Abstract
In the extratropical regions, surface winds enhance upward heat release from the ocean to atmosphere, resulting in cold surface ocean: surface ocean temperature is negatively correlated with upward heat flux. However, in the western boundary currents and eddy-rich regions, the warmer surface waters compared to surrounding waters enhance upward heat release–a positive correlation between upward heat release and surface ocean temperature, implying that the ocean drives the atmosphere. The atmospheric response to warm mesoscale ocean eddies with a horizontal extent of a few hundred kilometers remains unclear because of a lack of observations. By conducting regional atmospheric model experiments, we show that, in the Kuroshio–Oyashio Confluence region, wintertime warm eddies heat the marine atmospheric boundary layer (MABL), and accelerate westerly winds in the near-surface atmosphere via the vertical mixing effect, leading to wind convergence around the eastern edge of eddies. The warm-eddy-induced convergence forms local ascending motion where convective precipitation is enhanced, providing diabatic heating to the atmosphere above MABL. Our results indicate that warm eddies affect not only near-surface atmosphere but also free atmosphere, and possibly synoptic atmospheric variability. A detailed understanding of warm eddy–atmosphere interaction is necessary to improve in weather and climate projections.
Highlights
The global subtropical western boundary currents and their extensions, from which warm eddies are pinched off, show an accelerated warming over the 20th century that far exceeds the globally averaged surface warming rate[25]
Recent studies have shown that momentum diffusion is large in the MABL over subtropical warm ocean eddies in the South Atlantic[21] and Indian Ocean[22], which is consistent with our results
Past studies reported that the precipitation anomaly increase not above the near surface wind convergence zone but above the maximum SST anomaly of warm eddies in the Southern Ocean[23]
Summary
The global subtropical western boundary currents and their extensions, from which warm eddies are pinched off, show an accelerated warming over the 20th century that far exceeds the globally averaged surface warming rate[25]. Unraveling the processes through which warm eddies associated with changing western boundary current systems influence synoptic atmospheric variability require organized long-term observational and modeling efforts. This will enable more accurately predictions of the synoptic atmospheric variability response to future climate change
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
