Warming in the northwestern Indian Ocean associated with the El Niño event

This paper investigates possible warming effects of an El Niño event on the sea surface temperature anomaly (SSTA) in the northwestern Indian Ocean. Most pure positive Indian Ocean dipole (IOD) events (without an El Niño event co-occurring) have a maximum positive SSTA mainly in the central Indian Ocean south of the equator, while most co-occurrences with an El Niño event exhibit a northwest-southeast typical dipole mode. It is therefore inferred that warming in the northwestern Indian Ocean is closely related to the El Niño event. Based on the atmospheric bridge theory, warming in the northwestern Indian Ocean during co-occurring cases may be primarily caused by relatively less latent heat loss from the ocean due to reduced wind speed. The deepened thermocline also contributes to the warming along the east coast of Africa through the suppressed upwelling of the cold water. Therefore, the El Niño event is suggested to have a modulating effect on the structure of the dipole mode in the tropical Indian Ocean.