Sources of systematic errors in the climatology of a regional climate model over Europe

Noguer, M.; Jones, R. G.; Murphy, James M.

doi:10.1007/s003820050249

Cited by 126 publications

(134 citation statements)

References 35 publications

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“…LAMs also present specific issues like sensitivity to the size of the domain of simulation, to the boundary conditions, and to the frequency of update of boundary conditions (Bhaskaran et al, 1996;Seth and Giorgi, 1998;Noguer et al, 1998;Denis et al, 2002aDenis et al, , 2003. For longterm simulations, Lo et al(2008) showed that continuous runs can produce a very low score when the simulations are compared to observations and that simulations reinitialized periodically have better results than continuous runs.…”

Section: Introductionmentioning

confidence: 99%

Investigation of indiscriminate nudging and predictability in a nested quasi‐geostrophic model

Omrani

Drobinski

Dubos

2011

Quart J Royal Meteoro Soc

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In this work, we consider the effect of indiscriminate nudging time on an idealized high-resolution global model (GM) and limited-area model (LAM) simulations. The model used is a two-layer quasi-geostrophic model on the beta-plane.The effect of nudging is studied as a function of the predictability time, following a 'Big Brother' experimental approach: a high-resolution 'global' model is used to generate a 'reference run'. These fields are filtered afterwards to remove small scales and provide the coarse-resolution fields which are used to drive the high-resolution GM and the LAM. Comparison of the reference fields and the high-resolution runs over the same region allows the estimation of the ability of the high-resolution GM and LAM to regenerate the removed small scales. This fully nonlinear set-up mimics the configuration used for regional high-resolution atmospheric modelling.For the high-resolution GM, the results show that the behaviour of the nudged model depends primarily on the ratio of the nudging time to the predictability time. When the nudging time is very small compared to the predictability time, the model reproduces the large scale used to drive the model. On the other hand, if the nudging time is close to or larger than the predictability time, the nudging effect is weak and both large and small scales are poorly reproduced compared to the reference fields. The best result is obtained with a nudging time close to half the predictability time. This technique clearly improves the model capacity to reproduce the reference fields.For the high-resolution LAM, our results show that for a sufficiently small domain the simulation is largely controlled by the lateral boundary conditions (LBCs) and is quasi-insensitive to nudging. However, if the domain size exceeds a few Rossby radii, the high-resolution LAM becomes sensitive to initial conditions and the control exerted by LBCs becomes insufficient to prevent a divergence from the driving fields. Although the reconstructed fine scales are significantly damped, they are surprisingly well correlated to their reference values in a deterministic sense, not a statistical sense. Copyright c 2011 Royal Meteorological Society Key Words: downscaling; uncertainties; large/small-scale perturbations; potential vorticity

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Section: Introductionmentioning

confidence: 99%

Investigation of indiscriminate nudging and predictability in a nested quasi‐geostrophic model

Omrani

Drobinski

Dubos

2011

Quart J Royal Meteoro Soc

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“…This nesting technique can be one-way, so the circulations produced by the RCM do not feed back into the GCM, or two-way (Giorgi, 1990). Previous studies have investigated the sensitivity of the RCM predictions to initial and boundary conditions, frequency of update of boundary conditions, size and resolution of the domain of simulation, spin-up time, and physical parametrisations, in order to prevent these models misleading (Bhaskaran et al, 1996;Seth and Giorgi, 1998;Noguer et al, 1998;Laprise et al, 2000;Denis et al, 2002Denis et al, , 2003. For long-term RCM modelling, Qian et al (2003), Žagar et al (2006), and Lo et al (2008) showed that RCM simulations re-initialized periodically have better results than continuous runs.…”

Section: Introductionmentioning

confidence: 99%

The effect of indiscriminate nudging time on large and small scales in regional climate modelling: Application to the Mediterranean basin

Salameh

Drobinski

Dubos

2010

Quart J Royal Meteoro Soc

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A regional climate model (RCM) is driven by the ERA-40 reanalyses produced by the ECMWF general circulation model (GCM) to simulate the winter 1998 climate over the Mediterranean basin. In this article, we consider the effects on internal variability of temporal nudging. This technique consists of relaxing the RCM's prognostic variables towards the GCM values within a predetermined time-scale, with the aim of disallowing large and unrealistic departures between driving and driven fields. To interpret the significant effect of time nudging on the regional climate prediction, we develop a 'toy model' basically consisting of resolving a linear transport equation with a Newtonian relaxation term. This model predicts the existence of an optimal nudging time which depends on the time-scale over which numerical errors affect significantly the accuracy of the 'regional' solution at the large spatial scales, and the typical time-scale of the small-scale phenomena that are not resolved by the GCM.

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“…RCMs can also serve as experimental tools to understand regional climate processes and perform sensitivity studies (Gochis et al 2002;Seneviratne et al 2002;Wang et al 2004;Vannitsem and Chomé 2005;Anya et al 2006;Rowell and Jones 2006;Cuadra and da Rocha 2007;Yhang and Hong 2008). Although significant progress has been made in improving the physical formulation of RCMs, the most common remaining problem is the error inherited from the driving conditions, which are provided either by global analyses of observations or by GCM integrations (Noguer et al 1998;Giorgi and Bi 2000;Seth and Rojas 2003;Rojas and Seth 2003). Note that while RCMs have been used intensively to understand the SM-precipitation linkage in mid-latitudes and over various monsoon regions (Paegle et al 1996;Seth and Giorgi 1998;Hong and Pan 2000;Kanamitsu and Mo 2003;Anderson et al 2006;Kim and Hong 2007;Xu et al 2004;Nunes and Roads 2007), no attempts have been made for the WAM region.…”

Section: Introductionmentioning

confidence: 99%

Impact of soil moisture initialisation and lateral boundary conditions on regional climate model simulations of the West African Monsoon

Moufouma-Okia

Rowell

2009

Clim Dyn

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In this study, we use the Met Office Hadley Centre regional climate model HadRM3P to investigate the relative impact of initial soil moisture (SM) and lateral boundary conditions (LBC) on simulations of the West African Monsoon. Soil moisture data that are in balance with our particular model are generated using a 10-year (1997-2007) simulation of HadRM3P nested within the NCEP-R2 reanalyses. Three sets of experiments are then performed for six April-October seasons (2000 and 2003-2007) to assess the sensitivity to different sources of initial SM data and lateral boundary data. The results show that the only impact of the initial SM anomalies on precipitation is to generate small random intraseasonal, interannual and spatial variations. In comparison, the influence of the LBC dominates both in terms of magnitude and spatial coherency. Nevertheless, other sources of initial SM data or other models may respond differently, so it is recommended that the robustness of this conclusion is established using other model configurations.

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Sources of systematic errors in the climatology of a regional climate model over Europe

Cited by 126 publications

References 35 publications

Investigation of indiscriminate nudging and predictability in a nested quasi‐geostrophic model

Investigation of indiscriminate nudging and predictability in a nested quasi‐geostrophic model

The effect of indiscriminate nudging time on large and small scales in regional climate modelling: Application to the Mediterranean basin

Impact of soil moisture initialisation and lateral boundary conditions on regional climate model simulations of the West African Monsoon

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