Inter-decadal modulation of ENSO teleconnections to the Indian Ocean in a coupled model: Special emphasis on decay phase of El Nino

摘要

Inter-decadal modulation of El Nino-Southern Oscillation (ENSO) teleconnections to tropical Indian Ocean (TIO) is investigated in the coupled general circulation model Climate Forecast System (CFS) using a hundred year integration. The model is able to capture the periodicity of El Nino variability, which is similar to that of the observations. The maximum TIOorth Indian Ocean (NIO) SST warming (during spring following the decay phase of El Nino) associated with El Nino is well captured by the model. Detailed analysis reveals that the surface heat flux variations mainly contribute to the El Nino forced TIO SST variations both in observations and model. However, spring warming is nearly stationary throughout the model integration period, indicating poor inter-decadal El Nino teleconnections. The observations on the other hand displayed maximum SST warming with strong sea-sonality from epoch to epoch. The model El Nino decay delayed by more than two seasons, results in persistent TIO/NIO SST warming through the following December unlike in the observations. The ocean wave adjustments and persistent westerly wind anomalies over the equatorial Pacific are responsible for late decay of El Nino in the model. Consistent late decay of El Nino, throughout the model integration period (low variance), is mainly responsible for the poor inter-decadal ENSO teleconnections to TIO/NIO. This study deciphers that the model needs to produce El Nino decay phase variability correctly to obtain decadal-modulations in ENSO teleconnection.