Sea-ice and Stratospheric Ozone - Links and Impacts in the Arctic and Antarctic (ISOLAA)
Final Report Abstract
While Arctic sea-ice has dramatically decreased in the recent past, annual mean Antarctic sea-ice was found to have increased by about 1 % per decade for the years 1978-2006. The Arctic sea-ice retreat has been associated with the warming of the troposphere caused by increasing greenhouse gas (GHG) concentrations. The observed Antarctic changes have been suggested to be driven by the ozone depletion by man-made halogens in the polar stratosphere and its impacts on tropospheric circulation. However, there is still low confidence in the scientific understanding of the observed increase in Antarctic sea ice extent (SIE), due to low knowledge of internal variability and competing explanations for the causes of change. Hence, ISOLAA addressed the following research questions: • How does stratospheric ozone affect polar sea-ice? • How does the atmosphere respond to polar sea-ice changes, and are there inter-hemispheric differences in the atmospheric response? • How sensitive is the future evolution of ozone to changes in the sea-ice extent? • What will be the effects of polar ozone recovery on Antarctic sea-ice and SH climate? To this end, different multi-decadal simulations with the ECHAM/MESSy Atmospheric Chemistry (EMAC) model were carried out. EMAC is a stratosphere resolving chemistry-climate model including a complex interactive chemical model as well as a sophisticated radiation scheme. For the studies in ISOLAA, EMAC has been coupled with a deep ocean model to take the feedback of the oceans to different atmospheric drivers into account (EMAC-O). Two multi-decadal simulations with EMAC-O of 250 years in total, driven by constant concentrations of GHGs and ozone depleting substances (ODSs) allowed us to investigate the internal interannual and intraseasonal variability of the atmosphere-ocean system in a stable climate. A transient simulation of the period 1960-2100 including anthropogenic GHG and ozone forcing provided a probable projection of future climate taking natural and anthropogenic forcing into account. To investigate the individual role of anthropogenic ozone change a second transient simulation of the climate evolution between 1960 and 2100 in a world without climate change (non-climate change, NCC) but prescribed, observed and projected evolution of ODSs was carried out. In the following, some of the major findings are summarized: • EMAC-O captures the main characteristics of the tropical Madden-Julian Oscillation (MJO). This is an important outcome of the project, given the generally poor performance of the MJO in climate models. • While EMAC-O reproduces the observed connection between the tropical Cold Tongue Index (CTI) and the SAM, the Tropical Index (TI) is less important in the model. Different projections of the SAM and TI suggest a possible role of ozone recovery, which needs further study. • In a stable climate, EMAC-O reveals a positive correlation between the Southern Annular Mode (SAM) index and sea-ice extent (SIE) on interannual time-scales, consistent with observations, while a significant correlation at low frequencies is not found. In boreal winter, EMAC-O shows a more coherent behaviour on longer time scales, with extended SIE being associated with a reduced Atlantic Meridional Overturning Circulation (AMOC), and vice versa. • The polarity and intensity of the SAM are significantly affected by stratospheric ozone, with reduced stratospheric polar ozone being associated with a more positive SAM up to 3 months later. This correlation holds as well for a time lag of opposite sign, as a stronger polar vortex at positive SAM isolates the polar cap from intrusions of ozone-rich air from mid-latitudes, hence leads to lower polar ozone. • EMAC-O simulates a realistic Eulerian mean meridional overturning circulation (EMOC, Deacon cell), which is determined by the surface winds and wind-stress and strongly correlated with the SAM. Future projections show significant changes in the EMOC. • Future Antarctic sea-ice is projected by EMAC-O to decline in the first half of the 21st century due to the effect of rising GHGs, enhanced by the impact of Antarctic ozone recovery on the SAM in southern summer.
Publications
- (2014) Tropical influence independent of ENSO on the austral summer Southern Annular Mode, Geophysical Research Letters, 41, 3643-3648
Ding, H., Greatbatch, R. J. and Gollan, G.
(See online at https://doi.org/10.1002/2014GL059987) - (2015) On the extratropical influence of variations of the upper tropospheric equatorial zonal mean zonal wind during boreal winter, Journal of Climate, 28, 168-185
Gollan, G. and Greatbatch, R. J.
(See online at https://doi.org/10.1175/JCLI-D-14-00185.1) - (2015) Tropical Impact on the boreal winter troposphere, Christian-Albrechts-Universität zu Kiel, Kiel
Gollan, G.
- (2015) Tropical impact on the interannual variability and long-term trend of the Southern Annular Mode during austral summer from 1960/1961 to 2001/2002, Climate Dynamics, 44, 2215-2228
Ding, H., Greatbatch, R. J. and Gollan, G.
(See online at https://doi.org/10.1007/s00382-014-2299-x) - (2015), A chemistry-climate model study of past changes in the Brewer-Dobson circulation, Journal of Geophysical Research, 120, 6742-6752
Oberländer-Hayn, S., S. Meul, U. Langematz, J. Abalichin, und F. Haenel
(See online at https://doi.org/10.1002/2014JD022843) - (2015), Nonlinear response of modelled stratospheric ozone to changes in greenhouse gases and ozone depleting substances in the recent past, Atmospheric Chemistry and Physics, 15, 6897-6911
Meul, S., S. Oberländer-Hayn, J. Abalichin, und U. Langematz
(See online at https://doi.org/10.5194/acp-15-6897-2015) - (2016) Austral Winter External and Internal Atmospheric Variability between 1980 and 2014 Geophysical Research Letters, 43 (5). pp. 2234-2239
Ding, H., Greatbatch, R. J., Lin, H., Hansen, F., Gollan, G. and Jung, T.
(See online at https://doi.org/10.1002/2016GL067862) - (2016) Natürliche Variabilität und anthropogener Einfluss in Simulationen mit gekoppeltem Klima-Chemiemodell EMAC-O: Atmosphären-Ozean-Wechselwirkungen im Klimawandel der Südhemisphäre, Freie Universität Berlin, Berlin
Abalichin, J.
- (2016), Impact of rising greenhouse gas concentrations on future tropical ozone and UV exposure, Geophysical Research Letters
Meul, S., M. Dameris, U. Langematz, J. Abalichin, A. Kerschbaumer, A. Kubin, and S. Oberländer-Hayn
(See online at https://doi.org/10.1002/2016GL067997) - (2016), Is the Brewer-Dobson circulation increasing or moving upward?, Geophysical Research Letters, 43, 1772-1779
Oberländer-Hayn, S., E. P. Gerber, J. Abalichin, H. Akiyoshi, A.Kerschbaumer, A. Kubin, M. Kunze, U. Langematz, S. Meul, M. Michou, O. Morgenstern, and L. D. Oman
(See online at https://doi.org/10.1002/2015GL067545) - (2016), Meteorology and oceanography of the Atlantic sector of the Southern Ocean - a review of German achievements from the last decade, Ocean Dynamics
Hellmer, H. H., M. Rhein, G. Heinemann, J. Abalichin, W. Abouchami, O. Baars, U. Cubasch, K. Dethloff, L. Ebner, E. Fahrbach, M. Frank, G. Gollan, R. Greatbatch, J. Grieger, V. Gryanik, M. Gryschka, J. Hauck, M. Hoppema, O. Huhn, T. Kanzow, B. P. Koch, G. König-Langlo, U. Langematz, G. C. Leckebusch, C. Lüpkes, S. Paul, A. Rinke, M. Rutgers van der Loeff, B. Rost, M. Schröder, G. Seckmeyer, T. Stichel, V. Strass, R. Timmermann, S. Trimborn, U. Ulbrich, C. Venchiarutti, U. Wacker, S. Willmes, und D. Wolf-Gladrow
(See online at https://doi.org/10.1007/s10236-016-0988-1)
