Semiannual variation of zonal current along the equatorial Indian Ocean

Abstract

Semiannual current variation in the equatorial Indian Ocean is examined using currents velocity records from Research Moored Array for African-Asian-Australian Monsoon Analysis and Prediction (RAMA) Program. Spectral analysis shows that semiannual variation is the strongest variation in equatorial Indian Ocean. Further analysis exhibits that this variation is associated with Wyrtki Jet phenomenon and forced by wind along the equator. Upward phase propagation (downward energy propagation) is clearly shown as indication of the propagation of equatorial Kelvin wave. Cross correlation of two mooring data captures westward propagation of reflected Rossby wave that interferes the propagation of Kelvin wave. During IOD positive event, stronger reflected Rossby wave occurs and causes weakening of upward phase propagation. This result reveals that interferences of equatorial wave have important role on forming vertical structure of currents along equatorial Indian Ocean.