Effect of membrane character and solution chemistry on microfiltration performance

To help understand and predict the role of natural organic matter (NOM) in the fouling of low-pressure membranes, experiments were carried out with an apparatus that incorporates automatic backwashing and long filtration runs. Three hollow fibre membranes of varying character were included in the study, and the filtration of two different surface waters was compared. The hydrophilic membrane had greater flux recovery after backwashing than the hydrophobic membranes, but the efficiency of backwashing decreased at extended filtration times. NOM concentration of these waters (7.9 and 9.1 mg/L) had little effect on the flux of the membranes at extended filtration times, as backwashing of the membrane restored the flux to similar values regardless of the NOM concentration. The solution pH also had little effect at extended filtration times. The backwashing efficiency of the hydrophilic membrane was dramatically different for the two waters, and the presence of colloid NOM alone could not explain these differences. It is proposed that colloidal NOM forms a filter cake on the surface of the membranes and that small molecular weight organics that have an adsorption peak at 220 nm but not 254 nm were responsible for “gluing” the colloids to the membrane surface. Alum coagulation improved membrane performance in all instances, and this was suggested to be because coagulation reduced the concentration of “glue” that holds the organic colloids to the membrane surface

Impact of greenhouse gas concentration changes on the surface energetics in the IPSL-CM4 model: regional warming patterns, land/sea warming ratio, glacial/interglacial differences

International audienceThe direct effect of greenhouse gas (GHG) changes is a warming of the atmosphere due to greater long-wave (LW) radiation absorption. Nevertheless, many other processes and feedbacks also take place which modify the whole climatic system and especially the surface energy budget, which determine the precise value of the surface temperature change. In this study, we decompose the surface energy fluxes to determine and quantify the role of many different processes in explaining the surface temperature response to an increase in GHG forcing in a coupled Ocean-Atmosphere General Circulation Model (AOGCM), IPSL-CM4. In particular, we show that the direct feedback effect consisting of greater backward LW radiation due to greater LW emission is particularly strong as is the effect of an increase in water vapor in the atmosphere due to greater temperatures. Nevertheless, many other terms are also important. We use this decomposition to understand the role of the different processes in the polar amplification, the warming contrast between the oceans and the continents and the differences in the surface warming under interglacial (preindustrial) and glacial (Last Glacial Maximum) conditions. This decomposition could be usefull to compare the sensitivity of different AOGCMs to a GHG forcing

Impact of greenhouse gas concentration changes on the surface energetics in the IPSL-CM4 model: regional warming patterns, land/sea warming ratio, glacial/interglacial differences

International audienceThe direct effect of greenhouse gas (GHG) changes is a warming of the atmosphere due to greater long-wave (LW) radiation absorption. Nevertheless, many other processes and feedbacks also take place which modify the whole climatic system and especially the surface energy budget, which determine the precise value of the surface temperature change. In this study, we decompose the surface energy fluxes to determine and quantify the role of many different processes in explaining the surface temperature response to an increase in GHG forcing in a coupled Ocean-Atmosphere General Circulation Model (AOGCM), IPSL-CM4. In particular, we show that the direct feedback effect consisting of greater backward LW radiation due to greater LW emission is particularly strong as is the effect of an increase in water vapor in the atmosphere due to greater temperatures. Nevertheless, many other terms are also important. We use this decomposition to understand the role of the different processes in the polar amplification, the warming contrast between the oceans and the continents and the differences in the surface warming under interglacial (preindustrial) and glacial (Last Glacial Maximum) conditions. This decomposition could be usefull to compare the sensitivity of different AOGCMs to a GHG forcing

Impact of greenhouse gas concentration changes on the surface energetics in the IPSL-CM4 model: regional warming patterns, land/sea warming ratio, glacial/interglacial differences

International audienceThe direct effect of greenhouse gas (GHG) changes is a warming of the atmosphere due to greater long-wave (LW) radiation absorption. Nevertheless, many other processes and feedbacks also take place which modify the whole climatic system and especially the surface energy budget, which determine the precise value of the surface temperature change. In this study, we decompose the surface energy fluxes to determine and quantify the role of many different processes in explaining the surface temperature response to an increase in GHG forcing in a coupled Ocean-Atmosphere General Circulation Model (AOGCM), IPSL-CM4. In particular, we show that the direct feedback effect consisting of greater backward LW radiation due to greater LW emission is particularly strong as is the effect of an increase in water vapor in the atmosphere due to greater temperatures. Nevertheless, many other terms are also important. We use this decomposition to understand the role of the different processes in the polar amplification, the warming contrast between the oceans and the continents and the differences in the surface warming under interglacial (preindustrial) and glacial (Last Glacial Maximum) conditions. This decomposition could be usefull to compare the sensitivity of different AOGCMs to a GHG forcing

Last Glacial Maximum temperatures over the North Atlantic, Europe and western Siberia: a comparison between PMIP models, MARGO sea-surface temperatures and pollen-based reconstructions

International audienceEvaluating the ability of models to simulate climates different from the modern one is important for climate prediction. Here we present a first comparison between results from simulations of the Last Glacial Maximum climate and continental and surface ocean reconstructions for the North Atlantic, Europe and western Siberia. The simulations include prescribed sea surface temperature (SST) and slab-ocean atmospheric general circulation model runs performed within the PMIP1 project, and atmosphere-ocean fully coupled runs performed after PMIP1 and within the PMIP2 project. The surface ocean reconstructions are from the MARGO project. Continental reconstructions are based on pollen data. Over the North Atlantic, most models simulate the strengthening of the SST meridional gradient suggested by the reconstructions, but most do not reproduce the LGM-control SST anomaly at the right location, nor with the right amplitude. Over western Siberia, the model results are much improved when a new ice-sheet reconstruction (ICE-5G) is used to force the models. The main discrepancy remains for western Europe winter temperatures, for which LGM-control anomalies are significantly underestimated by all models. All models indicate that this region during the LGM experienced significantly higher interannual variability in coldest-month temperatures compared to the control runs. This increased variability could have conspired to bias the apparently extremely cold pollen-based temperature reconstructions. Crown Copyright (c) 2006 Published by Elsevier Ltd. All rights reserved

Land–atmosphere feedbacks amplify aridity increase over land under global warming

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