Coupled Processes that Determine the Basic States of Tropical Indian Ocean SeaSurface-Temperature (SST) and Asian Monsoon Precipitation

拟议工作的总体目标是找出在耦合模式中模拟印度洋季风持续误差的主要原因。该项目将确定对塑造印度洋季风降水基本状态至关重要的海-气相互作用耦合过程，并调查基本状态对变化的敏感性。这项研究将通过研究生和博士后研究员的支持，帮助培训年轻的气候科学家。海洋-大气耦合模式(地球模拟器的大气-海洋-海冰耦合模式，CFES)将被用作检验以下三个假设的工具：(I)在印度洋季风区以及在热带深处，发生深对流的必要条件是润湿自由对流层的过程，例如，暴露于蒸发的对流降水的夹带率和比例。(2)季风期间西南印度洋的正降水误差导致赤道西风减弱。弱东风反过来削弱了维特基急流，因此，温暖的水平流到东印度洋。此外，弱西风带南侧的卷风加深了西南印度洋的温跃层。由此导致的温度结构变化导致近赤道海表面温度(SST)异常，影响随后季节的季风，包括北半球夏季南亚上空错误的干燥条件。(3)由于降水和河流径流以及垂直混合、沿海波浪和水平输送造成的淡水流入，使孟加拉湾北部和印度洋东部的上层海洋分层。在某些情况下，盐度分层强烈到足以产生逆温，这抑制了北半球冬季海温的冷却，并有助于在下一个有利于深层对流的北半球夏季保持温暖的海温。将对现有的CFES模拟进行诊断，并与观测结果进行比较。此外，还将进行旨在隔离关键进程和探索解决方案对这些进程的敏感性的系统实验。在确定了这些过程之后，我们将研究它们在社区气候系统模式(CCSM4)中的参数化。这一努力将带来洞察力，有可能导致模型改进。

The overall goal of the proposed work is to identify the major causes for the persistent errors in simulating the Indian-Ocean monsoon in coupled models. This project will identify coupled air-sea interaction processes that are critical for shaping the basic state of monsoon precipitation in the Indian Ocean as well as investigate the sensitivity of the basic state to variations The research will help to train young climate scientists through the support of graduate students and a postdoctoral fellow. A coupled ocean-atmosphere model (the coupled atmosphere-ocean-sea ice model for the Earth Simulator, CFES) will be used as a tool to examine the following three hypotheses: (i) In the Indian-Ocean monsoon region as well as in the deep tropics, necessary conditions for the occurrence of deep convection are processes that moisten the free troposphere, e.g., the entrainment rate and fraction of convective precipitation exposed to evaporate. (ii) Positive precipitation errors in the southwestern Indian Ocean during the intermonsoons lead to weakened equatorial westerlies. The weak easterlies in turn weaken the Wyrtki Jets and, hence, the advection of warm water to the eastern Indian Ocean. Furthermore, wind curl on the southern flank of the weak westerlies deepens the thermocline in the southwestern Indian Ocean. The resulting changes in temperature structure lead to near-equatorial sea surface temperature (SST) anomalies that impact the monsoon in subsequent seasons, including erroneous dry conditions over South Asia during boreal summer. (iii) Freshwater influx due to precipitation and river run-off along with vertical mixing, coastal waves and horizontal transport stratifies the upper ocean over the northern Bay of Bengal and eastern Indian Ocean. In some instances, the salinity stratification is intense enough to create a temperature inversion, which inhibits cooling of SSTs during boreal winter and aids the maintenance of warm SSTs during the next boreal summer that is conducive for deep convection. Existing CFES simulations will be diagnosed and compared to observations. In addition, systematic experiments designed to isolate key processes and to explore the sensitivity of solutions to those processes, will be carried out. Having identified such processes, their parameterization in Community Climate System Model (CCSM4) will be examined. This effort will lead to insights that have the potential to lead to model improvements.