Scientific and human errors in a snow model intercomparison

International audienceTwenty-seven models participated in the Earth System Model - Snow Model Intercomparison Project (ESM-SnowMIP), the most data-rich MIP dedicated to snow modelling. Our findings do not support the hypothesis advanced by previous snow MIPs: evaluating models against more variables, and providing evaluation datasets extended temporally and spatially does not facilitate identification of key new processes requiring improvement to model snow mass and energy budgets, even at point scales. In fact, the same modelling issues identified by previous snow MIPs arose: albedo is a major source of uncertainty, surface exchange parametrizations are problematic and individual model performance is inconsistent. This lack of progress is attributed partly to the large number of human errors that led to anomalous model behaviour and to numerous resubmissions. It is unclear how widespread such errors are in our field and others; dedicated time and resources will be needed to tackle this issue to prevent highly sophisticated models and their research outputs from being vulnerable because of avoidable human mistakes. The design of and the data available to successive snow MIPs were also questioned. Evaluation of models against bulk snow properties was found to be sufficient for15 some but inappropriate for more complex snow models whose skills at simulating internal snow properties remained untested. Discussions between the authors of this paper on the purpose of MIPs revealed varied, and sometimes contradictory, motivations behind their participation. These findings started a collaborative effort to adapt future snow MIPs to respond to the diverse needs of the communit

Prise en compte de l\u27angle d\u27incidence dans la caractérisation en laboratoire de la transmission acoustique des éléments de façade

Cette thèse concerne la caractérisation de l\u27isolement acoustique des éléments de façade en fonction de l\u27angle d\u27incidence. Deux méthodes expérimentales ont été mises en oeuvre afin de mesurer l\u27indice d\u27affaiblissement suivant la direction de l\u27onde incidente. La première méthode consiste à exciter une paroi d\u27un local réverbérant par une onde plane, dans une direction donnée. La deuxième méthode s\u27appuie sur l\u27utilisation de la phonoscopie, technique d\u27holographie acoustique en milieu confiné. La paroi est excitée de manière diffuse, et une décomposition onde par onde du champ rayonné est obtenue par phonoscopie. Par ailleurs, différentes méthodes numériques ont été utilisées, afin de comparer les valeurs mesurées à des données calculées. Ces travaux ont montré la nécessité de considérer l\u27angle d\u27incidence dans la transmission acoustique quand l\u27excitation des éléments de façade est bien directive, par exemple dans le cas du bruit d\u27avion

Rate effects on aerodynamics of intervocalic stops : evidence from real speech data and model data

This paper is a first attempt towards a better understanding of the aerodynamic properties during speech production and their potential control. In recent years, studies on intraoral pressure in speech have been rather rare, and more studies concern the air flow development. However, the intraoral pressure is a crucial factor for analysing the production of various sounds. In this paper, we focus on the intraoral pressure development during the production of intervocalic stops. Two experimental methodologies are presented and confronted with each other: real speech data recorded for four German native speakers, and model data, obtained by a mechanical replica which allows reproducing the main physical mechanisms occurring during phonation. The two methods are presented and applied to a study on the influence of speech rate on aerodynamic properties

Implementing northern peatlands in a global land surface model: description and evaluation in the ORCHIDEE high-latitude version model (ORC-HL-PEAT)

International audienceWidely present in boreal regions, peatlands contain large carbon stocks because of their hydrologic properties and high water content, which makes primary productivity exceed decomposition rates. We have enhanced the global land surface model ORCHIDEE by introducing a hydrological representation of northern peatlands. These peatlands are represented as a new plant functional type (PFT) in the model, with specific hydrological properties for peat soil. In this paper, we focus on the representation of the hydrology of northern peatlands and on the evaluation of the hydrological impact of this implementation. A prescribed map based on the inventory of Yu et al. (2010) defines peatlands as a fraction of a grid cell represented as a PFT comparable to C 3 grasses, with adaptations to reproduce shallow roots and higher photosynthesis stress. The treatment of peatland hy-drology differs from that of other vegetation types by the fact that runoff from other soil types is partially directed towards the peatlands (instead of directly to the river network). The evaluation of this implementation was carried out at different spatial and temporal scales, from site evaluation to larger scales such as the watershed scale and the scale of all northern latitudes. The simulated net ecosystem exchanges agree with observations from three FLUXNET sites. Water table positions were generally close to observations, with some exceptions in winter. Compared to other soils, the simulated peat soils have a reduced seasonal variability in water storage. The seasonal cycle of the simulated extent of inundated peatlands is compared to flooded area as estimated from satellite observations. The model is able to represent more than 89.5 % of the flooded areas located in peatland areas, where the modelled extent of inundated peatlands reaches 0.83 × 10 6 km 2. However, the extent of peatlands in northern latitudes is too small to substantially impact the large-scale terrestrial water storage north of 45 • N. Therefore, the inclusion of peatlands has a weak impact on the simulated river discharge rates in boreal regions

Empirical Run-Time Bias Correction for Antarctic Regional Climate Projections With a Stretched-Grid AGCM

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Oceanic forcing of Antarctic climate change: A study using a stretched-grid atmospheric general circulation model

A variable-resolution atmospheric general circulation model (AGCM) is used for climate change projections over the Antarctic. The present-day simulation uses prescribed observed sea-surface conditions, while a set of five simulations for the end of the 21st century (2070-2099) under the SRES-A1B scenario uses sea- surface condition anomalies from selected CMIP3 coupled ocean-atmosphere climate models. Analysis of the results shows that the prescribed sea-surface condition anomalies have a very strong influence on the simulated climate change on the Antarctic continent, largely dominating the direct effect of the prescribed greenhouse gas concentration changes in the AGCM simulations. Complementary simulations with idealized forcings confirm these results. An analysis of circulation changes using self-organizing maps shows that the simulated climate change on regional scales is not principally caused by shifts of the frequencies of the dominant circulation patterns, except for precipitation changes in some coastal regions. The study illustrates that in some respects the use of bias-corrected sea- surface boundary conditions in climate projections with a variable-resolution atmospheric general circulation model has some distinct advantages over the use of limited-area atmospheric circulation models directly forced by generally biased coupled climate model output