P2C2: Testing Whether Internal Dynamics is the Pacemaker of the Indian Summer Monsoon Variability on Decadal to Centennial Timescales

研究人员的目标是开发千年长度（1000 - 2000年）、绝对年代和高分辨率（年际到次年代际）的洞穴化石氧同位素记录，这些洞穴来自印度西部、南部和北部的洞穴。本研究的目的是在区域水平上提供类似于不同宏观气象单位的仪器记录的印度夏季风（ISM）历史。研究者指出，与ISM相关的季节性降水倾向于由两个时间尺度的变率主导：(1)年际变化，这归因于缓慢演变的外部边界条件（如热带太平洋海温），以及(2)由内部动力学驱动的季节内振荡（如10-20天和30-60天的活动中断周期），这些振荡调节对流和嵌入式天气系统的传播。在年际和更长时间尺度上，没有确凿的证据表明这两种强迫中的哪一种是ISM变率的主要起搏器。本研究的前提是，印度中部和东北部现有的仪器校准和年际分解的氧同位素洞穴记录支持这样的假设，即在季风季节以混乱的降雨变化形式表现出来的内部强迫是ISM变率的主要起跳器。在现有数据的基础上，研究将验证这样一个工作假设，即在十年和百年的时间尺度上，主动中断周期频率特征的系统变化是ISM响应外部边界强迫变化的媒介。更广泛的影响包括对印度季风动力学的更好理解，以及来自目前代表性不足群体的本科生对研究工作的支持。

The researcher aims to develop millennial-length (1,000-2,000), absolute dated, and high resolution (inter-annual to sub-decadal) oxygen isotope records of speleothems from caves located in western, southern, and northern India. The goal of the research is to provide Indian summer monsoon (ISM) histories at the regional level that are analogous to the instrumental records from distinct macro-meteorological units.The investigator notes that seasonal precipitation associated with the ISM tends to be dominated by two time scales of variability: (1) interannual variations which are attributed to slowly evolving external boundary conditions (e.g., tropical Pacific SST), and (2) intraseasonal oscillations (e.g., 10-20 and 30-60 day active-break cycles) which are driven by internal dynamics that modulate convection and propagation of embedded synoptic systems. There is no conclusive evidence to indicate which one of these two forcings is the dominant pacemaker of ISM variability on interannual and longer timescales.The premise of the research is that existing instrumentally-calibrated and inter-annually resolved oxygen isotope speleothem records from central and northeast India supports the hypothesis that the internal forcing, which manifests in the form of chaotic rainfall variability during the monsoon season, is the dominant pacemaker of ISM variability. On the basis of the current data, the research will test the working hypothesis that, on decadal and centennial timescale, systematic changes in the frequency characteristics of active-break cycles serve as a medium by which ISM responds to changes in the external boundary forcing.The broader impacts involve a better understanding of Indian Monsoon dynamics and the support of undergraduates in the research effort from currently under-represented groups.