Abstract
Isotopic analysis of precipitation over the Andaman Island, Bay of Bengal was carried out for the year 2012 and 2013 in order to study the atmospheric controls on rainwater isotopic variations. The oxygen and hydrogen isotopic compositions are typical of the tropical marine sites but show significant variations depending on the ocean-atmosphere conditions; maximum depletion was observed during the tropical cyclones. The isotopic composition of rainwater seems to be controlled by the dynamical nature of the moisture rather than the individual rain events. Precipitation isotopes undergo systematic depletions in response to the organized convection occurring over a large area and are modulated by the integrated effect of convective activities. Precipitation isotopes appear to be linked with the monsoon intraseasonal variability in addition to synoptic scale fluctuations. During the early to mid monsoon the amount effect arose primarily due to rain re-evaporation but in the later phase it was driven by moisture convergence rather than evaporation. Amount effect had distinct characteristics in these two years, which appeared to be modulated by the intraseasonal variability of monsoon. It is shown that the variable nature of amount effect limits our ability to reconstruct the past-monsoon rainfall variability on annual to sub-annual time scale.
Highlights
Moisture generation and transportation is an important aspect of the hydrological cycle; this is especially important in the context of Indian monsoon as the agricultural and economic activities of the country significantly depend on summer monsoon rainfall
Transport may alter source signature[7]. In this regard it is crucial to improve our understanding of how moisture sources, convective activities affect precipitation isotopes, which will help in interpreting the paleoclimatic archives, such as tree rings, ice cores, cave deposits etc[2]
Whether the rain water isotopic composition is controlled by rainfall events or by the moisture fluxes that is believed to influence the intraseasonal characteristics of monsoon[4]
Summary
Moisture generation and transportation is an important aspect of the hydrological cycle; this is especially important in the context of Indian monsoon as the agricultural and economic activities of the country significantly depend on summer monsoon rainfall. The BoB possesses certain unique characteristics which are believed to play an important role in moisture generation and transport process It maintains a relatively high SST especially during the monsoon season than the rest of the Indian Ocean which often exceeds 28 °C favouring convection[1]. Identification of moisture sources consists of an important aspect of the hydrological study which can address issues like understanding the monsoon variability, water security, managing and mitigating the extreme rainfall events caused by tropical cyclone etc. Apart from this it is useful in paleoclimatic reconstruction and future climate change scenario. Whether the rain water isotopic composition is controlled by rainfall events or by the moisture fluxes that is believed to influence the intraseasonal characteristics of monsoon[4]
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