Alerte dans les hautes latitudes nord?: l’Arctique réagit au réchauffement climatique

L’Arctique serait-il le canari qui servait de sentinelle face aux risques du coup de grisou dans les mines de charbon, utilisé par les mineurs pour leur survie au siècle dernier? Depuis les 20 dernières, l’Arctique se réchauffe près de 6 fois plus vite que le reste du globe durant l’hiver. Pourquoi cet emballement qui s’inscrit dans une tendance lourde depuis 50 ans, particulièrement l’hiver ? Ce phénomène, qui pourrait être une « rétroaction positive au forçage radiatif », aussi appelé « effet d’amplification Arctique », fait débat. Mais de récentes publications commencent à faire consensus sur une possible conséquence (rétroaction) de la fonte de la glace de mer arctique, très marquée (-40% depuis 40 ans). Cet article présente d’abord 3 faits saillants observés de cet emballement : anomalies des températures à la hausse au-dessus de 60 °N de latitude, fonte drastique de l’étendue de la glace de mer lors du minimum de la fin de l’été (depuis que l’on fait des mesures satellites très précises), et fonte accélérée du Groenland, elle aussi mesurée par satellite. L’effet d’amplification arctique est ensuite expliqué de façon synthétique et discuté. Il pourrait avoir des conséquences importantes sur notre climat

Snow stratigraphic heterogeneity within ground-based passive microwave radiometer footprints: implications for emission modeling

Two-dimensional measurements of snowpack properties (stratigraphic layering, density, grain size and temperature) were used as inputs to the multi-layer Helsinki University of Technology (HUT) microwave emission model at a centimeter-scale horizontal resolution, across a 4.5 m transect of ground-based passive microwave radiometer footprints near Churchill, Manitoba, Canada. Snowpack stratigraphy was complex (between six and eight layers) with only three layers extending continuously throughout the length of the transect. Distributions of one-dimensional simulations, accurately representing complex stratigraphic layering, were evaluated using measured brightness temperatures. Large biases (36 to 68 K) between simulated and measured brightness temperatures were minimized (-0.5 to 0.6 K), within measurement accuracy, through application of grain scaling factors (2.6 to 5.3) at different combinations of frequencies, polarizations and model extinction coefficients. Grain scaling factors compensated for uncertainty relating optical SSA to HUT effective grain size inputs and quantified relative differences in scattering and absorption properties of various extinction coefficients. The HUT model required accurate representation of ice lenses, particularly at horizontal polarization, and large grain scaling factors highlighted the need to consider microstructure beyond the size of individual grains. As variability of extinction coefficients was strongly influenced by the proportion of large (hoar) grains in a vertical profile, it is important to consider simulations from distributions of one-dimensional profiles rather than single profiles, especially in sub-Arctic snowpacks where stratigraphic variability can be high. Model sensitivity experiments suggested the level of error in field measurements and the new methodological framework used to apply them in a snow emission model were satisfactory. Layer amalgamation showed a three-layer representation of snowpack stratigraphy reduced the bias of a one-layer representation by about 50%

La preuve par satellite

"En 1980, alors que le réchauffement climatique commençait à donner des signes d’accélération, près de la moitié de la population actuelle du Québec n’était pas encore née! Mais déjà, des satellites étaient en orbite, non pas pour le climat, mais pour la météo et pour observer la Terre. Quarante ans plus tard, ces observations spatiales s’avèrent être des outils extraordinaires pour étudier ce qui s’est passé et ce qui se passe actuellement dans l’Arctique. [...]

A North American Arctic Aerosol Climatology using Ground-based Sunphotometry

The Arctic is known as a key area for the detection of climate changes and atmospheric pollution on a global scale. In this paper we describe a new Canadian sunphotometer network called AEROCAN, whose primary mandate is to establish a climatology of atmospheric aerosols. This network is part of AERONET, the worldwide federated sunphotometer network managed by the NASA Goddard Space Flight Center. The potential of sunphotometer data from the AERONET/AEROCAN network for monitoring of Arctic aerosols is illustrated, using examples of the multiyear variation of aerosol optical properties and atmospheric precipitable water vapour content at some stations, and in particular at Bonanza Creek, Alaska since 1994. Despite its sparse spatial density, the network represents an important tool for monitoring the spatio-temporal variation of Arctic aerosols. It also represents an important source of independent aerosol data, which we feel should be further developed in northern areas to improve our understanding of how atmospheric aerosols influence global climate.L'Arctique est reconnu comme une région clé pour la détection des changements climatiques et de la pollution atmosphérique à l'échelle planétaire. Cet article présente un nouveau réseau canadien de photomètres solaires (AEROCAN) dont le mandat principal est d'établir une climatologie des aérosols atmosphériques. Ce réseau est intégré au réseau fédéré mondial de photomètres solaires AERONET géré par le Centre des vols spatiaux Goddard de la NASA. Le potentiel des données héliophotométriques générées par le réseau AERONET/AEROCAN pour la surveillance des aérosols dans l'Arctique est illustré à l'aide d'exemples de la variation pluriannuelle des paramètres optiques des aérosols et du contenu en vapeur d'eau atmosphérique précipitable à diverses stations, en particulier à Bonanza Creek (Alaska) depuis 1994. Malgré sa faible densité spatiale, le réseau représente un outil important pour la surveillance de la variation spatio-temporelle des aérosols arctiques. Il représente en outre une source majeure de données indépendantes sur les aérosols, données dont la provenance devrait, selon nous, englober les régions boréales afin que nous ayons une meilleure compréhension de l'influence des aérosols atmosphériques sur le climat de la planète

Simulation of Seasonal Snow Microwave TB Using Coupled Multi-Layered Snow Evolution and Microwave Emission Models

The accurate quantification of SWE has important societal benefits, including improving domestic and agricultural water planning, flood forecasting and electric power generation. However, passive-microwave SWE algorithms suffer from variations in TB due to snow metamorphism, difficult to distinguish from those due to SWE variations. Coupled snow evolution-emission models are able to predict snow metamorphism, allowing us to account for emissivity changes. They can also be used to identify weaknesses in the snow evolution model. Moreover, thoroughly evaluating coupled models is a contribution toward the assimilation of TB, which leads to a significant increase in the accuracy of SWE estimates

Thin ice clouds in the Arctic: cloud optical depth and particle size retrieved from ground-based thermal infrared radiometry

Multiband downwelling thermal measurements of zenith sky radiance, along with cloud boundary heights, were used in a retrieval algorithm to estimate cloud optical depth and effective particle diameter of thin ice clouds in the Canadian High Arctic. Ground-based thermal infrared (IR) radiances for 150 semitransparent ice clouds cases were acquired at the Polar Environment Atmospheric Research Laboratory (PEARL) in Eureka, Nunavut, Canada (80° N, 86° W). We analyzed and quantified the sensitivity of downwelling thermal radiance to several cloud parameters including optical depth, effective particle diameter and shape, water vapor content, cloud geometric thickness and cloud base altitude. A lookup table retrieval method was used to successfully extract, through an optimal estimation method, cloud optical depth up to a maximum value of 2.6 and to separate thin ice clouds into two classes: (1) TIC1 clouds characterized by small crystals (effective particle diameter  ≤  30 µm), and (2) TIC2 clouds characterized by large ice crystals (effective particle diameter  >  30 µm). The retrieval technique was validated using data from the Arctic High Spectral Resolution Lidar (AHSRL) and Millimeter Wave Cloud Radar (MMCR). Inversions were performed over three polar winters and results showed a significant correlation (R2 =  0.95) for cloud optical depth retrievals and an overall accuracy of 83 % for the classification of TIC1 and TIC2 clouds. A partial validation relative to an algorithm based on high spectral resolution downwelling IR radiance measurements between 8 and 21 µm was also performed. It confirms the robustness of the optical depth retrieval and the fact that the broadband thermal radiometer retrieval was sensitive to small particle (TIC1) sizes

High-pressure intrapleural chemotherapy: feasibility in the pig model.

International audienceABSTRACT: BACKGROUND: The usual treatments for pleural malignancies are mostly palliative. In contrast, peritoneal malignancies are often treated with a curative intent by cytoreductive surgery and intraperitoneal chemotherapy. As pressure has been shown to increase antitumor efficacy, we applied the concept of high-pressure intracavitary chemotherapy to the pleural space in a swine model. METHODS: Cisplatin and gemcitabine were selected because of their antineoplasic efficacy in vitro in a wide spectrum of cancer cell lines. The pleural cavity of 21 pigs was filled with saline solution; haemodynamic and respiratory parameters were monitored. The pressure was increased to 15-25 cm H2O. This treatment was associated with pneumonectomy in 6 pigs. Five pigs were treated with chemotherapy under pressure. RESULTS: The combination of gemcitabine (100 mg/l) and cisplatin (30 mg/l) was highly cytotoxic in vitro. The maximum tolerated pressure was 20 cm H20, due to haemodynamic failure. Pneumonectomy was not tolerated, either before or after pleural infusion. Five pigs survived intrapleural chemotherapy associating gemcitabine and cisplatin with 20 cm H2O pressure for 60 min. CONCLUSIONS: High-pressure intrapleural chemotherapy is feasible in pigs. Further experiments will establish the pharmacokinetics and determine whether the benefit already shown in the peritoneum is also obtained in the pleura

Improvement of microwave emissivity parameterization of frozen Arctic soils using roughness measurements derived from photogrammetry

Soil emissivity of Arctic regions is a key parameter for assessing surface properties from microwave brightness temperature (Tb) measurements. Particularly in winter, frozen soil permittivity and roughness are two poorly characterized unknowns that must be considered. Here, we show that after removing snow, the 3D soil roughness can be accurately inferred from in-situ photogrammetry using Structure from Motion (SfM). We focus on using SfM techniques to provide accurate roughness measurements and improve emissivity models parametrization of frozen arctic soil for microwave applications. Validation was performed from ground-based radiometric measurements at 19 and 37 GHz using three different soil emission models: the Wegmüller and Mätzler [1999, TGRS] model (Weg99), the Wang and Choudhury [1981, JGR] model (QNH), and a geometrical optics model (Geo Optics). Measured and simulated brightness temperatures over different tundra and rock sites in the Canadian High Arctic show that Weg99, parametrized with SfM-based roughness and optimized permittivity (ε), yielded an RMSE of 3.1 K (R2=0.71) for all frequencies and polarizations. Our SfM based approach allowed us to measure roughness with 0.1 mm accuracy at 55 locations of different land cover type using a digital camera and metal plates of know dimensions