Evidence is presented to show that the zonal westward geopotential gradient along the equator in the eastern Pacific between 95W and 120W exhibits a seasonal variation with vanishingly low values in March-May and high values (5 × 10-7 m s-2) in June-July followed by a gradual decrease toward the end of the year. This variation is found to be in phase with the seasonal variation of the westward component of the wind stress near the equator, which also shows low values in northern spring and high values in northern summer and fall.
Tsuchiya, Mizuki. 1979. "Seasonal variation of the equatorial zonal geopotential gradient in the eastern Pacific Ocean." Journal of Marine Research 37, (3). https://elischolar.library.yale.edu/journal_of_marine_research/1474