On the Response of the Equatorial Atmosphere and Ocean to Changes in Sea Surface Temperature along the Path of the North Equatorial Counter Current

The CESM climate model is used to test the hypothesis that changes observed during El Niños are, at least in part, a response of the coupled ocean/atmosphere system to changes in sea surface temperature along the path of the North Equatorial Counter Current. The results from the second month in a set of forced runs show that increased temperatures at the latitudes of the North Equatorial Counter Current produce a significant increase in deep atmospheric convection within the Intertropical Convergence Zone. This has a local effect on the ocean’s surface pressure field which reduces pressures on the Equator. The increased deep atmospheric convection also affects the longitude structure of the Hadley Circulation. In the south-east Pacific, an area associated with Hadley Cell sinking, surface pressure decreases. In the western Pacific, the pressure field increases with maxima north and south of the Equator. Together the surface pressure changes have similarities with those associated with the Southern Oscillation. They reduce the zonal component of wind stress along the Equator and produce an El Niño type response in the ocean.