Yoshida Jet

The Yoshida jet is an equatorially trapped, wind-driven zonal current that develops in response to zonal wind stress along the equator, named for Kozo Yoshida’s 1959 theory of equatorial flow. Because the Coriolis parameter vanishes at the equator, a westerly wind drives a strong, narrow eastward surface jet rather than an Ekman flow. The clearest real-ocean example is the semiannual Wyrtki jet in the equatorial Indian Ocean, which appears during the spring and fall monsoon transitions when equatorial westerlies blow. Kelvin and Rossby waves are excited as the basin adjusts, reflecting at the eastern and western boundaries.