scholarly journals What Determines the Position and Intensity of the South Atlantic Anticyclone in Austral Winter?—An AGCM Study

2008 ◽  
Vol 21 (2) ◽  
pp. 214-229 ◽  
Author(s):  
Ingo Richter ◽  
Carlos R. Mechoso ◽  
Andrew W. Robertson
Keyword(s):  
General Circulation ◽  
Large Scale ◽  
Circulation Model ◽  
South Atlantic ◽  
Sea Surface ◽  
Sea Surface Temperatures ◽  
Model Errors ◽  
Austral Winter ◽  
The South ◽  
Surface Temperatures

Abstract The South Atlantic anticyclone is a major feature of the austral winter climatology. An atmospheric general circulation model (AGCM) is used to study the dynamics of the South Atlantic anticyclone by means of control simulations and experiments to investigate sensitivity to prescribed orography, sea surface temperatures, and soil wetness. The South Atlantic anticyclone in the first control simulation is unrealistically zonally elongated and centered too far west—errors typical of coupled ocean–atmosphere GCMs. Results of the sensitivity experiments suggest that these deficiencies are associated with another family of systematic model errors: the overprediction of convection over the tropical land surfaces, particularly over eastern tropical Africa and India, and the concurrent large-scale westward shift in the divergence center at upper levels and the convergence center at lower levels. The results also confirm the important role of South American and African orography in localizing the South Atlantic anticyclone over the ocean. Other factors, however, like the regional zonal gradients of sea surface temperatures, are found to have only a minor impact on the anticyclone. To further substantiate these findings, the wintertime anticyclone is examined using a revised version of the atmospheric GCM. Improvements are found in both the anticyclone as well as the Asia–African summer monsoon circulations. The results demonstrate the existence of links between intensity and structure of the wintertime South Atlantic anticyclone and the major summer monsoons in the Northern Hemisphere.

Potential effects of climate change on marine growth and survival of Fraser River sockeye salmon

1995 ◽  
Vol 52 (12) ◽  
pp. 2651-2659 ◽  
Author(s):  
Scott G. Hinch ◽  
Michael C. Healey ◽  
Ron E. Diewert ◽  
Michael A. Henderson ◽  
Keith A. Thomson ◽  
...  
Keyword(s):  
General Circulation Model ◽  
General Circulation ◽  
Sockeye Salmon ◽  
Circulation Model ◽  
Zooplankton Biomass ◽  
Air Pressure ◽  
Sea Surface ◽  
Fraser River ◽  
Sea Surface Temperatures ◽  
Surface Temperatures

Simulation results from the Canadian Climate Centre's atmospheric general circulation model (CCC GCM) coupled to a simplified mixed-layer ocean model predict that doubled atmospheric CO2 concentrations would increase northeast Pacific Ocean sea surface temperatures and weaken existing north–south air pressure gradients. On the basis of predicted changes to air pressure and an empirical relationship between wind-driven upwelling and zooplankton biomass, we calculate that production of food for sockeye salmon (Oncorhynchus nerka) may decrease by 5–9%. We developed empirical relationships between sea surface temperature, zooplankton biomass, adult recruitment, and terminal ocean weight for the early Stuart stock of Fraser River sockeye salmon. Our analyses show that warmer sea surface temperatures, larger adult recruitment, and lower zooplankton biomass are correlated with smaller adult sockeye. Bioenergetics modeling suggests that higher metabolic costs in warmer water coupled with lower food availability could cause the observed reductions in size. Warmer sea surface temperatures during coastal migration by juveniles were correlated with lower recruitment 2 yr later. Warmer sea surface temperatures may be a surrogate for increased levels of predation or decreased food during the juvenile stage. We speculate that Fraser sockeye will be less abundant and smaller if the climate changes as suggested by the Canadian Climate Centre's general circulation model.

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.

scholarly journals Real World and Tropical Cyclone World. Part II: Sensitivity of Tropical Cyclone Formation to Uniform and Meridionally Varying Sea Surface Temperatures under Aquaplanet Conditions

2020 ◽  
Vol 33 (4) ◽  
pp. 1473-1486 ◽  
Author(s):  
K. J. E. Walsh ◽  
S. Sharmila ◽  
M. Thatcher ◽  
S. Wales ◽  
S. Utembe ◽  
...  
Keyword(s):  
Tropical Cyclone ◽  
Wind Shear ◽  
General Circulation ◽  
Vertical Wind Shear ◽  
Circulation Model ◽  
Static Stability ◽  
Sea Surface ◽  
Sea Surface Temperatures ◽  
Tropical Cyclone Formation ◽  
Surface Temperatures

AbstractThis study aims to investigate the response of simulated tropical cyclone formation to specific climate conditions, using an idealized aquaplanet framework of an ~40-km-horizontal-resolution atmospheric general circulation model. Two sets of idealized model experiments have been performed, one with a set of uniformly distributed constant global sea surface temperatures (SSTs) and another in which varying meridional SST gradients are imposed. The results show that the strongest relationship between climate and tropical cyclone formation is with vertical static stability: increased static stability is strongly associated with decreased tropical cyclone formation. Vertical wind shear and midtropospheric vertical velocity also appear to be related to tropical cyclone formation, although below a threshold value of wind shear there appears to be little relationship. The relationship of tropical cyclone formation with maximum potential intensity and mean sea surface temperature is weak and not monotonic. These simulations strongly suggest that vertical static stability should be part of any climate theory of tropical cyclone formation.

A Transfer Function for Estimating Paleoceanographic Conditions Based on Deep-Sea Surface Sediment Distribution of Radiolarian Assemblages in the South Atlantic

1979 ◽  
Vol 12 (3) ◽  
pp. 381-395 ◽  
Author(s):  
Joseph J. Morley
Keyword(s):  
Transfer Function ◽  
Surface Sediment ◽  
Deep Sea ◽  
South Atlantic ◽  
Sea Surface ◽  
Sea Surface Temperatures ◽  
The South ◽  
Sediment Distribution ◽  
Sediment Samples ◽  
Surface Temperatures

A quantitative analysis of radiolarian species in 57 deep-sea surface sediment samples from the South Atlantic Ocean produced four geographically distinct assemblages (tropical, polar, gyre margin, and subtropical). The distributions of these assemblages or factors coincide with present-day patterns of sea-surface temperatures or water masses.These four assemblages were used to construct a transfer function relating radiolarian distribution in the surface sediments to present-day winter and summer temperatures using standard regression techniques. As a test of the quality of this transfer function, temperatures were estimated on surface sediment samples from the eastern South Pacific. The temperatures produced by the transfer function compared favorably with the observed (present-day) winter and summer sea-surface temperatures at these sites.

scholarly journals A spatiotemporal reconstruction of sea-surface temperatures in the North Atlantic during Dansgaard–Oeschger events 5–8

2018 ◽  
Vol 14 (6) ◽  
pp. 901-922 ◽  
Author(s):  
Mari F. Jensen ◽  
Aleksi Nummelin ◽  
Søren B. Nielsen ◽  
Henrik Sadatzki ◽  
Evangeline Sessford ◽  
...  
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
North Atlantic ◽  
General Circulation ◽  
Sea Surface ◽  
Reconstruction Method ◽  
Sea Surface Temperatures ◽  
Proxy Data ◽  
Surface Temperatures ◽  
Temperature Reconstructions

Abstract. Here, we establish a spatiotemporal evolution of the sea-surface temperatures in the North Atlantic over Dansgaard–Oeschger (DO) events 5–8 (approximately 30–40 kyr) using the proxy surrogate reconstruction method. Proxy data suggest a large variability in North Atlantic sea-surface temperatures during the DO events of the last glacial period. However, proxy data availability is limited and cannot provide a full spatial picture of the oceanic changes. Therefore, we combine fully coupled, general circulation model simulations with planktic foraminifera based sea-surface temperature reconstructions to obtain a broader spatial picture of the ocean state during DO events 5–8. The resulting spatial sea-surface temperature patterns agree over a number of different general circulation models and simulations. We find that sea-surface temperature variability over the DO events is characterized by colder conditions in the subpolar North Atlantic during stadials than during interstadials, and the variability is linked to changes in the Atlantic Meridional Overturning circulation and in the sea-ice cover. Forced simulations are needed to capture the strength of the temperature variability and to reconstruct the variability in other climatic records not directly linked to the sea-surface temperature reconstructions. This is the first time the proxy surrogate reconstruction method has been applied to oceanic variability during MIS3. Our results remain robust, even when age uncertainties of proxy data, the number of available temperature reconstructions, and different climate models are considered. However, we also highlight shortcomings of the methodology that should be addressed in future implementations.

scholarly journals Southern Hemisphere anticyclonic circulation drives oceanic and climatic conditions in late Holocene southernmost Africa

2017 ◽  
Vol 13 (6) ◽  
pp. 649-665 ◽  
Author(s):  
Annette Hahn ◽  
Enno Schefuß ◽  
Sergio Andò ◽  
Hayley C. Cawthra ◽  
Peter Frenzel ◽  
...  
Keyword(s):  
South Africa ◽  
Climatic Conditions ◽  
Sea Surface ◽  
South Coast ◽  
Ice Age ◽  
Sea Surface Temperatures ◽  
The South ◽  
Anticyclonic Circulation ◽  
Surface Temperatures ◽  
Precipitation Regimes

Abstract. Due to the high sensitivity of southern Africa to climate change, a reliable understanding of its hydrological system is crucial. Recent studies of the regional climatic system have revealed a highly complex interplay of forcing factors on precipitation regimes. This includes the influence of the tropical easterlies, the strength of the southern hemispheric westerlies as well as sea surface temperatures along the coast of the subcontinent. However, very few marine records have been available in order to study the coupling of marine and atmospheric circulation systems. Here we present results from a marine sediment core, recovered in shallow waters off the Gouritz River mouth on the south coast of South Africa. Core GeoB18308-1 allows a closer view of the last  ∼  4 kyr. Climate sensitive organic proxies, like the distribution and isotopic composition of plant-wax lipids as well as indicators for sea surface temperatures and soil input, give information on oceanographic and hydrologic changes during the recorded time period. Moreover, the micropaleontology, mineralogical and elemental composition of the sediments reflect the variability of the terrigenous input to the core site. The combination of down-core sediment signatures and a catchment-wide provenance study indicate that the Little Ice Age ( ∼  300–650 cal yr BP) was characterized by climatic conditions favorable to torrential flood events. The Medieval Climate Anomaly ( ∼  950–650 cal yr BP) is expressed by lower sea surface temperatures in the Mossel Bay area and humid conditions in the Gouritz River catchment. These new results suggest that the coincidence of humid conditions and cooler sea surface temperatures along the south coast of South Africa resulted from a strengthened and more southerly anticyclonic circulation. Most probably, the transport of moisture from the Indian Ocean by strong subtropical easterlies was coupled with Agulhas Bank upwelling pulses, which were initiated by an increase in Agulhas Current strength.

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