Controls on stable isotopic characteristics of water vapour over Thailand

Abstract

This study examined the weekly water vapour isotopic composition (δ 18 O v ) in Thailand. The water vapour was cryogenically collected from eight sites across the country. Two observational samples were collected over one 24-h period each week (a daytime and a night-time sample), from September 2013 to September 2014. The primary aim was to investigate the environmental factors influencing water vapour isotopes. The results revealed differences in water vapour isotopic values between day and night samples. Three periods of depleted δ 18 O v were associated with largescale convective systems in September, December, and May. The statistical relationship between the climate variables and water vapour isotopes indicated that the amount of precipitation and relative humidity were the primary controls on both diurnal and seasonal isotopic variability. The temperature did not affect the δ 18 O v , mainly because the atmospheric processes are a function of vertical convection rather than temperature in tropical regions. The water vapour deuterium excess (d-excess) showed greater variability in 2013 than in 2014. The d-excess variation reflected the differences in convection occurring in the day and night. In addition, the vapour phase data were combined with the local meteoric water line to identify the local water vapour line and the interaction between the isotopic composition of water vapour and liquid water. The water vapour isotopic patterns paralleled the precipitation isotopes on rainy days because of equilibrium isotopic exchange. Water vapour and precipitation were isotopically similar under low humidity but showed greater differences from each other under wetter conditions. The study results provide insight into water vapour isotopic characteristics in tropical regions and constrain the role of large-scale atmospheric processes relative to isotopic variability of water vapour in Thailand and nearby countries. K E Y W O R D S convection, d-excess, monsoon, rainout effect, tropics, vapour isotopes, δ 18 O, δ 2 H | INTRODUCTIONStable water isotopes can be used as environmental tracers in hydrological and climatic applications (Craig, 1961;Gat & Dansgaard, 1972;Moser & Stichler, 1974;Stewart, 1975). The analysis of stable isotopes of hydrogen and oxygen (δ 2 H and δ 18 O) can extract useful information about the global hydrological cycle and reconstruct paleoclimatic conditions with high accuracy (Dansgaard et al., 1993;Jouzel et al., 1982;Meckler et al., 2012). The stable isotopes in water vapour represent an isotopic signal that must be mapped accurately to better

Ocean air masses from the East Asian monsoon dominate the land‐surface atmospheric water cycles in the coastal areas of Liaodong Bay, Northeast China

“…The long-time variations of atmospheric water vapour δ 2 H, δ 18 O and d-excess in the reed wetlands of Liaodong Bay were different from those of the other research site (Fiorella et al, 2018;Laonamsai et al, 2021;Lee et al, 2006;Wen et al, 2010). Apart from the noticeable intraseasonal variations occurring in each year, there were distinct inter-annual cycles for atmospheric water vapour isotopes between 2019 and 2020 (Figure 2).…”

“…precipitation and vertical atmospheric mixing) and local vegetation properties (e.g. soil evaporation and plant transpiration), the signatures of land‐surface water vapour δ vapor contain subtle information concerning water movements between the Atmospheric Boundary Layer (ABL) and Earth's surfaces (Huang & Wen, 2014; Laonamsai et al, 2021; Lee et al, 2006). Thus, there is a growing interest in high‐resolution measurements of atmospheric water vapour δ vapor from ecosystem to regional scales (Galewsky et al, 2016; Steen‐Larsen et al, 2013; Wei & Lee, 2019).…”

Innovative Assessment of Mun River Flow Components through ANN and Isotopic End-Member Mixing Analysis

“…The mean δ 18 O values in precipitation range from -6.53‰ to -5.85‰ across different locations (averaged -6.11‰ for all samples), demonstrating the influence of temperature, altitude, and rainfall amount on isotopic fractionation. δ 2 H values (-136.01‰ to 26.75‰, averaged -39.65‰) and d-excess in precipitation also vary, with d-excess values (-19.82‰ to 20.85‰, averaged 9.25‰) providing insights into the evaporative conditions at the moisture source regions and during raindrop fall [55,56]. The range of d-excess values, from negative to significantly positive, underscores the complex interplay between local and regional hydrological processes.…”

Innovative Assessment of Mun River Flow Components through ANN and Isotopic End-Member Mixing Analysis

“…The mean δ 18 O values in precipitation range from −6.53‰ to −5.85‰ across different locations (averaged −6.11‰ for all samples), demonstrating the influence of temperature, altitude, and rainfall amount on isotopic fractionation. δ 2 H values (−136.01‰ to 26.75‰, averaged −39.65‰) and d-excess in precipitation also vary, with d-excess values (−19.82‰ to 20.85‰, averaged 9.25‰) providing insights into the evapo-rative conditions at the moisture source regions and during raindrop fall [58,59]. The range of d-excess values, from negative to significantly positive, features the complex interplay between local and regional hydrological processes.…”