scholarly journals Physical Response of the Tropical–Subtropical North Atlantic Ocean to Decadal–Multidecadal Forcing by African Dust

2012 ◽  
Vol 25 (17) ◽  
pp. 5817-5829 ◽  
Author(s):  
Amato T. Evan ◽  
Gregory R. Foltz ◽  
Dongxiao Zhang
Keyword(s):  
Surface Temperature ◽  
Time Scales ◽  
Ocean Circulation ◽  
North Atlantic ◽  
General Circulation ◽  
Dust Storms ◽  
Upper Ocean ◽  
Temperature Anomalies ◽  
Tropical North Atlantic ◽  
Wide Range

Abstract Dust storms are a persistent feature of the tropical North Atlantic and vary over a wide range of temporal scales. While it is well known that mineral aerosols alter the local radiative fluxes, far less is understood about the oceanic response to such forced changes to the radiative budget, particularly on long time scales. This study uses an observation-based climatology of dust surface forcing and an ocean general circulation model to examine the influence of anomalous atmospheric dust cover over the tropical North Atlantic on upper ocean temperature and circulation during 1955–2008. It is found that surface temperature anomalies from the model experiments are forced primarily by local radiation-induced changes to the surface heat budget. The subsurface temperature anomalies are additionally influenced by upper ocean circulation anomalies, which are the response to dust-forced steric changes in dynamic height. The results herein suggest that on decadal time scales dust-forced variability of ocean surface and subsurface temperatures are of a magnitude comparable to observed variability. On longer time scales dust-forced sea surface temperature anomalies vary in phase with the Atlantic multidecadal oscillation, implying that tropical North Atlantic multidecadal variability is related to changes in dust emissions from West Africa.

scholarly journals Contributions of Atmospheric Stochastic Forcing and Intrinsic Ocean Modes to North Atlantic Ocean Interdecadal Variability

2020 ◽  
Vol 33 (6) ◽  
pp. 2351-2370 ◽  
Author(s):  
Olivier Arzel ◽  
Thierry Huck
Keyword(s):  
Ocean Circulation ◽  
North Atlantic ◽  
General Circulation ◽  
Thermal Structure ◽  
Ocean Dynamics ◽  
Dimensionless Number ◽  
Stochastic Forcing ◽  
The North ◽  
Wide Range ◽  
The North Atlantic

AbstractAtmospheric stochastic forcing associated with the North Atlantic Oscillation (NAO) and intrinsic ocean modes associated with the large-scale baroclinic instability of the North Atlantic Current (NAC) are recognized as two strong paradigms for the existence of the Atlantic multidecadal oscillation (AMO). The degree to which each of these factors contribute to the low-frequency variability of the North Atlantic is the central question in this paper. This issue is addressed here using an ocean general circulation model run under a wide range of background conditions extending from a supercritical regime where the oceanic variability spontaneously develops in the absence of any atmospheric noise forcing to a damped regime where the variability requires some noise to appear. The answer to the question is captured by a single dimensionless number Γ measuring the ratio between the oceanic and atmospheric contributions, as inferred from the buoyancy variance budget of the western subpolar region. Using this diagnostic, about two-thirds of the sea surface temperature (SST) variance in the damped regime is shown to originate from atmospheric stochastic forcing whereas heat content is dominated by internal ocean dynamics. Stochastic wind stress forcing is shown to substantially increase the role played by damped ocean modes in the variability. The thermal structure of the variability is shown to differ fundamentally between the supercritical and damped regimes, with abrupt modifications around the transition between the two regimes. Ocean circulation changes are further shown to be unimportant for setting the pattern of SST variability in the damped regime but are fundamental for a preferred time scale to emerge.

scholarly journals A spatiotemporal reconstruction of sea-surface temperatures in the North Atlantic during Dansgaard–Oeschger events 5–8

2018 ◽  
Vol 14 (6) ◽  
pp. 901-922 ◽  
Author(s):  
Mari F. Jensen ◽  
Aleksi Nummelin ◽  
Søren B. Nielsen ◽  
Henrik Sadatzki ◽  
Evangeline Sessford ◽  
...  
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
North Atlantic ◽  
General Circulation ◽  
Sea Surface ◽  
Reconstruction Method ◽  
Sea Surface Temperatures ◽  
Proxy Data ◽  
Surface Temperatures ◽  
Temperature Reconstructions

Abstract. Here, we establish a spatiotemporal evolution of the sea-surface temperatures in the North Atlantic over Dansgaard–Oeschger (DO) events 5–8 (approximately 30–40 kyr) using the proxy surrogate reconstruction method. Proxy data suggest a large variability in North Atlantic sea-surface temperatures during the DO events of the last glacial period. However, proxy data availability is limited and cannot provide a full spatial picture of the oceanic changes. Therefore, we combine fully coupled, general circulation model simulations with planktic foraminifera based sea-surface temperature reconstructions to obtain a broader spatial picture of the ocean state during DO events 5–8. The resulting spatial sea-surface temperature patterns agree over a number of different general circulation models and simulations. We find that sea-surface temperature variability over the DO events is characterized by colder conditions in the subpolar North Atlantic during stadials than during interstadials, and the variability is linked to changes in the Atlantic Meridional Overturning circulation and in the sea-ice cover. Forced simulations are needed to capture the strength of the temperature variability and to reconstruct the variability in other climatic records not directly linked to the sea-surface temperature reconstructions. This is the first time the proxy surrogate reconstruction method has been applied to oceanic variability during MIS3. Our results remain robust, even when age uncertainties of proxy data, the number of available temperature reconstructions, and different climate models are considered. However, we also highlight shortcomings of the methodology that should be addressed in future implementations.

scholarly journals Modeling dust emission response to MIS 3 millennial climate variations from the perspective of East European loess deposits

2013 ◽  
Vol 9 (1) ◽  
pp. 143-185 ◽  
Author(s):  
A. Sima ◽  
M. Kageyama ◽  
D.-D. Rousseau ◽  
G. Ramstein ◽  
Y. Balkanski ◽  
...  
Keyword(s):  
North Atlantic ◽  
General Circulation ◽  
Reference Site ◽  
Dust Emission ◽  
Dust Storms ◽  
Surface Model ◽  
Climate Signal ◽  
The North ◽  
Loess Deposits ◽  
The North Atlantic

Abstract. European loess sequences of the last glacial period (~ 100–15 kyr BP) show periods of strong dust accumulation alternating with episodes of reduced sedimentation, favoring soil development. In the western part of the loess belt centered around 50° N, these variations appear to have been caused by the North Atlantic rapid climate changes: the Dansgaard-Oeschger (DO) and Heinrich (H) events. It has been recently suggested that the North-Atlantic climate signal can be detected further east, in loess deposits from Stayky (50° 05.65' N, 30° 53.92' E), Ukraine. Here we use climate and dust emission modeling to investigate this data interpretation. We focus on the areas north and northeast of the Carpathians, where loess deposits can be found, and the corresponding main dust sources must have been located as well. The simulations, performed with the LMDZ atmospheric general circulation model and the ORCHIDEE land-surface model, represent a Greenland stadial, a DO interstadial and an H event respectively. Placed in Marine Isotope Stage 3 (~ 60–25 kyr BP) conditions, they only differ by the surface conditions imposed in the North Atlantic between 30° and 63° N. The main source for the loess deposits in the studied area is identified as a dust deflation band, with two very active spots located west–northwest from our reference site. Emissions only occur between February and June. Differences from one deflation spot to another, and from one climate state to another, are explained by analyzing the relevant meteorological and surface variables. Over most of the source region, the annual emission fluxes in the "interstadial" experiment are 30 to 50% lower than the "stadial" values; they would only be about 20% lower if the inhibition of dust uplift by the vegetation were not taken into account. Assuming that lower emissions result in reduced dust deposition leads us to the conclusion that the loess-paleosol stratigraphic succession in the Stayky area reflects indeed North-Atlantic millennial variations. In the main deflation areas of Western Europe, the vegetation effect alone determined most of the ~ 50% stadial-interstadial flux differences. Even if its impact in Eastern Europe is less pronounced, this effect remains a key factor in modulating aeolian emissions at millennial timescale. Conditions favorable to initiating particularly strong dust storms within a few hundred kilometers upwind from our reference site, simulated in the month of April of the "H event" experiment, support the identification of H events as layers of particularly coarse sedimentation in some very detailed profiles.

Using a novel combination of autonomous vehicles for air-sea interaction studies: Results from the Eurec4a campaign 

2021 ◽  
Author(s):  
Elizabeth Siddle ◽  
Karen J. Heywood ◽  
Ben Webber ◽  
Peter Bromley
Keyword(s):  
Time Series ◽  
North Atlantic ◽  
Heat Budget ◽  
Heat Content ◽  
Flux Measurement ◽  
Extreme Weather Events ◽  
Upper Ocean ◽  
Momentum Exchange ◽  
Tropical North Atlantic

<div> <p>The Tropical North Atlantic region is a key driver of climate variability and extreme weather events, driven largely by heat and momentum exchanges across the air-sea boundary. Observations of these fluxes by satellites and vessels are limited in their spatial resolution and length of time series respectively. In-situ samples across long time periods are needed, which can be obtained through developing a network of in-situ flux measurement platforms. UEA and AutoNaut have worked to address this challenge with the deployment of <em>Caravela</em> - an AutoNaut uncrewed surface vessel. <em>Caravela</em> is a wave and solar powered autonomous vessel, equipped with meteorological and oceanographic sensors and the ability to transport a Seaglider. <em>Caravela</em> successfully completed its first scientific deployment as part of the Eurec<sup>4</sup>a campaign. </p> </div><div> <p>Eurec<sup>4</sup>a ran from January—March 2020 from Barbados, investigating climate change feedback in the Tropical North Atlantic and the role of cloud systems. <em>Caravela</em> spent 11 days of her 33-day deployment occupying a 10 km square, co-located with other Eurec<sup>4</sup>a platforms to gather in-situ surface data on heat and momentum exchange. Preliminary results from <em>Caravela</em> give us an insight into heat exchange at the surface, downwelling radiation and wind conditions during deployment. There is an identifiable diurnal cycle during the deployment, particularly visible in temperature data, which will feed into our understanding of changes in fluxes at a local scale. Profiling ocean gliders at the study site allow us to determine a time series of upper ocean heat content changes. These data, alongside that collected by other platforms during Eurec<sup>4</sup>a, should enable an upper ocean heat budget to be calculated at <em>Caravela’s</em> study site. </p> </div>

scholarly journals A Comparison of North American Surface Temperature and Temperature Extreme Anomalies in Association with Various Atmospheric Teleconnection Patterns

Atmosphere ◽  
2019 ◽  
Vol 10 (4) ◽  
pp. 172 ◽  
Author(s):  
Bin Yu ◽  
Hai Lin ◽  
Nicholas Soulard
Keyword(s):  
North America ◽  
Surface Temperature ◽  
North Atlantic ◽  
North American ◽  
North Pacific ◽  
Temperature Anomaly ◽  
Temperature Extreme ◽  
Associated Anomalies ◽  
Atmospheric Teleconnection ◽  
Temperature Anomalies

The atmospheric teleconnection pattern reflects large-scale variations in the atmospheric wave and jet stream, and has pronounced impacts on climate mean and extremes over various regions. This study compares those patterns that have significant circulation anomalies over the North Pacific–North American–North Atlantic sector, which directly influence surface temperature and temperature extremes over North America. We analyze the pattern associated anomalies of surface temperature and warm and cold extremes over North America, during the northern winter and summer seasons. In particular, we assess the robustness of the regional temperature and temperature extreme anomaly patterns by evaluating the field significance of these anomalies over North America, and quantify the percentages of North American temperature and temperature extreme variances explained by these patterns. The surface temperature anomalies in association with the Pacific–North American pattern (PNA), Tropical–Northern Hemisphere pattern (TNH), North Pacific pattern (NP), North Atlantic Oscillation (NAO), Arctic Oscillation (AO), Western Pacific pattern (WP), circumglobal teleconnection (CGT), and Asian–Bering–North American (ABNA) patterns are similar to those reported in previous studies based on various datasets, indicating the robustness of the results. During winter, the temperature anomaly patterns considered are field significant at the 5% level over North America, except the WP-related one. These pattern associated anomalies explained about 5–15% of the total interannual temperature variance over North America, with relatively high percentages for the ABNA and PNA patterns, and low for the WP pattern. The pattern associated warm and cold extreme anomalies resemble the corresponding surface mean temperature anomaly patterns, with differences mainly in magnitude of the anomalies. Most of the anomalous extreme patterns are field significant at the 5% level, except the WP-related patterns. These extreme anomalies explain about 5–20% of the total interannual variance over North America. During summer, the pattern-related circulation and surface temperature anomalies are weaker than those in winter. Nevertheless, all of the pattern associated temperature anomalies are of field significance at the 5% level over North America, except the PNA-related one, and explain about 5–10% of the interannual variance. In addition, the temperature extreme anomalies, in association with the circulation patterns, are comparable in summer and winter. Over North America, the NP-, WP-, ABNA-, and CGT-associated anomalies of warm extremes are field significant at the 5% level and explain about 5–15% of the interannual variance. Most of the pattern associated cold extreme anomalies are field significant at the 5% level, except the PNA and NAO related anomalies, and also explain about 5–15% of the interannual variance over North America.

scholarly journals North Atlantic 20th century multidecadal variability in coupled climate models: sea surface temperature and ocean overturning circulation

Ocean Science ◽  
2011 ◽  
Vol 7 (3) ◽  
pp. 389-404 ◽  
Author(s):  
I. Medhaug ◽  
T. Furevik
Keyword(s):  
Surface Temperature ◽  
20Th Century ◽  
North Atlantic ◽  
General Circulation ◽  
General Circulation Models ◽  
Meridional Overturning Circulation ◽  
Overturning Circulation ◽  
Atlantic Sector ◽  
The North ◽  
The North Atlantic

Abstract. Output from a total of 24 state-of-the-art Atmosphere-Ocean General Circulation Models is analyzed. The models were integrated with observed forcing for the period 1850–2000 as part of the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report. All models show enhanced variability at multi-decadal time scales in the North Atlantic sector similar to the observations, but with a large intermodel spread in amplitudes and frequencies for both the Atlantic Multidecadal Oscillation (AMO) and the Atlantic Meridional Overturning Circulation (AMOC). The models, in general, are able to reproduce the observed geographical patterns of warm and cold episodes, but not the phasing such as the early warming (1930s–1950s) and the following colder period (1960s–1980s). This indicates that the observed 20th century extreme in temperatures are due to primarily a fortuitous phasing of intrinsic climate variability and not dominated by external forcing. Most models show a realistic structure in the overturning circulation, where more than half of the available models have a mean overturning transport within the observed estimated range of 13–24 Sverdrup. Associated with a stronger than normal AMOC, the surface temperature is increased and the sea ice extent slightly reduced in the North Atlantic. Individual models show potential for decadal prediction based on the relationship between the AMO and AMOC, but the models strongly disagree both in phasing and strength of the covariability. This makes it difficult to identify common mechanisms and to assess the applicability for predictions.

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