Simulation of long-term trends in Hadley circulation during boreal winter using an ocean data assimilation scheme with the coupled general circulation model FGOALS-s2

2017 ◽  
Vol 63 (4) ◽  
pp. 452-460 ◽  
Author(s):  
Yong Sun ◽  
Tianjun Zhou ◽  
Bo Wu
Keyword(s):  
Data Assimilation ◽  
General Circulation ◽  
Circulation Model ◽  
Hadley Circulation ◽  
Boreal Winter ◽  
Coupled General Circulation Model ◽  
Ocean Data Assimilation ◽  
Long Term Trends ◽  
Assimilation Scheme

scholarly journals Influence of the Seasonal Cycle on the Termination of El Niño Events in a Coupled General Circulation Model

2006 ◽  
Vol 19 (9) ◽  
pp. 1850-1868 ◽  
Author(s):  
Matthieu Lengaigne ◽  
Jean-Philippe Boulanger ◽  
Christophe Menkes ◽  
Hilary Spencer
Keyword(s):  
El Niño ◽  
General Circulation ◽  
El Nino ◽  
Circulation Model ◽  
Coupled System ◽  
Equatorial Pacific ◽  
Boreal Winter ◽  
Coupled General Circulation Model ◽  
El Niño Events ◽  
El Nino Events

Abstract In this study, the mechanisms leading to the El Niño peak and demise are explored through a coupled general circulation model ensemble approach evaluated against observations. The results here suggest that the timing of the peak and demise for intense El Niño events is highly predictable as the evolution of the coupled system is strongly driven by a southward shift of the intense equatorial Pacific westerly anomalies during boreal winter. In fact, this systematic late-year shift drives an intense eastern Pacific thermocline shallowing, constraining a rapid El Niño demise in the following months. This wind shift results from a southward displacement in winter of the central Pacific warmest SSTs in response to the seasonal evolution of solar insolation. In contrast, the intensity of this seasonal feedback mechanism and its impact on the coupled system are significantly weaker in moderate El Niño events, resulting in a less pronounced thermocline shallowing. This shallowing transfers the coupled system into an unstable state in spring but is not sufficient to systematically constrain the equatorial Pacific evolution toward a rapid El Niño termination. However, for some moderate events, the occurrence of intense easterly wind anomalies in the eastern Pacific during that period initiate a rapid surge of cold SSTs leading to La Niña conditions. In other cases, weaker trade winds combined with a slightly deeper thermocline allow the coupled system to maintain a broad warm phase evolving through the entire spring and summer and a delayed El Niño demise, an evolution that is similar to the prolonged 1986/87 El Niño event. La Niña events also show a similar tendency to peak in boreal winter, with characteristics and mechanisms mainly symmetric to those described for moderate El Niño cases.

A Reanalysis of Ocean Climate Using Simple Ocean Data Assimilation (SODA)

2008 ◽  
Vol 136 (8) ◽  
pp. 2999-3017 ◽  
Author(s):  
James A. Carton ◽  
Benjamin S. Giese
Keyword(s):  
Data Assimilation ◽  
Interannual Variability ◽  
General Circulation ◽  
Heat Content ◽  
Circulation Model ◽  
Surface Boundary ◽  
Model Forecast ◽  
Simple Ocean Data Assimilation ◽  
Ocean Climate ◽  
Ocean Data Assimilation

Abstract This paper describes the Simple Ocean Data Assimilation (SODA) reanalysis of ocean climate variability. In the assimilation, a model forecast produced by an ocean general circulation model with an average resolution of 0.25° × 0.4° × 40 levels is continuously corrected by contemporaneous observations with corrections estimated every 10 days. The basic reanalysis, SODA 1.4.2, spans the 44-yr period from 1958 to 2001, which complements the span of the 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) atmospheric reanalysis (ERA-40). The observation set for this experiment includes the historical archive of hydrographic profiles supplemented by ship intake measurements, moored hydrographic observations, and remotely sensed SST. A parallel run, SODA 1.4.0, is forced with identical surface boundary conditions, but without data assimilation. The new reanalysis represents a significant improvement over a previously published version of the SODA algorithm. In particular, eddy kinetic energy and sea level variability are much larger than in previous versions and are more similar to estimates from independent observations. One issue addressed in this paper is the relative importance of the model forecast versus the observations for the analysis. The results show that at near-annual frequencies the forecast model has a strong influence, whereas at decadal frequencies the observations become increasingly dominant in the analysis. As a consequence, interannual variability in SODA 1.4.2 closely resembles interannual variability in SODA 1.4.0. However, decadal anomalies of the 0–700-m heat content from SODA 1.4.2 more closely resemble heat content anomalies based on observations.

Application of Coupled Bred Vectors to Seasonal-to-Interannual Forecasting and Ocean Data Assimilation

2009 ◽  
Vol 22 (11) ◽  
pp. 2850-2870 ◽  
Author(s):  
Shu-Chih Yang ◽  
Christian Keppenne ◽  
Michele Rienecker ◽  
Eugenia Kalnay
Keyword(s):  
Data Assimilation ◽  
General Circulation ◽  
Coupled Model ◽  
Circulation Model ◽  
Model Errors ◽  
Background Error ◽  
Salinity Field ◽  
Ocean Data Assimilation ◽  
Bred Vectors ◽  
The Impact

Abstract Coupled bred vectors (BVs) generated from the NASA Global Modeling and Assimilation Office (GMAO) coupled general circulation model are designed to capture the uncertainties related to slowly varying coupled instabilities. Two applications of the BVs are investigated in this study. First, the coupled BVs are used as initial perturbations for ensemble-forecasting purposes. Results show that the seasonal-to-interannual variability forecast skill can be improved when the oceanic and atmospheric perturbations are initialized with coupled BVs. The impact is particularly significant when the forecasts are initialized from the cold phase of tropical Pacific SST (e.g., August and November), because at these times the early coupled model errors, not accounted for in the BVs, are small. Second, the structure of the BVs is applied to construct hybrid background error covariances carrying flow-dependent information for the ocean data assimilation. Results show that the accuracy of the ocean analyses is improved when Gaussian background covariances are supplemented with a term obtained from the BVs. The improvement is especially noticeable for the salinity field.

Influence of the Extratropical Ocean Circulation on the Intertropical Convergence Zone in an Idealized Coupled General Circulation Model

2013 ◽  
Vol 26 (13) ◽  
pp. 4612-4629 ◽  
Author(s):  
Neven S. Fučkar ◽  
Shang-Ping Xie ◽  
Riccardo Farneti ◽  
Elizabeth A. Maroon ◽  
Dargan M. W. Frierson
Keyword(s):  
Deep Water ◽  
General Circulation ◽  
Circulation Model ◽  
Hadley Circulation ◽  
Water Source ◽  
Intertropical Convergence Zone ◽  
Convergence Zone ◽  
Water Production ◽  
Coupled General Circulation Model ◽  
Main Pycnocline

Abstract The authors present coupled model simulations in which the ocean's meridional overturning circulation (MOC) sets the zonal mean location of the intertropical convergence zone (ITCZ) in the hemisphere with deep-water production. They use a coarse-resolution single-basin sector coupled general circulation model (CGCM) with simplified atmospheric physics and two idealized land–sea distributions. In an equatorially symmetric closed-basin setting, unforced climate asymmetry develops because of the advective circulation–salinity feedback that amplifies the asymmetry of the deep-MOC cell and the upper-ocean meridional salinity transport. It confines the deep-water production and the dominant extratropical ocean heat release to a randomly selected hemisphere. The resultant ocean heat transport (OHT) toward the hemisphere with the deep-water source is partially compensated by the atmospheric heat transport (AHT) across the equator via an asymmetric Hadley circulation, setting the ITCZ in the hemisphere warmed by the ocean. When a circumpolar channel is open at subpolar latitudes, the circumpolar current disrupts the poleward transport of the upper-ocean saline water and suppresses deep-water formation poleward of the channel. The MOC adjusts by lowering the main pycnocline and shifting the deep-water production into the opposite hemisphere from the channel, and the ITCZ location follows the deep-water source again because of the Hadley circulation adjustment to cross-equatorial OHT. The climate response is sensitive to the sill depth of the channel but becomes saturated when the sill is deeper than the main pycnocline depth in subtropics. In simulations with a circumpolar channel, the ITCZ is in the Northern Hemisphere (NH) because of the Southern Hemisphere (SH) circumpolar flow that forces northward OHT.

scholarly journals A Multivariate Balanced Initial Ensemble Generation Approach for an Atmospheric General Circulation Model

Water ◽  
2021 ◽  
Vol 13 (2) ◽  
pp. 122
Author(s):  
Juan Du ◽  
Fei Zheng ◽  
He Zhang ◽  
Jiang Zhu
Keyword(s):  
Data Assimilation ◽  
General Circulation Model ◽  
General Circulation ◽  
Atmospheric General Circulation Model ◽  
Circulation Model ◽  
Atmospheric General Circulation ◽  
Ensemble Data ◽  
Initial Ensemble ◽  
Assimilation Scheme ◽  
Ensemble Generation

Based on the multivariate empirical orthogonal function (MEOF) method, a multivariate balanced initial ensemble generation method was applied to the ensemble data assimilation scheme. The initial ensembles were generated with a reasonable consideration of the physical relationships between different model variables. The spatial distribution derived from the MEOF analysis is combined with the 3-D random perturbation to generate a balanced initial perturbation field. The Local Ensemble Transform Kalman Filter (LETKF) data assimilation scheme was established for an atmospheric general circulation model. Ensemble data assimilation experiments using different initial ensemble generation methods, spatially random and MEOF-based balanced, are performed using realistic atmospheric observations. It is shown that the ensembles integrated from the balanced initial ensembles maintain a much more reasonable spread and a more reliable horizontal correlation compared with the historical model results than those from the randomly perturbed initial ensembles. The model predictions were also improved by adopting the MEOF-based balanced initial ensembles.

scholarly journals Assessment of Several Ocean Reanalyzes about North Equatorial Current at 160° E

2020 ◽  
Vol 8 (9) ◽  
pp. 648
Author(s):  
Jiahao Wang ◽  
Kefeng Mao ◽  
Xi Chen
Keyword(s):  
Data Assimilation ◽  
General Circulation ◽  
Single Point ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Ocean Model ◽  
North Equatorial Current ◽  
Satellite Measurement ◽  
Ocean Data Assimilation ◽  
Equatorial Current

Three ocean reanalyzes including Simple Ocean Data Assimilation (SODA), Hybrid Coordinate Ocean Model, and the Navy Coupled Ocean Data Assimilation (HYCOM+NCODA) analysis, and the Ocean General Circulation Model for the Earth Simulator (OFES) are assessed about their ability of depicting the structure of North Equatorial Current (NEC) at 160° E. We found that these products could reflect the structure of NEC relatively well at the whole section, but not at the single point through comparing their results with mooring and cruising measurement, and the OFES is the best choice to study mesoscale processes versus the other two reanalyzes through comparing their results with satellite measurement.

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