Publication Date:
2017-08-30
Description:
We present a 1-year long record of the isotopic composition of near-surface water vapor (δ 18 O v ) at the Maïdo atmospheric observatory (Reunion Island, Indian Ocean, 22°S, 55°E) from November 1 st , 2014 to October 31 st , 2015, using Wavelength-Scanned Cavity Ring Down Spectroscopy. Except during cyclone periods where δ 18 O v is highly depleted (-20.5 ‰), a significant diurnal variability can be seen on both δ 18 O v and q v with enriched (depleted) water vapor (mean δ 18 O 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 δ 18 O v diurnal cycle arises from mixing processes for 65 % of cases with two distinct sources of water vapor. We suggest that δ 18 O 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, δ 18 O v record also shows that some nights (15 %) are extremely depleted (mean δ 18 O 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.
Print ISSN:
0148-0227
Topics:
Geosciences
,
Physics