scholarly journals The Meridional Shift of the Midlatitude Westerlies over Arid Central Asia during the Past 21 000 Years Based on the TraCE-21ka Simulations

2020 ◽  
Vol 33 (17) ◽  
pp. 7455-7478
Author(s):  
Nanxuan Jiang ◽  
Qing Yan ◽  
Zhiqing Xu ◽  
Jian Shi ◽  
Ran Zhang
Keyword(s):  
Indian Ocean ◽  
North Atlantic ◽  
North Atlantic Ocean ◽  
Last Deglaciation ◽  
The Past ◽  
The North ◽  
External Forcings ◽  
The Indian Ocean ◽  
The Last Deglaciation ◽  
The North Atlantic

AbstractTo advance our knowledge of the response of midlatitude westerlies to various external forcings, we investigate the meridional shift of midlatitude westerlies over arid central Asia (ACA) during the past 21 000 years, which experienced more varied forcings than the present day based on a set of transient simulations. Our results suggest that the evolution of midlatitude westerlies over ACA and driving factors vary with time and across seasons. In spring, the location of midlatitude westerlies over ACA oscillates largely during the last deglaciation, driven by meltwater fluxes and continental ice sheets, and then shows a long-term equatorward shift during the Holocene controlled by orbital insolation. In summer, orbital insolation dominates the meridional shift of midlatitude westerlies, with poleward and equatorward migration during the last deglaciation and the Holocene, respectively. From a thermodynamic perspective, variations in zonal winds are linked with the meridional temperature gradient based on the thermal wind relationship. From a dynamic perspective, variations in midlatitude westerlies are mainly induced by anomalous sea surface temperatures over the Indian Ocean through the Matsuno–Gill response and over the North Atlantic Ocean by the propagation of Rossby waves, or both, but their relative importance varies across forcings. Additionally, the modeled meridional shift of midlatitude westerlies is broadly consistent with geological evidence, although model–data discrepancies still exist. Overall, our study provides a possible scenario for a meridional shift of midlatitude westerlies over ACA in response to various external forcings during the past 21 000 years and highlights important roles of both the Indian Ocean and the North Atlantic Ocean in regulating Asian westerlies, which may shed light on the behavior of westerlies in the future.

Ice-sheet variability around the North Atlantic Ocean during the last deglaciation

Nature ◽  
10.1038/32866 ◽  
1998 ◽  
Vol 392 (6674) ◽  
pp. 373-377 ◽  
Author(s):  
A. Marshall McCabe ◽  
Peter U. Clark
Keyword(s):  
Atlantic Ocean ◽  
North Atlantic ◽  
North Atlantic Ocean ◽  
Ice Sheet ◽  
Last Deglaciation ◽  
The North ◽  
The Last Deglaciation ◽  
The North Atlantic

Changes in surface salinity of the North Atlantic Ocean during the last deglaciation

Nature ◽  
1992 ◽  
Vol 358 (6386) ◽  
pp. 485-488 ◽  
Author(s):  
J. C. Duplessy ◽  
L. Labeyrie ◽  
M. Arnold ◽  
M. Paterne ◽  
J. Duprat ◽  
...  
Keyword(s):  
Atlantic Ocean ◽  
North Atlantic ◽  
North Atlantic Ocean ◽  
Last Deglaciation ◽  
Surface Salinity ◽  
The North ◽  
The Last Deglaciation ◽  
The North Atlantic

scholarly journals The Linear Sensitivity of the North Atlantic Oscillation and Eddy-Driven Jet to SSTs

2019 ◽  
Vol 32 (19) ◽  
pp. 6491-6511 ◽  
Author(s):  
Hugh S. Baker ◽  
Tim Woollings ◽  
Chris E. Forest ◽  
Myles R. Allen
Keyword(s):  
Indian Ocean ◽  
North Atlantic Oscillation ◽  
North Atlantic ◽  
High Sensitivity ◽  
Internal Variability ◽  
The North ◽  
The Indian Ocean ◽  
The North Atlantic ◽  
The North Atlantic Oscillation ◽  
The Impact

Abstract The North Atlantic Oscillation (NAO) and eddy-driven jet contain a forced component arising from sea surface temperature (SST) variations. Due to large amounts of internal variability, it is not trivial to determine where and to what extent SSTs force the NAO and jet. A linear statistical–dynamic method is employed with a large climate ensemble to compute the sensitivities of the winter and summer NAO and jet speed and latitude to the SSTs. Key regions of sensitivity are identified in the Indian and Pacific basins, and the North Atlantic tripole. Using the sensitivity maps and a long observational SST dataset, skillful reconstructions of the NAO and jet time series are made. The ability to skillfully forecast both the winter and summer NAO using only SST anomalies is also demonstrated. The linear approach used here allows precise attribution of model forecast signals to SSTs in particular regions. Skill comes from the Atlantic and Pacific basins on short lead times, while the Indian Ocean SSTs may contribute to the longer-term NAO trend. However, despite the region of high sensitivity in the Indian Ocean, SSTs here do not provide significant skill on interannual time scales, which highlights the limitations of the imposed SST approach. Given the impact of the NAO and jet on Northern Hemisphere weather and climate, these results provide useful information that could be used for improved attribution and forecasting.

scholarly journals The Role of an Indian Ocean Heating Dipole in the ENSO Teleconnection to the North Atlantic European Region in Early Winter during the Twentieth Century in Reanalysis and CMIP5 Simulations

2021 ◽  
Vol 34 (3) ◽  
pp. 1047-1060
Author(s):  
Manish K. Joshi ◽  
Muhammad Adnan Abid ◽  
Fred Kucharski
Keyword(s):  
Indian Ocean ◽  
North Atlantic ◽  
Enso Event ◽  
Late Winter ◽  
Early Winter ◽  
The North ◽  
The Indian Ocean ◽  
The North Atlantic ◽  
Dipole Response

AbstractIn this study the role of an Indian Ocean heating dipole anomaly in the transition of the North Atlantic–European (NAE) circulation response to El Niño–Southern Oscillation (ENSO) from early to late winter is analyzed using a twentieth-century reanalysis and simulations from phase 5 of the Coupled Model Intercomparison Project (CMIP5). It is shown that in early winter a warm (cold) ENSO event is connected through an atmospheric bridge with positive (negative) rainfall anomalies in the western Indian Ocean and negative (positive) anomalies in the eastern Indian Ocean. The early winter heating dipole, forced by a warm (cold) ENSO event, can set up a wave train emanating from the subtropical South Asian jet region that reaches the North Atlantic and leads to a response that spatially projects onto the positive (negative) phase of the North Atlantic Oscillation. The Indian Ocean heating dipole is partly forced as an atmospheric teleconnection by ENSO, but can also exist independently and is not strongly related to local Indian Ocean sea surface temperature (SST) forcing. The Indian Ocean heating dipole response to ENSO is much weaker in late winter (i.e., February and March) and not able to force significant signals in the North Atlantic region. CMIP5 multimodel ensemble reproduces the early winter Indian Ocean heating dipole response to ENSO and its transition in the North Atlantic region to some extent, but with weaker amplitude. Generally, models that have a strong early winter ENSO response in the subtropical South Asian jet region along with tropical Indian Ocean heating dipole also reproduce the North Atlantic response.

scholarly journals Dissolved Pb and Pb isotopes in the North Atlantic from the GEOVIDE transect (GEOTRACES GA-01) and their decadal evolution

2018 ◽  
Author(s):  
Cheryl M. Zurbrick ◽  
Edward A. Boyle ◽  
Rick Kayser ◽  
Matthew K. Reuer ◽  
Jingfeng Wu ◽  
...  
Keyword(s):  
North Atlantic ◽  
Sea Water ◽  
North Atlantic Ocean ◽  
Isotope Analysis ◽  
The Past ◽  
The North ◽  
Anthropogenic Inputs ◽  
Source Regions ◽  
The North Atlantic ◽  
Seawater Samples

Abstract. During the 2014 GEOVIDE transect, seawater samples were collected for dissolved Pb and Pb isotope analysis. These samples provide a high resolution snapshot of the source regions for the present Pb distribution in the North Atlantic Ocean. Some of these stations were previously occupied for Pb from as early as 1981, and we compare the 2014 data with these older data some of which are reported here for the first time. Lead concentrations were highest in subsurface Mediterranean Water (MW) near the coast of Portugal, which agrees well with other recent observations by the U.S. GEOTRACES program (Noble et al., 2015). The recently formed Labrador Sea Water (LSW) between Greenland and Nova Scotia is much lower in Pb concentration than the older LSW found in the Western European Basin due to decreases in Pb emissions into the atmosphere during the past 20 years. Comparison of North Atlantic data from 1989–2014 shows decreasing Pb concentrations consistent with decreased anthropogenic inputs, active scavenging, and advection/convection. The nearly-homogenous isotopic composition of northern North Atlantic seawater implies that the relative proportions of U.S. and European Pb sources to the ocean have been relatively uniform during the past two decades. Using our measurements in conjunction with emissions inventories, we support the findings of previous atmospheric analyses that up to 50 % of the Pb deposited to the ocean in 2014 was natural, although it remains unclear if that natural dust is from the mid- or high-latitudes.

Immediate temperature response in northern Iberia to last deglacial changes in the North Atlantic

Geology ◽  
2021 ◽  
Author(s):  
J.L. Bernal-Wormull ◽  
A. Moreno ◽  
C. Pérez-Mejías ◽  
M. Bartolomé ◽  
A. Aranburu ◽  
...  
Keyword(s):  
North Atlantic ◽  
Deep Convection ◽  
Temperature Response ◽  
Last Deglaciation ◽  
Climate Feedbacks ◽  
The North ◽  
Heinrich Event ◽  
Northern Iberian Peninsula ◽  
The Last Deglaciation ◽  
The North Atlantic

Major disruptions in the North Atlantic circulation during the last deglaciation triggered a series of climate feedbacks that influenced the course of Termination I, suggesting an almost synchronous response in the ocean-atmosphere system. We present a replicated δ18O stalagmite record from Ostolo cave in the northern Iberian Peninsula with a robust chronological framework that continuously covers the last deglaciation (18.5–10.5 kyr B.P.). The Ostolo δ18O record, unlike other speleothem records in the region that were related to humidity changes, closely tracks the well-known high-latitude temperature evolution, offering important insights into the structure of the last deglaciation in the Northern Hemisphere. In addition, this new record is accompanied by a clear signal of the expected cooling events associated with the deglacial disruptions in North Atlantic deep convection during Heinrich event 1.

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