Air moisture control on ocean surface temperature, hidden key to the warm bias enigma

Frédéric Hourdin (1) , Alina Găinusă-Bogdan , Pascale Braconnot (2, 3) , Jean-Louis Dufresne (1) , Aboul-Khadre Traore , Catherine P Rio (1)

1 LMD - Laboratoire de Météorologie Dynamique (UMR 8539)
2 LSCE - Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette]
3 MERMAID - Modelling the Earth Response to Multiple Anthropogenic Interactions and Dynamics

The systematic overestimation by climate models of the surface temperature over the eastern tropical oceans is generally attributed to an insufficient oceanic cooling or to an underestimation of stratocumulus clouds. We show that surface evaporation contributes as much as clouds to the dispersion of the warm bias intensity in a multimodel simulations ensemble. The models with the largest warm biases are those with the highest surface heating by radiation and lowest evaporative cooling in atmospheric simulations with prescribed sea surface temperatures. Surface evaporation also controls the amplitude of the surface temperature response to this overestimated heating, when the atmosphere is coupled to an ocean. Evaporation increases with temperature both because of increasing saturation humidity and of an unexpected drying of the near-surface air. Both the origin of the bias and this temperature adjustment point to the key role of near-surface relative humidity and its control by the atmospheric model.

Domaines: Océan, Atmosphère; Interfaces continentales, environnement

Frédéric Hourdin, Alina Găinusă-Bogdan, Pascale Braconnot, Jean-Louis Dufresne, Aboul-Khadre Traore, et al.. Air moisture control on ocean surface temperature, hidden key to the warm bias enigma. Geophysical Research Letters, 2015, 42 (24), pp.10,885 - 10,893. ⟨10.1002/2015GL066764⟩. ⟨hal-01805157⟩