Errors and uncertainties introduced by a regional climate model in climate impact assessments: example of crop yield simulations in West Africa

16 pagesInternational audienceThe challenge of estimating the potential impacts of climate change has led to an increasing use of dynamical downscaling to produce fine spatial-scale climate projections for impact assessments. In this work, we analyze if and to what extent the bias in the simulated crop yield can be reduced by using the Weather Research and Forecasting (WRF) regional climate model to downscale ERA-Interim (European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis) rainfall and radiation data. Then, we evaluate the uncertainties resulting from both the choice of the physical parameterizations of the WRF model and its internal variability. Impact assessments were performed at two sites in Sub-Saharan Africa and by using two crop models to simulate Niger pearl millet and Benin maize yields. We find that the use of the WRF model to downscale ERA-Interim climate data generally reduces the bias in the simulated crop yield, yet this reduction in bias strongly depends on the choices in the model setup. Among the physical parameterizations considered, we show that the choice of the land surface model (LSM) is of primary importance. When there is no coupling with a LSM, or when the LSM is too simplistic, the simulated precipitation and then the simulated yield are null, or respectively very low; therefore, coupling with a LSM is necessary. The convective scheme is the second most influential scheme for yield simulation, followed by the shortwave radiation scheme. The uncertainties related to the internal variability of the WRF model are also significant and reach up to 30% of the simulated yields. These results suggest that regional models need to be used more carefully in order to improve the reliability of impact assessments

Books Fit for a King: The Presentation Copies of Martin Bucer's De regno Christi (London, British Library, Royal MS. 8 B. VII) and Johannes Sturm's De periodis (Cambridge, Trinity College, II.12.21 and London, British Library, C.24.e.5)

This article discusses the presentation copies of two sixteenth-century works, Martin Bucer’s De regno Christi and Johannes Sturm’s De periodis, both of which were sent in fine copies by Bucer to John Cheke in 1550. The covering letter that accompanied these books survives today at Corpus Christi College, Cambridge, whilst the presentation copy of De regno Christi intended for King Edward VI is British Library, Royal MS. 8 B. VII. The circumstances surrounding these books, their production and transmission can be reconstructed in unusual and intriguing detail. This article presents several new and important discoveries, including the identification of the two presentation copies of Sturm’s De periodis mentioned by Bucer in his letter (today London, British Library, C.24.e.5 and Cambridge, Trinity College, II.12.21), as well as the tentative attribution of the binding of Royal MS. 8 B. VII to Bucer’s collaborator, the Strasbourg-based printer Remigius Guidon. An in-depth analysis of these artefacts and their codicological features confirms that TCC II.12.21 was intended for Edward VI, whereas BL C.24.e.5 can be identified, for the first time, as a book designed for and received by Princess Elizabeth. The dynamics governing the production and exchange of presentation copies between the Edwardian court and the Protestant reformers serve to paint a sharply focused picture of Bucer’s activities around 1550, that is, at a key moment of religious change in England

Regionalizing rainfall at very high resolution over la Réunion island using a regional climate model.

23 pagesInternational audienceRegional climate models (RCMs) should be evaluated with respect to their ability to downscale large-scale climate information to the local scales, which are sometimes strongly modulated by surface conditions. This is the case for La Reunion (southwest Indian Ocean) because of its island context and its complex topography. Large-scale atmospheric configurations such as tropical cyclones (TCs) may have an amplifying effect on local rainfall patterns that only a very high-resolution RCM, forced by the large scales and resolving finescale processes, may simulate properly. This paper documents the capability of the Weather Research and Forecasting Model (WRF) RCM to regionalize rainfall variability at very high resolution (680 m) over La Reunion island for daily to seasonal time scales and year-to-year differences. Two contrasted wet seasons (November-April) are selected: 2000-01 (abnormally dry) and 2004-05 (abnormally wet). WRF rainfall is compared to a dense network of rain gauge records interpolated onto the WRF grid through the regression-kriging (RK) technique. RK avoids the point-to-grid comparison issue, but produces imperfect estimates due to sampling, so its quality also needs to be tested. Seasonal rainfall amounts and contrasts produced by WRF are fairly realistic. At intraseasonal and daily time scales, differences to RK are more sizable. These differences are not easy to interpret in sectors where the rain gauge network is less dense and the quality of RK more uncertain, as over the eastern slopes of Piton de la Fournaise volcano where WRF seems to simulate more realistic rainfall than RK. Finally, the heavy rainfall associated with TC Ando on 6 January 2001, is documented. WRF shows weak disagreements with RK, indicating its capability to regionalize rainfall during extreme events

SENSIBILITE D'UN MODELE A AIRE LIMITEE A SA PARAMETRISATION PHYSIQUE : APPLICATION EN AFRIQUE AUSTRALE

Cette étude examine pour la première fois en Afrique australe les incertitudes d'un modèle à aire limitée (Advanced Weather Research Forecast (WRF-ARW V3011)) liées à sa paramétrisation physique. Les incertitudes sont analysées au pas de temps saisonnier en déterminant les principaux points communs et différences de 27 expériences numériques, avec un focus sur le champ pluviométrique. Ces 27 expériences documentent le trimestre Décembre-Janvier-Février 1993-94, coeur de la saison des pluies de l'Afrique du Sud à régime pluvial tropical, et correspondent à toutes les combinaisons possibles entre 3 schémas de couche limite, 3 schémas de convection et 3 schémas de microphysique. Quelle que soit la paramétrisation testée, la distribution spatiale des pluies est similaire et relativement proche des estimations de pluies. WRF sous-estime la pluviométrie des deux zones de convergence de la région (ZCIT et ZCSI) et la surestime en Afrique subtropicale, surtout sur les reliefs. Les principales différences inter-membres concernent l'amplitude des cumuls saisonniers et les processus pluviogènes qui dépendent principalement des schémas de convection. Grell simule des quantités comparables aux observations in situ alors que Kain-Fritsch et Betts-Miller-Janjic les surestiment nettement, ce qui peut résulter d'une sous-estimation (surestimation) de l'humidité spécifique en moyenne et basse couche observée avec Grell (Kain-Fritsch et Betts-Miller-Janjic). Grell et Kain-Fritsch simulent essentiellement des pluies convectives, ce qui semble cohérent avec l'influence de la circulation tropicale sur cette région. Comparée aux réanalyses ERA40 utilisées pour le forçage latéral, la convergence d'humidité associée à la majorité des expériences est renforcée sur le subcontinent, de même que la vitesse verticale de l'air en moyenne atmosphère. C'est la raison pour laquelle WRF corrige généralement les biais secs d'ERA40. Les différences inter-membres des champs thermo-dynamiques sont fonction des schémas de convection à ce pas de temps, mais aussi d'alliances non systématiques entre les trois types de schémas testés

Southern African summer-rainfall variability, and its teleconnections, on interannual to interdecadal timescales in CMIP5 models

23 pagesInternational audienceThis study provides the first assessment of CMIP5 model performances in simulating southern Africa (SA) rainfall variability in austral summer (Nov–Feb), and its teleconnections with large-scale climate variability at different timescales. Observed SA rainfall varies at three major timescales: interannual (2–8 years), quasi-decadal (8–13 years; QDV) and interdecadal (15–28 years; IDV). These rainfall fluctuations are, respectively, associated with El Niño Southern Oscillation (ENSO), the Interdecadal Pacific Oscillation (IPO) and the Pacific Decadal Oscillation (PDO), interacting with climate anomalies in the South Atlantic and South Indian Ocean. CMIP5 models produce their own variability, but perform better in simulating interannual rainfall variability, while QDV and IDV are largely underestimated. These limitations can be partly explained by spatial shifts in core regions of SA rainfall variability in the models. Most models reproduce the impact of La Niña on rainfall at the interannual scale in SA, in spite of limitations in the representation of ENSO. Realistic links between negative IPO are found in some models at the QDV scale, but very poor performances are found at the IDV scale. Strong limitations, i.e. loss or reversal of these teleconnections, are also noted in some simulations. Such model errors, however, do not systematically impact the skill of simulated rainfall variability. This is because biased SST variability in the South Atlantic and South Indian Oceans strongly impact model skills by modulating the impact of Pacific modes of variability. Using probabilistic multi-scale clustering, model uncertainties in SST variability are primarily driven by differences from one model to another, or comparable models (sharing similar physics), at the global scale. At the regional scale, i.e. SA rainfall variability and associated teleconnections, while differences in model physics remain a large source of uncertainty, the contribution of internal climate variability is increasing. This is particularly true at the QDV and IDV scales, where the individual simulations from the same model tend to differentiate, and the sampling error increase

Dynamical downscaling of temperature variability over Tunisia: evaluation a 21-year-long simulation performed with the WRF model.

8 pagesInternational audienceThis study evaluates the capabilities of the Weather Research and Forecasting (WRF) model to reproduce the space-time variability of near-surface air temperature over Tunisia. Downscaling is based on two nested domains with a first domain covering the Mediterranean Basin and forced by 21 years of ERA-Interim reanalysis (1991-2011), and a second domain (12 km spatial resolution) centered on Tunisia. Analyses and comparisons are focused on daily average (Tavg), minimum (Tmin) and maximum (Tmax) near-surface air temperatures and are carried out at the annual and seasonal timescales. WRF results are assessed against various climatological products (ERA-Interim, EOBS and a local network of 18 surface weather stations). The model correctly reproduces the spatial patterns of temperature being significantly superimposed with local topographic features. However, it broadly tends to underestimate temperatures especially in winter. Temporal variability of temperature is also properly reproduced by the model although systematic cold biases mostly concerning Tmax, reproduced throughout the whole simulation period, and prevailing during the winter months. Comparisons also suggest that the WRF errors are not rooted in the driving model but could be probably linked to deficiencies in the model parameterizations of diurnal/nocturnal physical processes that largely impact Tmax / Tmin

Strong amplitude-phase coupling in submonolayer quantum dots

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Appl. Phys. Lett. 109, 201102 (2016) and may be found at https://doi.org/10.1063/1.4967833.Submonolayer quantum dots promise to combine the beneficial features of zero- and two-dimensional carrier confinement. To explore their potential with respect to all-optical signal processing, we investigate the amplitude-phase coupling (α-parameter) in semiconductor optical amplifiers based on InAs/GaAs submonolayer quantum dots in ultrafast pump-probe experiments. Lateral coupling provides an efficient carrier reservoir and gives rise to a large α-parameter. Combined with a high modal gain and an ultrafast gain recovery, this makes the submonolayer quantum dots an attractive gain medium for nonlinear optical signal processing

Robert of Torigni’s “pragmatic literacy”:some theoretical considerations

This article offers some theoretical considerations on the literacy of Robert of Torigni (1106-1186), monk/prior of Le Bec (dép. Eure, cant. Brionne) and abbot of Mont-Saint-Michel (dép. Manche, cant. Pontorson), and one of the most celebrated historians of the twelfth century. In recent years, scholars have shown a renewed interest in Robert as an author and scribe, including his handwriting, his librarianship, his use of archival sources, and his working methods as a historian. At the same time, however, there is no study that approaches Robert’s relationship with the written word from a conceptual point of view. The present article attempts to fill this lacuna by revisiting Robert’s literary activities in the light of what is known amongst medievalists as the concept of “pragmatic literacy”