Transportwege von Feuchte und Wasserdampfisotopologe
Zusammenfassung der Projektergebnisse
The strong coupling between water vapour, clouds and circulation is an important feedback mechanism that needs to be understood for reliable weather and climate modelling. This project investigates the use of tropospheric water vapour isotopologues as proxies for this coupling. The focus is on paired distributions of H2O and δD (δD=1000*{(HDO/H2O) / VSMOW - 1} with VSMOW = 3.1152*10-4 standing for the “Vienna Standard Mean Ocean Water”), because such so-called {H2O, δD} pairs group along different lines depending on the underlying process. In the framework of this project, we developed a quasi-operational chain for the processing of satellite data. This enabled us to generate more than 1.5 billion individual tropospheric {H2O, δD}-pair profile data (together with other 7.5 billion profile data of other trace gas products) using the thermal nadir spectra measured by an operational satellite instrument. We also validated these satellite products by comparison to different reference data sets. Furthermore, we applied processing tools developed in previous projects for generating about 2000 individual {H2O, δD}-pair profiles from the infrared spectra measured at three different ground-based stations. All these remote sensing data are published, already used in several international projects, and offer many international collaboration possibilities in the field of water cycle research ({H2O, δD}-pair data) as well as for the investigation of anthropogenic greenhouse gas emissions (CH4 and N2O). We made a large amount of water vapour isotopologue simulation experiments, whereby two different atmospheric isotope-enabled models have been used. Simulations from these models have been compared to the extensive observational data set (the remote sensing data generated within the project and in-situ aircraft profile data available from previous projects). The comparisons proved the good performance, in particular if the simulations are made at high horizontal resolution (14km or better). A very innovative modelling aspect was the tagging of water for pre-defined source regions, which allows a direct mapping of different source regions and transport processes with the modelled {H2O, δD}-pair data. In addition, we used a backward trajectory tool for investigating how different processes modify the modelled and observed {H2O, δD}-pair distributions. The model simulations and the remote sensing data have been used for investigating moisture transport pathways in the subtropical North Atlantic and in West Africa. For the subtropical North Atlantic, we identified four predominant pathways for free tropospheric air, each with distinct {H2O, δD}-pair distributions: upward transport within the Saharan Heat Low (SHL), air from the free troposphere above the SHL, moist convective injections from mesoscale convective systems in the Sahel, subsiding air from the upper-level extratropical North Atlantic. These results are in line with previous studies, but are by far more detailed and robust, mainly by the use of the very extensive remote sensing and modelling data sets. For the research of West Africa, the extensive data sets enabled us to investigate the moisture transport pathways and the {H2O, δD}-pair distribution from seasonal down to convective scales. During winter, the northeasterly trade winds transport Saharan air masses into the Sahel, then the air is dry and δD values are low. During the monsoon season in summer, moisture is transported from the tropical Atlantic into the Sahel and we observe humid air, but at the same time also low δD values. We show that the anti-correlation between H2O and δD is associated with micro-physical processes in the context of convective systems. We conclude that the free tropospheric {H2O, δD}-pair distribution can be used to assess the importance of convective activity for the moistening of the free troposphere. This project has demonstrated that the free tropospheric {H2O, δD}-pair distribution can be observed quasi-globally and on a daily time scale using an operational satellite instrument. We showed that this pair data set has valid information on the moisture sources and transport pathways and thus it offers novel possibilities to identify and better understand the deficits of existing weather and climate models concerning their treatment of moisture processes.
Projektbezogene Publikationen (Auswahl)
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MUSICA MetOp/IASI {H2O,δD} pair retrieval simulations for validating tropospheric moisture pathways in atmospheric models, Atmos. Meas. Tech., 10, 507-525, 2017
Schneider, M., Borger, C., Wiegele, A., Hase, F., García, O. E., Sepúlveda, E., and Werner, M.
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Evaluation of MUSICA IASI tropospheric water vapour profiles using theoretical error assessments and comparisons to GRUAN Vaisala RS92 measurements, Atmos. Meas. Tech., 11, 4981–5006, 2018
Borger, C., Schneider, M., Ertl, B., Hase, F., García, O. E., Sommer, M., Höpfner, M., Tjemkes, S. A., and Calbet, X.
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From climatological to small scale applications: Simulating water isotopologues with ICON-ART-Iso (version 2.3), Geoscientific Model Development, 11, 5113-5133, 2018
Eckstein, J., Ruhnke, R., Pfahl, S., Christner, E., Diekmann, C., Dyroff, C., Reinert, D., Rieger, D., Schneider, M., Schröter, J., Zahn, A., Braesicke, P.
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A Lagrangian perspective on stable water isotopes during the West African Monsoon, submitted to Journal of Geophysical Research, Atmospheres, Earth and Space Science Open Archive, 43, 2021
Diekmann, C. J., Schneider, M., Knippertz, P., de Vries, A. J., Pfahl, S., Aemisegger, F., Dahinden, F., Ertl, B., Khosrawi, F., Wernli, H., Braesicke, P.
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Analysis of stable water isotopes in tropospheric moisture during the West African Monsoon, PhD Thesis, Institute of Meteorology and Climate Research - Atmospheric Trace Gases and Remote Sensing (IMK-ASF), Karlsruhe Institute of Technology
Diekmann C. J.
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How Rossby wave breaking modulates the water cycle in the North Atlantic trade wind region, Weather Clim. Dynam., 2, 281–309, 2021
Aemisegger, F., Vogel, R., Graf, P., Dahinden, F., Villiger, L., Jansen, F., Bony, S., Stevens, B., and Wernli, H.
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Potential of mid-tropospheric water vapor isotopes to improve large-scale circulation and weather predictability, Geophys. Res. Lett., 48, e2020GL091 698, 2021
Toride, K., Yoshimura, K., Tada, M., Diekmann, C., Ertl., B., Khosrawi, F., and Schneider, M.
