Via Hexagons to Squares in Ferrofluids: Experiments on Hysteretic Surface Transformations under Variation of the Normal Magnetic Field

We report on different surface patterns on magnetic liquids following the Rosensweig instability. We compare the bifurcation from the flat surface to a hexagonal array of spikes with the transition to squares at higher fields. From a radioscopic mapping of the surface topography we extract amplitudes and wavelengths. For the hexagon--square transition, which is complex because of coexisting domains, we tailor a set of order parameters like peak--to--peak distance, circularity, angular correlation function and pattern specific amplitudes from Fourier space. These measures enable us to quantify the smooth hysteretic transition. Voronoi diagrams indicate a pinning of the domains. Thus the smoothness of the transition is roughness on a small scale.Comment: 17 pages, 14 figure

The possible role of local air pollution in climate change in West Africa

The climate of West Africa is characterized by a sensitive monsoon system that is associated with marked natural precipitation variability. This region has been and is projected to be subject to substantial global and regional-scale changes including greenhouse-gas-induced warming and sea-level rise, land-use and land-cover change, and substantial biomass burning. We argue that more attention should be paid to rapidly increasing air pollution over the explosively growing cities of West Africa, as experiences from other regions suggest that this can alter regional climate through the influences of aerosols on clouds and radiation, and will also affect human health and food security. We need better observations and models to quantify the magnitude and characteristics of these impacts

Modelling of future mass balance changes of Norwegian glaciers by application of a dynamical–statistical model

The long-term behaviour of Norwegian glaciers is reflected by the long mass-balance records provided by the Norwegian Water Resources and Energy Directorate. These show positive annual mass balances in the 1980s and 1990s at maritime glaciers followed by rapid mass loss since 2000. This study assesses the influence of various atmospheric variables on mass changes of selected Norwegian glaciers by correlation- and cross-validated stepwise multiple regression analyses. The atmospheric variables are constructed from reanalyses by the National Centers for Environmental Prediction and the European Centre for Medium-Range Weather Forecasts. Transfer functions determined by the multiple regression are applied to predictors derived from a multi-model ensemble of climate projections to estimate future mass-balance changes until 2100. The statistical relationship to the North Atlantic Oscillation (NAO), the strongest predictor, is highest for maritime glaciers and less for more continental ones. The mass surplus in the 1980s and 1990s can be attributed to a strong NAO phase and lower air temperatures during the ablation season. The mass loss since 2000 can be explained by an increase of summer air temperatures and a slight weakening of the NAO. From 2000 to 2100 the statistical model predicts predicts changes for glaciers in more continental settings of c. −20 m w.e. (water equivalent) or 0.2 m w.e./a. The corresponding range for their more maritime counterparts is −0.5 to +0.2 m w.e./a. Results from Bayesian classification of observed atmospheric states associated with high melt or high accumulation in the past into different simulated climates in the future suggest that climatic conditions towards the end of the twenty-first century favour less winterly accumulation and more ablation in summer. The posterior probabilities for high accumulation at the end of the twenty-first century are typically 1.5–3 times lower than in the twentieth century while the posterior probabilities for high melt are often 1.5–3 times higher at the end of the twenty-first century than in the twentieth and early twenty-first century

Monsoon Multidisciplinary Analysis (AMMA) : an integrated project for understanding of the West African climate system and its human dimension

We review the recent progress in dynamical and statistical downscaling approaches for west African precipitation and perform a regional climate model (RCM) intercomparison using the novel multi-model RCM data set from the Ensembles-based Predictions of Climate Changes and Their Impacts (ENSEMBLES) and African Monsoon Multidisciplinary Analyses (AMMA) projects. Present RCMs have distinct systematic errors in terms of west African precipitation varying in amplitude and pattern across models. This is also reflected in a relatively large spread in projected future precipitation trends. Altogether, the ENSEMBLES RCMs indicate a prevailing drying tendency in sub-Saharan Africa. Statistical post-processing of simulated precipitation is a promising tool to reduce systematic model errors before application in impact studies

Progress in regional downscaling of west African precipitation

International audienceWe review the recent progress in dynamical and statistical downscaling approaches for west African precipitation and perform a regional climate model (RCM) intercomparison using the novel multi-model RCM data set from the Ensembles-based Predictions of Climate Changes and Their Impacts (ENSEMBLES) and African Monsoon Multidisciplinary Analyses (AMMA) projects. Present RCMs have distinct systematic errors in terms of west African precipitation varying in amplitude and pattern across models. This is also reflected in a relatively large spread in projected future precipitation trends. Altogether, the ENSEMBLES RCMs indicate a prevailing drying tendency in sub-Saharan Africa. Statistical post-processing of simulated precipitation is a promising tool to reduce systematic model errors before application in impact studies