Evaluation of lower stratospheric water vapor variability in a state-of-the art climate model with the new MIPAS2D global observational dataset

Global variations of water vapor into the lower stratosphere (LS) are important drivers of decadal surface climate change. Therefore, assessing water vapor distribution and variability in the LS for climate models is a key issue. This evaluation is performed in a long-term simulation performed with a state-of-the-art climate model. The model has a well-resolved stratosphere with a high vertical resolution and is fully coupled to a dynamical ocean model. The model simulation is compared with the MIPAS2D observational data. MIPAS2D is a new database of physical and chemical quantities obtained from 10 years of observations made by MIPAS onboard ENVISAT. MIPAS2D is homogenous in time and uses a full 2D tomographic retrieval approach that enables to account for the horizontal inhomogeneity of the atmosphere. It includes all MIPAS main targets (p, T, H2O, O3, HNO3, CH4, N2O, NO2) along with other minor species. The data have been obtained on a fixed vertical grid (from 6 to 68 km) and on two horizontal grids: one at fixed latitudes and one on the average lat of MIPAS scans. This new dataset is fully global, with a fixed grid, homogenous in time and freely available. It is therefore well suited for comparison with global climate model simulations. The evaluation exercise focuses on the impact of the ocean coupling and the representation of the tropical stratospheric dynamics on the modeled LS water vapor distribution and variability at intraseasonal and interannual timescales.