Exploring the Causes for Indian Ocean Decadal Climate Variability

印度洋（IO）海表面温度（SST）的十年到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。 从流域平均来看，自1950年代以来，IO SST一直在增加，其速度往往快于其他热带海洋的SST，即使在最近的全球变暖间歇期也继续增加。 本研究的目的是了解产生IO SST的年代际变化和伴随的海平面气压（SLP），地面风和其他气象条件的变化的机制。 一个特别的目标是确定来自太平洋部门的远程影响的单独作用，以及IO部门内部的耦合海洋-大气动力学，在产生十年IO SST变化。 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SST异常模式，与厄尔尼诺/南方涛动事件中更快速演变的SST有一些相似之处。 以前的工作表明，IPO的积极阶段，当SST温暖的赤道太平洋中部，可以产生均匀的变暖IO。 PI假设变暖是由步行者环流的加强引起的，这增强了IO上空的沉降，并通过减少云量来增加地面日射。 但最近的观测记录显示，即使IPO已经过渡到其负阶段，平均IO SST也在持续增加，因此IPO以外的因素也必须在全流域IO变暖和冷却中发挥作用。 虽然太平洋的影响与统一的SST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，其中海盆西半部的温暖SST伴随着印度尼西亚沿海的寒冷异常，称为印度洋偶极子（IOD）。 PI假设IOD是由耦合的大气-海洋动力学驱动的，其中次表层热传输起着关键作用。 除了在内部动力学和来自太平洋的外部影响方面归因于IO变化之外，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，太阳变化和人为气溶胶。 在观测、再分析产品和气候模式模拟中，各种统计技术被应用于诊断IO变率的机制。 此外，专门的气候模式实验中进行的大气-海洋相互作用，使只有在IO部门，以确定在何种程度上IO部门动态可以产生十年变化。 互补的实验是用来确定在IO部门的十年变化的程度是由于耦合的大气-海洋动力学外部的盆地。 进一步的气候模式实验通过改变温室气体、气溶胶和太阳辐照度来研究外部强迫的作用，这项工作具有社会和科学意义，因为印度洋的条件影响着邻近陆地地区的天气和气候，而该地区可能是世界人口的三分之一，其中大部分在脆弱性较高的发展中国家。 此外，如上所述，有证据表明IO SST的年代际变化与全球范围内的各种气候影响有关，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，从而在这一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.