A model intercomparison of Titan's climate and low-latitude environment

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Seasonal evolution of temperatures in Titan's lower stratosphere

International audienceThe Cassini mission offered us the opportunity to monitor the seasonal evolution of Titan's atmosphere from 2004 to 2017, i.e. half a Titan year. The lower part of the stratosphere (pressures greater than 10 mbar) is a region of particular interest as there are few available temperature measurements, and because its thermal response to the seasonal and meridional insolation variations undergone by Titan remain poorly known. In this study, we measure temperatures in Titan's lower stratosphere between 6 mbar and 25 mbar using Cassini/CIRS spectra covering the whole duration of the mission (from 2004 to 2017) and the whole latitude range. We can thus characterize the meridional distribution of temperatures in Titan's lower stratosphere, and how it evolves from northern winter (2004) to summer solstice (2017). Our measurements show that Titan's lower stratosphere undergoes significant seasonal changes, especially at the South pole, where temperature decreases by 19 K at 15 mbar in 4 years

Fixation of 4-part fractures of the proximal humerus: Can we identify radiological criteria that support locking plates or IM nailing? Comparative, retrospective study of 107 cases

International audienceINTRODUCTION:No objective criteria exist to help surgeons choose between IM nailing and plate fixation for 4-part fractures of the proximal humerus. The goal of this study was to identify radiological criteria that would make one technique a better choice than the other.MATERIAL AND METHODS:This was a comparative, multicentre, retrospective study of 54 cases of antegrade nailing and 53 cases of plating performed between 1st January 2009 and 31 December 2011 for 4-part fractures of the proximal humerus. All patients had a minimum radiological and clinical follow-up of 18 months. The functional outcomes were evaluated using the weighted Constant score; a poor result was defined as a weighted Constant score<70%. The following radiological criteria were evaluated during the preoperative assessment and at the last follow-up: initial displacement and reduction of humeral head and tuberosities; morphology of the medial column (i.e. calcar comminution, posteromedial hinge, size of metaphyseal head extension); occurrence of avascular necrosis (AVN).RESULTS:After an average follow-up of 42 months, the weighted Constant scores and rate of poor outcomes were 77% and 48% in the nail group and 81% and 38% in the plate group, respectively (ns). The humeral head was reduced into an anatomical position, valgus or varus in 57%, 30% and 13% of cases in the nail group, and 58%, 29% and 13% in the plate group, respectively. The tuberosities healed in an anatomical position in 72% of nail cases and 70% of plate cases (ns). Only the presence of a medial hinge preoperatively had an effect on the functional outcomes in the nail and plate groups: the weighted Constant scores (P=0.05) and rate of poor outcomes (P=0.02) were 82% and 52% in the nail group and 97% and 9% in the plate group, respectively. The complication rates were comparable: the rates of AVN and articular screw penetration were 17% and 11% in the nail group, and 15% and 11% in the plate group, respectively. The surgical revision rate was 18.5% in the nail group and 30% in the plate group.CONCLUSION:If the medial hinge is preserved, we recommend locking plate fixation. In other cases, either technique can be used as long as the general rules of internal fixation are applied: reduction of the tuberosities, varus correction and stabilization of the calcar area.LEVEL OF EVIDENCE:IV, retrospective study

Seasonal changes in the middle atmosphere of Titan from Cassini/CIRS observations: Temperature and trace species abundance profiles from 2004 to 2017

International audienceThe Cassini/Composite InfraRed Spectrometer (CIRS) instrument has been observing the middle atmosphere of Titan over almost half a Saturnian year. We used the CIRS dataset processed through the up-to-date calibration pipeline to characterize seasonal changes of temperature and abundance profiles in the middle atmosphere of Titan, from mid-northern winter to early northern summer all around the satellite. We used limb spectra from 590 to 1500 cm−1 at 0.5-cm−1 spectral resolution, which allows us to probe different altitudes. We averaged the limb spectra recorded during each flyby on a fixed altitude grid to increase the signal-to-noise ratio. These thermal infrared data were analyzed by means of a radiative transfer code coupled with an inversion algorithm, in order to retrieve vertical temperature and abundance profiles. These profiles cover an altitude range of approximately 100 to 600 km, at 10- or 40-km vertical resolution (depending on the observation). Strong changes in temperature and composition occur in both polar regions where a vortex is in place during the winter. At this season, we observe a global enrichment in photochemical compounds in the mesosphere and stratosphere and a hot stratopause located around 0.01 mbar, both linked to downwelling in a pole-to-pole circulation cell. After the northern spring equinox, between December 2009 and April 2010, a stronger enhancement of photochemical compounds occurred at the north pole above the 0.01-mbar region, likely due to combined photochemical and dynamical effects. During the southern autumn in 2015, above the South pole, we also observed a strong enrichment in photochemical compounds that contributed to the cooling of the stratosphere above 0.2 mbar (∼300 km). Close to the northern spring equinox, in December 2009, the thermal profile at 74°N exhibits an oscillation that we interpret in terms of an inertia-gravity wave

Temperature and chemical species distributions in the middle atmosphere observed during Titan’s late northern spring to early summer

International audienceWe present a study of the seasonal evolution of Titan’s thermal field and distributions of haze, C2H2, C2H4, C2H6, CH3C2H, C3H8, C4H2, C6H6, HCN, and HC3N from March 2015 (Ls = 66°) to September 2017 (Ls = 93°) (i.e., from the last third of northern spring to early summer). We analyzed thermal emission of Titan’s atmosphere acquired by the Cassini Composite Infrared Spectrometer with limb and nadir geometry to retrieve the stratospheric and mesospheric temperature and mixing ratios pole-to-pole meridional cross sections from 5 mbar to 50 μbar (120–650 km). The southern stratopause varied in a complex way and showed a global temperature increase from 2015 to 2017 at high-southern latitudes. Stratospheric southern polar temperatures, which were observed to be as low as 120 K in early 2015 due to the polar night, showed a 30 K increase (at 0.5 mbar) from March 2015 to May 2017 due to adiabatic heating in the subsiding branch of the global overturning circulation. All photochemical compounds were enriched at the south pole by this subsidence. Polar cross sections of these enhanced species, which are good tracers of the global dynamics, highlighted changes in the structure of the southern polar vortex. These high enhancements combined with the unusually low temperatures (<120 K) of the deep stratosphere resulted in condensation at the south pole between 0.1 and 0.03 mbar (240–280 km) of HCN, HC3N, C6H6 and possibly C4H2 in March 2015 (Ls = 66°). These molecules were observed to condense deeper with increasing distance from the south pole. At high-northern latitudes, stratospheric enrichments remaining from the winter were observed below 300 km between 2015 and May 2017 (Ls = 90°) for all chemical compounds and up to September 2017 (Ls = 93°) for C2H2, C2H4, CH3C2H, C3H8, and C4H2. In September 2017, these local enhancements were less pronounced than earlier for C2H2, C4H2, CH3C2H, HC3N, and HCN, and were no longer observed for C2H6 and C6 H6, which suggests a change in the northern polar dynamics near the summer solstice. These enhancements observed during the entire spring may be due to confinement of this enriched air by a small remaining winter circulation cell that persisted in the low stratosphere up to the northern summer solstice, according to predictions of the Institut Pierre Simon Laplace Titan Global Climate Model (IPSL Titan GCM). In the mesosphere we derived a depleted layer in C2H2, HCN, and C2H6 from the north pole to mid-southern latitudes, while C4H2, C3H4, C2H4, and HC3N seem to have been enriched in the same region. In the deep stratosphere, all molecules except C2H4 were depleted due to their condensation sink located deeper than 5 mbar outside the southern polar vortex. HCN, C4H2, and CH3C2H volume mixing ratio cross section contours showed steep slopes near the mid-latitudes or close to the equator, which can be explained by upwelling air in this region. Upwelling is also supported by the cross section of the C2H4 (the only molecule not condensing among those studied here) volume mixing ratio observed in the northern hemisphere. We derived the zonal wind velocity up to mesospheric levels from the retrieved thermal field. We show that zonal winds were faster and more confined around the south pole in 2015 (Ls = 67−72°) than later. In 2016, the polar zonal wind speed decreased while the fastest winds had migrated toward low-southern latitudes