Robust uncertainty assessment of the spatio-temporal transferability of glacier mass and energy balance models

Energy and mass-balance modelling of glaciers is a key tool for climate impact studies of future glacier behaviour. By incorporating many of the physical processes responsible for surface accumulation and ablation, they offer more insight than simpler statistical models and are believed to suffer less from problems of stationarity when applied under changing climate conditions. However, this view is challenged by the widespread use of parameterizations for some physical processes which introduces a statistical calibration step. We argue that the reported uncertainty in modelled mass balance (and associated energy flux components) are likely to be understated in modelling studies that do not use spatio-temporal cross-validation and use a single performance measure for model optimization. To demonstrate the importance of these principles, we present a rigorous sensitivity and uncertainty assessment workflow applied to a modelling study of two glaciers in the European Alps, extending classical best guess approaches. The procedure begins with a reduction of the model parameter space using a global sensitivity assessment that identifies the parameters to which the model responds most sensitively. We find that the model sensitivity to individual parameters varies considerably in space and time, indicating that a single stated model sensitivity value is unlikely to be realistic. The model is most sensitive to parameters related to snow albedo and vertical gradients of the meteorological forcing data. We then apply a Monte Carlo multi-objective optimization based on three performance measures: model bias and mean absolute deviation in the upper and lower glacier parts, with glaciological mass balance data measured at individual stake locations used as reference. This procedure generates an ensemble of optimal parameter solutions which are equally valid. The range of parameters associated with these ensemble members are used to estimate the cross-validated uncertainty of the model output and computed energy components. The parameter values for the optimal solutions vary widely, and considering longer calibration periods does not systematically result in better constrained parameter choices. The resulting mass balance uncertainties reach up to 1300&thinsp;kg&thinsp;m−2, with the spatial and temporal transfer errors having the same order of magnitude. The uncertainty of surface energy flux components over the ensemble at the point scale reached up to 50&thinsp;% of the computed flux. The largest absolute uncertainties originate from the short-wave radiation and the albedo parameterizations, followed by the turbulent fluxes. Our study highlights the need for due caution and realistic error quantification when applying such models to regional glacier modelling efforts, or for projections of glacier mass balance in climate settings that are substantially different from the conditions in which the model was optimized.</p

Dynamic volume-return relationship: evidence from an emerging capital market

The relationship between the changes in trading volume and subsequent returns for stocks traded on the Warsaw Stock Exchange (WSE) is tested. High volume stocks are found to experience strong price reversals and low volume stocks to experience weak price reversals and even continuations. Focusing on longer portfolio selection periods does not strengthen these results, and focusing on extreme change in past trading volume and past returns does so only for some high volume portfolios. The sign of volume changes is more informative than the magnitude. The results can be interpreted as evidence of the prevalence of uninformed traders on the WSE.

Reanalysis of a 10-year record (2004-2013) of seasonal mass balances at Langenferner/Vedretta Lunga, Ortler Alps, Italy

Records of glacier mass balance represent important data in climate science and their uncertainties affect calculations of sea level rise and other societally relevant environmental projections. In order to reduce and quantify uncertainties in mass balance series obtained by direct glaciological measurements, we present a detailed reanalysis workflow which was applied to the 10-year record (2004 to 2013) of seasonal mass balance of Langenferner, a small glacier in the European Eastern Alps. The approach involves a methodological homogenization of available point values and the creation of pseudo-observations of point mass balance for years and locations without measurements by the application of a process-based model constrained by snow line observations. We examine the uncertainties related to the extrapolation of point data using a variety of methods and consequently present a more rigorous uncertainty assessment than is usually reported in the literature. Results reveal that the reanalyzed balance record considerably differs from the original one mainly for the first half of the observation period. For annual balances these misfits reach the order of &gt; 300 kg m-2 and could primarily be attributed to a lack of measurements in the upper glacier part and to the use of outdated glacier outlines. For winter balances respective differences are smaller (up to 233 kg m-2) and they originate primarily from methodological inhomogeneities in the original series. Remaining random uncertainties in the reanalyzed series are mainly determined by the extrapolation of point data to the glacier scale and are on the order of ±79 kg m-2 for annual and ±52 kg m-2 for winter balances with values for single years/seasons reaching ±136 kg m-2. A comparison of the glaciological results to those obtained by the geodetic method for the period 2005 to 2013 based on airborne laser-scanning data reveals that no significant bias of the reanalyzed record is detectable.</p

Non-acid gastro-oesophageal reflux in children with suspected pulmonary aspiration

Background & aims: In a group of children with suspected pulmonary aspiration, we aimed to describe the type and physical characteristics of gastro-oesophageal reflux (GOR) episodes, and to determine their correlation with the lipid-laden macrophage (LLM) content in bronchoalveolar lavage (BAL). Patients and methods: Twenty-one children with a diagnosis of bronchial asthma, recurrent lung consolidations and recurrent laryngotracheitis underwent 24-h multichannel intraluminal impedance and pH (MII-pH) monitoring, fibreoptic bronchoscopy and BAL. The following parameters were evaluated: total number of reflux episodes, number of acid reflux [AR: pH 4], height of reflux episodes, LLM content and percentage of neutrophils in the BAL. Results: The number of NAR episodes and the number of those reaching the proximal oesophagus were significantly higher in patients with recurrent lung consolidations than ill those with bronchial asthma and laryngotracheitis (p < 0.01 and p < 0.01). BAL studies showed a significantly higher LLM content in children with recurrent lung consolidations than in those with bronchial asthma and laryngotracheitis (p < 0.01). The LLM content correlated significantly with the total number of reflux episodes (r = 0.73; p < 0.001) and with those reaching the proximal oesophagus (r = 0.67: p < 0.001). Finally, the LLM content cot-related with the number of NAR episodes (r = 0.61: p < 0.01), with those reaching the proximal oesophagus (r = 0.64: p < 0.01) and with the percentage of BAL neutrophils (r = 0.7; p < 0.01). Conclusion: NAR episodes reaching the proximal oesophagus correlate with diagnostic marker for Pulmonary micro-aspiration. MII-pH monitoring increases the yield in identifying types and proximal extension of reflux episodes, that discriminate between patients with and without pulmonary aspiration. (C) 2009 Editrice Gastroenterologica Italiana S.r.l. Published by Elsevier Ltd. All rights reserved