Analysis of a general circulation model: 2. Distribution of kinetic energy in the South Atlantic and Kuroshio/Oyashio systems

1992 ◽  
Vol 97 (C12) ◽  
pp. 20139 ◽  
Author(s):  
Zulema Garraffo ◽  
Silvia L. Garzoli ◽  
William Haxby ◽  
Donald Olson
Keyword(s):  
Kinetic Energy ◽  
General Circulation Model ◽  
General Circulation ◽  
Circulation Model ◽  
South Atlantic ◽  
The South

scholarly journals Coupled Ocean–Atmosphere Variations over the South Atlantic Ocean

2012 ◽  
Vol 25 (18) ◽  
pp. 6349-6358 ◽  
Author(s):  
Paulo Nobre ◽  
Roberto A. De Almeida ◽  
Marta Malagutti ◽  
Emanuel Giarolla
Keyword(s):  
Atlantic Ocean ◽  
Atmospheric Circulation ◽  
General Circulation Model ◽  
General Circulation ◽  
Circulation Model ◽  
South Atlantic ◽  
Convergence Zone ◽  
Tropical Atlantic ◽  
The South ◽  
Ocean Atmosphere

Abstract The impact of ocean–atmosphere interactions on summer rainfall over the South Atlantic Ocean is explored through the use of coupled ocean–atmosphere models. The Brazilian Center for Weather Forecast and Climate Studies (CPTEC) coupled ocean–atmosphere general circulation model (CGCM) and its atmospheric general circulation model (AGCM) are used to gauge the role of coupled modes of variability of the climate system over the South Atlantic at seasonal time scales. Twenty-six years of summer [December–February (DJF)] simulations were done with the CGCM in ensemble mode and the AGCM forced with both observed sea surface temperature (SST) and SST generated by the CGCM forecasts to investigate the dynamics/thermodynamics of the two major convergence zones in the tropical Atlantic: the intertropical convergence zone (ITCZ) and the South Atlantic convergence zone (SACZ). The results present both numerical model and observational evidence supporting the hypothesis that the ITCZ is a thermally direct, SST-driven atmospheric circulation, while the SACZ is a thermally indirect atmospheric circulation controlling SST variability underneath—a consequence of ocean–atmosphere interactions not captured by the atmospheric model forced by prescribed ocean temperatures. Six CGCM model results of the Ensemble-based Predictions of Climate Changes and their Impacts (ENSEMBLES) project, NCEP–NCAR reanalysis data, and oceanic and atmospheric data from buoys of the Prediction and Research Moored Array in the Tropical Atlantic (PIRATA) Project over the tropical Atlantic are used to validate CPTEC’s coupled and uncoupled model simulations.

scholarly journals Revisiting remote drivers of the 2014 drought in South-Eastern Brazil

2020 ◽  
Vol 55 (11-12) ◽  
pp. 3197-3211
Author(s):  
Kathrin Finke ◽  
Bernat Jiménez-Esteve ◽  
Andréa S. Taschetto ◽  
Caroline C. Ummenhofer ◽  
Karl Bumke ◽  
...  
Keyword(s):  
Indian Ocean ◽  
General Circulation ◽  
Circulation Model ◽  
Tropical Pacific ◽  
South Atlantic ◽  
The South ◽  
South Eastern ◽  
Eastern Brazil ◽  
The Indian Ocean ◽  
Sst Anomalies

Abstract South-Eastern Brazil experienced a devastating drought associated with significant agricultural losses in austral summer 2014. The drought was linked to the development of a quasi-stationary anticyclone in the South Atlantic in early 2014 that affected local precipitation patterns over South-East Brazil. Previous studies have suggested that the unusual blocking was triggered by tropical Pacific sea surface temperature (SST) anomalies and, more recently, by convection over the Indian Ocean related to the Madden–Julian Oscillation. Further investigation of the proposed teleconnections appears crucial for anticipating future economic impacts. In this study, we use numerical experiments with an idealized atmospheric general circulation model forced with the observed 2013/2014 SST anomalies in different ocean basins to understand the dominant mechanism that initiated the 2014 South Atlantic anticyclonic anomaly. We show that a forcing with global 2013/2014 SST anomalies enhances the chance for the occurrence of positive geopotential height anomalies in the South Atlantic. However, further sensitivity experiments with SST forcings in separate ocean basins suggest that neither the Indian Ocean nor tropical Pacific SST anomalies alone have contributed significantly to the anomalous atmospheric circulation that led to the 2014 South-East Brazil drought. The model study rather points to an important role of remote forcing from the South Pacific, local South Atlantic SSTs, and internal atmospheric variability in driving the persistent blocking over the South Atlantic.

scholarly journals Lagrangian Drifter Dispersion in the Southwestern Atlantic Ocean

2011 ◽  
Vol 41 (9) ◽  
pp. 1659-1672 ◽  
Author(s):  
Stefano Berti ◽  
Francisco Alves Dos Santos ◽  
Guglielmo Lacorata ◽  
Angelo Vulpiani
Keyword(s):  
Atlantic Ocean ◽  
General Circulation ◽  
Time Lag ◽  
Circulation Model ◽  
South Atlantic ◽  
Relative Dispersion ◽  
Mean Square ◽  
The South ◽  
Southwestern Atlantic Ocean ◽  
Wide Range

Abstract In the framework of Monitoring by Ocean Drifters (MONDO) project, a set of Lagrangian drifters were released in proximity of the Brazil Current, the western branch of the subtropical gyre in the South Atlantic Ocean. The experimental strategy of deploying part of the buoys in clusters offers the opportunity to examine relative dispersion on a wide range of scales. Adopting a dynamical systems approach, the authors focus their attention on scale-dependent indicators, like the finite-scale Lyapunov exponent (FSLE) and the finite-scale (mean square) relative velocity (FSRV) between two drifters as a function of their separation and compare them with classic time-dependent statistical quantities like the mean-square relative displacement between two drifters and the effective diffusivity as functions of the time lag from the release. The authors find that, dependently on the given observable, the quasigeostrophic turbulence scenario is overall compatible with their data analysis, with discrepancies from the expected behavior of 2D turbulent trajectories likely to be ascribed to the nonstationary and nonhomogeneous characteristics of the flow, as well as to possible ageostrophic effects. Submesoscale features of ~O(1) km are considered to play a role, to some extent, in determining the properties of relative dispersion as well as the shape of the energy spectrum. The authors also present numerical simulations of an ocean general circulation model (OGCM) of the South Atlantic and discuss the comparison between experimental and model data about mesoscale dispersion.

scholarly journals Subtropical Dipole Modes Simulated in a Coupled General Circulation Model

2012 ◽  
Vol 25 (12) ◽  
pp. 4029-4047 ◽  
Author(s):  
Yushi Morioka ◽  
Tomoki Tozuka ◽  
Sebastien Masson ◽  
Pascal Terray ◽  
Jing-Jia Luo ◽  
...  
Keyword(s):  
General Circulation Model ◽  
Latent Heat ◽  
Mixed Layer ◽  
General Circulation ◽  
Circulation Model ◽  
South Atlantic ◽  
Shortwave Radiation ◽  
Coupled General Circulation Model ◽  
Austral Spring ◽  
Negative Pole

Abstract The growth and decay mechanisms of subtropical dipole modes in the southern Indian and South Atlantic Oceans and their impacts on southern African rainfall are investigated using results from a coupled general circulation model originally developed for predicting tropical climate variations. The second (most) dominant mode of interannual sea surface temperature (SST) variations in the southern Indian (South Atlantic) Ocean represents a northeast–southwest oriented dipole, now called subtropical dipole mode. The positive (negative) SST interannual anomaly pole starts to grow in austral spring and reaches its peak in February. In austral late spring, the suppressed (enhanced) latent heat flux loss associated with the variations in the subtropical high causes a thinner (thicker) than normal mixed layer thickness that, in turn, enhances (reduces) the warming of the mixed layer by the climatological shortwave radiation. The positive (negative) pole gradually decays in austral fall because the mixed layer cooling by the entrainment is enhanced (reduced), mostly owing to the larger (smaller) temperature difference between the mixed layer and the entrained water. The increased (decreased) latent heat loss due to the warmer (colder) SST also contributes to the decay of the positive (negative) pole. Although further verification using longer observational data is required, the present coupled model suggests that the South Atlantic subtropical dipole may play a more important role in rainfall variations over the southern African region than the Indian Ocean subtropical dipole.

scholarly journals Relationships between South Atlantic SST Variability and Atmospheric Circulation over the South African Region during Austral Winter

2005 ◽  
Vol 18 (16) ◽  
pp. 3339-3355 ◽  
Author(s):  
C. J. C. Reason ◽  
D. Jagadheesha
Keyword(s):  
Interannual Variability ◽  
General Circulation ◽  
Large Scale ◽  
Rainfall Variability ◽  
Circulation Model ◽  
South Atlantic ◽  
The South ◽  
Winter Rainfall ◽  
Southwest Atlantic ◽  
Sst Anomalies

Abstract The Southwestern Cape (SWC) region of South Africa is characterized by winter rainfall brought mainly via cold fronts and by substantial interannual variability. Previous work has found evidence that the interannual variability in SWC winter rainfall may be related to sea surface temperature (SST) in the South Atlantic Ocean and to large-scale ocean–atmosphere interaction in this region. During wet winters, SST tends to be anomalously warm (cool) in the southwest Atlantic and southeast Atlantic (central South Atlantic). Atmospheric general circulation model experiments with various idealized SST anomalies in the South Atlantic are used to explore mechanisms potentially associated with the rainfall variability. The model results suggest that the atmosphere is sensitive to subtropical–midlatitude SST anomalies in the South Atlantic during winter. Locally, there are changes to the jet position and strength, low-level relative vorticity, and convergence of moisture and latent heat flux that lead to changes in rainfall over the SWC. The model response to the SST forcing also shows large-scale anomalies in the midlatitude Southern Hemisphere circulation, namely, an Antarctic Oscillation–type mode and wavenumber-3 changes, similar to those observed during anomalous winters in the region.

Reproducibility of South American Precipitation due to Subtropical South Atlantic SSTs

2008 ◽  
Vol 21 (12) ◽  
pp. 2835-2851 ◽  
Author(s):  
Andréa S. Taschetto ◽  
Ilana Wainer
Keyword(s):  
General Circulation ◽  
Climate Model ◽  
Function Analysis ◽  
Regional Climate ◽  
Circulation Model ◽  
Internal Variability ◽  
South Atlantic ◽  
The South ◽  
Potential Predictability ◽  
The Impact

Abstract This work investigates the reproducibility of precipitation simulated with an atmospheric general circulation model (AGCM) forced by subtropical South Atlantic sea surface temperature (SST) anomalies. This represents an important test of the model prior to investigating the impact of SSTs on regional climate. A five-member ensemble run was performed using the National Center for Atmospheric Research (NCAR) Community Climate Model, version 3 (CCM3). The CCM3 was forced by observed monthly SST over the South Atlantic from 20° to 60°S. The SST dataset used is from the Hadley Centre covering the period of September 1949–October 2001; this covers more than 50 yr of simulation. A statistical technique is used to determine the reproducibility in the CCM3 runs and to assess potential predictability in precipitation. Empirical orthogonal function analysis is used to reconstruct the ensemble using the most reproducible forced modes in order to separate the atmospheric response to local SST forcing from its internal variability. Results for reproducibility show a seasonal dependence, with higher values during austral autumn and spring. The spatial distribution of reproducibility shows that the tropical atmosphere is dominated by the underlying SSTs while variations in the subtropical–extratropical regions are primarily driven by internal variability. As such, changes in the South Atlantic convergence zone (SACZ) region are mainly dominated by internal atmospheric variability while the ITCZ has greater external dependence, making it more predictable. The reproducibility distribution reveals increased values after the reconstruction of the ensemble.

scholarly journals Geostrophic Turbulence in the Frequency–Wavenumber Domain: Eddy-Driven Low-Frequency Variability*

2014 ◽  
Vol 44 (8) ◽  
pp. 2050-2069 ◽  
Author(s):  
Brian K. Arbic ◽  
Malte Müller ◽  
James G. Richman ◽  
Jay F. Shriver ◽  
Andrew J. Morten ◽  
...  
Keyword(s):  
High Resolution ◽  
Kinetic Energy ◽  
General Circulation Model ◽  
General Circulation ◽  
Low Frequency ◽  
Circulation Model ◽  
Satellite Altimeter ◽  
Low Frequencies ◽  
Low Frequency Variability ◽  
Geostrophic Turbulence

Abstract Motivated by the potential of oceanic mesoscale eddies to drive intrinsic low-frequency variability, this paper examines geostrophic turbulence in the frequency–wavenumber domain. Frequency–wavenumber spectra, spectral fluxes, and spectral transfers are computed from an idealized two-layer quasigeostrophic (QG) turbulence model, a realistic high-resolution global ocean general circulation model, and gridded satellite altimeter products. In the idealized QG model, energy in low wavenumbers, arising from nonlinear interactions via the well-known inverse cascade, is associated with energy in low frequencies and vice versa, although not in a simple way. The range of frequencies that are highly energized and engaged in nonlinear transfer is much greater than the range of highly energized and engaged wavenumbers. Low-frequency, low-wavenumber energy is maintained primarily by nonlinearities in the QG model, with forcing and friction playing important but secondary roles. In the high-resolution ocean model, nonlinearities also generally drive kinetic energy to low frequencies as well as to low wavenumbers. Implications for the maintenance of low-frequency oceanic variability are discussed. The cascade of surface kinetic energy to low frequencies that predominates in idealized and realistic models is seen in some regions of the gridded altimeter product, but not in others. Exercises conducted with the general circulation model suggest that the spatial and temporal filtering inherent in the construction of gridded satellite altimeter maps may contribute to the discrepancies between the direction of the frequency cascade in models versus gridded altimeter maps seen in some regions. Of course, another potential reason for the discrepancy is missing physics in the models utilized here.

scholarly journals The distribution of kinetic energy in the Southern Ocean: a comparison between observations and an eddy resolving general circulation model

1992 ◽  
Vol 338 (1285) ◽  
pp. 251-257 ◽  
Keyword(s):  
Kinetic Energy ◽  
Southern Ocean ◽  
General Circulation Model ◽  
General Circulation ◽  
Circulation Model ◽  
Transient Eddy ◽  
Buoyancy Forcing ◽  
Model Studies ◽  
Eddy Field ◽  
Good Agreement

It is widely believed from model studies that the transient eddy field plays an important role in the dynamics of the Southern Ocean. Accordingly, the distribution and partition of kinetic energy from an eddy resolving general circulation model of the Southern Ocean is compared with existing non-altimetric observations. Good agreement in distribution is found with some of the more recent observations. The amplitudes of the model energies, while for the most part well correlated with observations, are significantly lower than those observed (although observations differ greatly in their estimates). This reduction of energy is in agreement with other recent eddy resolving models, and is partly caused by the lack of correctly varying wind and buoyancy forcing, together with inadequate representation of instability processes. Nevertheless, the correlations suggest that the model results may be used as a proxy for reality in many circumstances.

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