A Proposed Modification to the Robert–Asselin Time Filter*

Williams, Paul D.

doi:10.1175/2009mwr2724.1

Cited by 116 publications

(99 citation statements)

References 19 publications

(9 reference statements)

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“…This phenomenon is referred to as time-splitting. The Robert-Asselin lter [2,42] is an oft-used time-ltering solution (for a list of examples in climate models see, e.g, Williams [50]) that dampens this computational mode and thus controls the time-splitting instability. The combination of the leapfrog scheme with the Robert-Asselin lter results in the Asselin-leapfrog scheme:…”

Section: A Appendixmentioning

confidence: 99%

Covariate-based stochastic parameterization of baroclinic ocean eddies

Verheul¹,

Viebahn²,

Crommelin³

2017

Mathematics of Climate and Weather Forecasting

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Abstract:In this study we investigate a covariate-based stochastic approach to parameterize unresolved turbulent processes within a standard model of the idealised, wind-driven ocean circulation. We focus on vertical instead of horizontal coarse-graining, such that we avoid the subtle di culties of horizontal coarsegraining. The corresponding eddy forcing is uniquely de ned and has a clear physical interpretation related to baroclinic instability. We propose to emulate the baroclinic eddy forcing by sampling from the conditional probability distribution functions of the eddy forcing obtained from the baroclinic reference model data. These conditional probability distribution functions are approximated here by sampling uniformly from discrete reference values. We analyze in detail the di erent performances of the stochastic parameterization dependent on whether the eddy forcing is conditioned on a suitable ow-dependent covariate or on a timelagged covariate or on both. The results demonstrate that our non-Gaussian, non-linear methodology is able to accurately reproduce the rst four statistical moments and spatial/temporal correlations of the stream function, energetics, and enstrophy of the reference baroclinic model.

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Section: A Appendixmentioning

confidence: 99%

Covariate-based stochastic parameterization of baroclinic ocean eddies

Verheul¹,

Viebahn²,

Crommelin³

2017

Mathematics of Climate and Weather Forecasting

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“…Em termos de dinâmica, BRAMS possui agora um aperfeiçoamento no filtro de Asselin (usado no esquema leapfrog de integração temporal) descrito por Williams (2009). Este aperfeiçoamento mantém a ordem de acurácia do esquema de integração que é reduzida para primeira ordem quando se aplica o filtro de Asselin em sua forma original.…”

Section: Modelo Regional Bramsunclassified

Calibração do modelo regional BRAMS para a previsão de eventos climáticos extremos

Freire

Freitas

Coelho

2015

Rev. bras. meteorol.

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RESUMOAs previsões climáticas sazonais têm contribuído efetivamente para o planejamento de atividades de diversos setores da sociedade, tais como, energia, agricultura e saúde. A necessidade de um maior detalhamento das previsões, através da diminuição da escala espacial da informação climática, tem concentrado nos últimos anos esforços científicos em várias regiões do globo. A aplicação da técnica de redução de escala através da modelagem dinâmica regional, conhecida como downscaling dinâmico, vem sendo utilizada com esse objetivo. Desta forma, o presente trabalho teve como objetivo calibrar e avaliar o modelo regional BRAMS, aninhado unidirecionalmente ao modelo global MCGA/CPTEC, em prever os eventos climáticos extremos de 1983 (El Niño) e 1989 (La Niña) sobre a América do Sul (AS), para o trimestre março-abril-maio (MAM). As previsões com o BRAMS foram produzidas na resolução espacial de 30 km, tendo como condições de contorno a temperatura da superfície do mar persistida e a umidade do solo climatológica. Após o processo de calibração, o modelo BRAMS conseguiu capturar o padrão de precipitação associada aos eventos climáticos extremos, como a redução (aumento) da precipitação principalmente no leste da região Norte e Nordeste do Brasil e o aumento (redução) de precipitação na região Sul para o ano e 1983 (1989). Palavras-chave: Downscaling; ENOS; previsão sazonal. ABSTRACT: CALIBRATION OF THE BRAMS REGIONAL MODEL FOR PREDICTING CLIMATE EXTREME EVENTSThe seasonal climate predictions have effectively contributed to the planning on various sectors of society, such as energy, agriculture and health activities. The need for more detailed forecasts by increasing spatial resolution climate information has concentrated research efforts recently in various regions of the globe. Downscaling technique by regional dynamic modeling, known as dynamic downscaling, has been used for this purpose. Thus, the present study aimed to evaluate and calibrate the regional BRAMS model, unidirectionally nested with AGCM/CPTEC global model, in predicting the extreme weather events of 1983 (El Niño) and 1989 (La Niña) over South America (SA) for March-April-May (MAM). The predictions were produced at spatial resolution of 30 km, having the persisted sea surface temperature and climatological soil moisture as boundary conditions. After the calibration process, the BRAMS was able to capture the rainfall pattern associated with extreme weather events, such as the decrease (increase) in precipitation pattern mainly on the eastern of North region and Northeast Brazil, and the increase (decrease) of rainfall in the Southern region for the year 1983 (1989).

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“…There are two important recent improvements in SEGMENT-Ice numerics. The RAW filter (Amezcua et al 2011;Williams 2009) is adopted instead of the more commonly used Asselin time filter. It improves both spin-up and conservation energetics of the physical processes (Paul Williams, personal communication, January 2011).…”

Section: Model Spin-up and Improved Numericsmentioning

confidence: 99%

“…The ice motion is now measured using Interferometric Synthetic-aperature Radar (InSAR) data from the Canadian Space Agency Radarsat-1 satellite (2000( -2009( , Jezek 2008, Japanese Space Agency phased array l-band synthetic aperture radar palsar (2006)(2007)(2008)(2009) satellite, and the European Space Agency Earth Remote Sensing satellites ERS-1/2 ( , 1996( , Rignot et al 2011a. This study involves two surface ice velocity datasets: Radarsat-1 SAR sensor via Modified Antarctic Mapping Mission (MAMM, Jezek 2008, http://bprc.osu.edu/rsl/radarsat/data/ ) and MEaSUREs.…”

Section: Input and Verification Datamentioning

confidence: 99%

Verification of model simulated mass balance, flow fields and tabular calving events of the Antarctic ice sheet against remotely sensed observations

2012

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The Antarctic ice sheet (AIS) has the greatest potential for global sea level rise. This study simulates AIS ice creeping, sliding, tabular calving, and estimates the total mass balances, using a recently developed, advanced ice dynamics model, known as SEGMENT-Ice. SEGMENTIce is written in a spherical Earth coordinate system. Because the AIS contains the South Pole, a projection transfer is performed to displace the pole outside of the simulation domain. The AIS also has complex ice-watergranular material-bedrock configurations, requiring sophisticated lateral and basal boundary conditions. Because of the prevalence of ice shelves, a 'girder yield' type calving scheme is activated. The simulations of present surface ice flow velocities compare favorably with InSAR measurements, for various ice-water-bedrock configurations. The estimated ice mass loss rate during [2003][2004][2005][2006][2007][2008][2009] agrees with GRACE measurements and provides more spatial details not represented by the latter. The model estimated calving frequencies of the peripheral ice shelves from 1996 (roughly when the 5-km digital elevation and thickness data for the shelves were collected) to 2009 compare well with archived scatterometer images. SEG-MENT-Ice's unique, non-local systematic calving scheme is found to be relevant for tabular calving. However, the exact timing of calving and of iceberg sizes cannot be simulated accurately at present. A projection of the future mass change of the AIS is made, with SEGMENT-Ice forced by atmospheric conditions from three different coupled general circulation models. The entire AIS is estimated to be losing mass steadily at a rate of *120 km 3 /a at present and this rate possibly may double by year 2100.

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A Proposed Modification to the Robert–Asselin Time Filter*

Cited by 116 publications

References 19 publications

Covariate-based stochastic parameterization of baroclinic ocean eddies

Covariate-based stochastic parameterization of baroclinic ocean eddies

Calibração do modelo regional BRAMS para a previsão de eventos climáticos extremos

Verification of model simulated mass balance, flow fields and tabular calving events of the Antarctic ice sheet against remotely sensed observations

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