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- Title
The isotopic composition of near-surface water vapor at the Maïdo observatory (Reunion Island, southwestern Indian Ocean) documents the controls of the humidity of the subtropical troposphere.
- Authors
Guilpart, Etienne; Vimeux, Françoise; Evan, Stéphanie; Brioude, Jérôme; Metzger, Jean-Marc; Barthe, Christelle; Risi, Camille; Cattani, Olivier
- Abstract
We present a 1 year long record of the isotopic composition of near-surface water vapor (δ18O v) at the Maïdo atmospheric observatory (Reunion Island, Indian Ocean, 22°S, 55°E) from 1 November 2014 to 31 October 2015, using wavelength-scanned cavity ring down spectroscopy. Except during cyclone periods where δ18O v is highly depleted (−20.5‰), a significant diurnal variability can be seen on both δ18O v and q v with enriched (depleted) water vapor (mean δ18O 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 δ18Ov diurnal cycle arises from mixing processes for 65% of cases with two distinct sources of water vapor. We suggest that δ18Ov 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, δ18O v record also shows that some nights (15%) are extremely depleted (mean δ18Ov 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.
- Publication
Journal of Geophysical Research. Atmospheres, 2017, Vol 122, Issue 18, p9628
- ISSN
2169-897X
- Publication type
Article
- DOI
10.1002/2017JD026791