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

这位研究人员的目标是开发印度西部、南部和北部洞穴中洞穴的千年长度(1,000-2,000)、绝对年代和高分辨率(年际到亚十年)的氧同位素记录。这项研究的目的是提供印度夏季风(ISM)在区域一级的历史，类似于来自不同宏观气象单位的仪器记录。调查者指出，与ISM有关的季节降水往往由两个时间尺度的变化主导：(1)可归因于缓慢演变的外部边界条件(例如热带太平洋海温)的年际变化；(2)由内部动力驱动的季节内振荡(例如10-20天和30-60天的活动-中断周期)，这些内部动力调制了嵌入的天气系统的对流和传播。没有确凿的证据表明，在年际和更长的时间尺度上，这两种强迫中的哪一种是ISM变率的主要起搏器。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辨的氧同位素洞穴记录支持这样的假设，即内部强迫是ISM变率的主要起搏器，它在季风季以混乱的降雨变率的形式表现出来。在现有数据的基础上，这项研究将检验工作假设，即在十年和百年时间尺度上，活动-休息周期频率特征的系统变化作为ISM对外部边界强迫变化做出反应的媒介。更广泛的影响包括更好地理解印度季风动力学，以及来自目前代表不足的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.