The Hadley Circulation represents the Earth's major atmospheric overturning, responsible for heat exchange between the tropics and extratropics. For the 21st Century, a weakening and poleward expansion of the Hadley Circulation has been projected. The future behavior of the Hadley Circulation bears obvious societal importance as its descending branch is associated with the world's arid regions in the subtropics and links have been made to regional precipitation changes and extreme events. Whether or not these projections are robust regionally are open questions and arguably a pressing concern in terms of the challenge how human and natural systems adapt to climate change.
While current research focuses on changes in the meridional circulation in the atmosphere and the consequences for hydroclimate, subtropical highs, aridity, and vegetation changes on land – the marine impacts are being overlooked. This is despite the fact that the Hadley Circulation is intimately tied to variations in the upwelling-favorable meridional winds along the eastern ocean basins. These regions have experienced considerable trends in meridional winds in recent decades. In the proposed, the effects of changing meridional winds on upperocean properties over the eastern ocean basins will be explored, including the strength and position of upwelling, Ekman transport, stratification, mixed layer depth, and ventilation. It is important to understand variability and change in these physical processes setting the backdrop for productive ecosystems along eastern boundaries of the subtropical ocean basins, which are anticipated to undergo considerable changes in a warming climate.
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