How is the stratospheric water vapour affected by climate change, and which processes are responsible? (SHARPI-WV)
Zusammenfassung der Projektergebnisse
During the second phase of SHARP, the understanding of water vapour variability and trends in the upper troposphere and stratosphere was further advanced. For this purpose, improved observational data sets and climate model simulations were generated. Previous publications that had based mainly on Boulder frost point hygrometer measurements found a continuous increase of water vapour in the lower stratosphere. Our work in contrast confirmed more recent findings that satellite data indicate a slight global decrease of water vapour in the lower stratosphere over the last 25 years. This trend assessment was possible through the separation of the solar cycle impact from the linear trend. In lower stratospheric water vapour, a solar cycle signal could be identified that shows its lowest values about 2 years after the solar maximum and we could explain it by the solar heating of sea surface temperatures that leads to increased convection and a cooling of the tropopause cold point. The altitude-latitude pattern of the strength of seasonal variations identified from observational data sets was linked to the properties of the Brewer-Dobson circulation (BDC). Strongest annual variations were all related to transport processes in the context of the BDC, either by tropical upwelling (the tropical tape recorder) or subsidence over the poles. As a new and striking feature related to the BDC, a region of very high variability in the upper stratosphere of the Southern subtropics was identified. This feature has the potential to serve as a diagnostic tool for validation of atmospheric models in future. The very high inter-annual variability of water vapour, and in particular the famous “millennium drop” in the tropical water vapour time series was further assessed. We found that the interplay between strong El Niño/La Niña events with the QBO triggers a significant reduction of the water vapour transport into the stratosphere, if the QBO is changing its phase from west to east. Besides the tropics, the monsoon systems play a relevant role for water vapour transport into the stratosphere. The Asian summer monsoon was studied in several analyses, leading to the finding that the strength of the monsoon is positively correlated with the upward water vapour transport, and that water vapour enters the stratosphere predominantly on its pathway towards higher latitudes at the northeastern edge of the Asian monsoon anticyclone. Investigations with application of the water vapour isotopologue HDO demonstrated that the import of water vapour into the stratosphere through the Asian monsoon anticyclone is mainly ruled by convective processes and ice-lofting, while in-mixing of older wet stratospheric air alone is not capable of explaining the full amount of uplifted water vapour. The impact of volcanic aerosols on the water vapour budget in the lower stratosphere was investigated as well. The volcanic aerosols enhance the lower stratospheric water vapour by increasing heating rates and subsequently lead to a warming of the tropical tropopause and stratosphere. Also for this mechanism, the Asian monsoon system plays a relevant role in transporting enhanced amounts of water vapour into the stratosphere. The work of SHARP-WV Phase II was a major contribution to the WCRP/SPARC Water Vapour Assessment II (WAVAS-II) activity. By intercomparing and validating all available water vapour records from satellites operating in the year 2000 and later, the WAVAS-II activity has laid the basis for the construction of an all-satellite data record of water vapour covering the last 30 years.
Projektbezogene Publikationen (Auswahl)
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(2014), The generic MESSy submodel TENDENCY (v1.0) for processbased analyses in Earth system models, Geoscientific Model Development, 7, 1573–1582
Eichinger, R. und Jöckel, P.
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(2015), Is there a solar signal in lower stratospheric water vapour?, Atmos. Chem. Phys., 15, 9851 – 9863
Schieferdecker, T., S. Lossow, G. P. Stiller und T. von Clarmann
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(2015), Simulation of the isotopic composition of stratospheric water vapour and methane – Part 1: Description and evaluation of the EMAC model, Atmos. Chem. Phys., 15, 5537 – 5555
Eichinger, R., P. Jöckel, S. Brinkop, M. Werner und S. Lossow
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(2015), Simulation of the isotopic composition of stratospheric water vapour and methane – Part 2: Investigation of HDO/H2O variations, Atmos. Chem. Phys., 15, 7003 – 7015
Eichinger, R., P. Jöckel und S. Lossow
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(2016), Impact of major volcanic eruptions on stratospheric water vapour, Atmos. Chem. Phys., 16, 6547–6562
Löffler, M., Brinkop, S., und Jöckel, P.
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(2016), The millennium water vapour drop in chemistry-climate model simulations, Atmos. Chem. Phys., 16, 8125 – 8140
Brinkop, S., M. Dameris, P. Jöckel, H. Garny, S. Lossow und G. P. Stiller
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(2016), UTLS water vapour from SCIAMACHY limb measurements V3.01 (2002 – 2012), Atmos. Meas. Tech., 9, 133 – 158
Weigel, K., A. Rozanov, F. Azam, K. Bramstedt, R. Damadeo, K.-U. Eichmann, C. Gebhardt, D. Hurst, M. Kraemer, S. Lossow, W. Read, N. Spelten, G. P. Stiller, K. A. Walker, M. Weber, H. Bovensmann und J. P. Burrows
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(2017), An island in the stratosphere – On the enhanced annual variation of water vapour in the middle and upper stratosphere in the southern tropics and subtropics, Atmos. Chem. Phys., 17, 11521 – 11539
Lossow, S., H. Garny und P. Jöckel
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(2017), The SPARC water vapour assessment II: Comparison of annual, semi-annual and quasi-biennial variations in stratospheric and lower mesospheric water vapour observed from satellites, Atmos. Meas. Tech., 10, 1111 – 1137
Lossow, S., F. Khosrawi, G. E. Nedoluha, F. Azam, K. Bramstedt, J. P. Burrows, B. M. Dinelli, P. Eriksson, P J. Espy, M. Garcia-Comas, J. C. Gille, M. Kiefer, S. Noël, P. Raspollini, W. G. Read, K. H. Rosenlof, A. Rozanov, C. E. Sioris, G. P. Stiller, K. A. Walker und K. Weigel
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(2017), The SPARC water vapour assessment II: Intercomparison of satellite and ground-based microwave measurements, Atmos. Chem. Phys., 17, 14543-14558
Nedoluha G. E., M. Kiefer, S. Lossow, R. M. Gomez, N Kämpfer, M. Lainer, P. Forkman, O. M. Christensen, J. J. Oh, P. Hartogh, J. Anderson, K. Bramstedt, B. M. Dinelli, M. Garcia-Comas, M. Hervig, D. P. Murtagh, P. Raspollini, W. G. Read, K. H. Rosenlof, G. P. Stiller und K. A. Walker
