears a complementary interesting approach to interpret those observations Taking a sub-surface dynamo and a sharp realistic VAL- like scale profile from photosphere to corona, with a fixed temperature profile in time, we investigate the necessary conditions implied on the structures and dynamics of the atmosphere to keep this thermal structuration, as well as their implication in the energy budget of the atmosphere. Under those hypothesis we show that :i) the transverse photospheric field below 100km plays a major role; ii) an associated scale of one megameter activity naturally results to produce a zone above the photosphere with high confined electric currents, which then expands into the chromosphere and releases energy(4 500 W/m2) through small-scale eruptions driving sonic motions; iii) meso scale structuration, leads to the formation of larger coherent twisted flux ropes, and associated eruptive like activity in a way similar to large scale eruptive phenomena, as result of cancellation, emergence, and convergence motions. Finally a wave dynamics is also naturally driven in core corona associated to above 300 W/m2

Predictors of mortality following emergency open colectomy for ischemic colitis: a single-center experience

Background: Ischemic colitis (IC) is a severe emergency in gastrointestinal surgery. The aim of the present study was to identify the predictors of postoperative mortality after emergent open colectomy for IC treatment. Additionally, we compared postoperative outcomes of patients undergoing emergent colectomy due to aortic surgery-related IC (AS-IC group) vs. other IC etiologies (Other-IC group). Methods: We analyzed records of consecutive patients who underwent emergency open colectomy for IC between 2008 and 2019. Logistic regression analysis was performed to identify clinical and operative parameters associated with postoperative mortality. The AS-IC and Other-IC groups were compared for mortality, morbidity, ICU stay, hospital stay, and survival. Results: During the study period, 94 patients (mean age, 67.4 ± 13.7 years) underwent emergent open colectomy for IC. In the majority of cases, IC involved the entire colon (53.2%) and vasopressor agents were required preoperatively (63.8%) and/or intraoperatively (78.8%). Thirty-four patients underwent surgery due to AS-IC, whereas 60 due to Other-IC causes. In the AS-IC group, 9 patients had undergone endovascular aortic repair and 25 open aortic surgery; 61.8% of patients needed aortic surgery for ruptured abdominal aortic aneurism (AAA). Overall, 66 patients (70.2%) died within 90 days from surgery. The AS-IC and Other-IC groups showed similar operative outcomes and postoperative complication rates. However, the duration of the ICU stay (19 days vs. 11 days; p = 0.003) and of the total hospital stay (22 days vs. 16 days; p = 0.016) was significantly longer for the AS-IC group than for the Other-IC group. The rate of intestinal continuity restoration at 1 year after surgery was higher for the Other-IC group than for the AS-IC group (58.8% vs. 22.2%; p = 0.05). In the multivariate model, preoperative increased lactate levels, a delay between signs/symptoms' onset and surgery > 12 h, and the occurrence of postoperative acute kidney injury were statistically associated with postoperative mortality. Neither IC etiology (aortic surgery vs. other etiology) nor ruptured AAA was associated with postoperative mortality. Conclusion: Emergency open colectomy for IC is associated with high postoperative mortality, which appears to be unrelated to the IC etiology. Preoperative lactate levels, > 12-h delay to surgery, and postoperative acute kidney injury are independent predictors of postoperative mortality