scholarly journals Detection and Attribution of Twentieth-Century Northern and Southern African Rainfall Change

2006 ◽  
Vol 19 (16) ◽  
pp. 3989-4008 ◽  
Author(s):  
Martin Hoerling ◽  
James Hurrell ◽  
Jon Eischeid ◽  
Adam Phillips
Keyword(s):  
Twentieth Century ◽  
Indian Ocean ◽  
Atlantic Ocean ◽  
North Atlantic ◽  
General Circulation ◽  
Time History ◽  
South Atlantic ◽  
Boreal Summer ◽  
The South ◽  
African Rainfall

Abstract The spatial patterns, time history, and seasonality of African rainfall trends since 1950 are found to be deducible from the atmosphere’s response to the known variations of global sea surface temperatures (SSTs). The robustness of the oceanic impact is confirmed through the diagnosis of 80 separate 50-yr climate simulations across a suite of atmospheric general circulation models. Drying over the Sahel during boreal summer is shown to be a response to warming of the South Atlantic relative to North Atlantic SST, with the ensuing anomalous interhemispheric SST contrast favoring a more southern position of the Atlantic intertropical convergence zone. Southern African drying during austral summer is shown to be a response to Indian Ocean warming, with enhanced atmospheric convection over those warm waters driving subsidence drying over Africa. The ensemble of greenhouse-gas-forced experiments, conducted as part of the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, fails to simulate the pattern or amplitude of the twentieth-century African drying, indicating that the drought conditions were likely of natural origin. For the period 2000–49, the ensemble mean of the forced experiments yields a wet signal over the Sahel and a dry signal over southern Africa. These rainfall changes are physically consistent with a projected warming of the North Atlantic Ocean compared with the South Atlantic Ocean, and a further warming of the Indian Ocean. However, considerable spread exists among the individual members of the multimodel ensemble.

scholarly journals An Objective Climatology of Tropical Plumes

2013 ◽  
Vol 26 (14) ◽  
pp. 5044-5060 ◽  
Author(s):  
Luise Fröhlich ◽  
Peter Knippertz ◽  
Andreas H. Fink ◽  
Esther Hohberger
Keyword(s):  
Geographical Distribution ◽  
North Atlantic ◽  
South Pacific ◽  
South Atlantic ◽  
Boreal Summer ◽  
Minimum Length ◽  
Width Ratio ◽  
The South ◽  
Important Indicator ◽  
Upper Level

Abstract The first global objective climatology of tropical plumes (TPs), obtained from a novel algorithm based on gridded 10.8-μm brightness temperatures Tb, is presented for 1983–2006. TPs are defined as continuous cloud bands (>2000 km) crossing 15°N or 15°S with Tb anomalies of less than −20 K and a lifetime of at least 3 h. A minimum length-to-width ratio of 3 filters out elongated features. Numbers of identified TPs are sensitive to the chosen thresholds but not their geographical distribution and seasonal cycle. TPs are an important indicator of tropical–extratropical interactions with impacts on radiation and moisture. TP occurrence during boreal winter is largely confined to oceanic regions with main maxima over the South Pacific and South Atlantic as well as the eastern North Atlantic and Pacific Oceans. The geographical distribution during boreal summer is similar, but with lower frequencies, except for monsoon-influenced regions. Interannual variations over the Indo-Pacific region are strongly related to El Niño. TPs often develop downstream of extratropical upper-level troughs propagating into low latitudes, particularly over the wintertime eastern North Pacific and North Atlantic, but also in regions where mean upper-level easterlies do not generally favor equatorward Rossby wave propagation. Synoptic-scale variations in the quasi-permanent cloud bands associated with the South Pacific and South Atlantic convergence zones frequently produce TP-like anomalies, which are climatologically associated with downstream upper-level troughs. Some regions also feature TPs associated with mesoscale tropical disturbances. The new TP algorithm will serve as a basis for more in-depth studies in the future.

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.

Diaphus hudsoni (Pisces: Myctophidae), a new lanternfish from the South Atlantic Ocean

1976 ◽  
Vol 54 (9) ◽  
pp. 1538-1541
Author(s):  
R. E. Zurbrigg ◽  
W. B. Scott
Keyword(s):  
Atlantic Ocean ◽  
North Atlantic ◽  
North Atlantic Ocean ◽  
South Atlantic ◽  
South Atlantic Ocean ◽  
The South ◽  
Gill Rakers ◽  
Royal Ontario Museum ◽  
The North ◽  
The North Atlantic

A new myctophid species, Diaphus hudsoni, was captured in the South Atlantic Ocean, and is described. It is similar to Diaphus subtilis Nafpaktitis, which occurs in the North Atlantic Ocean, but is definitely distinct with its slender, more numerous gill rakers (total 23–25), and non-continuous AOp–Prc series. The AO series numbers 5 + 5–6. The holotype is deposited in the Royal Ontario Museum, ROM 27569.

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 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.

Interdecadal Changes of 30-Yr SST Normals during 1871–2000

2003 ◽  
Vol 16 (10) ◽  
pp. 1601-1612 ◽  
Author(s):  
Yan Xue ◽  
Thomas M. Smith ◽  
Richard W. Reynolds
Keyword(s):  
Indian Ocean ◽  
North Atlantic ◽  
North Pacific ◽  
Tropical Indian Ocean ◽  
South Atlantic ◽  
Equatorial Pacific ◽  
The South ◽  
The North ◽  
Eastern Equatorial Pacific ◽  
Interdecadal Changes

Abstract SST predictions are usually issued in terms of anomalies and standardized anomalies relative to a 30-yr normal: climatological mean (CM) and standard deviation (SD). The World Meteorological Organization (WMO) suggests updating the 30-yr normal every 10 yr. In complying with the WMO's suggestion, a new 30-yr normal for the 1971–2000 base period is constructed. To put the new 30-yr normal in historical perspective, all the 30-yr normals since 1871 are investigated, starting from the beginning of each decade (1871–1900, 1881–1910, … , 1971–2000). Using the extended reconstructed sea surface temperature (ERSST) on a 2° grid for 1854–2000 and the Hadley Centre Sea Ice and SST dataset (HadISST) on a 1° grid for 1870–1999, eleven 30-yr normals are calculated, and the interdecadal changes of seasonal CM, seasonal SD, and seasonal persistence (P) are discussed. The interdecadal changes of seasonal CM are prominent (0.3°–0.6°) in the tropical Indian Ocean, the midlatitude North Pacific, the midlatitude North Atlantic, most of the South Atlantic, and the sub-Antarctic front. Four SST indices are used to represent the key regions of the interdecadal changes: the Indian Ocean (“INDIAN”; 10°S–25°N, 45°–100°E), the Pacific decadal oscillation (PDO; 35°–45°N, 160°E–160°W), the North Atlantic Oscillation (NAO; 40°–60°N, 20°–60°W), and the South Atlantic (SATL; 22°S–2°N, 35°W–10°E). Both INDIAN and SATL show a warming trend that is consistent between ERSST and HadISST. Both PDO and NAO show a multidecadal oscillation that is consistent between ERSST and HadISST except that HadISST is biased toward warm in summer and cold in winter relative to ERSST. The interdecadal changes in Niño-3 (5°S–5°N, 90°–150°W) are small (0.2°) and are inconsistent between ERSST and HadISST. The seasonal SD is prominent in the eastern equatorial Pacific, the North Pacific, and North Atlantic. The seasonal SD in Niño-3 varies interdecadally: intermediate during 1885–1910, small during 1910–65, and large during 1965–2000. These interdecadal changes of ENSO variance are further verified by the Darwin sea level pressure. The seasonality of ENSO variance (smallest in spring and largest in winter) also varies interdecadally: moderate during 1885–1910, weak during 1910–65, and strong during 1965–2000. The interdecadal changes of the seasonal SD of other indices are weak and cannot be determined well by the datasets. The seasonal P, measured by the autocorrelation of seasonal anomalies at a two-season lag, is largest in the eastern equatorial Pacific, the tropical Indian, and the tropical North and South Atlantic Oceans. It is also seasonally dependent. The “spring barrier” of P in Niño-3 (largest in summer and smallest in winter) varies interdecadally: relatively weak during 1885–1910, moderate during 1910–55, strong during 1955–75, and moderate during 1975–2000. The interdecadal changes of SD and P not only have important implications for SST forecasts but also have significant scientific values to be explored.

A new record of Sphaeroma annandalei Stebbing, 1911 (Crustacea: Isopoda: Sphaeromatidae) from the Persian Gulf, and description of a new related species (Sphaeroma silvai nov. sp.) from the South Atlantic Ocean

Zootaxa ◽  
2010 ◽  
Vol 2508 (1) ◽  
pp. 30 ◽  
Author(s):  
VALIALLAH KHALAJI-PIRBALOUTY ◽  
JOHANN-WOLFGANG WÄGELE
Keyword(s):  
Indian Ocean ◽  
Atlantic Ocean ◽  
Persian Gulf ◽  
South Atlantic ◽  
South Atlantic Ocean ◽  
Similar Species ◽  
The South ◽  
Northern Areas ◽  
The Indian Ocean ◽  
The Persian Gulf

Two similar species of Sphaeroma (Sphaeromatidae: Isopoda) are studied and described from two different Oceans. Sphaeroma annandalei Stebbing, 1911 is redescribed from different localities of the Indian Ocean, and Sphaeroma silvai sp. nov. is described from the South Atlantic Ocean. Sphaeroma silvai sp. nov. is easily distinguished from S. annandalei by its pereopod 5, where the basis carries a well extended inferior lobe; the shape of the pleotelson and the tuberculation of pereonites and pleon. Both species are distinguished from other species of the genus by transverse ridges on their pereonites. The known distribution of S. annandalei is limited to the northern areas of the Indian Ocean, from the Persian Gulf to Malaysia.

Origins of the IOD-like Biases in CMIP Multimodel Ensembles: The Atmospheric Component and Ocean–Atmosphere Coupling

2020 ◽  
Vol 33 (24) ◽  
pp. 10437-10453
Author(s):  
Shang-Min Long ◽  
Gen Li ◽  
Kaiming Hu ◽  
Jun Ying
Keyword(s):  
Indian Ocean ◽  
General Circulation ◽  
Boreal Summer ◽  
Model Intercomparison ◽  
South Asian Summer Monsoon ◽  
The South ◽  
Easterly Wind ◽  
South Indian ◽  
Ocean Atmosphere ◽  
Intercomparison Project

AbstractPrevious studies reveal that the last generation of coupled general circulation models (CGCMs) commonly suffer from the so-called Indian Ocean dipole (IOD)-like biases, lowering the models’ ability in climate prediction and projection. The present study shows that such IOD-like biases are reduced insignificantly or even worsen in CGCMs from phase 5 to phase 6 of the Coupled Model Intercomparison Project (CMIP). The origins of the IOD-like biases in CGCMs are further investigated by comparing model outputs from CMIP and the Atmospheric Model Intercomparison Project (AMIP). The CGCMs’ errors are divided into the biases from the AMIP simulation (AMIP biases) and ocean–atmosphere coupling (coupling biases). For the multimodel ensemble mean, the AMIP (coupling) biases account for about two-thirds (one-third) of the IOD-like CMIP biases. In AMIP simulations, the South Asian summer monsoon (SASM) is overly strong; therefore, it could advect overly large easterly momentum from the south Indian Ocean (IO) to the equator. The resultant equatorial easterly wind bias would initiate the convection–circulation feedback and develop large IOD-like AMIP biases. In contrast, the coupling biases weaken the SASM and hence generate warm SST error over the western IO during boreal summer. Such SST error persists to boreal autumn and triggers the Bjerknes feedback, developing the IOD-like coupling biases. Furthermore, the intermodel spread in the IOD-like CMIP biases is largely explained by the intermodel differences in the coupling biases rather than the AMIP biases. The results imply that substantial efforts should be respectively made on reducing the atmospheric models’ intrinsic monsoon biases as well as advancing the simulations of ocean–atmosphere coupling processes.

South Atlantic circulation in a world ocean model

1994 ◽  
Vol 12 (9) ◽  
pp. 812-825 ◽  
Author(s):  
Matthew H. England ◽  
Véronique C. Garçon
Keyword(s):  
Indian Ocean ◽  
Atlantic Ocean ◽  
North Atlantic ◽  
Drake Passage ◽  
South Atlantic ◽  
South Atlantic Ocean ◽  
Global Ocean ◽  
Intermediate Water ◽  
Agulhas Current ◽  
Benguela Current

Abstract. The circulation in the South Atlantic Ocean has been simulated within a global ocean general circulation model. Preliminary analysis of the modelled ocean circulation in the region indicates a rather close agreement of the simulated upper ocean flows with conventional notions of the large-scale geostrophic currents in the region. The modelled South Atlantic Ocean witnesses the return flow and export of North Atlantic Deep Water (NADW) at its northern boundary, the inflow of a rather barotropic Antarctic Circumpolar Current (ACC) through the Drake Passage, and the inflow of warm saline Agulhas water around the Cape of Good Hope. The Agulhas leakage amounts to 8.7 Sv, within recent estimates of the mass transport shed westward at the Agulhas retroflection. Topographic steering of the ACC dominates the structure of flow in the circumpolar ocean. The Benguela Current is seen to be fed by a mixture of saline Indian Ocean water (originating from the Agulhas Current) and fresher Subantarctic surface water (originating in the ACC). The Benguela Current is seen to modify its flow and fate with depth; near the surface it flows north-westwards bifurcating most of its transport northward into the North Atlantic Ocean (for ultimate replacement of North Atlantic surface waters lost to the NADW conveyor). Deeper in the water column, more of the Benguela Current is destined to return with the Brazil Current, though northward flows are still generated where the Benguela Current extension encounters the coast of South America. At intermediate levels, these northward currents trace the flow of Antarctic Intermediate Water (AAIW) equatorward, though even more AAIW is seen to recirculate poleward in the subtropical gyre. In spite of the model's rather coarse resolution, some subtle features of the Brazil-Malvinas Confluence are simulated rather well, including the latitude at which the two currents meet. Conceptual diagrams of the recirculation and interocean exchange of thermocline, intermediate and deep waters are constructed from an analysis of flows bound between isothermal and isobaric surfaces. This analysis shows how the return path of NADW is partitioned between a cold water route through the Drake Passage (6.5 Sv), a warm water route involving the Agulhas Current sheeding thermocline water westward (2.5 Sv), and a recirculation of intermediate water originating in the Indian Ocean (1.6 Sv).

Toxigenicity and biogeography of the diatom Pseudo-nitzschia across distinct environmental regimes in the South Atlantic Ocean

2015 ◽  
Vol 526 ◽  
pp. 67-87 ◽  
Author(s):  
ML Guannel ◽  
D Haring ◽  
MJ Twiner ◽  
Z Wang ◽  
AE Noble ◽  
...  
Keyword(s):  
Atlantic Ocean ◽  
South Atlantic ◽  
South Atlantic Ocean ◽  
The South ◽  
Environmental Regimes
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