Caractérisation de la variabilité interne des modèles régionaux de climat

Les modèles régionaux de climat (MRC) sont maintenant reconnus comme des outils efficaces pour augmenter la résolution des simulations climatiques à un ordre d'environ 50 km. Cette résolution est jugée nécessaire pour décrire de nombreux impacts liés aux changements climatiques. Un modèle régional de climat (MRC) performe une simulation climatique sur une sous-région du globe. Pour cette raison, un MRC doit utiliser des données pilotes au pourtour de la sous-région pour tenir compte de la circulation atmosphérique qui parcourt le globe. Les données provenant d'un MRC sont de plus en plus utilisées par les décideurs pour prendre des mesures d'adaptation adéquates en fonction des changements climatiques projetés. Pour cette raison, les scientifiques qui livrent les données climatiques aux décideurs doivent fournir les données les plus précises possibles. L'une des incertitudes des projections de changements climatiques produites par les MRC est associée au comportement chaotique du système climatique qui est simulé. En raison de ce comportement, le climat simulé avec un MRC peut diverger d'un autre climat simulé lancé avec des conditions initiales légèrement différentes tout en étant en accord avec les mêmes forçages imposés. La variabilité mesurée entre les simulations lancées avec différentes conditions initiales est appelée variabilité interne. La variabilité interne des MRC est étudiée depuis quelques années. Ces études sont généralement limitées par les ensembles de simulations nécessaires au calcul de la variabilité interne. Ces ensembles comportent généralement peu de simulations qui sont courtes et qui sont intégrées sur de petits domaines. Le premier objectif de cette thèse consistait à vérifier les hypothèses émises dans les articles précédents sur la variabilité interne des MRC en utilisant un ensemble de simulations actuel. Afin de répondre à cet objectif, un ensemble comportant dix simulations de dix ans couvrant l'Amérique du nord a été réalisé avec le modèle régional canadien du climat. L'évolution temporelle de la variabilité interne de cet ensemble pour la pression au niveau moyen de la mer (PNM) et pour la température au niveau de l'abri (TA) révèle un cycle annuel faible avec des valeurs en hiver et au printemps légèrement plus élevées. Ce résultat, qui se distingue de celui des études précédentes; suggère que l'augmentation de la dimension du domaine diminue l'efficacité du contrôle du pilote sur le MRC, ce qui augmente la variabilité interne. Pour les variables étudiées, la variabilité interne augmente généralement d'ouest en est du domaine selon la circulation générale vers l'est. Une comparaison de la variabilité interne avec la variabilité temporelle montre que la variabilité interne pour la PNM est près de son maximum en été dans le nord-est du domaine. Une comparaison du climat de dix ans pour la TA en été de chacune des simulations avec la moyenne d'ensemble montre que la variabilité interne peut avoir un impact important sur le climat simulé. Le deuxième objectif de cette thèse consistait à trouver un outil capable de quantifier le contrôle du pilote sur une simulation effectuée avec un MRC. Cet outil est un traceur qui calcule le temps de résidence des parcelles atmosphériques à l'intérieur du domaine d'un MRC. Ce traceur a été utilisé pour première fois dans l'ensemble de simulations décrit précédemment. Les diagnostiques du climat généré par l'ensemble montre le bon fonctionnement du traceur. Le temps de résidence est plus élevé en été qu'en hiver en liaison avec la circulation atmosphérique qui est plus rapide en hiver. Le temps de résidence augmente d'ouest en est à l'intérieur du domaine aussi en relation avec la circulation atmosphérique générale vers l'est. Un diagramme de disperison généré avec les distributions spatiales de la variabilité interne relative des variables étudiées et du temps de résidence montre que la variabilité interne augmente linéairement avec le temps de résidence similairement en été qu'en hiver. Ce résultat appuie plusieurs études précédentes qui proposaient un lien entre la circulation atmosphérique et la variabilité interne. D'après la relation trouvée, le temps de résidence peut être utilisé comme un indicateur quantitatif du contrôle des données pilotes exercé sur un MRC. On envisage que cet outil sera utile pour les analyses futures effectuées avec les MRC. ______________________________________________________________________________ MOTS-CLÉS DE L’AUTEUR : Variabilité interne, Modélisation régionale du climat, Ensemble de simulations, Temps de résidence, Climat nord-américain

Evidence of added value in North American regional climate model hindcast simulations using ever-increasing horizontal resolutions

Commonly termed “added value”, the additional regional details gained by high-resolution regional climate models (RCMs) over the coarser resolution reanalysis driving data are often indistinguishable at the 0.44° grid mesh computationally affordable large CORDEX domains. In an attempt to highlight the benefits of finer resolutions to study the RCM added value, five North American weather phenomena are evaluated in RCM hindcast simulations using grid meshes of 0.44°, 0.22° and 0.11° with available observations. The results show that the orographic precipitation on the west coast of North America is enhanced and more realistic, with two distinct rain bands in the finer resolution simulation. The spatial distribution of precipitation in August and the high frequency of summer precipitation extremes over southwestern United States reveal that the North American monsoon is improved with increasing resolution. Only the finer RCM simulation shows skill at producing snowbelts around the Great Lakes by capturing lake-effect snow. A comparison of wind roses in the St. Lawrence River Valley indicates that only the finer RCM simulation is able to reproduce wind channeling by resolving complex orography. Finally, the simulation of the summer land-sea breezes by the RCM simulations leads to added value in the diurnal cycle of precipitation over the Florida peninsula and the Caribbean islands. Overall, the almost systematic improvements of the finer resolution simulations suggest that higher resolutions, only computationally affordable over smaller domains, might get a higher priority to promote RCM added value

Erratum to: Spatial spin-up of fine scales in a regional climate model simulation driven by low-resolution boundary condition

The capture of the public servant in a criminal investigation is subject to special rules and different to those for the capture of individuals, since the imprisonment of an official can affect continuity, speed and efficiency of the civil service, an equally important constitutional value. Therefore, as a rule capturing the public servant must be preceded by a request for suspensión by the prosecution, and to proceed without suspension, the prosecutor in his providence should motivate the reasons and arguments why not affects the normal functioning of public administration. The lack of motivation for this essential aspect, affords a fact that becomes appropriate procedural habeas corpus as an effective mechanism guarantees of personal freedom. Similarly appropriate habeas corpus when catching public server ordered by a prosecutor without functional competence to advance research, by setting a path made by organic defect.La captura del servidor público investigado en un proceso penal está sujeta a reglas especiales y diversas a las previstas para la captura de los particulares, por cuanto la privación de la libertad de un funcionario puede afectar la continuidad, celeridad y eficacia de la función pública, como un valor constitucional igualmente relevante. Por tal motivo, como regla general,la captura del servidor público debe estar precedida de la solicitud de suspensión por parte de la Fiscalía General de la Nación y para que proceda sin suspensión previa, el fiscal debe consignar en su providencia las razones y argumentos por los cuales no se afecta el normal funcionamiento de la administración pública. La ausencia de motivación de este aspecto esencial constituye una vía de hecho procedimental que torna procedente la acción de habeas corpus, como mecanismo efectivo de garantía de la libertad personal. De igual manera, procede el habeas corpus cuando la captura del servidor público la ordena un fiscal sin competencia funcional para adelantar la investigación, por configuración de una vía de hecho por defecto orgánico

Spatial spin-up of fine scales in a regional climate model simulation driven by low-resolution boundary conditions

In regional climate modelling, it is well known that domains should be neither too large to avoid a large departure from the driving data, nor too small to provide a sufficient distance from the lateral inflow boundary to allow the full development of the small-scale (SS) features permitted by the finer resolution. Although most practitioners of dynamical downscaling are well aware that the jump of resolution between the lateral boundary condition (LBC) driving data and the nested regional climate model affects the simulated climate, this issue has not been fully investigated. In principle, as the jump of resolution becomes larger, the region of interest in the limited-area domain should be located further away from the lateral inflow boundary to allow the full development of the SS features. A careless choice of domain might result in a suboptimal use of the full finer resolution potential to develop fine-scale features. To address this issue, regional climate model (RCM) simulations using various resolution driving data are compared following the perfect-prognostic Big-Brother protocol. Several experiments were carried out to evaluate the width of the spin-up region (i.e. the distance between the lateral inflow boundary and the domain of interest required for the full development of SS transient eddies) as a function of the RCM and LBC resolutions, as well as the resolution jump. The spin-up distance turns out to be a function of the LBC resolution only, independent of the RCM resolution. When varying the RCM resolution for a given resolution jump, it is found that the spin-up distance corresponds to a fixed number of RCM grid points that is a function of resolution jump only. These findings can serve a useful purpose to guide the choice of domain and RCM configuration for an optimal development of the small scales allowed by the increased resolution of the nested model

A metrics-based analysis of seasonal daily precipitation and near-surface temperature within seven Coordinated Regional Climate Downscaling Experiment domains

We compare ensemble mean daily precipitation and near-surface temperatures from regional climate model simulations over seven Coordinated Regional Climate Downscaling Experiment domains for the winter and summer seasons. We use Taylor diagrams to show the domain-wide pattern similarity between the model ensemble and the observational data sets. We use the Climatic Research Unit (CRU) and the University of Delaware gridded observations and ERA-Interim reanalysis data as an additional observationally based estimate of historical climatology. Taylor diagrams determine the relative skill of the seven sets of simulations and quantify these results in terms of center pattern root-mean square error and correlation coefficient. Results suggest that there is good agreement between the models and the CRU, in terms of their respective seasonal cycles, as shown in Taylor diagrams and bias plots. There is also good agreement between both gridded observation sets. In addition, downscaled ERA-Interim precipitation is closer to observations than raw ERA-Interim precipitation. Domains located in the low latitudes and those having high topography appear to have larger biases, especially precipitation.Fil: Glisan, Justin M.. IOWA STATE UNIVERSITY (ISU);Fil: Jones, Richard. No especifíca;Fil: Lennard, Chris. University of Cape Town; SudáfricaFil: Castillo Pérez, Nadia Itzel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; ArgentinaFil: Lucas Picher, Philippe. Université du Québec a Montreal; CanadáFil: Rinke, Annette. Helmholtz Centre for Polar and Marine Research; AlemaniaFil: Solman, Silvina Alicia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; ArgentinaFil: Gutowski, William J.. IOWA STATE UNIVERSITY (ISU)

Mass balance of the Greenland ice sheet (2003-2008) from ICESat data:The impact of interpolation, sampling and firn density

ICESat has provided surface elevation measurements of the ice sheets since the launch in January 2003, resulting in a unique dataset for monitoring the changes of the cryosphere. Here, we present a novel method for determining the mass balance of the Greenland ice sheet, derived from ICESat altimetry data. <br><br> Three different methods for deriving elevation changes from the ICESat altimetry dataset are used. This multi-method approach provides a method to assess the complexity of deriving elevation changes from this dataset. <br><br> The altimetry alone can not provide an estimate of the mass balance of the Greenland ice sheet. Firn dynamics and surface densities are important factors that contribute to the mass change derived from remote-sensing altimetry. The volume change derived from ICESat data is corrected for changes in firn compaction over the observation period, vertical bedrock movement and an intercampaign elevation bias in the ICESat data. Subsequently, the corrected volume change is converted into mass change by the application of a simple surface density model, in which some of the ice dynamics are accounted for. The firn compaction and density models are driven by the HIRHAM5 regional climate model, forced by the ERA-Interim re-analysis product, at the lateral boundaries. <br><br> We find annual mass loss estimates of the Greenland ice sheet in the range of 191 ± 23 Gt yr<sup>−1</sup> to 240 ± 28 Gt yr<sup>−1</sup> for the period October 2003 to March 2008. These results are in good agreement with several other studies of the Greenland ice sheet mass balance, based on different remote-sensing techniques

Towards Constraining Glacial Isostatic Adjustment in Greenland Using ICESat and GPS Observations

Constraining glacial isostatic adjustment (GIA) i.e. the Earth’s viscoelastic response to past ice changes, is an important task, because GIA is a significant correction in gravity-based ice sheet mass balance estimates. Here, we investigate how temporal variations in the observed and modeled crustal displacements due to the Earth’s response to ongoing ice mass changes can contribute to the process of constraining GIA. We use mass change grids of the Greenland ice sheet (GrIS) derived from NASA’s high resolution Ice, Cloud and land Elevation Satellite (ICESat) data in three overlapping time spans covering the period 2004–2009 to estimate temporal variations in the elastic response due to present day ice mass loss. The modeled crustal displacements (elastic + GIA) are compared with GPS time series from five permanent sites (KELY, KULU, QAQ1, THU2, and SCOR). We find, that the modeled pattern of elastic crustal displacements shows pronounced variation during the observation period, where an increase in elastic displacement is found at the northwest coast of Greenland, while a decrease is found at the southeast coast. This pattern of temporal changes is supported by the GPS observations. We find, that the temporal behavior of the ICESat-based modeled elastic response agrees well with the GPS observations at the sites KELY, QAQ1, and SCOR. This suggests, that our elastic models are able to resolve the temporal changes in the observed uplift, which indicates that the elastic uplift models are reliable at these sites. Therefore, we conclude that these sites are useful for constraining GIA

Nocturnal surface ozone enhancement over Portugal during winter: Influence of different atmospheric conditions

our distinct nocturnal surface ozone (NSO) enhancement events were observed, with NSO concentration exceeding 80μg/m3, at multiple ozone (O3) monitoring stations (32 sites) in January, November and December between year 2000–2010, in Portugal. The reasonable explanation for the observed bimodal pattern of surface ozone with enhanced NSO concentration during nighttime has to be transport processes, as the surface ozone production ceases at nighttime. Simultaneous measurements of O3 at multiple stations during the study period in Portugal suggest that horizontal advection alone cannot explain the observed NSO enhancement. Thus, detailed analysis of the atmospheric conditions, simulated with the Weather Research and Forecasting (WRF) model, were performed to evaluate the atmospheric mechanisms responsible for NSO enhancement in the region. Simulations revealed that each event occurred as a result of one or the combination of different atmospheric processes such as, passage of a cold front followed by a subsidence zone; passage of a moving surface trough, with associated strong horizontal wind speed and vertical shear; combination of vertical and horizontal transport at the synoptic scale; formation of a low level jet with associated vertical mixing below the jet stream. The study confirmed that large-scale flow pattern resulting in enhanced vertical mixing in the nocturnal boundary layer, plays a key role in the NSO enhancement events, which frequently occur over Portugal during winter months

The future potential for wine production in Scotland under high-end climate change

Wine production is climate dependent and highly sensitive to weather variability, which makes the sector a good indicator of ongoing and future climate change impacts. Under high-end climate change (HECC), temperatures in Scotland are projected to increase significantly by the end of the twenty-first century. This raises the possibility of future temperatures becoming sufficiently high to support the growth of wine grapes. In this paper, we explore to what extent Scotland might become suitable for wine production under HECC using a climate analogue approach. Specifically, we address the following questions. What are the projected late twenty-first century temperature changes in Scotland? Where in Europe are current climates (based on summer and annual temperatures) similar to those projected for Scotland by the end of the twenty-first century under HECC? Are any of these locations currently wine grape growing regions? The temperature analogues towards the end of the twenty-first century occurred at more southerly latitudes in Europe, with some variability from west to east arising from the influence of continental climates. Temperature analogues alone match with several current wine grape growing regions of Europe, suggesting that future climates in Scotland could support wine production. However, when precipitation and/or lithology and topography are also taken into account, no matches were found with existing European wine grape growing regions. This study demonstrates how the use of climate analogues in combination with other environmental datasets can be useful in understanding future climate change impacts, especially under HECC