Exceptionally Strong Equatorial Intermediate Current Events in the Indian Ocean Associated with Climate Modes

Knowledge of the effects of climate modes on the equatorial intermediate current (EIC) remains limited. This paper investigates exceptional events of the EIC in the Indian Ocean and their relationships with climate modes at various time scales by using observations, reanalysis outputs, and a continuously stratified linear ocean model (LOM). A mooring at 80 degrees E from 2015 to 2019 revealed four exceptionally strong EIC events, occurring in 2015 July-August (JA), 2016 January-February (JF), 2016 JA, and 2019 JF. Component analysis revealed that these exceptional events are attributed to the co-occurrence of the seasonal components peaking during JF and JA, as well as the larger current anomalies associated with intraseasonal and interannual components. In the intraseasonal band, the Madden-Julian oscillation (MJO) generates a significant EIC anomaly through a 40-50-day process involving equatorial waves. The MJO exerts a substantial effect when the amplitude of the MJO index exceeds 1 and the oscillation is in phase 4. In the interannual band, El Ni & ntilde;o- Southern Oscillation and the Indian Ocean dipole (IOD) can each independently contribute to the EIC anomaly. This contribution initiates during the mature phase and persists throughout the subsequent year. Concurrent occurrences of these effects can lead to larger interannual anomalies. Notably, El Ni & ntilde;o-positive IOD (El Ni & ntilde;o-pIOD) and La Ni & ntilde;a-negative IOD (La Ni & ntilde;a-nIOD) synergies are most pronounced in August and in January of the following year.