Exploring the Causes for Indian Ocean Decadal Climate Variability

印度洋（IO）海表温度（SST）的十年至十年的变化与各种全球气候波动有关，包括印度季风降雨的变化、阿拉伯海气旋频率的变化以及美国、地中海和非洲部分地区干旱频率的变化。自20世纪50年代以来，整个盆地的平均海温一直在增加，其速度往往比其他热带海洋的海温更快，甚至在最近的全球变暖中断期间也在继续增加。本研究的目的是了解产生IO海温年代际变化及其伴随的海平面压力（SLP）、地面风和其他气象条件变化的机制。一个特别的目标是确定来自太平洋部门的远程影响和印度洋部门内部耦合的海洋-大气动力在产生印度洋海温年代际变率方面的不同作用。太平洋的影响与年代际太平洋涛动（IPO）有关，这是一种缓慢变化的海温异常模式，与厄尔尼诺/南方涛动事件中更快演变的海温有一些相似之处。以前的工作表明，当海温在赤道太平洋中部变暖时，IPO的正相位可以在IO上产生均匀的变暖。PI假设变暖是由Walker环流的增强引起的，Walker环流增强了IO上空的下沉，并通过减少云量增加了地表日照。但是，最近的观测记录显示，即使首次公开募股已过渡到负阶段，平均IO海温仍在持续增加，因此，除首次公开募股外，其他因素也必须在整个盆地的IO增温和降温中发挥作用。虽然太平洋的影响与均匀海温异常有关，但IO盆地包含第二个突出的年代际变率模式，该模式在很大程度上独立于IPO。这种模式是一种东西向的模式，在这种模式中，盆地西半部的温暖海温伴随着印度尼西亚海岸外的寒冷异常，称为印度洋偶极子（IOD）。PI假设IOD是由大气-海洋耦合动力学驱动的，其中地下热输送起关键作用。除了从内部动力学和来自太平洋的外部影响的角度将IO变率归因之外，该项目还试图了解外部强迫的作用，包括温室气体引起的变暖、太阳变率和人为气溶胶。各种静力学技术被用于诊断观测、再分析产品和气候模式模拟中IO变率的机制。此外，还进行了专门的气候模式实验，其中仅在IO部门启用大气-海洋相互作用，以确定IO部门动力学可以产生年代际变率的程度。补充实验用于确定IO部门的年代际变化在多大程度上是由盆地外的大气-海洋耦合动力学引起的。进一步的气候模式实验考察了通过施加温室气体、气溶胶和太阳辐照度变化的外部强迫的作用。考虑到印度洋的条件影响着邻近陆地地区的天气和气候，这项工作具有社会和科学意义，而印度洋地区的人口可能占世界人口的三分之一，其中大部分生活在发展中国家，脆弱性更高。此外，如上所述，有证据表明，IO海温的年代际变化与全球各种气候影响有关，包括影响美国的一些气候影响。此外，该项目将支持和培训博士后，从而为该研究领域提供劳动力发展。

Decade-to-decade changes in the sea surface temperature (SST) of the Indian Ocean (IO) have been implicated in a variety of worldwide climatic fluctuations, including variations in Indian monsoon rainfall, changes in the frequency of cyclones in the Arabian Sea, and changes in drought frequency in the US, the Mediterranean, and parts of Africa. Averaged over the basin, IO SSTs have been increasing since the 1950s, often at a faster rate than SSTs in other tropical oceans, and have continued to increase even during the recent global warming hiatus. The goal of this research is to understand the mechanisms that produce decadal variability of IO SSTs and accompanying variations of sea level pressure (SLP), surface winds, and other meteorological conditions. A particular goal is to identify the separate roles of remote influences from the Pacific sector, and coupled ocean-atmosphere dynamics internal to the IO sector, in generating decadal IO SST variability. The Pacific influence is associated with the interdecadal Pacific oscillation (IPO), a slowly varying pattern of SST anomalies with some resemblance to the more rapidly evolving SSTs of El Nino/Southern Oscillation events. Previous work suggests that the positive phase of the IPO, when SSTs warm over the central equatorial Pacific, can produce uniform warming over the IO. The PI hypothesizes that the warming is caused by strengthening of the Walker circulation, which enhances subsidence over the IO and increases surface insolation by reducing cloudiness. But the more recent observational record shows a continued increase in mean IO SSTs even as the IPO has transitioned to its negative phase, so factors other than the IPO must also play a role in basin-wide IO warming and cooling. While the Pacific influence is linked to uniform SST anomalies, the IO basin contains a second prominent decadal variability mode which is largely independent of the IPO. This mode is an east-west pattern in which warm SSTs in the western half of the basin are accompanied by cold anomalies off the coast of Indonesia, referred to as the Indian Ocean dipole (IOD). The PI hypothesizes that the IOD is driven by coupled atmosphere-ocean dynamics in which subsurface heat transport plays a key role. In addition to attribution of IO variability in terms of internal dynamics and external influences from the Pacific, the project also seeks to understand the role of external forcing, including greenhouse gas-induced warming, solar variability, and anthropogenic aerosols. A variety of statical techniques are applied to diagnose the mechanisms of IO variability in observations, reanalysis products, and climate model simulations. In addition, specialized climate model experiments are performed in which atmosphere-ocean interactions are enabled only in the IO sector to determine the extent to which IO-sector dynamics can produce decadal variability. Complementary experiments are used to determine the extent to which decadal variability in the IO sector is due to coupled atmosphere-ocean dynamics external to the basin. Further climate model experiments examine the role of external forcing by imposing changes in greenhouse gases, aerosols, and solar irradiance.The work is of societal as well as scientific interest given that that conditions in the Indian Ocean affect the weather and climate of the adjacent land region, which is home to perhaps a third of the world's population, much of it in developing countries with heightened vulnerability. Also, as noted above, there is evidence that the decadal variability of IO SSTs are linked to a variety of climatic impacts worldwide, including some that affect the US. In addition, the project would support and train a postdoc, thereby providing workforce development in this research area.