Intraseasonal modulation of Wyrtki jet in the eastern Indian Ocean by equatorial waves during spring 2013

摘要

A strong spring Wyrtki jet(WJ)presents in May 2013 in the eastern equatorial Indian Ocean.The entire buildup and retreat processes of the spring WJ were well captured by two adjacent Acoustic Doppler Current Profilers mounted on the mooring systems.The observed zonal jet behaved as one intraseasonal event with the significant features of abrupt emergence as well as slow disappearance.Further research illustrate that the pronounced surface westerly wind burst during late-April to mid-May,associated with the active phase of a robust eastwardpropagating Madden–Julian oscillation in the tropical Indian Ocean,was the dominant reason for the rapid acceleration of surface WJ.In contrasting,the governing mechanism for the jet termination was equatorial wave dynamics rather than wind forcing.The decomposition analysis of equatorial waves and the corresponding changes in the ocean thermocline demonstrated that strong WJ was produced rapidly by the wind-generated oceanic downwelling equatorial Kelvin wave and was terminated subsequently by the westward-propagating equatorial Rossby wave reflecting from eastern boundaries of the Indian Ocean.