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Importance of the advection scheme for the simulation of water 1 isotopes over Antarctica by atmospheric general circulation models: a case study for present-day and Last Glacial Maximum with LMDZ-iso

Abstract : Atmospheric general circulation models (AGCMs) are known to have a warm and isotopically enriched 13 bias over Antarctica. We test here the hypothesis that these biases are consequences of a too diffusive advection. 14 Exploiting the LMDZ-iso model, we show that a less diffusive representation of the advection, especially on the 15 horizontal, is very important to reduce the bias in the isotopic contents of precipitation above this area. The 16 choice of an appropriate representation of the advection is thus essential when using GCMs for paleoclimate 17 applications based on polar water isotopes. Too much diffusive mixing along the poleward transport leads to 18 overestimated isotopic contents in water vapor because dehydration by mixing follows a more enriched path 19 than dehydration by Rayleigh distillation. The near-air surface temperature is also influenced, in a more minor 20 way, by the diffusive properties of the advection scheme directly via the advection of the air and indirectly via 21 the radiative effects of changes in high cloud fraction and water vapor. A too diffusive horizontal advection 22 increases the temperature and so also contributes to enrich the isotopic contents of water vapor over Antarctica 23 through a reduction of the distillation. The temporal relationship, from Last Glacial Maximum (LGM) to present-24 day conditions, between the mean annual near-air surface temperature and the water isotopic contents of 25 precipitation for a specific location can also be impacted, with significant consequences on the paleo-26 temperature reconstruction from observed changes in water isotopes. 27
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Submitted on : Tuesday, November 5, 2019 - 10:04:38 AM
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Alexandre Cauquoin, Camille Risi, Etienne Vignon. Importance of the advection scheme for the simulation of water 1 isotopes over Antarctica by atmospheric general circulation models: a case study for present-day and Last Glacial Maximum with LMDZ-iso. Earth and Planetary Science Letters, Elsevier, 2019, ⟨10.1016/j.epsl.2019.115731⟩. ⟨insu-02346765⟩

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