Variations of oceanic and atmospheric heat fluxes in the North Atlantic and their link to the North Atlantic Oscillation Index

2020 ◽  
Author(s):  
Diana Iakovleva ◽  
Igor Bashmachnikov
Keyword(s):  
North Atlantic ◽  
Heat Content ◽  
Heat Fluxes ◽  
Upper Ocean ◽  
Subpolar Gyre ◽  
Heat Advection ◽  
Norwegian Sea ◽  
The North ◽  
The North Atlantic ◽  
The North Atlantic Oscillation

<p>Interannual variations in the upper ocean heat and freshwater contents in the subpolar North Atlantic has important climatic effect. It affects the intensity of deep convection, which, in turn, forms the link between upper and deep ocean circulation of the global ocean Conveyor Belt.</p><p>The upper ocean heat content is primarily affected by two main process: by the ocean-atmosphere heat exchange and by oceanic heat advection. The intensity of both fluxes in the subpolar gyre is linked to the character of atmospheric circulation, largely determined by the phase of the North Atlantic Oscillation (NAO).</p><p>To study the interannual variability of the oceanic heat advection (in the upper 500<sup>th</sup> meters layer) we compare the results from four different data-sets: ARMOR-3D (1993-2018), SODA3.4.2 and SODA3.12.2 (1980-2017), and ORAS5 (1958-2017). The ocean-atmosphere heat exchange is accessed as the sum of the latent and the sensible heat fluxes, obtained from OAFlux data-set (1958-2016).</p><p>The oceanic heat advection to the Labrador and to the Irminger seas has high negative correlation (-0.79) with that into the Nordic Seas. During the years with high winter NAO Index (NAOI) the oceanic heat advection into the Subpolar Gyre decreases, while to the Nordic Seas – increases. These variations go in parallel with the intensification of the Norwegian, the West Spitsbergen and the slope East Greenland currents and weakening of the West Greenland and the Irminger Currents. During the years with high NAOI, the ocean heat release (both sensible and latent) over the Labrador and Irminger seas increases, but over the Norwegian Sea it decreases.</p><p>In summary, the results show that, during the positive NAO phase, the observed decrease of the heat content in the upper Labrador and Irminger seas is linked to both, a higher oceanic het release and a lower intensity of advection of warm water from the south. In the Norwegian Sea, the opposite sign of variations of the fluxes above leads to a simultaneous warming of the upper ocean.</p><p>The investigation is supported by the Russian Scientific Foundation (RSF), number of project 17-17-01151.</p><p> </p><p> </p>

A Simple Model of the Response of the Atlantic to the North Atlantic Oscillation

2014 ◽  
Vol 27 (11) ◽  
pp. 4052-4069 ◽  
Author(s):  
Xiaoming Zhai ◽  
Helen L. Johnson ◽  
David P. Marshall
Keyword(s):  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Heat Content ◽  
Meridional Overturning Circulation ◽  
Wind Forcing ◽  
Western Boundary ◽  
Ekman Pumping ◽  
The North ◽  
The North Atlantic ◽  
The North Atlantic Oscillation

Abstract The response of an idealized Atlantic Ocean to wind and thermohaline forcing associated with the North Atlantic Oscillation (NAO) is investigated both analytically and numerically in the framework of a reduced-gravity model. The NAO-related wind forcing is found to drive a time-dependent “leaky” gyre circulation that integrates basinwide stochastic wind Ekman pumping and initiates low-frequency variability along the western boundary. This is subsequently communicated, together with the stochastic variability induced by thermohaline forcing at high latitudes, to the remainder of the Atlantic via boundary and Rossby waves. At low frequencies, the basinwide ocean heat content changes owing to NAO wind forcing and thermohaline forcing are found to oppose each other. The model further suggests that the recently reported opposing changes of the meridional overturning circulation in the Atlantic subtropical and subpolar gyres between 1950–70 and 1980–2000 may be a generic feature caused by interplay between the NAO wind and thermohaline forcing.

scholarly journals Why is the North Atlantic Oscillation More Predictable in December?

Atmosphere ◽  
2019 ◽  
Vol 10 (8) ◽  
pp. 477 ◽  
Author(s):  
Baoqiang Tian ◽  
Ke Fan
Keyword(s):  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Heat Fluxes ◽  
Surface Heat Fluxes ◽  
The North ◽  
Sea Surface Temperature Anomaly ◽  
Stratospheric Circulation ◽  
The North Atlantic ◽  
The North Atlantic Oscillation ◽  
The Relationship

The prediction skill of the Climate Forecast System, version 2 (CFSv2), for the North Atlantic Oscillation (NAO) is evaluated in three winter months (December, January, and February). The results show that the CFSv2 model can skillfully predict the December NAO one month in advance. There are two main contributors to NAO predictability in December. One is the predictability of the relationship between the North Atlantic sea surface temperature anomaly (SSTA) tripole and the NAO and the other is the second empirical orthogonal function (EOF) mode of the geopotential height at 50 hPa (Z50-EOF2). The relationship between the NAO and SSTA tripole index in December is the most significant in the three winter months. The significant monthly differences of surface heat fluxes in December over the whole North Atlantic are favorable for promoting the interaction between the NAO and North Atlantic SSTAs, in addition to improving the predictability of the December NAO. When the NAO is in a positive phase, easterly anomalies are located at the low and high latitudes and westerly anomalies prevail in the mid-latitudes of the troposphere. The correlation between the December Z50-EOF2 and zonal-mean zonal wind anomalies shows a similar spatial structure to that for the NAO. The possible reason why the CFSv2 model can predict the December NAO one month ahead is that it can reasonably reproduce the relationship between the December NAO and both the North Atlantic SST and stratospheric circulation.

On the Temporally Varying Northward Penetration of Mediterranean Overflow Water and Eastward Penetration of Labrador Sea Water

2008 ◽  
Vol 38 (9) ◽  
pp. 2097-2103 ◽  
Author(s):  
M. Susan Lozier ◽  
Nicole M. Stewart
Keyword(s):  
North Atlantic ◽  
Water Mass ◽  
Sea Water ◽  
Labrador Sea ◽  
Subpolar Gyre ◽  
The North ◽  
The North Atlantic ◽  
Eastern North Atlantic ◽  
The North Atlantic Oscillation ◽  
Water Mass Transformations

Abstract Historical hydrographic data in the eastern North Atlantic are used to suggest a connection between the northward penetration of Mediterranean Overflow Water (MOW) and the location of the subpolar front, the latter of which is shown to vary with the North Atlantic Oscillation (NAO). During persistent high-NAO periods, when the subpolar front moves eastward, waters in the subpolar gyre essentially block the northward-flowing MOW, preventing its entry into the subpolar gyre. Conversely, during low NAO periods, the subpolar front moves westward, allowing MOW to penetrate past Porcupine Bank into the subpolar gyre. The impacts of an intermittent penetration of MOW into the subpolar gyre, including the possible effect on water mass transformations, remain to be investigated.

scholarly journals Low-Frequency SST and Upper-Ocean Heat Content Variability in the North Atlantic

2014 ◽  
Vol 27 (13) ◽  
pp. 4996-5018 ◽  
Author(s):  
Martha W. Buckley ◽  
Rui M. Ponte ◽  
Gaël Forget ◽  
Patrick Heimbach
Keyword(s):  
Time Scales ◽  
Mixed Layer ◽  
North Atlantic ◽  
Heat Budget ◽  
Low Frequency ◽  
Heat Fluxes ◽  
Upper Ocean ◽  
The North ◽  
Local Forcing ◽  
The North Atlantic

A recent state estimate covering the period 1992–2010 from the Estimating the Circulation and Climate of the Ocean (ECCO) project is utilized to quantify the upper-ocean heat budget in the North Atlantic on monthly to interannual time scales (seasonal cycle removed). Three novel techniques are introduced: 1) the heat budget is integrated over the maximum climatological mixed layer depth (integral denoted as H), which gives results that are relevant for explaining SST while avoiding strong contributions from vertical diffusion and entrainment; 2) advective convergences are separated into Ekman and geostrophic parts, a technique that is successful away from ocean boundaries; and 3) air–sea heat fluxes and Ekman advection are combined into one local forcing term. The central results of our analysis are as follows: 1) In the interior of subtropical gyre, local forcing explains the majority of H variance on all time scales resolved by the ECCO estimate. 2) In the Gulf Stream region, low-frequency H anomalies are forced by geostrophic convergences and damped by air–sea heat fluxes. 3) In the interior of the subpolar gyre, diffusion and bolus transports play a leading order role in H variability, and these transports are correlated with low-frequency variability in wintertime mixed layer depths.

scholarly journals Determining the Origins of Advective Heat Transport Convergence Variability in the North Atlantic

2015 ◽  
Vol 28 (10) ◽  
pp. 3943-3956 ◽  
Author(s):  
Martha W. Buckley ◽  
Rui M. Ponte ◽  
Gaël Forget ◽  
Patrick Heimbach
Keyword(s):  
Heat Transport ◽  
Time Scales ◽  
North Atlantic ◽  
North Atlantic Ocean ◽  
Heat Content ◽  
Heat Fluxes ◽  
Ocean Dynamics ◽  
The North ◽  
The North Atlantic ◽  
Advective Heat Transport

Abstract A recent state estimate covering the period 1992–2010 from the Estimating the Circulation and Climate of the Ocean (ECCO) project is utilized to quantify the roles of air–sea heat fluxes and advective heat transport convergences in setting upper-ocean heat content anomalies H in the North Atlantic Ocean on monthly to interannual time scales. Anomalies in (linear) advective heat transport convergences, as well as Ekman and geostrophic contributions, are decomposed into parts that are due to velocity variability, temperature variability, and their covariability. Ekman convergences are generally dominated by variability in Ekman mass transports, which reflect the instantaneous response to local wind forcing, except in the tropics, where variability in the temperature field plays a significant role. In contrast, both budget analyses and simple dynamical arguments demonstrate that geostrophic heat transport convergences that are due to temperature and velocity variability are anticorrelated, and thus their separate treatment is not insightful. In the interior of the subtropical gyre, the sum of air–sea heat fluxes and Ekman heat transport convergences is a reasonable measure of local atmospheric forcing, and such forcing explains the majority of H variability on all time scales resolved by ECCO. In contrast, in the Gulf Stream region and subpolar gyre, ocean dynamics are found to be important in setting H on interannual time scales. Air–sea heat fluxes damp anomalies created by the ocean and thus are not set by local atmospheric variability.

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