The Gulf Stream transports large amounts of heat from the tropics to mid-and high-latitudes, and thereby affects cyclogenesis 1,2 and low cloud formation 3 . Its influence on climate on monthly and longer timescales remains poorly understood, however. In particular, it is unclear to what depth the warm current affects the free atmosphere above the marine atmospheric boundary layer. Here we consider the Gulf Stream's influence on the troposphere using a combination of operational weather analyses, satellite observations, and an atmospheric general circulation model 4 . Our results reveal that the Gulf Stream affects the entire troposphere. In the marine boundary layer, atmospheric pressure adjustments to sharp sea surface temperature gradients lead to surface wind convergence that anchors a narrow precipitation band along the Gulf Stream. In this rain band, upward motions and cloud formation extend into the upper troposphere as corroborated by the frequent occurrence of very cold cloud-top temperatures. These mechanisms offer a direct pathway by which the Gulf Stream can affect the atmosphere both locally and possibly in remote regions via planetary wave propagation 5,6 . This pathway may have implications for our understanding of climate change because the Gulf Stream is the upper limb of the Atlantic meridional overturning circulation, which displays large variations in records of past climate change 7 and is predicted to slow down in response to global warming 8 .

Potential impacts of pronounced decadal-scale variations in the North Pacific sea surface temperature (SST) that tend to be confined to the subarctic frontal zone (SAFZ) upon seasonally varying atmospheric states are investigated, by using 48-yr observational data and a 120-yr simulation with an ocean-atmosphere coupled general circulation model (CGCM). SST fields based on in situ observations and the ocean component of the CGCM have horizontal resolutions of 2.08 and 0.58, respectively, which can reasonably resolve frontal SST gradient across the SAFZ. Both the observations and CGCM simulation provide a consistent picture between SST anomalies in the SAFZ yielded by its decadal-scale meridional displacement and their association with atmospheric anomalies. Correlated with SST anomalies persistent in the SAFZ from fall to winter, a coherent decadal-scale signal in the wintertime atmospheric circulation over the North

[1] The relative importance of remote and local influences in the development of Benguela Niños is examined using observations and a coupled general circulation model capable of simulating interannual variability in the tropical Atlantic. While previous studies have emphasized the role of equatorially excited Kelvin waves, the present study finds that meridional wind anomalies along the southwest African coast contribute substantially. Both observations and model output indicate that sea-surface temperatures along the southwest African coast respond rapidly to changes in meridional wind stress. These wind anomalies form part of a basin-scale weakening of the subtropical anticyclone that extends to the equator. As the weakening begins three months before the peak of the event it might have some predictive potential. Results also indicate that the close correlation between Benguela and Atlantic Niños in observations might result from the large spatially coherent wind stress anomalies associated with the weakened anticyclone. Citation: Richter, I

many of the coupled ocean-atmosphere global circulation models in the coming decade will represent oceanic fronts reasonably well, and it is hoped that this review along with the table of metrics will provide a useful benchmark for evaluating these models.

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