Estimating Supraglacial Melt Lake Volume Changes in West Central Greenland Using Multiple Remote Sensing Methods

The Greenland Ice Sheet (GrIS) is losing ice mass as the climate warms. Supraglacial melt lakes (SGLs), which are present in the ablation (melt) zone of the GrIS are found to be responsive - and reinforce - changes in glaciological and climatological dynamics. Developing a spatiotemporal model to monitor lake volume change throughout the melt season (late-April through September) can enhance our understanding of subsequent GrIS changes. Supraglacial melt lakes accumulate in volume and in some cases drain to the ice sheet base during the melting season. In this study we utilize Landsat satellite imagery paired with high resolution digital elevation model data (DEMs) to estimate melt lake depth (per satellite pixel) and derive melt lake volume during the 2021 melt season. We further explore a meteorologically-driven lake-filling method by modeling surface melt across the melt lake watershed, and route meltwater to the lake basin. With expected increase in temperature in the Arctic region, we hypothesize that melt lakes will move further inland, and be larger in area, on the GrIS, which could be a positive feedback to increased ice mass discharge

Crystalline silicate dust around evolved stars I. The sample stars

This is the first paper in a series of three where we present the first comprehensive inventory of solid state emission bands observed in a sample of 17 oxygen-rich circumstellar dust shells surrounding evolved stars. The data were taken with the Short and Long Wavelength Spectrographs on board of the Infrared Space Observatory (ISO) and cover the 2.4 to 195 micron wavelength range. The spectra show the presence of broad 10 and 18 micron bands that can be attributed to amorphous silicates. In addition, at least 49 narrow bands are found whose position and width indicate they can be attributed to crystalline silicates. Almost all of these bands were not known before ISO. We have measured the peak positions, widths and strengths of the individual, continuum subtracted bands. Based on these measurements, we were able to order the spectra in sequence of decreasing crystalline silicate band strength. We found that the strength of the emission bands correlates with the geometry of the circumstellar shell, as derived from direct imaging or inferred from the shape of the spectral energy distribution. This naturally divides the sample into objects that show a disk-like geometry (strong crystalline silicate bands), and objects whose dust shell is characteristic of an outflow (weak crystalline silicate bands). All stars with the 33.6 micron forsterite band stronger than 20 percent over continuum are disk sources. We define spectral regions (called complexes) where a concentration of emission bands is evident, at 10, 18, 23, 28, 33, 40 and 60 micron. We derive average shapes for these complexes and compare these to the individual band shapes of the programme stars.Comment: 41 pages, 20 figures, accepted by A&A. Tables 4 to 20 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A

Évaluation de l'éco-efficience des processus de mise à niveau d'hélicoptères en tant qu'alternative à la fin de vie

Les méthodes classiques de production industrielle engendrent une pression importante sur les gisements de ressources naturelles et génèrent des contraintes liées à la gestion des produits en fin de vie. Les chaines logistiques inverses fermées sont reconnues comme étant des méthodes de production alternatives plus éco-efficientes, présentant d’importants bénéfices économiques et environnementaux à l’échelle du cycle de vie du produit. Ceci est accompli notamment via une réduction importante des coûts de production, des besoins en ressources nouvelles et en énergies, ainsi que de la proportion d’éléments en fin de vie destinée à l’enfouissement. Les hélicoptères légers non pressurisés, de par leur conception modulaire et la dynamique particulière de leur opération, ont démontré une grande capacité à être partiellement ou totalement remis à neuf et mis à niveau. Ceci permet notamment d’étendre leur durée de vie, d’augmenter leurs performances et de moderniser leurs équipements, souvent pour une fraction du coût d’un nouvel appareil. Cependant, il existe peu d’information de nature environnementale permettant de conclure sur l’éco-efficience générale de ces processus. L’étude a conduit à la mise en place d’une méthode de caractérisation systémique des processus rencontrés au cours de la vie utile d’un appareil. L’agencement subséquent de ces processus au cours du temps permet ensuite la construction de cycles d’exploitation, représentatifs de la vie utile d’un hélicoptère. La comparaison de leur éco-efficience respective est ensuite effectuée, selon divers critères liés aux designs des appareils et à leur type d’utilisation. Une étude de cas, basée sur un modèle d’affaire industriel de mise à niveau d’hélicoptère actuellement en opération, illustre finalement l’application de la méthode développée. Celle-ci se veut être un premier niveau d’évaluation du potentiel économique, technique et environnemental de la remise à neuf et de la mise à niveau d’un hélicoptère, en tant que voie de production alternative. L’étude a montré qu’en comparaison avec le remplacement d’un hélicoptère par un neuf, sa mise à niveau est généralement une décision plus éco-efficiente. Des réductions importantes ont été observées pour la plupart des profils étudiés, soit jusqu’à 51 % de réduction pour les coûts d’acquisition de l’appareil, à hauteur de 77,5 % en termes de matières résiduelles destinées à l’enfouissement et jusqu’à 54 % de réduction de la consommation énergétique. La méthode développée se présente comme un outil d’évaluation à destination des constructeurs et opérateurs d’appareils. Celle-ci permet notamment de reprendre les considérations liées à l’écoconception orientée fin de vie, dans le but de mieux comprendre l’adaptabilité d’un design d’appareil donné à satisfaire aux exigences d’une logistique inverse optimisée

The Effect of an Underwater Treadmill on HbA1c Levels in Lower Limb Amputees with Diabetes

https://louis.uah.edu/research-horizons/1101/thumbnail.jp

Characterizing swells in the southern Pacific from seismic and infrasonic noise analyses

International audienceA temporary network of 10 broad-band seismic stations has been installed in French Polynesia for the Polynesian Lithosphere and Upper Mantle Experiment (PLUME). All the seismic stations were installed either on volcanic islands or on atolls of the various archipelagos of French Polynesia in a manner which complements the geographic coverage provided by the regional permanent stations. The primary aim of PLUME is to image the upper mantle structures related to plate motion and hotspot activity. However, because of its proximity to all sites, the ocean is responsible for a high level of noise in the seismic data and we show that these data can also be used to analyse ocean wave activity. The power spectral density (PSD) analyses of the seismic data recorded in French Polynesia show clear peaks in the 0.05– 0.10 Hz band (periods between 10 and 20 s), which corresponds to swell frequencies. Clear peaks in this frequency band are also observed in infrasonic data recorded on Tahiti. Ground motion analysis shows that the swell-related seismic noise (SRSN) is linearly polarized in the horizontal plane and its amplitude decreases rapidly with the distance from the shore. The microseismic and the infrasonic 'noise' amplitudes show very similar variations from station to station and both are strongly correlated with the swell amplitudes predicted by the National Oceanic and Atmospheric Administration (NOAA), wind-forced, 'WaveWatch' models. The swell direction can be estimated from SRSN polarization analysis but this has to be done with care since, for some cases, the ground motions are strongly controlled by the islands' anisometric shapes and by swell refraction processes. We find cases, however, such as Tahiti or roughly circular Tuamotu atolls, where the azimuth of the swell is in good agreement with the seismic estimates. We, therefore, demonstrate that the SRSN and the infrasonic signal observed in French Polynesia can be used in such cases as a proxy for swell amplitude and azimuth. From the continuous analysis of the data recorded in 2003 at the permanent seismic station PPTL in Tahiti, transfer functions have been obtained. This could provide a way to quantify the swell activity during the last two decades and, therefore, assist in the investigation of climate changes

Global modeling of tropospheric iodine aerosol

Natural aerosols play a central role in the Earth system. The conversion of dimethyl sulfide to sulfuric acid is the dominant source of oceanic secondary aerosol. Ocean emitted iodine can also produce aerosol. Using a GEOS-Chem model, we present a simulation of iodine aerosol. The simulation compares well with the limited observational data set. Iodine aerosol concentrations are highest in the tropical marine boundary layer (MBL) averaging 5.2 ng (I) m −3 with monthly maximum concentrations of 90 ng (I) m −3. These masses are small compared to sulfate (0.75% of MBL burden, up to 11% regionally) but are more significant compared to dimethyl sulfide sourced sulfate (3% of the MBL burden, up to 101% regionally). In the preindustrial, iodine aerosol makes up 0.88% of the MBL burden sulfate mass and regionally up to 21%. Iodine aerosol may be an important regional mechanism for ocean-atmosphere interaction