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Dive into the research topics where Leo Separovic is active.

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Featured researches published by Leo Separovic.


Monthly Weather Review | 2009

Sensitivity Study of Regional Climate Model Simulations to Large-Scale Nudging Parameters

Adelina Alexandru; Ramón de Elía; René Laprise; Leo Separovic; Sébastien Biner

Abstract Previous studies with nested regional climate models (RCMs) have shown that large-scale spectral nudging (SN) seems to be a powerful method to correct RCMs’ weaknesses such as internal variability, intermittent divergence in phase space (IDPS), and simulated climate dependence on domain size and geometry. Despite its initial success, SN is not yet in widespread use because of disagreement regarding the main premises—the unconfirmed advantages of removing freedom from RCMs’ large scales—and lingering doubts regarding its potentially negative side effects. This research addresses the latter issue. Five experiments have been carried out with the Canadian RCM (CRCM) over North America. Each experiment, performed under a given SN configuration, consists of four ensembles of simulations integrated on four different domain sizes for a summer season. In each experiment, the effects of SN on internal variability, time means, extremes, and power spectra are discussed. As anticipated from previous investiga...


Climate Dynamics | 2013

Present climate and climate change over North America as simulated by the fifth-generation Canadian regional climate model

Leo Separovic; Adelina Alexandru; René Laprise; Andrey Martynov; Laxmi Sushama; Katja Winger; Kossivi Tete; Michel Valin

The fifth-generation Canadian Regional Climate Model (CRCM5) was used to dynamically downscale two Coupled Global Climate Model (CGCM) simulations of the transient climate change for the period 1950–2100, over North America, following the CORDEX protocol. The CRCM5 was driven by data from the CanESM2 and MPI-ESM-LR CGCM simulations, based on the historical (1850–2005) and future (2006–2100) RCP4.5 radiative forcing scenario. The results show that the CRCM5 simulations reproduce relatively well the current-climate North American regional climatic features, such as the temperature and precipitation multiannual means, annual cycles and temporal variability at daily scale. A cold bias was noted during the winter season over western and southern portions of the continent. CRCM5-simulated precipitation accumulations at daily temporal scale are much more realistic when compared with its driving CGCM simulations, especially in summer when small-scale driven convective precipitation has a large contribution over land. The CRCM5 climate projections imply a general warming over the continent in the 21st century, especially over the northern regions in winter. The winter warming is mostly contributed by the lower percentiles of daily temperatures, implying a reduction in the frequency and intensity of cold waves. A precipitation decrease is projected over Central America and an increase over the rest of the continent. For the average precipitation change in summer however there is little consensus between the simulations. Some of these differences can be attributed to the uncertainties in CGCM-projected changes in the position and strength of the Pacific Ocean subtropical high pressure.


Archive | 2012

Considerations of Domain Size and Large-Scale Driving for Nested Regional Climate Models: Impact on Internal Variability and Ability at Developing Small-Scale Details

René Laprise; Dragana Kornic; Maja Rapaić; Leo Separovic; Martin Leduc; Oumarou Nikiema; Alejandro Di Luca; Emilia Paula Diaconescu; Adelina Alexandru; Philippe Lucas-Picher; Ramón de Elía; Daniel Caya; Sébastien Biner

The premise of dynamical downscaling is that a high-resolution, nested Regional Climate Model (RCM), driven by large-scale atmospheric fields at its lateral boundary, generates fine scales that are dynamically consistent with the large scales. An RCM is hence expected to act as a kind of magnifying glass that will reveal details that could not be resolved on a coarse mesh. The small scales represent the main potential added value of a high-resolution RCM.


Climate Dynamics | 2012

Impact of spectral nudging and domain size in studies of RCM response to parameter modification

Leo Separovic; Ramón de Elía; René Laprise

The paper aims at finding an RCM configuration that facilitates studies devoted to quantifying RCM response to parameter modification. When using short integration times, the response of the time-averaged variables to RCM modification tend to be blurred by the noise originating in the lack of predictability of the instantaneous atmospheric states. Two ways of enhancing the signal-to-noise ratio are studied in this work: spectral nudging and reduction of the computational domain size. The approach followed consists in the analysis of the sensitivity of RCM-simulated seasonal averages to perturbations of two parameters controlling deep convection and stratiform condensation, perturbed one at a time. Sensitivity is analyzed within different simulation configurations obtained by varying domain size and using the spectral nudging option. For each combination of these factors multiple members of identical simulations that differ exclusively in initial conditions are also generated to provide robust estimates of the sensitivities (the signal) and sample the noise. Results show that the noise magnitude is decreased both by reduction of domain size and the spectral nudging. However, the reduction of domain size alters some sensitivity signals. When spectral nudging is used significant alterations of the signal are not found.


Monthly Weather Review | 2008

Reproducible and Irreproducible Components in Ensemble Simulations with a Regional Climate Model

Leo Separovic; Ramón de Elía; René Laprise

Abstract High-resolution limited-area models (LAMs) have been widely employed to downscale coarse-resolution climate simulations or objective analyses. The growing evidence that LAM climate statistics can be sensitive to initial conditions suggests that a deterministic verification of LAM solutions in terms of finescale atmospheric features might be misguided. In this study a 20-member ensemble of LAM integrations with perturbed initial conditions, driven by NCEP–NCAR reanalyses, is conducted for a summer season over a midlatitude domain. Ensemble simulations allow for the separation of the downscaled information in two parts: a unique, reproducible component associated with lateral-boundary and surface forcing, and an irreproducible component associated with internal variability. The partition in the reproducible and irreproducible components and their seasonal statistics is examined as a function of horizontal length scale, geographical position within the domain, height, and weather episodes during the...


Journal of Climate | 2016

Is Institutional Democracy a Good Proxy for Model Independence

Martin Leduc; René Laprise; Ramón de Elía; Leo Separovic

AbstractClimate models developed within a given research group or institution are prone to share structural similarities, which may induce resembling features in their simulations of the earth’s climate. This assertion, known as the “same-center hypothesis,” is investigated here using a subsample of CMIP3 climate projections constructed by retaining only the models originating from institutions that provided more than one model (or model version). The contributions of individual modeling centers to this ensemble are first presented in terms of climate change projections. A metric for climate change disagreement is then defined to analyze the impact of typical structural differences (such as resolution, parameterizations, or even entire atmosphere and ocean components) on regional climate projections. This metric is compared to a present climate performance metric (correlation of error patterns) within a cross-model comparison framework in terms of their abilities to identify the same-center models. Overal...


Climate Dynamics | 2013

Reanalysis-driven climate simulation over CORDEX North America domain using the Canadian Regional Climate Model, version 5: model performance evaluation

Andrey Martynov; René Laprise; Laxmi Sushama; Katja Winger; Leo Separovic; Bernard Dugas


Archive | 2012

Considerations of Domain Size and Large-Scale Driving for Nested Regional Climate Models: Impact on

René Laprise; D. Kornic; Maja Rapaić; Leo Separovic; Michele Leduc; Oumarou Nikiema; A. di Luca; Emilia Paula Diaconescu; Adriana Alexandru; Philippe Lucas-Picher


Archive | 2012

Simulation strategies for optimal detection of regional climate model response to parameter modifications

Leo Separovic


Archive | 2007

Les composantes reproductibles et non reproductibles dans un ensemble de simulations par un modèle régional du climat

Leo Separovic

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René Laprise

Université du Québec à Montréal

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Ramón de Elía

Université du Québec à Montréal

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Adelina Alexandru

Université du Québec à Montréal

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Andrey Martynov

Université du Québec à Montréal

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Emilia Paula Diaconescu

Université du Québec à Montréal

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Katja Winger

Université du Québec à Montréal

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Laxmi Sushama

Université du Québec à Montréal

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Maja Rapaić

Université du Québec à Montréal

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Martin Leduc

Université du Québec à Montréal

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Oumarou Nikiema

Université du Québec à Montréal

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