Klimavariabilität in der oberen Troposphäre und Stratosphäre über Asien und ihre Darstellung in modernen Re-Analysen
Zusammenfassung der Projektergebnisse
The main goal of the project was to validate different reanalysis products with respect to their abilities to resolve transport in the upper troposphere and stratosphere (UTS) with a special focus on the Asian summer monsoon (ASM) and the North American summer monsoon (NASM). Our results are based on the comparison of four reanalysis products: (i) ERA-Interim from ECMWF, (ii) JRA-55 from JMA, (iii) MERRA-2 from NASA and (iv) the newest ECMWF product ERA5. Using age of air (AoA) and stratospheric water vapor (SWV) derived from the Chemical Lagrangian Model of Stratosphere (CLaMS) driven by these reanalyses, we studied their performance to represent the Brewer Dobson Circulation (BDC). Compared with the older products (ERA-40, JRA-25, MERRA) the differences between the reanalyses became smaller and the simulated AoA/SWV distributions compare better with the observations. However, there are still significant differences, with JRA-55, ERA-Interim showing too young AoA distribution and too fast upward propagation of the SWV taperecoder on the one side and with MERRA-2 creating too old AoA distribution and too slow ascend of the SWV taperecoder on the other side. ERA5 shows some clear improvements, e.g. a significantly slower BDC than in ERA-Interim. We traced back these differences to still significant differences in the heating rates, mainly within the Tropical Tropopause Layer (TTL), with too much tropical upwelling for JRA-55 and ERA-Interim and too low heating rates in MERRA-2. In the tropical lower stratosphere, heating rates in ERA5 correct the well-known high-bias in ERA-Interim. Thus, ERA5-related distributions of AoA are less old-biased as those derived from MERRA-2 indicating that some similarities in these two assimilation schemes could be the reason in a better representation of the BDC in ERA5. We found that only MERRA-2 and ERA5 among the reanalyses produce tropical-mean values of outgoing long-wave radiation close to those observed. ERA5 tends to underestimate cloud effects, while MERRA-2 overestimates this variability. Thus, clouds have a strong impact on the diabatic vertical velocities in the TTL revising our understanding of the level of zero net radiative heating (LZRH) defining the base the upward branch of the BDC. This simple picture with LZRH marking the boundary between negative radiative heating rates (net descent) in the tropical troposphere and positive radiative heating rates (net ascent) works only for clear-sky conditions but not for the atmosphere with clouds (all-sky heating rates) where layers with ascent are permeated by layers with descent, even in climatological mean. Finally, we focused on transport into the stratosphere via the ASM and NASM anticyclones. By releasing artificial tracers in several vertical layers from the middle troposphere to the lower stratosphere we found that more air mass is transported from the ASM and NASM regions to the tropical stratosphere, and even to the southern hemispheric (SH) stratosphere, when the tracers are released clearly below the tropopause than when they are released close to the tropopause. For tracers released close to the tropopause, transport is primarily into the NH lower stratosphere. Results for different vertical layers of air origin reveal two transport pathways from the upper troposphere over the ASM and NASM regions to the tropical pipe: (i) quasi-horizontal transport to the tropics below the tropopause followed by ascent to the stratosphere via tropical upwelling, and (ii) ascent into the stratosphere inside the ASM/NASM followed by quasi-horizontal transport to the tropical lower stratosphere and further to the tropical pipe. Overall, the tropical pathway (i) is faster than the monsoon pathway (ii). The air mass contributions from the ASM to the tropical pipe are about 3 times larger than the corresponding contributions from the NASM. The inter-hemispheric transport is mainly driven by the ASM. We found that it is an interplay between the ASM and westerly ducts which triggers such cross-Equator transport from the NH extratropics to the SH, mainly during boreal summer to fall.
Projektbezogene Publikationen (Auswahl)
- From ERA-Interim to ERA5: the considerable impact of ECMWF’s next-generation reanalysis on Lagrangian transport simulations. Atmos. Chem. Phys., 19(5):3097–3124, 2019
L. Hoffmann, G. Günther, D. Li, O. Stein, X. Wu, S. Griessbach, Y. Heng, P. Konopka, R. Müller, B. Vogel, and J. S. Wright
(Siehe online unter https://doi.org/10.5194/acp-19-3097-2019) - How robust are stratospheric age of air trends from different reanalyses? Atmos. Chem. Phys., 19(9):6085–6105, 2019
F. Ploeger, B. Legras, E. Charlesworth, X. Yan, M. Diallo, P. Konopka, T. Birner, M. Tao, A. Engel, and M. Riese
(Siehe online unter https://doi.org/10.5194/acp-19-6085-2019) - Multitimescale variations in modeled stratospheric water vapor derived from three modern reanalysis products. Atmos. Chem. Phys., 19(9):6509– 6534, 2019
M. Tao, P. Konopka, F. Ploeger, X. Yan, J. S. Wright, M. Diallo, S. Fueglistaler, and M. Riese
(Siehe online unter https://doi.org/10.5194/acp-19-6509-2019) - The efficiency of transport into the stratosphere via the Asian and North American summer monsoon circulations. Atmos. Chem. Phys., 19(24):15629–15649, 2019
X. Yan, P. Konopka, F. Ploeger, A. Podglajen, J. S. Wright, R. Müller, and M. Riese
(Siehe online unter https://doi.org/10.5194/acp-19-15629-2019) - Differences in tropical high clouds among reanalyses: origins and radiative impacts. Atmos. Chem. Phys., 20(14):8989–9030, 2020
J. S. Wright, X. Sun, P. Konopka, K. Krüger, B. Legras, A. M. Molod, S. Tegtmeier, G. J. Zhang, and X. Zhao
(Siehe online unter https://doi.org/10.5194/acp-20-8989-2020) - Asymmetry and pathways of inter-hemispheric transport in the upper troposphere and lower stratosphere. Atmos. Chem. Phys., 21(9):6627–6645, 2021
X. Yan, P. Konopka, M. Hauck, A. Podglajen, and F. Ploeger
(Siehe online unter https://doi.org/10.5194/acp-21-6627-2021) - The stratospheric Brewer– Dobson circulation inferred from age of air in the ERA5 reanalysis. Atmos. Chem. Phys., 21(11):8393–8412, 2021
F. Ploeger, M. Diallo, E. Charlesworth, P. Konopka, B. Legras, J. C. Laube, J.-U. Grooß, G. Günther, A. Engel, and M. Riese
(Siehe online unter https://doi.org/10.5194/acp-21-8393-2021) - Upward transport into and within the Asian monsoon anticyclone as inferred from StratoClim trace gas observations. Atmos. Chem. Phys., 21(2):1267–1285, 2021
M. von Hobe, F. Ploeger, P. Konopka, C. Kloss, A. Ulanowski, V. Yushkov, F. Ravegnani, C. M. Volk, L. L. Pan, S. B. Honomichl, S. Tilmes, D. E. Kinnison, R. R. Garcia, and J. S. Wright
(Siehe online unter https://doi.org/10.5194/acp-21-1267-2021)
