Enhanced aridity and atmospheric high-pressure stability over the western Mediterranean during the North Atlantic cold events of the past 50 k.y.

Geology ◽  
2002 ◽  
Vol 30 (10) ◽  
pp. 863 ◽  
Author(s):  
N. Combourieu Nebout ◽  
J.L. Turon ◽  
R. Zahn ◽  
L. Capotondi ◽  
L. Londeix ◽  
...  
Keyword(s):  
High Pressure ◽  
North Atlantic ◽  
Western Mediterranean ◽  
The Past ◽  
The North ◽  
Cold Events ◽  
The North Atlantic ◽  
Pressure Stability

scholarly journals Enhanced western Mediterranean rainfall during past interglacials driven by North Atlantic pressure changes

2019 ◽  
Author(s):  
Yama Dixit ◽  
Samuel Toucanne ◽  
Juan M. Lora ◽  
Christophe Fontanier ◽  
Virgil Pasquier ◽  
...  
Keyword(s):  
North Atlantic ◽  
Western Mediterranean ◽  
Sea Surface ◽  
Tyrrhenian Sea ◽  
Winter Rainfall ◽  
The Past ◽  
The North ◽  
Hydrological Changes ◽  
The North Atlantic ◽  
The Mediterranean

Abstract. There is increasing concern with anthropogenic greenhouse gas emissions that ocean warming, in concert with summer and winter precipitation changes, will induce anoxia in multiple ocean basins. In particular the Mediterranean Sea is susceptible to severe hydrological changes. Mediterranean hydroclimate is controlled primarily by two phenomena – the latitudinal migration of the Inter-Tropical Convergence Zone and the North Atlantic climatic processes. While the former brings about the African summer monsoon rainfall the latter drives the wintertime storm tracks into the western Mediterranean. Although the hydrological changes in the eastern Mediterranean are quite well constrained, evidence of past changes in temperature and rainfall in the western Mediterranean across the past interglacials is relatively scarce. In this study, we use trace element and stable isotope composition of planktonic foraminifera from a sediment core off Corsica at the mouth of Golo river in the western Mediterranean to reconstruct variations in sea surface temperature (SST) and sea surface salinities (SSS) during the Holocene and warm periods of the past two interglacials. Our data suggest that the warm periods of the last interglacials were characterised by high river discharge and lower SSS in the northern Tyrrhenian Sea, suggesting increased winter rainfall. We find evidence that enhanced winter rainfall during periods of precession minima and high seasonality across interglacials coincide with changes in the respective eccentricity maxima suggesting a causal link. Our model simulations for representative orbital configurations such as the mid-Holocene support increased south-westerly moisture transport into the western Mediterranean originating from the North Atlantic. We suggest that these hydrologic changes in the western and the northern Mediterranean borderlands were a contributing factor to basin-wide anoxia in the past. Our findings offer new insights into the cause and impact of winter rainfall changes in the Mediterranean during past warm periods.

scholarly journals The Combined Effects of SST and the North Atlantic Subtropical High-Pressure System on the Atlantic Basin Tropical Cyclone Interannual Variability

Atmosphere ◽  
2021 ◽  
Vol 12 (3) ◽  
pp. 329
Author(s):  
Albenis Pérez-Alarcón ◽  
José C. Fernández-Alvarez ◽  
Rogert Sorí ◽  
Raquel Nieto ◽  
Luis Gimeno
Keyword(s):  
High Pressure ◽  
Interannual Variability ◽  
Central America ◽  
North Atlantic ◽  
The West ◽  
The Bahamas ◽  
Pressure System ◽  
North Atlantic Subtropical High ◽  
The North ◽  
The North Atlantic

The combined effect of the sea surface temperature (SST) and the North Atlantic subtropical high-pressure system (NASH) in the interannual variability of the genesis of tropical cyclones (TCs) and landfalling in the period 1980–2019 is explored in this study. The SST was extracted from the Centennial Time Scale dataset from the National Oceanic and Atmospheric Administration (NOAA), and TC records were obtained from the Atlantic Hurricane Database of the NOAA/National Hurricane Center. The genesis and landfalling regions were objectively clustered for this analysis. Seven regions of TC genesis and five for landfalling were identified. Intercluster differences were observed in the monthly frequency distribution and annual variability, both for genesis and landfalling. From the generalized least square multiple regression model, SST and NASH (intensity and position) covariates can explain 22.7% of the variance of the frequency of TC genesis, but it is only statistically significant (p < 0.1) for the NASH center latitude. The SST mostly modulates the frequency of TCs formed near the West African coast, and the NASH latitudinal variation affects those originated in the Lesser Antilles arc. For landfalling, both covariates explain 38.7% of the variance; however, significant differences are observed in the comparison between each region. With a statistical significance higher than 90%, SST and NASH explain 33.4% of the landfalling variability in the archipelago of the Bahamas and central–eastern region of Cuba. Besides, landfalls in the Gulf of Mexico and Central America seem to be modulated by SST. It was also found there was no statistically significant relationship between the frequency of genesis and landfalling with the NASH intensity. However, the NASH structure modulates the probability density of the TCs trajectory that make landfall once or several times in their lifetime. Thus, the NASH variability throughout a hurricane season affects the TCs trajectory in the North Atlantic basin. Moreover, we found that the landfalling frequency of TCs formed near the West Africa coast and the central North Atlantic is relatively low. Furthermore, the SST and NASH longitude center explains 31.6% (p < 0.05) of the variance of the landfalling intensity in the archipelago of the Bahamas, while the SST explains 26.4% (p < 0.05) in Central America. Furthermore, the 5-year moving average filter revealed decadal and multidecadal variability in both genesis and landfalling by region. Our findings confirm the complexity of the atmospheric processes involved in the TC genesis and landfalling.

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.

scholarly journals Modeling the climatic implications of the Guliya δ<sup>18</sup>O record during the past 130 ka

2012 ◽  
Vol 8 (3) ◽  
pp. 1885-1914
Author(s):  
D. Xiao ◽  
P. Zhao ◽  
Y. Wang ◽  
X. Zhou
Keyword(s):  
North Atlantic ◽  
Climate Model ◽  
Surface Air Temperature ◽  
Late Summer ◽  
The Arctic ◽  
The Past ◽  
The North ◽  
Precession Cycle ◽  
The North Atlantic ◽  
Anomalous Pattern

Abstract. Using an intermediate-complexity UVic Earth System Climate Model (UVic Model), the geographical and seasonal implications and an indicative sense of the historical climate found in the δ18O record of the Guliya ice core (hereinafter, the Guliya δ18O) are investigated under time-dependent orbital forcing with an acceleration factor of 100 over the past 130 ka. The results reveal that the simulated late-summer (August–September) Guliya surface air temperature (SAT) reproduces the 23-ka precession and 43-ka obliquity cycles in the Guliya δ18O. Furthermore, the Guliya δ18O is significantly correlated with the SAT over the Northern Hemisphere (NH), which suggests the Guliya δ18O is an indicator of the late-summer SAT in the NH. Corresponding to the warm and cold phases of the precession cycle in the Guliya temperature, there are two anomalous patterns in the SAT and sea surface temperature (SST) fields. The first anomalous pattern shows an increase in the SAT (SST) toward the Arctic, possibly associated with the joint effect of the precession and obliquity cycles, and the second anomalous pattern shows an increase in the SAT (SST) toward the equator, possibly due to the influence of the precession cycle. Additionally, the summer (winter) Guliya and NH temperatures are higher (lower) in the warm phases of Guliya late-summer SAT than in the cold phases. Furthermore, the Guliya SAT is closely related to the North Atlantic SST, in which the Guliya precipitation may act as a "bridge" linking the Guliya SAT and the North Atlantic SST.

Impact of Seasonality in the North Atlantic Jet Stream and Storm Migration on the Seasonality of Hurricane Translation Speed Changes

2021 ◽  
pp. 1-38
Author(s):  
Xi Guo ◽  
James P. Kossin ◽  
Zhe-Min Tan
Keyword(s):  
North Atlantic ◽  
Atlantic Coast ◽  
Jet Stream ◽  
Translation Speed ◽  
Multidecadal Variability ◽  
The Past ◽  
The North ◽  
Term Variation ◽  
The North Atlantic

AbstractTropical cyclone (TC) translation speed (TCTS) can affect the duration of TC-related disasters, which is critical to coastal and inland areas. The long-term variation of TCTS and their relationship to the variability of the mid-latitude jet stream and storm migration are discussed here for storms near the North Atlantic coast during 1948-2019. Our results reveal the prominent seasonality in the long-term variation of TCTS, which can be largely explained by the seasonality in the covariations of the mid-latitude jet stream and storm locations. Specifically, significant increases of TCTS occur in June and October during the past decades, which may result from the equatorward displacement of the jet stream and poleward migration of storm locations. Prominent slowdown of TCTS is found in August, which is related to the weakened jet strength and equatorward storm migration. In September, the effects of poleward displacement and weakening of the jet stream on TCTS are largely compensated by the poleward storm migration, therefore, no significant change in TCTS is observed. Meanwhile, the multidecadal variability of the Atlantic may contribute to the multidecadal variability of TCTS. Our findings emphasize the significance in taking a seasonality view in discussing the variability and trends of near-coast Atlantic TCTS under climate change.

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