Amplitude and timing of temperature and salinity variability in the subpolar North Atlantic over the past 10 k.y.

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.

Download Full-text

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

Climate of the Past Discussions ◽

10.5194/cpd-8-1885-2012 ◽

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.

Download Full-text

Impact of Agulhas Leakage on the Atlantic Overturning Circulation in the CCSM4

Journal of Climate ◽

10.1175/jcli-d-12-00714.1 ◽

2014 ◽

Vol 27 (1) ◽

pp. 101-110 ◽

Cited By ~ 17

Author(s):

Wilbert Weijer ◽

Erik van Sebille

Keyword(s):

North Atlantic ◽

South Atlantic ◽

Meridional Overturning Circulation ◽

Overturning Circulation ◽

Climate System Model ◽

The North ◽

Salinity Variability ◽

Meridional Overturning ◽

The North Atlantic ◽

The Impact

Abstract The impact of Agulhas leakage variability on the strength of the Atlantic meridional overturning circulation (AMOC) in the Community Climate System Model, version 4 (CCSM4) is investigated. In this model an advective connection exists that transports salinity anomalies from the Agulhas region into the North Atlantic on decadal (30–40 yr) time scales. However, there is no identifiable impact of Agulhas leakage on the strength of the AMOC, suggesting that the salinity variations are too weak to significantly modify the stratification in the North Atlantic. It is argued that this study is inconclusive with respect to an impact of Agulhas leakage on the AMOC. Salinity biases leave the South Atlantic and Indian Oceans too homogeneous, in particular erasing the observed salinity front in the Agulhas retroflection region. Consequently, salinity variability in the southeastern South Atlantic is found to be much weaker than observed.

Download Full-text

A centennial-scale Arctic - North Atlantic recharge oscillator in a coupled climate model

10.5194/egusphere-egu21-5888 ◽

2021 ◽

Author(s):

Robin Waldman ◽

Christophe Cassou ◽

Aurore Voldoire

Keyword(s):

Atlantic Ocean ◽

North Atlantic ◽

Climate Model ◽

Natural Variability ◽

Meridional Overturning Circulation ◽

The Arctic ◽

Western Boundary ◽

Coupled Climate Model ◽

Overturning Circulation ◽

Salinity Variability

<p>In global climate models, low-frequency natural variability related to the Atlantic Ocean overturning circulation is a common behaviour. Such intrinsic climate variability is a potential source of decadal climate predictability. However, over longer term scenario simulations, this natural variability becomes a major source of uncertainty. In this study, we document a large and sustained centennial variability in the 3500-year pre-industrial control run of the CNRM-CM6 coupled climate model which is driven by the North Atlantic ocean, and more specifically its meridional overturning circulation (AMOC). We propose a new AMOC dynamical decomposition highlighting the dominant role of mid-depth density anomalies at the western boundary as the driver of this centennial variability. We relate such density variability to deep convection and overflows in the western subpolar gyre, themselves controlled by and intense salinity variability of the upper layers. Finally, we show that such salinity variability is the result of periodic freshwater recharge and descharge events from the Arctic Ocean, themselves triggered by stochastic atmospheric forcing.</p>

Download Full-text

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

Journal of Climate ◽

10.1175/jcli-d-20-0642.1 ◽

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.

Download Full-text