scholarly journals Intraseasonal variability of wind waves in the western South Atlantic: the role of cyclones and the Pacific South-American pattern

2021 ◽  
Author(s):  
Dalton Kei Sasaki ◽  
Carolina Barnez Gramcianinov ◽  
Belmiro Castro ◽  
Marcelo Dottori
Keyword(s):  
Time Scales ◽  
Spatial Patterns ◽  
Extreme Values ◽  
Wind Waves ◽  
Storm Track ◽  
South Atlantic ◽  
Extratropical Cyclones ◽  
South American ◽  
The Pacific ◽  
Cyclone Genesis

Abstract. Extratropical cyclones are known to generate extreme significant wave height (swh) values in the western South Atlantic (wSA), which are highly influenced by intraseasonal scales. This work aims to investigate the importance of intraseasonal time scales (30–180 days) in the regional wave climate and its atmospheric forcing. The variability is explained by analyzing the storm track modulation due to westerlies winds. These winds present time-scales and spatial patterns compatible with the intraseasonal component of the Pacific South–American (PSA) patterns. The analysis are made using ECMWF’s ERA5 from 1979 to 2019 and a database of extratropical cyclones based on the same reanalysis. Empirical orthogonal function (EOF) analysis of the 10 m zonal wind and swh are used to assess the westerlies and waves regime in the wSA. The EOF1 of u10 presented a core centred at 45° W and 40° S, while the EOF2 is represented by two cores organized into a see-saw pattern with a center between 30° S–40° S and another to the south of 40° S. Composites of cyclone genesis and track densities, and swh fields were calculated based on the phases of both EOFs. In short, EOF phases presenting cores with a positive (negative) u10 anomaly provides a favorable (unfavorable) environment for cyclone genesis and track densities and, therefore, positive (negative) swh anomalies. The modulation of the cyclones track are significant for extreme values of the swh. The spatial patterns of the EOFs of u10 are physically and statistically consistent with 200 hPa and 850 hPa geopotential height signals from the Pacific, indicating the importance of the remote influence of the PSA patterns over the wSA.

scholarly journals Intraseasonal variability of ocean surface wind waves in the western South Atlantic: the role of cyclones and the Pacific South American pattern

2021 ◽  
Vol 2 (4) ◽  
pp. 1149-1166
Author(s):  
Dalton K. Sasaki ◽  
Carolina B. Gramcianinov ◽  
Belmiro Castro ◽  
Marcelo Dottori
Keyword(s):  
Spatial Patterns ◽  
Zonal Wind ◽  
Extreme Values ◽  
Surface Wind ◽  
Ocean Surface ◽  
South Atlantic ◽  
Extratropical Cyclones ◽  
South American ◽  
The Pacific ◽  
Cyclone Genesis

Abstract. Extratropical cyclones are known to generate extreme significant wave height (swh) values at the ocean surface in the western South Atlantic (wSA), which are highly influenced by intraseasonal scales. This work aims to investigate the importance of intraseasonal timescales (30–180 d) in the regional climatology of waves and its atmospheric forcing. The variability is explained by analyzing the storm track modulation due to westerly winds. These winds present timescales and spatial patterns compatible with the intraseasonal component of the Pacific South American (PSA) patterns. The analyses are made using ECMWF’s ERA5 from 1979 to 2019 and a database of extratropical cyclones based on the same reanalysis. Empirical orthogonal function (EOF) analyses of the 10 m zonal wind and swh are used to assess the regime of westerlies and waves in the wSA. The EOF1 of the 10 m zonal wind (u10) presented a core centered at 45∘ W and 40∘ S, while the EOF2 is represented by two cores organized into a seesaw pattern with a center between 30–40∘ S and another to the south of 40∘ S. Composites of cyclone genesis and track densities as well as swh fields were calculated based on the phases of both EOFs. In short, EOF phases presenting cores with a positive (negative) u10 anomaly provide a favorable (unfavorable) environment for cyclone genesis and track densities and, therefore, positive (negative) swh anomalies. The modulation of the cyclone tracks is significant for extreme values of the swh. The spatial patterns of the EOFs of u10 are physically and statistically consistent with 200 and 850 hPa geopotential height signals from the Pacific, indicating the importance of the remote influence of the PSA patterns over the wSA.

scholarly journals A Multiscale Reexamination of the Pacific–South American Pattern

2017 ◽  
Vol 145 (1) ◽  
pp. 379-402 ◽  
Author(s):  
Terence J. O’Kane ◽  
Didier P. Monselesan ◽  
James S. Risbey
Keyword(s):  
Time Scales ◽  
Wave Train ◽  
Hadley Circulation ◽  
South American ◽  
Tropical Forcing ◽  
Tropical Variability ◽  
Higher Order Modes ◽  
The Pacific ◽  
Total Variability

Abstract The authors undertake a multiscale spectral reexamination of the variability of the Pacific–South American (PSA) pattern and the mechanisms by which this variability occurs. Time scales from synoptic to interannual are investigated, focusing on the means by which tropical variability is communicated to the midlatitudes and on in situ forcing within the midlatitude waveguides. Particular interest is paid to what fraction of the total variability associated with the PSA, occurring on interannual time scales, is attributable to tropical forcing relative to that occurring on synoptic and intraseasonal time scales via internal waveguide dynamics. In general, it is found that the eastward-propagating wave train pattern typically associated with the PSA manifests across time scales from synoptic to interannual, with the majority of the variability occurring on synoptic-to-intraseasonal time scales largely independent of tropical convection. It is found that the small fraction of the total variance with a tropical signal occurs via the zonal component of the thermal wind modulating both the subtropical and polar jets. The respective roles of the Hadley circulation and stationary Rossby wave sources are also examined. Further, a PSA-like mode is identified in terms of the slow components of higher-order modes of tropospheric geopotential height. This study reestablishes the multiscale nonlinear nature of the PSA modes arising largely as a manifestation of internal midlatitude waveguide dynamics and local disturbances.

scholarly journals The Role of Extratropical Cyclones and Fronts for Southern Ocean Freshwater Fluxes

2014 ◽  
Vol 27 (16) ◽  
pp. 6205-6224 ◽  
Author(s):  
Lukas Papritz ◽  
Stephan Pfahl ◽  
Irina Rudeva ◽  
Ian Simmonds ◽  
Harald Sodemann ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Interannual Variability ◽  
High Latitude ◽  
Storm Track ◽  
Extratropical Cyclones ◽  
Freshwater Flux ◽  
Freshwater Fluxes ◽  
South Indian ◽  
The Pacific

Abstract In this study, the important role of extratropical cyclones and fronts for the atmospheric freshwater flux over the Southern Ocean is analyzed. Based on the Interim ECMWF Re-Analysis (ERA-Interim), the freshwater flux associated with cyclones is quantified and it is revealed that the structure of the Southern Hemispheric storm track is strongly imprinted on the climatological freshwater flux. In particular, during austral winter the spiraliform shape of the storm track leads to a band of negative freshwater flux bending toward and around Antarctica, complemented by a strong freshwater input into the midlatitude Pacific, associated with the split storm track. The interannual variability of the wintertime high-latitude freshwater flux is shown to be largely determined by the variability of strong precipitation (>75th percentile). Using a novel and comprehensive method to attribute strong precipitation uniquely to cyclones and fronts, it is demonstrated that over the Southern Ocean between 60% and 90% of the strong precipitation events are due to these synoptic systems. Cyclones are the dominant cause of strong precipitation around Antarctica and in the midlatitudes of the Atlantic and the Pacific, while in the south Indian Ocean and the eastern Atlantic fronts bring most of the strong precipitation. A detailed analysis of the spatial variations of intense front and cyclone precipitation associated with the interannual variability of the wintertime frequency of cyclones in the midlatitude and high-latitude branches of the Pacific storm track underpins the importance of considering both fronts and cyclones in the analysis of the interannual variability of freshwater fluxes.

scholarly journals Projected Change in Wintertime Precipitation in California Using Projected Changes in Extratropical Cyclone Activity

2018 ◽  
Vol 31 (9) ◽  
pp. 3451-3466 ◽  
Author(s):  
Luke Osburn ◽  
Kevin Keay ◽  
Jennifer L. Catto
Keyword(s):  
Storm Track ◽  
Storm Tracks ◽  
Cmip5 Models ◽  
Extratropical Cyclones ◽  
The Pacific ◽  
Projected Change ◽  
Direct Model ◽  
The Future ◽  
Projected Changes ◽  
The Relationship

Abstract Wintertime extratropical cyclones in the east Pacific region are the source of much of the precipitation over California. There is a lot of uncertainty in future projections of Californian precipitation associated with predicted changes in the jet stream and the midlatitude storm tracks. The question this work seeks to answer is how the changes in the frequency and the intensity of extratropical cyclones in the Pacific storm track influence future changes in Californian precipitation. The authors used an objective cyclone identification method applied to 25 CMIP5 models for the historical and RCP8.5 simulations and investigated the changing relationships between storm frequency, intensity and precipitation. Cyclone data from the historical simulations and differences between the historical and RCP8.5 simulations were used to “predict” the modeled precipitation in the RCP8.5 simulations. In all models, the precipitation predicted using historical relationships gives a lower future precipitation change than the direct model output. In the future, the relationship between track density and precipitation indicates that for the same number of tracks, more precipitation is received. The relationship between track intensity and precipitation (which is quite weak in the historical simulations) does not change in the future. This suggests that other sources, likely enhanced moisture availability, are more important than changes in the intensity of cyclones for the rainfall associated with the storm tracks.

scholarly journals Genetic diversity and kinship relationships in one of the largest South American fur seal ( Arctocephalus australis ) populations of the Pacific Ocean

2021 ◽  
Author(s):  
Josefina Gutiérrez ◽  
Mauricio Seguel ◽  
Pablo Saenz‐Agudelo ◽  
Gerardo Acosta‐Jamett ◽  
Claudio Verdugo
Keyword(s):  
Genetic Diversity ◽  
Pacific Ocean ◽  
South American ◽  
The Pacific ◽  
Fur Seal ◽  
The Pacific Ocean

scholarly journals The Annular Response to Tropical Pacific SST Forcing

2006 ◽  
Vol 19 (9) ◽  
pp. 1802-1819 ◽  
Author(s):  
Shuanglin Li ◽  
Martin P. Hoerling ◽  
Shiling Peng ◽  
Klaus M. Weickmann
Keyword(s):  
General Circulation ◽  
Storm Track ◽  
Circulation Model ◽  
Tropical Pacific ◽  
Transient Eddy ◽  
West Pacific ◽  
Core Energy ◽  
The Pacific ◽  
Sst Forcing ◽  
Sst Anomaly

Abstract The leading pattern of Northern Hemisphere winter height variability exhibits an annular structure, one related to tropical west Pacific heating. To explore whether this pattern can be excited by tropical Pacific SST variations, an atmospheric general circulation model coupled to a slab mixed layer ocean is employed. Ensemble experiments with an idealized SST anomaly centered at different longitudes on the equator are conducted. The results reveal two different response patterns—a hemispheric pattern projecting on the annular mode and a meridionally arched pattern confined to the Pacific–North American sector, induced by the SST anomaly in the west and the east Pacific, respectively. Extratropical air–sea coupling enhances the annular component of response to the tropical west Pacific SST anomalies. A diagnosis based on linear dynamical models suggests that the two responses are primarily maintained by transient eddy forcing. In both cases, the model transient eddy forcing response has a maximum near the exit of the Pacific jet, but with a different meridional position relative to the upper-level jet. The emergence of an annular response is found to be very sensitive to whether transient eddy forcing anomalies occur within the axis of the jet core. For forcing within the jet core, energy propagates poleward and downstream, inducing an annular response. For forcing away from the jet core, energy propagates equatorward and downstream, inducing a trapped regional response. The selection of an annular versus a regionally confined tropospheric response is thus postulated to depend on how the storm tracks respond. Tropical west Pacific SST forcing is particularly effective in exciting the required storm-track response from which a hemisphere-wide teleconnection structure emerges.

Landscape of Migration

2020 ◽  
Author(s):  
Ben Nobbs-Thiessen
Keyword(s):  
Food Security ◽  
South American ◽  
Santa Cruz ◽  
Cash Crop ◽  
Revolutionary Movement ◽  
Export Agriculture ◽  
The Pacific ◽  
Regional Capital ◽  
Tropical Lowlands ◽  
Do So

In the wake of a 1952 revolution, leaders of Bolivia's National Revolutionary Movement (MNR) embarked on a program of internal colonization known as the "March to the East." In an impoverished country dependent on highland mining, the MNR sought to convert the nation’s vast "undeveloped" Amazonian frontier into farmland, hoping to achieve food security, territorial integrity, and demographic balance. To do so, they encouraged hundreds of thousands of Indigenous Bolivians to relocate from the "overcrowded" Andes to the tropical lowlands, but also welcomed surprising transnational migrant streams, including horse-and-buggy Mennonites from Mexico and displaced Okinawans from across the Pacific. Ben Nobbs-Thiessen details the multifaceted results of these migrations on the environment of the South American interior. As he reveals, one of the "migrants" with the greatest impact was the soybean, which Bolivia embraced as a profitable cash crop while eschewing earlier goals of food security, creating a new model for extractive export agriculture. Half a century of colonization would transform the small regional capital of Santa Cruz de la Sierra into Bolivia's largest city, and the diverging stories of Andean, Mennonite, and Okinawan migrants complicate our understandings of tradition, modernity, foreignness, and belonging in the heart of a rising agro-industrial empire.

Intraseasonal-to-Interannual Variability of South Indian Ocean Sea Level and Thermocline: Remote versus Local Forcing

2012 ◽  
Vol 42 (4) ◽  
pp. 602-627 ◽  
Author(s):  
Laurie L. Trenary ◽  
Weiqing Han
Keyword(s):  
Indian Ocean ◽  
Interannual Variability ◽  
Sea Level ◽  
Time Scales ◽  
Ekman Pumping ◽  
Remote Forcing ◽  
South Indian ◽  
The Pacific ◽  
The Indian Ocean ◽  
Thermocline Variability

Abstract The relative importance of local versus remote forcing on intraseasonal-to-interannual sea level and thermocline variability of the tropical south Indian Ocean (SIO) is systematically examined by performing a suite of controlled experiments using an ocean general circulation model and a linear ocean model. Particular emphasis is placed on the thermocline ridge of the Indian Ocean (TRIO; 5°–12°S, 50°–80°E). On interannual and seasonal time scales, sea level and thermocline variability within the TRIO region is primarily forced by winds over the Indian Ocean. Interannual variability is largely caused by westward propagating Rossby waves forced by Ekman pumping velocities east of the region. Seasonally, thermocline variability over the TRIO region is induced by a combination of local Ekman pumping and Rossby waves generated by winds from the east. Adjustment of the tropical SIO at both time scales generally follows linear theory and is captured by the first two baroclinic modes. Remote forcing from the Pacific via the oceanic bridge has significant influence on seasonal and interannual thermocline variability in the east basin of the SIO and weak impact on the TRIO region. On intraseasonal time scales, strong sea level and thermocline variability is found in the southeast tropical Indian Ocean, and it primarily arises from oceanic instabilities. In the TRIO region, intraseasonal sea level is relatively weak and results from Indian Ocean wind forcing. Forcing over the Pacific is the major cause for interannual variability of the Indonesian Throughflow (ITF) transport, whereas forcing over the Indian Ocean plays a larger role in determining seasonal and intraseasonal ITF variability.

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