MUSICA MetOp/IASI {H<sub>2</sub>O,<i>δ</i>D} pair retrieval simulations for validating tropospheric moisture pathways in atmospheric models

Abstract

Abstract. The project MUSICA (MUlti-platform remote Sensing of Isotopologues for investigating the Cycle of Atmospheric water) has shown that the sensor IASI aboard the satellite MetOp can measure the free tropospheric {H2O,δD} pair distribution twice per day on a quasi-global scale. Such data are very promising for investigating tropospheric moisture pathways, however, the complex data characteristics compromise their usage in the context of model evaluation studies. Here we present a tool that allows for simulating MUSICA MetOp/IASI {H2O,δD} pair remote sensing data for a given model atmosphere, thereby creating model data that have the remote sensing data characteristics assimilated. This model data can then be compared to the MUSICA data. The retrieval simulation method is based on the physical principles of radiative transfer and we show that the uncertainty of the simulations is within the uncertainty of the MUSICA MetOp/IASI products, i.e. the retrieval simulations are reliable enough. We demonstrate the working principle of the simulator by applying it to ECHAM5-wiso model data. The few case studies clearly reveal the large potential of the MUSICA MetOp/IASI {H2O,δD} data pairs for evaluating modelled moisture pathways. The tool is made freely available in form of MATLAB and Python routines and can be easily connected to any atmospheric water vapour isotopologue model.

From climatological to small scale applications: Simulating water isotopologues with ICON-ART-Iso (version 2.1)

“…In winter, this may also be the case, but there are only few humid values simulated at all. In general, the model shows a similar behavior as ECHAM5-wiso, the results of which are presented by Schneider et al (2017).…”

“…In addition, Schneider et al (2017) show in a sensitivity study that errors on the order of 10% in this value have only a limited influence on the averaging kernels as simulated by the Retrieval Simulator. From the output of the Retrieval Simulator, values were only used where the sensitivity metric s err < 0.05, as recommended by Schneider et al (2017). This assures meaningful results.…”

“…There is also a daily cycle in H 2 O in the tropics: During morning overpasses, H 2 O values are higher than in the evening. Schneider et al (2017) argue that this is due to the cloud filter, which removes areas of heavy convection in the evening. In the morning, the clouds have disappeared, but high humidity remains, especially in the lower troposphere.…”

“…In doing so, the section closely follows the case studies presented by Schneider et al (2017), who compare IASI and data from the global, hydrostatic model ECHAM5-wiso (Werner et al, 2011). software is used for simulating the MUSICA averaging kernel, using the atmospheric state of the model atmosphere.…”

“…In the retrieval process, the satellite radiance measurements are used for estimating the deviation of the actual atmospheric state from the a priori assumed state, where it is important to note that the remote sensing retrieval product is not independent from the a priori assumptions (see Schneider et al (2016) for more details). In Schneider et al (2017), these guidelines have been followed for comparison Sec. 3.1, the amount of water remaining in the troposphere from initialization is negligible by using lead times of three months (also for vapor, not shown).…”