Influence d'un changement climatique dû à une hausse de gaz à effet de serre sur l'agriculture au quebec     

Bhawan Singh  Mustapha El Maayar  Pierre André  Jean‐Pierre Thouez  Christopher Bryant  Denis Provençal 《大气与海洋》2013,51(2):379-399

Abstract

This study, using a climate change scenario generated by the Canadian Climate Centre (CCC) general circulation model (GCM) examines the impacts of such a climate change on agriculture in southern Quebec. Using a crop model from the Food and Agriculture Organization (FAO), yield responses of a variety of cereals, legumes, oleaginous and special crops to climate change are analysed and discussed.

Results show that under the 2 × CO₂ climate scenario the growing season would be longer and accumulation of corn heat units and growing degree days would be more important than under actual climate (1961–1990). One of the more important results of this study is that, on the one hand yield of C₃ cereals would be lower and that of C₄ cereals higher in most agricultural regions. On the other hand, the direct fertilisation effect of increased CO₂ is not considered. It must be cautioned however that we can not generalise results obtained for one legume crop to all legumes.  相似文献   

Properties of unstable waves in the lower St Lawrence Estuary     

Gordon Mertz  Yves Gratton  Jacques A. Gagné 《大气与海洋》2013,51(2):230-240

Abstract

The lower St Lawrence Estuary is an interesting case amongst estuaries in that it is wide enough to accommodate the development of mesoscale unstable waves and eddies. These features are generated by the runoff‐driven jet along this body's south shore. We present data yielding estimates of the length, time and velocity scales of these unstable disturbances. To relate these quantities to the dynamics we employ a 2‐layer quasigeos‐trophic instability model featuring realistic lateral shear. All model runs show short time and length scales, e‐folding periods of less than 10 days and wavelengths less than 50 km.  相似文献   

A simple gravity wave drag parametrization for use in medium‐range weather forecast models     

C. Chouinard  M. Béland  N. McFarlane 《大气与海洋》2013,51(2):91-110

Abstract

A simple gravity wave drag parametriiation over mountainous terrain is tested for its ability to reduce the systematic errors of medium‐range weather forecasts. Following Boer et al. (1984), this parametrization is a function of the low‐level wind speed and stability, the local Froude number, and the variance of the subgrid‐scale orographie features.

A comparison study of ten 7‐day forecasts obtained with envelope orography, wave drag or standard orography, shows that wave drag is as effective as envelope orography in reducing the systematic errors. A further comparison where the combined effects of the wave drag and that of a complementary enhanced orography (that is one that includes only the subgrid‐scale elements not treated separately by wave drag) are taken into account shows this latter approach to be the most promising in reducing orographically‐related systematic errors.  相似文献   

Canadian middle atmosphere model: Preliminary results from the chemical transport module     

J. de Grandpré  J.W. Sandilands  J.C. McConnell  S.R. Beagley  P.C. Croteau  M.Y. Danilin 《大气与海洋》2013,51(4):385-431

Abstract

An important objective of middle atmosphere global climate modelling is the development of the capability of predicting the response of the middle atmosphere to natural or anthropogenic perturbations. To achieve this, a comprehensive chemistry package interactively coupled with radiative and dynamical modules is required. This paper presents preliminary results obtained with a photochemistry module which has been incorporated in the Canadian Middle Atmosphere Model (CMAM). The module contains 42 species including necessary oxygen, hydrogen, nitrogen, chlorine, bromine and methane oxidation cycle species. Photochemical balance equations are solved on‐line throughout the middle atmosphere at every dynamical time step. A full diurnal cycle is simulated with photolysis rates provided by a look‐up table. The chemistry solver is a mass conserving, fully implicit, backward difference scheme which currently uses less than 10% of the GCM run time. We present the results obtained from short integrations and compare them with UARS measurements. The model ozone distribution appears in quantitative agreement with observations showing peak values near 10 ppmv and confined to the 35‐km region. The abundance of nitrogen, chlorine, bromine oxides and their respective contributions to the overall ozone budget is realistic. The study illustrates the capability of the model to simulate middle atmosphere photochemistry for the disparate conditions occurring throughout the region.  相似文献   

Climate and climate change in western canada as simulated by the Canadian regional climate model     

Rene Laprise  Daniel Caya  Michel Giguere  Guy Bergeron  Hélène Côté  Jean‐Pierre Blanchet 《大气与海洋》2013,51(2):119-167

Abstract

A þrst climate simulation performed with the novel Canadian Regional Climate Model (CRCM) is presented. The CRCM is based on fully elastic non‐hydrostatic þeld equations, which are solved with an efþcient semi‐implicit semi‐Lagrangian (SISL) marching algorithm, and on the parametrization package of subgrid‐scale physical effects of the second‐generation Canadian Global Climate Model (GCMII). Two 5‐year integrations of the CRCM nested with GCMII simulated data as lateral boundary conditions are made for conditions corresponding to current and doubled CO₂ scenarios. For these simulations the CRCM used a grid size of 45 km on a polar‐stereographic projection, 20 scaled‐height levels and a time step of 15 min; the nesting GCMII has a spectral truncation of T32, 10 hybrid‐pressure levels and a time step of 20 min. These simulations serve to document: (1) the suitability of the SISL numerical scheme for regional climate modelling, (2) the use of GCMII physics at much higher resolution than in the nesting model, (3) the ability of the CRCM to add realistic regional‐scale climate information to global model simulations, and (4) the climate of the CRCM compared to that of GCMII under two greenhouse gases (GHG) scenarios.  相似文献   

Application of the Canadian regional climate model to the Laurentian great lakes region: Implementation of a lake model     

Stéphane Goyette  N.A. McFarlane  Gregory M. Flato 《大气与海洋》2013,51(3):481-503

Abstract

This study reports on the implementation of an interactive mixed‐layer/thermodynamic‐ice lake model coupled with the Canadian Regional Climate Model (CRCM). For this application the CRCM, which uses a grid mesh of 45 km on a polar stereographic projection, 10 vertical levels, and a timestep of 15 min, is nested with the second generation Canadian General Circulation Model (GCM) simulated output. A numerical simulation of the climate of eastern North America, including the Laurentian Great Lakes, is then performed in order to evaluate the coupled model. The lakes are represented by a “mixed layer” model to simulate the evolution of the surface water temperature, and a thermodynamic ice model to simulate evolution of the ice cover. The mixed‐layer depth is allowed to vary spatially. Lake‐ice leads are parametrized as a function of ice thickness based on observations. Results from a 5‐year integration show that the coupled CRCM/lake model is capable of simulating the seasonal evolution of surface temperature and ice cover in the Great Lakes. When compared with lake climatology, the simulated mean surface water temperature agrees within 0.12°C on average. The seasonal evolution of the lake‐ice cover is realistic but the model tends to underestimate the monthly mean ice concentration on average. The simulated winter lake‐induced precipitation is also shown, and snow accumulation patterns on downwind shores of the lakes are found to be realistic when compared with observations.  相似文献   

Modulation of soil moisture–precipitation interactions over France by large scale circulation     

Julien Boé 《Climate Dynamics》2013,40(3-4):875-892

How soil moisture affects precipitation is an important question—with far reaching consequences, from weather prediction to centennial climate change—, albeit a poorly understood one. In this paper, an analysis of soil moisture–precipitation interactions over France based on observations is presented. A first objective of this paper is to investigate how large scale circulation modulates soil moisture–precipitation interactions, thanks to a weather regime approach. A second objective is to study the influence of soil moisture not only on precipitation but also on the difference between precipitation and evapotranspiration. Indeed, to have a total positive soil moisture–precipitation feedback, the potential decrease in precipitation associated with drier soils should be larger than the decrease in evapotranspiration that drier soils may also cause. A potential limited impact of soil moisture on precipitation is found for some weather regimes, but its sign depends on large scale circulation. Indeed, antecedent dry soil conditions tend to lead to smaller precipitation for the negative phase of the North Atlantic Oscillation (NAO) regime but to larger precipitation for the Atlantic Low regime. This differential response of precipitation to soil moisture anomalies depending on large scale circulation is traced back to different responses of atmospheric stability. For all circulation regimes, dry soils tend to increase the lifted condensation level, which is unfavorable to precipitation. But for the negative phase of the NAO, low soil moisture tends to lead to an increase of atmospheric stability while it tends to lead to a decrease of stability for Atlantic Low. Even if the impact of soil moisture anomalies varies depending on large scale circulation (it is larger for Atlantic low and the positive phase of the NAO), dry soils always lead to a decrease in evapotranspiration. As the absolute effect of antecedent soil moisture on evapotranspiration is always much larger than its effects on precipitation, for all circulation regimes dry soil anomalies subsequently lead to positive precipitation minus evapotranspiration anomalies i.e. the total soil moisture feedback is found to be negative. This negative feedback is stronger for the Atlantic Low and the positive phase of the NAO regimes.  相似文献   

Downscaling large-scale climate variability using a regional climate model: the case of ENSO over Southern Africa   总被引：1，自引：1，他引：0  

Damien Boulard  Benjamin Pohl  Julien Crétat  Nicolas Vigaud  Thanh Pham-Xuan 《Climate Dynamics》2013,40(5-6):1141-1168

  相似文献   

Potential for small scale added value of RCM’s downscaled climate change signal   总被引：1，自引：1，他引：0  

Alejandro Di Luca  Ramón de Elía  René Laprise 《Climate Dynamics》2013,40(3-4):601-618

In recent decades, the need of future climate information at local scales have pushed the climate modelling community to perform increasingly higher resolution simulations and to develop alternative approaches to obtain fine-scale climatic information. In this article, various nested regional climate model (RCM) simulations have been used to try to identify regions across North America where high-resolution downscaling generates fine-scale details in the climate projection derived using the “delta method”. Two necessary conditions were identified for an RCM to produce added value (AV) over lower resolution atmosphere-ocean general circulation models in the fine-scale component of the climate change (CC) signal. First, the RCM-derived CC signal must contain some non-negligible fine-scale information—independently of the RCM ability to produce AV in the present climate. Second, the uncertainty related with the estimation of this fine-scale information should be relatively small compared with the information itself in order to suggest that RCMs are able to simulate robust fine-scale features in the CC signal. Clearly, considering necessary (but not sufficient) conditions means that we are studying the “potential” of RCMs to add value instead of the AV, which preempts and avoids any discussion of the actual skill and hence the need for hindcast comparisons. The analysis concentrates on the CC signal obtained from the seasonal-averaged temperature and precipitation fields and shows that the fine-scale variability of the CC signal is generally small compared to its large-scale component, suggesting that little AV can be expected for the time-averaged fields. For the temperature variable, the largest potential for fine-scale added value appears in coastal regions mainly related with differential warming in land and oceanic surfaces. Fine-scale features can account for nearly 60 % of the total CC signal in some coastal regions although for most regions the fine scale contributions to the total CC signal are of around ～5 %. For the precipitation variable, fine scales contribute to a change of generally less than 15 % of the seasonal-averaged precipitation in present climate with a continental North American average of ～5 % in both summer and winter seasons. In the case of precipitation, uncertainty due to sampling issues may further dilute the information present in the downscaled fine scales. These results suggest that users of RCM simulations for climate change studies in a delta method framework have little high-resolution information to gain from RCMs at least if they limit themselves to the study of first-order statistical moments. Other possible benefits arising from the use of RCMs—such as in the large scale of the downscaled fields– were not explored in this research.  相似文献   

An approximate energy cycle for inter-member variability in ensemble simulations of a regional climate model     

Oumarou Nikiéma  René Laprise 《Climate Dynamics》2013,41(3-4):831-852

The presence of internal variability (IV) in ensembles of nested regional climate model (RCM) simulations is now widely acknowledged in the community working on dynamical downscaling. IV is defined as the inter-member spread between members in an ensemble of simulations performed by a given RCM driven by identical lateral boundary conditions (LBC), where different members are being initialised at different times. The physical mechanisms responsible for the time variations and structure of such IV have only recently begun to receive attention. Recent studies have shown empirical evidence of a close parallel between the energy conversions associated with the time fluctuations of IV in ensemble simulations of RCM and the energy conversions taking place in weather systems. Inspired by the classical work on global energetics of weather systems, we sought a formulation of an energy cycle for IV that would be applicable for limited-area domain. We develop here a novel formalism based on local energetics that can be applied to further our understanding IV. Prognostic equations for ensemble-mean kinetic energy and available enthalpy are decomposed into contributions due to ensemble-mean variables (EM) and those due to deviations from the ensemble mean (IV). Together these equations constitute an energy cycle for IV in ensemble simulations of RCM. Although the energy cycle for IV was developed in a context entirely different from that of energetics of weather systems, the exchange terms between the various reservoirs have a rather similar mathematical form, which facilitates some interpretations of their physical meaning.  相似文献