Guilpart E., Vimeux Françoise, Evan S., Brioude J., Metzger J. M., Barthe C., Risi C., Cattani O. (2017). The isotopic composition of near-surface water vapor at the Maido observatory (Reunion Island, southwestern Indian Ocean) documents the controls of the humidity of the subtropical troposphere. Journal of Geophysical Research : Atmospheres, 122 (18), p. 9628-9650. ISSN 2169-897X.
Titre du document
The isotopic composition of near-surface water vapor at the Maido observatory (Reunion Island, southwestern Indian Ocean) documents the controls of the humidity of the subtropical troposphere
Guilpart E., Vimeux Françoise, Evan S., Brioude J., Metzger J. M., Barthe C., Risi C., Cattani O.
Source
Journal of Geophysical Research : Atmospheres, 2017,
122 (18), p. 9628-9650 ISSN 2169-897X
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.
