Development of an isotopic configuration of LMDZ

Since 2008, an isotopic configuration of the successive LMDZ versions, named LMDZ-iso, has been developped. Several isotopic species of water coexist in nature: H216O, the most abundant one, but also HDO (D for Deuterium), HTO (T for tritium), H218O or H217O. These different species can now be transported all along the water cycle in LMDZ (Risi et al 2010a).

Water tagging has also been implemented. The user can tag water following some criteria (e.g. water evaporating from a given region, or going through a given region, or undergoing a given process) and track this water all along the water cycle (Risi et al 2010b).

LMDZ-iso has been used for different kinds of applications:

  1. Evaluate the representation of moist processes in models. Due to isotopic fractionation during phase changes, the isotopic composition of water tracks the various phases changes along the water cycle. In particular, the isotopic composition of water vapor or of precipitation is sensitive to processes such as rain reevaporation, convective detrainment or unsaturated downdrafts (e.g. Risi et al 2008). The emergence of a broad range of new satellite datasets (TES, SCIAMACHY, GOSAT, MIPAS, ACE, IASI) allow us to evaluate the three-dimensional distribution of water vapor isotopic composition (Risi et al 2012).
  2. Analyze land surface-atmosphere interactions. The isotopic composition is sensitive to the evaporative origin of water vapor, continental or oceanic. Isotopic measurements could help quantify continental recycling. With this purpose, water isotopes were also included in the land surface model ORCHIDEE (Risi et al 2012).
  3. Interpret paleoclimatic records. Water isotopic composition of precipitation is recorded in a broad range of paleoclimatic archives, from ice cores to speleothems and tree rings. What do these isotopic records tell us abut the past climate variability? To address this question, paleoclimatic simulations using LMDZiso are performed (e.g. Liu et al 2014). The zoomed configuration is particularly useful for simulating paleo records in high terrain regions (e.g. Eagle et al 2013).
  4. Exploitation of field compaign measurements. To better understand what controls the isotopic compsoition of water vapor, field campaigns are organized. The emergence of new laser insruments to continuously measure the in-situ water vapor isotopic composition makes isotopic monitoring during field campaigns more and more widespread. LMDZiso is routinely used to help and analyse measurements during these campaigns (e.g. Steen-Larsen et al 2013). Again, the zoomed configuration is particularly useful for this purpose (e.g. Vimeux et al 2011).

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