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

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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.