资源环境科技发展态势分析平台

We present a 1 year long record of the isotopic composition of near-surface water vapor (delta O-18(v)) at the Maido atmospheric observatory (Reunion Island, Indian Ocean, 22 degrees S, 55 degrees E) from 1 November 2014 to 31 October 2015, using wavelength-scanned cavity ring down spectroscopy. Except during cyclone periods where delta O-18(v) is highly depleted (-20.5%), a significant diurnal variability can be seen on both delta O-18(v) and q(v) with enriched (depleted) water vapor (mean delta O-18(v) is -13.4% (-16.6%)) and moist (dry) conditions (mean q(v) is 9.7 g/kg (6.4 g/kg)) during daytime (nighttime). We show that d18Ov diurnal cycle arises from mixing processes for 65% of cases with two distinct sources of water vapor. We suggest that delta O-18(v) diurnal cycle is controlled by an interplay of thermally driven land-sea breezes and upslope-downslope flows, bringing maritime air to the observatory during daytime, whereas at night, the observatory is above the atmospheric boundary layer and samples free tropospheric air. Interestingly, delta O-18(v) record also shows that some nights (15%) are extremely depleted (mean delta O-18(v) is -21.4%). They are among the driest of the record (mean q(v) is 2.9 g/kg). Based on different modeling studies, we suggest that extreme nocturnal isotopic depletions are caused by large-scale atmospheric transport and subsidence of dry air masses from the upper troposphere to the surface, induced by the subtropical westerly jet.