HDO Modeling in a 3D Climate Model of Venus

HDO is an isotopic form of water that can provide clues about the history and evolution of water. By comparing the ratio of HDO to H2O on Venus with that of other planets or comets that have similar origins, we can estimate how much water Venus received during its formation and early evolution. The Venus Global Climate Model (VGCM) developed in several laboratories (LMD, LATMOS) of Institute Pierre-Simon Laplace (IPSL, in Paris area) can simulate the dynamics of the Venusian atmosphere. However, VGCM does not include the influence of HDO. In this work, we dedicate to implement HDO as a new tracer into the model to investigate the influence of HDO fractionation and spatial and temporal distribution. Two new tracers are added, HDO(g) and HDO(l), to account for both the vaporous phase and the condensed phase. As an isotope of water, HDO participates in many chemical and physical processes where water is involved. Therefore, we implement HDO(g) and HDO(l) in every routine where H₂O(g) and H₂O(l) are present except for photochemical processes. The initial value for HDO is set to 10^-2 times the value of H₂O. HDO(l) is then calculated by using the equation of the isotopic fractionation of water during condensation. The results indicate that when there is no isotopic fractionation, HDO(g) and HDO(l) are exact copies of H₂O(g) and H₂O(l).