%0 Journal Article %T Discovery of a lunar air temperature tide over the ocean: a diagnostic of air-sea coupling %J - %D 2018 %R https://doi.org/10.1038/s41612-018-0033-9 %X The lunar semidiurnal (L2) tide in the Earth¡¯s atmosphere is unique as a purely mechanically forced periodic signal and it has been detected in upper atmosphere winds and temperature and in surface barometric pressure. L2 signals in surface air temperature, L2(T), have only been detected at a single land station (results published almost a century ago). We report observational determinations of L2(T) over the ocean by using data from 38 moored buoys across the tropical Pacific and Atlantic. In contrast to published speculation that L2(T) should be negligible over ocean, we find that the observed L2(T) is fairly close to that consistent with an adiabatic L2 pressure variation. Any deviations from purely adiabatic behavior are a measure of diabatic effects on the surface air¡ªexpected to be dominated by damping processes, notably heat exchange with the ocean surface. With the aid of climate model simulations that include L2-tide-like variations, we demonstrate that our observations of L2(T) provide a unique diagnosis for the strength of air-sea coupling and a useful constraint on climate model formulations of this coupling %U https://www.nature.com/articles/s41612-018-0033-9