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2003-2006 (12 locations in 2003 and 18 locations in 2004-2006). The amount of rainfall along with air temperature and humidity were also measured. The meteoric water line developed for India using isotopic data of precipitation samples, namely, d 2 H = 7.93 (±0.06) × d18 O + 9.94(±0.51) (n = 272, r 2 = 0.98), differs slightly from the global meteoric water line. Regional meteoric water lines were developed for several Indian regions (i.e., northern and southern regions of India, western Himalayas) and found to be different from each other (southern Indian meteoric water line, slope is 7.82, intercept or D excess is 10.23; northern Indian meteoric water line, slope is 8.15, intercept is 9.55) which is attributed to differences in their geographic and meteorological conditions and their associated atmospheric processes (i.e., ambient temperature, humidity, organ, and source of vapor masses). The local meteoric water lines developed for a number of locations show wide variations in the slope and intercept. These variations are due to different vapor sources such as the northeast (NE) monsoon that originates in the Bay of Bengal; the southwest monsoon (SW) that originates in the Arabian Sea; a mixture of NE and SW monsoons; retreat of NE and SW monsoons and western disturbances that originate in the Mediterranean Sea. The altitude effect in the isotopic composition of precipitation estimated for western Himalayan region also varies from month to month.

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[1] Results of a 4 year (2005)(2006)(2007)(2008)) study of stable isotopic composition of daily rain and ground-level vapor (GLV) at a semiarid station in western India are reported. The GLV samples were collected by complete cryogenic trapping. The sampling was mostly limited to the rainy season (June, July, August, and September) and about a month before and after. The maximum number of samples was collected during the year 2007. The GLV has a steady baseline d18 O and dD composition without distinguishable seasonal differences. The d-excess of GLV indicates that its isotopic composition has a significant contribution from kinetic evaporation of nonlocal water sources. During a rain event, GLV rapidly interacts with raindrops and tends to move toward isotopic equilibrium. On cessation of rain, the d18 O and dD of GLV quickly return to the typical baseline values. Therefore, use of isotopic composition of monthly rainfall for estimating average monthly isotopic composition of GLV can lead to erroneous results. Within a rainy season, certain large rain events have depleted d18 O and dD values compared to other equally large rain events with significantly enriched d18 O and dD. These isotopic differences are apparently not related to amount of rainfall. Variable magnitude of evaporation from falling raindrops and/or cloud liquid water fraction cannot explain the observed differences. Instead, it is shown that varying source regions (Arabian Sea or Bay of Bengal) and cloud top temperature may be responsible for observed differences.Citation: Deshpande, R. D., A. S. Maurya, B. Kumar, A. Sarkar, and S. K. Gupta (2010), Rain-vapor interaction and vapor source identification using stable isotopes from semiarid western India,

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