Sensitivity of the MAR regional climate model snowpack to the parameterization of the assimilation of satellite-derived wet-snow masks on the Antarctic Peninsula

Both regional climate models (RCMs) and remote sensing (RS) data are essential tools in understanding the response of polar regions to climate change. RCMs can simulate how certain climate variables, such as surface melt, runoff and snowfall, are likely to change in response to different climate scenarios but are subject to biases and errors. RS data can assist in reducing and quantifying model uncertainties by providing indirect observations of the modeled variables on the present climate. In this work, we improve on an existing scheme to assimilate RS wet snow occurrence data with the “Modèle Atmosphérique Régional” (MAR) RCM and investigate the sensitivity of the RCM to the parameters of the scheme. The assimilation is performed by nudging the MAR snowpack temperature to match the presence of liquid water observed by satellites. The sensitivity of the assimilation method is tested by modifying parameters such as the depth to which the MAR snowpack is warmed or cooled, the quantity of water required to qualify a MAR pixel as “wet” (0.1 % or 0.2 % of the snowpack mass being water), and assimilating different RS datasets. Data assimilation is carried out on the Antarctic Peninsula for the 2019–2021 period. The results show an increase in meltwater production (+66.7 % on average, or +95 Gt), along with a small decrease in surface mass balance (SMB) (−4.5 % on average, or −20 Gt) for the 2019–2020 melt season after assimilation. The model is sensitive to the tested parameters, albeit with varying orders of magnitude. The prescribed warming depth has a larger impact on the resulting surface melt production than the liquid water content (LWC) threshold due to strong refreezing occurring within the top layers of the snowpack. The values tested for the LWC threshold are lower than the LWC for typical melt days (approximately 1.2 %) and impact results mainly at the beginning and end of the melting period. The assimilation method will allow for the estimation of uncertainty in MAR meltwater production and will enable the identification of potential issues in modeling near-surface snowpack processes, paving the way for more accurate simulations of snow processes in model projections.</p

An experimental and kinetic modelling study of the oxidation of the four isomers of butanol

Butanol, an alcohol which can be produced from biomass sources, has received recent interest as an alternative to gasoline for use in spark ignition engines and as a possible blending compound with fossil diesel or biodiesel. Therefore, the autoignition of the four isomers of butanol (1-butanol, 2-butanol, iso-butanol, and tert-butanol) has been experimentally studied at high temperatures in a shock tube and a kinetic mechanism for description of their high-temperature oxidation has been developed. Ignition delay times for butanol/oxygen/argon mixtures have been measured behind reflected shock waves at temperatures and pressures ranging from approximately 1200 to 1800 K and 1 to 4 bar. Electronically excited OH emission and pressure measurements were used to determine ignition delay times. A detailed kinetic mechanism has been developed to describe the oxidation of the butanol isomers and validated by comparison to the shock tube measurements. Reaction flux and sensitivity analysis indicate that the consumption of 1 butanol and iso-butanol, the most reactive isomers, takes place primarily by H-atom abstraction resulting in the formation of radicals, the decomposition of which yields highly reactive branching agents, H-atoms and OH radicals. Conversely, the consumption of tert butanol and 2-butanol, the least reactive isomers, takes place primarily via dehydration, resulting in the formation of alkenes, which lead to resonance stabilized radicals with very low reactivity. To our knowledge, the ignition delay measurements and oxidation mechanism presented here for 2-butanol, iso-butanol, and tert butanol are the first of their kind.

Surface mechanisms investigation for negative ion production

Proc. on lineInternational audienc

Distribution radiale de la densité électronique et de la densité des atomes excités dans une colonne de plasma produite par une onde de surface

We have observed the radial density distribution of excited atoms in an argon plasma produced by a surface wave. The measurements are made by recording both emission and absorption at a given wavelength, as a function of radius. Depending on the neutral gas pressure (between 50 and 350 mtorr) and on the surface wave frequency, the radial distribution is either flat or has a minimum on the axis and a maximum near the tube wall. This behaviour is explained theoretically for radiative levels by showing that their population density should be proportional to n(r) E2(r) where r is the radius, n(r) is the electron density and E2 (r) is the electric field strength of the surface wave. The same radial dependence occurs theoretically and experimentally for the density of a metastable level, provided its destruction mainly results from collisions with neutral atoms. The radial distribution of the electrons is known only through a calculation assuming ambipolar diffusion. With this assumption, the radial distribution of electrons can be well approximated by a J 0 Bessel function, though the electron production varies radially with the electric field intensity.On détermine expérimentalement la distribution radiale de la densité des atomes excités dans une colonne de plasma d'argon produite par une onde de surface. Ces mesures sont réalisées en enregistrant directement par prospection radiale, soit l'émission des atomes excités, soit l'absorption que ces atomes produisent sur un rayonnement incident de référence. Suivant la pression du gaz (entre 50 et 350 mtorr) et la fréquence de l'onde de surface, les distributions radiales observées présentent une forme presque plate ou, au contraire, montrent un creux plus ou moins profond sur l'axe avec un maximum relatif situé au voisinage de la paroi. On explique ce comportement pour un niveau radiatif en montrant théoriquement que sa densité doit être proportionnelle à n(r) E2(r) où r est la position radiale, n(r), la densité électronique et E2(r), l'intensité du champ électrique de l'onde de surface. La même dépendance apparaît théoriquement et expérimentalement pour la densité d'un niveau métastable, lorsque la destruction de ce niveau est principalement assurée par collisions avec des atomes neutres. La distribution radiale des électrons n'est pas mesurée mais calculée. Bien que la production des électrons dépende localement de la forme du champ électrique de l'onde de surface, dans la mesure où la diffusion ambipolaire est le principal mécanisme de pertes des particules chargées, la distribution radiale des électrons s'écarte assez peu d'une fonction de Bessel J0

Optical properties of TiAlC/TiAlCN/TiAlSiCN/TiAlSiCO/TiAlSiO tandem absorber coatings by phase-modulated spectroscopic ellipsometry

International audienc

Kinetic Study of the Combustion of Phosphorus Containing Species

The combustion of organophosphorus compounds is of great interest for the incineration of chemical warfare agent and their use in flame inhibition as halon replacement. The thermochemical data of these species and the reactions involved at high temperature are not well known, despite some recent experimental studies. With BAC-MP4 ab initio estimations as a basis and semi-empirical estimations for many new compounds, the thermochemistry of organophosphorus compounds is studied. New group additivity values are proposed for enthalpies of formation at 298K, entropies and heat capacities of species involving pentavalent phosphorus bonded to carbon, hydrogen, oxygen, fluorine, nitrogen and sulfur atoms. The kinetic of unimolecular elimination is investigated by modeling pyrolysis experiments of DEMP, TEP and DIMP. A new combustion mechanism is described and applied to the modeling of DMMP reaction in a H{sub 2}/O{sub 2} flame