Modeling abrupt excursions in water vapor isotopic variability at Amsterdam Island is a challenge for atmospheric models
| Autor: | Landais, Amaëlle, Agosta, Cécile, Vimeux, Françoise, Magand, Olivier, Solis, Cyrielle, Cauquoin, Alexandre, Risi, Camille, Fourré, Elise, Leroy-Dos Santos, Christophe, Cattani, Olivier, Minster, Bénédicte, Casado, Mathieu |
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| Jazyk: | angličtina |
| Rok vydání: | 2023 |
| Zdroj: | XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG) |
| Popis: | In order to complement the picture of the atmospheric water cycle over the Indian Ocean, a main moisture source for Antarctica, we have continuously monitored water vapor isotopes at Amsterdam Island (37.7983 °S, 77.5378 °E) since November 2019. We present here the first 2-year-long water vapor isotopic record monitored on site.We show that the vapor isotopic composition largely follows the vapor mixing ratio, as expected in marine boundary layers, but we evidence 13 periods of a few days where the correlation between δ18O and mixing ratio collapses. These periods are associated with abrupt negative excursions of vapor δ18Ο, often occurring toward the end of precipitation events. We evaluate two isotope-enabled global atmospheric models nudged to the ERA5 reanalyses, and we found than one of them, ECHAM6-wiso, is able to reproduce most of the sharp negative δ18O excursions, while the other, LMDZ6-iso, is only able to reproduce excursions associated with the strongest atmospheric subsidence. Using model outputs together with back-trajectories and with other observations obtained in parallel on site, we conclude that these events are caused by the vertical advection of moist and d18O-depleted air from upper levels to the surface, at the rear of precipitation events. These events are imprinted in the surface isotopic profile and not in the mixing ratio. Our study highlights that water isotope observations at Amsterdam Island monitor synoptic-scale atmosphere dynamics in the Indian Ocean, and can be used as a benchmark to evaluate low-level vertical dynamics in isotope-enabled atmospheric models. The 28th IUGG General Assembly (IUGG2023) (Berlin 2023) |
| Databáze: | OpenAIRE |
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