Modulation of the Precipitation Isotopes by the Dynamic and Thermodynamic Variables of the Atmosphere in Southern Parts of India

The isotopic values of rainfall in the southern parts of India exhibit strong seasonality. Such a contrast in isotopic values arises mainly due to the seasonal reversal of the monsoon winds. During the summer monsoon season, moisture is primarily transported from the Arabian Sea, while during the winter, it is sourced mainly from the Bay of Bengal. Additionally, atmospheric processes contribute to these differences. We collected precipitation samples from a southern Indian site and two neighboring island locations to study their isotopic characteristics from intra-seasonal to seasonal timescale. Oxygen isotopes in the marine environment seem to respond differently to the surface and tropospheric temperature than their counterparts from the land region. The seasonal isotopic gradient in the marine environment appears to be modulated by the tropospheric temperature anomaly. Oxygen isotopic values showed a strong association with the Webster-Yang monsoon index. Two distinct clusters were formed when the oxygen isotopes were plotted against the above-mentioned monsoon index. The formation of these clusters indicates the precipitation isotopes' response to moisture dynamics, which significantly change during the transition phase of the southwest to the northeast monsoon. Finally, we examine the potential of the precipitation isotopic records in studying the monsoon process, viz, the use of precipitation isotopes in characterizing the thermodynamical properties of the atmosphere and estimating the summer monsoon withdrawal phase.