It is a long-standing mystery that the climatological equator departs from the geographical one and is located around 10 ¿N over the eastern Pacific. Key to maintaining the Northern Hemisphere position of the atmospheric intertropical convergence zone (ITCZ) is a hemispheric asymmetry in sea surface temperature (SST) with higher SSTs north of the equator (Fig. 1A). Using ship and satellite observations, we show that the scalar wind speed difference across the equator, through latent heat flux, is the main cause of this SST asymmetry while the sun-shielding effect of precipitating clouds at the ITCZ is largely offset by the effect of high relative humidity. In the far eastern Pacific, non-precipitating stratiform clouds also play a role in cooling the Southern Hemisphere. Surface air-sea temperature difference field displays a distribution that acts to reduce the observed latitudinal asymmetry of SST.¿ 1997 American Geophysical Union