scholarly journals Atlantic Thermohaline Circulation in a Coupled General Circulation Model: Unforced Variations versus Forced Changes

2005 ◽  
Vol 18 (16) ◽  
pp. 3270-3293 ◽  
Author(s):  
Aiguo Dai ◽  
A. Hu ◽  
G. A. Meehl ◽  
W. M. Washington ◽  
W. G. Strand
Keyword(s):  
Atlantic Ocean ◽  
Sea Ice ◽  
North Atlantic ◽  
Thermohaline Circulation ◽  
Sharp Peak ◽  
Future Climate Change ◽  
Large Temperature ◽  
The North ◽  
The North Atlantic ◽  
Atlantic Thermohaline Circulation

Abstract A 1200-yr unforced control run and future climate change simulations using the Parallel Climate Model (PCM), a coupled atmosphere–ocean–land–sea ice global model with no flux adjustments and relatively high resolution (∼2.8° for the atmosphere and 2/3° for the oceans) are analyzed for changes in Atlantic Ocean circulations. For the forced simulations, historical greenhouse gas and sulfate forcing of the twentieth century and projected forcing for the next two centuries are used. The Atlantic thermohaline circulation (THC) shows large multidecadal (15–40 yr) variations with mean-peak amplitudes of 1.5–3.0 Sv (1 Sv ≡ 106 m3 s−1) and a sharp peak of power around a 24-yr period in the control run. Associated with the THC oscillations, there are large variations in North Atlantic Ocean heat transport, sea surface temperature (SST) and salinity (SSS), sea ice fraction, and net surface water and energy fluxes, which all lag the variations in THC strength by 2–3 yr. However, the net effect of the SST and SSS variations on upper-ocean density in the midlatitude North Atlantic leads the THC variations by about 6 yr, which results in the 24-yr period. The simulated SST and sea ice spatial patterns associated with the THC oscillations resemble those in observed SST and sea ice concentrations that are associated with the North Atlantic Oscillation (NAO). The results suggest a dominant role of the advective mechanism and strong coupling between the THC and the NAO, whose index also shows a sharp peak around the 24-yr time scale in the control run. In the forced simulations, the THC weakens by ∼12% in the twenty-first century and continues to weaken by an additional ∼10% in the twenty-second century if CO2 keeps rising, but the THC stabilizes if CO2 levels off. The THC weakening results from stabilizing temperature increases that are larger in the upper and northern Atlantic Ocean than in the deep and southern parts of the basin. In both the control and forced simulations, as the THC gains (loses) strength and depth, the separated Gulf Stream (GS) moves southward (northward) while the subpolar gyre centered at the Labrador Sea contracts from (expands to) the east with the North Atlantic Current (NAC) being shifted westward (eastward). These horizontal circulation changes, which are dynamically linked to the THC changes, induce large temperature and salinity variations around the GS and NAC paths.

scholarly journals Effect of the North Atlantic Thermohaline Circulation on Changes in Climatic Conditions and River Flow in Poland

Water ◽  
2019 ◽  
Vol 11 (8) ◽  
pp. 1622 ◽  
Author(s):  
Dariusz Wrzesiński ◽  
Andrzej A. Marsz ◽  
Anna Styszyńska ◽  
Leszek Sobkowiak
Keyword(s):  
North Atlantic ◽  
Cloud Cover ◽  
River Flow ◽  
Thermohaline Circulation ◽  
Sunshine Duration ◽  
The Arctic ◽  
Strong Increase ◽  
The North ◽  
The North Atlantic ◽  
Atlantic Thermohaline Circulation

The purpose of this study is to find connections between the North Atlantic Thermohaline Circulation (NA THC), climate elements, such as cloud cover, precipitation, air temperature, sunshine duration, and relative humidity, and flow of rivers in Poland. The intensity of NA THC was characterized by the DG3L index, which was established to assess changes in the amount of heat transported by NA THC along with the transport of water to the Arctic. The paper explains and discusses the mechanism of impact of the NA THC changeability on the elements of the catchment water balance variability. The positive and negative phases of the DG3L index are strongly correlated with the heat anomalies in the upper layer of the North Atlantic waters. The obtained results show that changes of NA THC have significant impact on weather conditions and selected climate elements in Poland. Statistically significant positive correlations were found between the DG3L index and average annual air temperatures, particularly in April, July, and August, while negative between the DG3L index and the total cloud cover. Consequently, in the years with the positive values of the DG3L index, there are favorable conditions for the strong increase in evaporation and evapotranspiration from the ground surface. This has impact on flow of rivers in Poland, which shows considerable regional differences.

Variability of the North Atlantic thermohaline circulation during the last interglacial period

Nature ◽  
10.1038/36540 ◽  
1997 ◽  
Vol 390 (6656) ◽  
pp. 154-156 ◽  
Author(s):  
Jess F. Adkins§ ◽  
Edward A. Boyle ◽  
Lloyd Keigwin ◽  
Elsa Cortijo
Keyword(s):  
North Atlantic ◽  
Thermohaline Circulation ◽  
Interglacial Period ◽  
Last Interglacial ◽  
The North ◽  
Last Interglacial Period ◽  
The North Atlantic ◽  
Atlantic Thermohaline Circulation

scholarly journals A Hemispheric Mechanism for the Atlantic Multidecadal Oscillation

2007 ◽  
Vol 20 (11) ◽  
pp. 2706-2719 ◽  
Author(s):  
Mihai Dima ◽  
Gerrit Lohmann
Keyword(s):  
Sea Ice ◽  
North Atlantic ◽  
North Pacific ◽  
Thermohaline Circulation ◽  
Atlantic Multidecadal Oscillation ◽  
Sea Surface ◽  
The North ◽  
Sea Surface Temperature Anomalies ◽  
The North Atlantic ◽  
The North Pacific

Abstract The physical processes associated with the ∼70-yr period climate mode, known as the Atlantic multidecadal oscillation (AMO), are examined. Based on analyses of observational data, a deterministic mechanism relying on atmosphere–ocean–sea ice interactions is proposed for the AMO. Variations in the thermohaline circulation are reflected as uniform sea surface temperature anomalies in the North Atlantic. These anomalies are associated with a hemispheric wavenumber-1 sea level pressure (SLP) structure in the atmosphere that is amplified through atmosphere–ocean interactions in the North Pacific. The SLP pattern and its associated wind field affect the sea ice export through Fram Strait, the freshwater balance in the northern North Atlantic, and consequently the strength of the large-scale ocean circulation. It generates sea surface temperature anomalies with opposite signs in the North Atlantic and completes a negative feedback. The authors find that the time scale of the cycle is associated with the thermohaline circulation adjustment to freshwater forcing, the SST response to it, the oceanic adjustment in the North Pacific, and the sea ice response to the wind forcing. Finally, it is argued that the Great Salinity Anomaly in the late 1960s and 1970s is part of AMO.

Sign in / Sign up

Export Citation Format

Share Document