Roles Of The Indonesian Throughflow In The Seasonal To Interannual Variability Of The Tropical Indo-pacific Climate

The Indonesia Throughflow (ITF) provides the only low-latitude pathway forwarm and fresh water to move from the Pacific to the Indian Ocean, thus serves aspart of the upper branch of the global heat conveyor belt. The ITF is very importantto the global climate due to its huge volumn and heat transport between the Pacificand the Indian Ocean. In this paper, we focus on the role of the ITF and itsvariability in the seasonal to interannual variabilities of the tropical Indo-Pacificclimate. The paper is organized into two parts, which are described as following.Part IIn this part, the skills of the CMIP5coupled climate models in simulating theIOD-ENSO teleconnection at the time lag of one year are assessed through lagcorrelation analyses and comparing with those of observations.It have been suggested that the interannual variability of the ITF serves asimportant oceanic signal channel for the Indian Ocean anomalies impacting on thePacific ENSO. Lag correlation analyses of observaed sea surface temperature/heightanomalies (SSTA/SSHA) over the Indo-Pacific basin have shown significantcorrelation between the Indian Ocean Dipole events in the tropical Indian Ocean andthe ENSO events in the following year in the Pacific Ocean, which suggestpredictability of the ENSO events beyond the period of one year since1990s. Theskills of FGOALS-g2coupled system model in reproduce the inter-basinteleconeection is assessed by lag correlation analyses of the historical simulationprovided by the CMIP5in comparison with those in the observations. The resultsshow that the FGOALS-g2has simulated the oceanic teleconnection well. Theatmospheric teleconnection, however, is found to be over-estimated in theFGOALS-g2coupled system model.The teleconeection between the Indian and Pacific Oceans is further found tosubject to variations at decadal time scales refer to HadISST and NCEP/NCAR reanalysis zonal wind, with the oceanic channel and the atmospheric bridge shift rolesin dominating the inter-basin teleconnection. The skills of the CMIP5climatemodels in simulating these teleconnection processes between the two basins areassessed using lag correlation analyses of the CMIP5historical simulations incomparison with those in the observations. Composite analyses of the positive(oceanic teleconnection significant) and negative (oceanic teleconnection weak)phases of CMIP5simulations suggest that the lag correlations during the positivephases are simulated well by most of the CMIP5coupled system models, whereas,during the negative phases, almost all of the23CMIP5coupled system modelsanalyzed failed to reproduce the significant lag correlations between the westernPacific surface zonal wind anomalies and the cold tongue oceanic anomalies at theone-year time lag in the observation. The comparisons suggest model deficiencies insimulating the atmospheric bridge of the inter-basin teleconnection at the decadal timescales.Part IIIn this part, the influences of mean transport of the ITF and its seasonl andinterannual variability on the Indo-Pacific climate are investigated through numericalexperiment using a two and half layer reduced gravity ocean model coupled with anatmospheric general circulation model.It has been suggested that the existence of the ITF has significant influences onthe tropical Indo-Pacific Ocean, including both annual mean states and interannualvariability. These studies, however, were based simply on the numericalexperiments of ITF switch off and on, which can not distinguish the influence of ITFvariability from the mean state. In this paper, the ITF relaxation schemes areemployed in a two and half layer reduced gravity ocean model coupled with theECHAM4atmospheric general circulation model, to investigate the influence of themean transport of the ITF and its annual and interannual variability on the tropicalindo-Pacific Ocean. The sensitivity experiments are conducted as EXP1, in whichthe ITF was relaxed to zero; EXP2, in which the ITF was relaxed to the annual mean of the benchmark experiment (CTRL); and EXP3, in which the ITF was relaxed to themonthly climatology derived from the CTRL.The differences between EXP2and EXP1indicate the influences of the meantransport of the ITF. In response to the reduction of ITF, SST becomes warmer inthe equatorial Pacific Ocean, but cooler in the eastern tropical Indian Ocean. Thethermocline deepens in the equatorial Pacific Ocean, but elevates in the tropicalIndian Ocean. In addition, the gradient of thermocline and the Walker Circulation inthe equatorial Pacific are weken in EXP1, leading to a longer time scale of energyrecharge of the western Pacific warm pool.The differences between EXP3and EXP2indicate the influences of the seasonalvariability of the ITF. It is found that the seasonal variability of ITF forces reduced(enhanced) warm water transport from the western Pacific Ocean to the Indian Oceanin boreal winter (summer), generating seasonal anomailes of thermocline in theequatorial Indian and Pacific Oceans to propagate toward the ocean boundary. In theequatorial Pacific, the equatorial Kelvin wave and off-equatorial Rossby wave(reflected form eastern boundary) induce zonal currents anomalies to displace theeastern edge of the western Pacific warm pool, thus produce SST anomalies in thecentral equatorial PacificThe differences between CTRL and EXP3indicate the influences of theinterannual variability of the ITF. The results have shown significant interannualvariability of thermocline and zonal advection in the equatorial Indo-Pacific Oceans,which then impact on the interannual variability of the tropical Indo-Pacific climatethrough air-sea coupling and advective-reflective process..The coupled numerical experiments have shown significant influences of ITFvariability on the seasonal to interannual variability of the tropical Indo-Pacificclimate. It is important to simulate properly ITF and its oceanic channel dynamicsfor understanding and simulating the tropical Indo-Pacific climate variability.