Hydrogen and oxygen isotopic compositions of water vapor over the Bay of Bengal during monsoon

Abstract

[1] δD v and δ 18 O v of~70 water vapor samples collected at 6 and 25 m above sea level over the Bay of Bengal (BoB) during July-August 2012 are reported. This helps characterize the isotopic signature of monsoon vapor. No significant vertical variation is observed in δD v , δ 18 O v , or deuterium excess (defined as δD-8δ 18 O); δD v and δ 18 O v are significantly correlated (r = 0.92) at each height; the deuterium excess values do not, because the variation of δD v and δ 18 O v relative to their uncertainties is much larger than that of the latter. The temporal variations of δD v and δ 18 O v correlate well with air temperature rather than sea surface temperature. The control of normalized humidity on deuterium excess is less prominent. While the distribution of water vapor isotopologues over the BoB is primarily determined by the ocean surface conditions, they are significantly altered by laterally advected vapor from rain en route during the monsoon. Citation: Midhun, M., P. R. Lekshmy, and R. Ramesh (2013), Hydrogen and oxygen isotopic compositions of water vapor over the Bay of Bengal during monsoon, Geophys. Res. Lett., 40,[6324][6325][6326][6327][6328]

Isotopic composition of daily precipitation along the southern foothills of the Himalayas: impact of marine and continental sources of atmospheric moisture

“…Regional thermal gradients are virtually non-existent during ISM; hence, they cannot be used to explain the observed gradual reduction of δ 18 O, with sea surface temperatures in the Bay of Bengal fluctuating between 28 and 29 • C (e.g. Midhun et al, 2013) and mean surface air temperatures at three low-elevation stations of the study transect (Jammu, Jorhat, Dibrugarth) around 28 • C (cf. Table 2).…”

“…cruising the Bay of Bengal during the ISM period (from 13 July to 3 August 2012), varied between ca. −10 and −14 ‰ (Midhun et al, 2013). If one adopts −10 ‰ as a representative δ 18 O value for unaltered oceanic moisture from which monsoon precipitation is formed, and further assumes that this moisture is transported towards the southern foothills of the Himalayas without any noticeable rainout effect, the expected δ 18 O value of the first condensate would be around −1.0 ‰.…”

“…The isotopic patterns of precipitation in the tropics are expected to be different from the sub-tropics and temperate regions due to largescale convection systems, cyclonic storms and a multitude of vapour sources (e.g. Midhun et al, 2013;Lekshmy et al, 2014Lekshmy et al, , 2015. Consequently, the well-established isotope effects such as the amount effect, the temperature effect and the altitude effect are not clearly visible in the precipitation isotope data sets available for the Indian subcontinent (Jeelani and Deshpande, 2017;Deshpande and Gupta, 2012;Deshpande et al, 2010;Warrier et al, 2010;Yavada, 2007).…”

Isotopic composition of daily precipitation along southern foothills of the Himalayas: impact of marine and continental sources of atmospheric moisture

“…Regional thermal gradients are virtually nonexistent during ISM and hence cannot be used to explain the 10 observed heavy-isotope depletion, with sea surface temperatures in the Bay of Bengal fluctuating between 28 and 29°C (e.g. Midhun et al, 2013) and mean surface air temperatures at three low-elevation stations of the studied transect (Jammu, Jorhat, Dibrugarth) around 28°C (cf. Table 2).…”

“…The isotopic patterns of precipitation in the tropics are expected to be different from the sub-tropics and temperate regions due to large scale convection systems, cyclonic storms and multitude of vapour sources (e.g. Midhun et al, 2013;Lekshmy et al, 2014;Lekshmy et al, 2015). Consequently, the well-established isotope effects such as amount effect, temperature effect 20 and altitude effect are not clearly visible in precipitation isotope data sets available for the Indian subcontinent (Deshpande and Gupta, 2012;Deshpande et al, 2010;Warrier et al, 2010).…”