Discovery of a lunar air temperature tide over the ocean: a diagnostic of air-sea coupling

Abstract The lunar semidiurnal ( L 2 ) 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. L 2 signals in surface air temperature, L 2 (T), have only been detec...

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Bibliographic Details
Published in:NPJ climate and atmospheric science 2018-01, Vol.1 (1), Article 25
Main Authors: Sakazaki, T., Hamilton, K.
Format: Article
Language:English
Subjects:
Adiabatic
Adiabatic flow
Air temperature
Atmosphere
Atmospheric pressure
Buoys
Climate models
Computer simulation
Constraint modelling
Coupling
Damping
Diagnosis
Diagnostic systems
Diurnal variations
Gravity
Heat exchange
Heat transfer
Lunar surface
Lunar tides
Moon
Ocean surface
Pressure
Temperature
Upper atmosphere
Variation
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Summary:Abstract The lunar semidiurnal ( L 2 ) 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. L 2 signals in surface air temperature, L 2 (T), have only been detected at a single land station (results published almost a century ago). We report observational determinations of L 2 (T) over the ocean by using data from 38 moored buoys across the tropical Pacific and Atlantic. In contrast to published speculation that L 2 (T) should be negligible over ocean, we find that the observed L 2 (T) is fairly close to that consistent with an adiabatic L 2 pressure variation. Any deviations from purely adiabatic behavior are a measure of diabatic effects on the surface air—expected to be dominated by damping processes, notably heat exchange with the ocean surface. With the aid of climate model simulations that include L 2 -tide-like variations, we demonstrate that our observations of L 2 (T) provide a unique diagnosis for the strength of air-sea coupling and a useful constraint on climate model formulations of this coupling.
ISSN:2397-3722
2397-3722
DOI:10.1038/s41612-018-0033-9