Isotopic variation in Indian Monsoon precipitation: Records from Bombay and New Delhi

Abstract

[1] The stable isotope composition and the tritium content of precipitation analysed within the framework of the IAEA/ WMO Global Network for Isotopes in Precipitation (GNIP) have been evaluated for the Indian stations Bombay and New Delhi representing two different regions of the Indian Monsoon. The rainfall at New Delhi is controlled by northwest moving depressions with diverse routes and variable transit times over the land subsequent to their formation at the head of Bay of Bengal. In contrast, Bombay rains are caused by spatially locked cyclonic vortices on the west coast of India with continuous supply of oceanic moisture resulting in negligible isotopic variation over the rainy months. The evaluation of the long-term isotope data of the two stations provided specific information on monsoon rain formation mechanism and the moisture source of the monsoon rains. The average isotope ratios clearly represent an imprint of oceanic moisture during the summer monsoon and of continental moisture during the winter monsoon period. The rainout efficiency is about 30% in case of Bombay (representative of west coast region) and about 56% in case of New Delhi (representative of north Indian Plains). Furthermore, the isotope data indicate that the moisture for low-intensity rains during the post-monsoon phase originates from the Asian continent.

Synoptic-scale variation of δ 18O in summer monsoon rainfall at Lijiang, China

“…2, the simulated δ 18 O values at Bangkok from 7th October to 14th October are anomalously low, also probably resulting from the recycling of monsoon precipitation in the late monsoon month. Bhattacharya et al [25] reported that the δ 18 O values in precipitation in New Delhi after the monsoon months (October and November) are also low, moreover, the deuterium excess values in this period are almost equal to those in the summer monsoon months, suggesting that the influence of recycling processes of monsoon precipitation on δ 18 O values after the monsoon months is still significant in New Delhi. In addition, the deuterium excess values in Yamuna River water during October are higher because of recycled moisture contributions to precipitation [10] .…”

Isotopic variations in precipitation at Bangkok and their climatological significance

“…From the wind field in winter, we can see clearly that the northeasterly wind and the equatorial easterlies converge between the islands of Taiwan and the Philippines, finally blowing towards the Indo-China Peninsula (Figure 1b (Ingraham and Taylor, 1991). Moreover, precipitation produced from a continental air mass has a higher 3 H content than that from a maritime air mass (Rozanski et al, 1991;Bhattacharya et al, 2003).…”

Water vapour source identification for daily rain events at Ahmedabad in semi‐arid western India: wind trajectory analyses

“…In last two decades, stable isotope variations in precipitation, groundwater and atmospheric water vapour have been used to identify water vapour source for the rainfall at different locations (Krishnamurthy and Bhattacharya, 1991;Bhattacharya et al, 2003;Deshpande et al, 2003;Gupta et al, 2005;Sengupta and Sarkar, 2006;Breitenbach et al, 2010;Deshpande et al, 2010;Warrier et al, 2010). In these studies, it has not been possible to unambiguously ascribe the observed precipitation isotope variation to a particular causality (namely, vapour source, amount of rainfall, temperature, elevation, relative humidity variation, sub-cloud evaporation, continental recycling rainout history).…”