1. Department of Natural History Sciences, Graduate School of Science, Hokkaido University, Sapporo 060-0810, Japan
2. Earth Simulator Center, Japan Agency for Marine-Earth Science and Technology, Yokohama 236-0001, Japan
3. International Pacific Research Center,
4. Department of Meteorology, University of Hawaii at Manoa, Honolulu, Hawaii 96822, USA

Correspondence to: Shoshiro Minobe¹ Correspondence and requests for materials should be addressed to S.M. (Email: minobe@sci.hokudai.ac.jp).

The Gulf Stream transports large amounts of heat from the tropics to middle and high latitudes, and thereby affects weather phenomena such as cyclogenesis^{1, 2} and low cloud formation³. But its climatic influence, on monthly and longer timescales, remains poorly understood. In particular, it is unclear how 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 model⁴. 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, which anchors a narrow band of precipitation along the Gulf Stream. In this rain band, upward motion and cloud formation extend into the upper troposphere, as corroborated by the frequent occurrence of very low cloud-top temperatures. These mechanisms provide a pathway by which the Gulf Stream can affect the atmosphere locally, and possibly also in remote regions by forcing planetary waves^{5, 6}. The identification of this pathway may have implications for our understanding of the processes involved in climate change, because the Gulf Stream is the upper limb of the Atlantic meridional overturning circulation, which has varied in strength in the past⁷ and is predicted to weaken in response to human-induced global warming in the future⁸.

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