Shear dispersion and delayed propagation of temperature anomalies along
                        the Norwegian Atlantic Slope Current

Broomé, Sara; Nilsson, Johan

doi:10.1080/16000870.2018.1453215

Cited by 8 publications

(14 citation statements)

References 46 publications

(118 reference statements)

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“…Compatible with these results are the findings of, for example, Chafik et al (2015) and Holliday et al (2008), who showed that temperature anomalies take about 1 year to reach the interior Norwegian Sea from the FSC. Broomé and Nilsson (2018) showed that the relatively slow propagation of temperature and salinity anomalies, compared to the faster downstream advection, can be explained by mixing between the boundary current and the interior region of weak mean flow.…”

Section: Discussionmentioning

confidence: 99%

Recent Warming and Freshening of the Norwegian Sea Observed by Argo Data

2019

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Climate variability in the Norwegian Sea, comprising the Norwegian and Lofoten Basins, was investigated based upon monthly estimates of ocean heat and freshwater contents using data from Argo floats during 2002–18. Both local air–sea exchange and advective processes were examined and quantified for monthly to interannual time scales. In the recent years, 2011–18, the Norwegian Sea experienced a decoupling of the temperature and salinity, with a simultaneous warming and freshening trend. This was mainly explained by two different processes; reduced ocean heat loss to the atmosphere and advection of fresher Atlantic water into the Norwegian Sea. The local air–sea heat fluxes are important in modifying the ocean heat content, although this relationship varied with time scale and basins. On time scales exceeding 4 months in the Lofoten Basin and 6 months in the Norwegian Basin, the air–sea heat flux explained half or even more of the local ocean heat content change. There were both a short-term and long-term response of the wind forcing on the ocean heat content. The monthly to seasonal response of increased southerly wind cooled and freshened the Norwegian Basin, due to eastward surface Ekman transport, and increased the influence of Arctic Water. However, after about a 1-yr delay the ocean warmed and became saltier due to an increased advection of Atlantic Water into the region. Increased westerly winds decreased the ocean heat content in both cases due to increased transport of Arctic Water into the Norwegian Sea.

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Section: Discussionmentioning

confidence: 99%

Recent Warming and Freshening of the Norwegian Sea Observed by Argo Data

2019

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“…We find that interannual heat content anomalies in the Norwegian Sea are more related to the variable strength of the Atlantic water inflow than to temperature changes of the inflowing water. Observations nevertheless show that on multiannual to decadal time scales, temperature anomalies are able to propagate into and through the Norwegian Sea (Årthun et al, ; Broomé & Nilsson, ), something which suggests that temperature anomalies advected by the mean current could play a more important role in the heat budget on longer time scales. The time period covered by ECCOv4 is, however, too short to assess decadal variability in Norwegian Sea heat content.…”

Section: Discussionmentioning

confidence: 99%

Mechanisms of Ocean Heat Anomalies in the Norwegian Sea

et al. 2019

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Ocean heat content in the Norwegian Sea exhibits pronounced variability on interannual to decadal time scales. These ocean heat anomalies are known to influence Arctic sea ice extent, marine ecosystems, and continental climate. It nevertheless remains unknown to what extent such heat anomalies are produced locally within the Norwegian Sea, and to what extent the region is more of a passive receiver of anomalies formed elsewhere. A main practical challenge has been the lack of closed heat budget diagnostics. In order to address this issue, a regional heat budget is calculated for the Norwegian Sea using the ECCOv4 ocean state estimate—a dynamically and kinematically consistent model framework fitted to ocean observations for the period 1992–2015. The depth‐integrated Norwegian Sea heat budget shows that both ocean advection and air‐sea heat fluxes play an active role in the formation of interannual heat content anomalies. A spatial analysis of the individual heat budget terms shows that ocean advection is the primary contributor to heat content variability in the Atlantic domain of the Norwegian Sea. Anomalous heat advection furthermore depends on the strength of the Atlantic water inflow, which is related to large‐scale circulation changes in the subpolar North Atlantic. This result suggests a potential for predicting Norwegian Sea heat content based on upstream conditions. However, local surface forcing (air‐sea heat fluxes and Ekman forcing) within the Norwegian Sea substantially modifies the phase and amplitude of ocean heat anomalies along their poleward pathway, and, hence, acts to limit predictability.

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“…Several mechanisms have been proposed to explain the decadal-scale propagation and alongpath modification of SST anomalies along the Atlantic water pathway. This includes advection along the major currents (e.g., Furevik 2000;Krahmann et al, 2001;Årthun et al, 2017), local air-sea interaction (e.g., Saravanan and McWilliams 1998), Rossby waves (e.g., Liu et al, 1999), boundary waves (Marshall and Johnson, 2013), and shear-dispersion effects (Broomé and Nilsson 2018). This study does not aim to assess the relative importance of these mechanisms.…”

Section: Introductionmentioning

confidence: 99%

Propagation of Thermohaline Anomalies and Their Predictive Potential along the Atlantic Water Pathway

et al. 2022

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We assess to what extent seven state-of-the-art dynamical prediction systems can retrospectively predict winter sea surface temperature (SST) in the subpolar North Atlantic and the Nordic Seas in the period 1970-2005. We focus on the region where warm water flows poleward, i.e., the Atlantic water pathway to the Arctic, and on interannual-to-decadal time scales. Observational studies demonstrate predictability several years in advance in this region, but we find that SST skill is low with significant skill only at lead time 1-2 years. To better understand why the prediction systems have predictive skill or lack thereof, we assess the skill of the systems to reproduce a spatio-temporal SST pattern based on observations. The physical mechanism underlying this pattern is a propagation of oceanic anomalies from low to high latitudes along the major currents; the North Atlantic Current and the Norwegian Atlantic Current. We find that the prediction systems have difficulties in reproducing this pattern. To identify whether the misrepresentation is due to incorrect model physics, we assess the respective uninitialized historical simulations. These simulations also tend to misrepresent the spatio-temporal SST pattern, indicating that the physical mechanism is not properly simulated. However, the representation of the pattern is slightly degraded in the predictions compared to historical runs, which could be a result of initialization shocks and forecast drift effects. Ways to enhance predictions, could be through improved initialization, and better simulation of poleward circulation of anomalies. This might require model resolutions in which flow over complex bathymetry and physics of mesoscale ocean eddies and their interactions with the atmosphere are resolved.

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Shear dispersion and delayed propagation of temperature anomalies along the Norwegian Atlantic Slope Current

Cited by 8 publications

References 46 publications

Recent Warming and Freshening of the Norwegian Sea Observed by Argo Data

Recent Warming and Freshening of the Norwegian Sea Observed by Argo Data

Mechanisms of Ocean Heat Anomalies in the Norwegian Sea

Propagation of Thermohaline Anomalies and Their Predictive Potential along the Atlantic Water Pathway

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