Re-emergence of North Atlantic subsurface ocean temperature anomalies in a seasonal forecast system

Grist, Jeremy P.; Sinha, Bablu; Hewitt, Helene. T.; Duchez, Aurélie; MacLachlan, Craig; Hyder, Patrick; Josey, Simon A.; Hirschi, Joël J.-M.; Blaker, Adam T.; New, Adrian. L.; Scaife, Adam A.; Roberts, Chris D.. 2019 Re-emergence of North Atlantic subsurface ocean temperature anomalies in a seasonal forecast system. Climate Dynamics. 22, pp.

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A high-resolution coupled ocean atmosphere model is used to study the effects of seasonal re-emergence of North Atlantic subsurface ocean temperature anomalies on northern hemisphere winter climate. A 50-member control ensemble is integrated from 1 September 2007 to 28 February 2008 and compared with a parallel ensemble with perturbed ocean initial conditions. The perturbation consists of a density-compensated subsurface Atlantic temperature anomaly corresponding to the observed subsurface temperature anomaly for September 2010. The experiment is repeated for two atmosphere horizontal resolutions (~ 60 km and ~ 25 km) in order to determine whether the sensitivity of the atmosphere to re-emerging temperature anomalies is dependent on resolution. A wide range of re-emergence behavior is found within the perturbed ensembles. While the observations seem to indicate that most of the re-emergence is occurring in November, most members of the ensemble show re-emergence occurring later in the winter. However, when re-emergence does occur it is preceded by an atmospheric pressure pattern that induces a strong flow of cold, dry air over the mid-latitude Atlantic, and enhances oceanic latent heat loss. In response to re-emergence (negative SST anomalies), there is reduced latent heat loss, less atmospheric convection, a reduction in eddy kinetic energy and positive low-level pressure anomalies downstream. Within the framework of a seasonal forecast system the results highlight the atmospheric conditions required for re-emergence to take place and the physical processes that may lead to a significant effect on the winter atmospheric circulation.

Item Type: Publication - Article
Digital Object Identifier (DOI):
ISSN: 0930-7575
Date made live: 06 Aug 2019 14:08 +0 (UTC)

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