Decadal Variation of the Indian Ocean Dipole

研究了影响印度洋偶极子(IOD)年代际变化的过程。1)利用高分辨率耦合环流模式(CGCM)的输出，研究了厄尔尼诺/南方涛动(ENSO)的年代际调制。结果表明，ENSO的锁相特性对季节循环的变化在ENSO的年代际调制中起着重要作用。这反过来又调制了印尼贯穿流的热量输送，因此IOD2)利用上述模式的输出进行的热量收支分析表明，IOD事件的发生是由横跨15°S的向南Ekman热输送的变化所支配的，这与Mascarene高压活动有很强的联系。3)为了了解影响印度洋热量收支的Agulas流的变化，研究了非洲西海岸的年际变化。研究发现，位于上述地区的安哥拉冰穹经历了与大西洋尼诺相关的显著年际变化，大西洋尼诺是热带大西洋的主要气候模式。4)由于了解过去的IOD有助于理解IOD的当前和未来的变化，我们进行了大气环流模式(AGCM)实验，该模式使用上新世出现的永久IOD和厄尔尼诺情况。在这种情况下，热带地区大气对海洋的热吸收和中纬度海洋向大气的热释放明显减少。

The processes that affect the decadal variation of the Indian Ocean Dipole (IOD) are investigated.1) Using outputs from a high-resolution coupled general circulation model (CGCM), decadal modulations of El Nino/Southern Oscillation (ENSO) is examined. Changes in the phase-locking nature of the ENSO to the seasonal cycle are shown to play an important role in the decadal modulation of the ENSO. This, in turn, modulates the heat transport by the Indonesian Throughflow, and thus the occurrence of the IOD.2) Heat budget analysis using the above model outputs has revealed that the occurrence of IOD events is governed by variations in the southward Ekman heat transport across 15°S, which is strongly linked with the Mascarene high activities.3) To understand the variability of the Agulhas Current, which influences the heat budget of the Indian Ocean, the interannual variation in the west coast of Africa is studied. It is found that the Angola Dome located in the above region undergoes significant interannual variations associated with the Atlantic Nino, which is a major climate mode in the tropical Atlantic.4) Since understanding of the past IOD is useful in understanding the current and future variability of the IOD, atmospheric general circulation model (AGCM) experiments with the permanent IOD and E1 Nino condition seen in Pliocene are conducted. The heat absorption from the atmosphere to the ocean in the tropics and the heat release from the ocean to the atmosphere in the mid-latitude are significantly reduced under this condition.