Future changes in wintertime stratospheric Arctic variability in CCMI models B. Ayarzagüena 1, U. Langematz 1, J. Abalichin 1, H. Akiyoshi 2, M. Michou 3, O. Morgenstern 4 & L. Oman 5 1 Institut für Meteorologie, Freie Universität Berlin (Germany); 2 NIES, Tsukuba (Japan); 3 Meteo-France, (France); 4 NIWA, (New Zealand); 5 NASA/GSFC (USA)
Motivation Major Stratospheric Warmings in the future No clear consensus among recent studies about a possible impact of climate change on MSWs by analyzing chemistry climate models (CCM) simulations [Butchart et al. 2010; Mitchell et al. 2012]. Change in SSW freq. (1960-2000 vs 2040-2080) in REF-B2 run [Mitchell et al., 2012] Possible reason for the uncertainty: competition of different forcings. 2
Motivation In a previous EMAC work (with SCN-B2d CCMVal run and sensitivity runs) no significant future change in the mean frequency of MSWs was detected but the seasonal distribution of MSWs was found to change in agreement with the basic state. SCN-B2d Daily ū@10 hpa Future-minus-past 4 Events/Decade 3 2 1 0 Nov Dec Jan Feb Mar Past Future Ayarzagüena et al. (2013) 3
Motivation In a previous EMAC work any significant future change in the mean frequency of MSWs was detected but the seasonal distribution of MSWs was found to change in agreement with the basic state in SCN-B2d CCMVal runs. Events/Decade 4 3 2 SCN-B2d Do we also find these results in the new CCMI runs? Past 1 Future 0 Nov Dec Jan Feb Mar Ayarzagüena et al. (2013) 4
Data & models REF-C2: transient run from 1960-2100 under RCP6.0 scenario (GHGs) and A1 scenario (ODS, WMO 2010) CCMI models Model resolution QBO Solar variability SSTs GEOS-CCM 2.5º x 2º, L72 (top:0.01hpa) Internally generated No Prescribed (CESM1) CNRM-CCM T42L60 (top: 0.07 hpa) Internally generated Yes Prescribed (CNRM) NIWA-UKCA 3.75º x 2.5º, L60 (top: 84 km) Internally generated No Coupled to ocean model CCSRNIES- MIROC 3.2 T42L34 (top: 0.012 hpa) Nudged Yes Prescribed (MIROC 3.2) EMAC T42L39 (top: 0.01hPa) Nudged Yes Prescribed (HadGEM-ES2) 5
Mean frequency of MSWs Periods of study: PAST (first 40 winters) and FUTURE (last 40 winters) Model Past (MSWs/dec) Future (MSWs/dec) CCSRNIES-MIROC3.2 2.3 3.0 NIWA-UKCA 0.8 (!) 3.3 GEOS-CCM 1.8 1.8 CNRM-CCM 7.5 7.3 EMAC 6.8 7.3 No statistically significant future changes in the mean frequency of MSWs are found except for NIWA-UKCA ERA-40 6.0 Criterion for MSWs identification Simultaneous reversal of ū at 60ºN and 10 hpa & ΔT (90 N-60 N) at 10 hpa 10 consecutive days of westerly winds after the central date 6
Future changes in climatology and variability of the middle stratosphere CCSRNIESMIROC3.2 Climatology Standard dev. NIWA-UKCA Daily ū@10 hpa (m/s) Future-minus-past GEOS-CCM - CCSRNIES-MIROC3.2 and NIWA-UKCA show: Early winter: stronger future PNJ and reduced variability Mid- and late winter: weaker future PNJ and enhanced variability - Slight changes in GEOS-CCM but in the same direction Shading: statistically significant values at a 95% conf. level 7
Future changes in climatology and variability of the middle stratosphere CNRM-CCM Daily ū@10 hpa (m/s) Future-minus-past EMAC Climatology CNRM-CCM and EMAC show: Early and late winter: weaker future PNJ and enhanced variability Midwinter: stronger future PNJ and reduced variability Standard dev. Shading: statistically significant values at a 95% conf. level 8
Changes in tropospheric forcing Daily climatology of heat flux @ 100 hpa (averaged ~45 N-75 N) CCSRNIES-MIROC3.2 NIWA-UKCA Past Future GEOS-CCM CNRM-CCM EMAC - Models with similar changes in PNJ show similar changes in the tropospheric forcing. Thick red line: statistically significant values at a 95% conf. level 9
Changes in tropospheric forcing: causes Changes in climatological SSTs (Future-minus-past) CCSRNIES-MIROC3.2 (SSTs from MIROC3.2) GEOS-CCM (SSTs from CESM1) K NIWA-UKCA - An El Niño-like pattern in December-January as SST response to global warming in CCSRNIES-MIROC3.2 and NIWA-UKCA Homogeneous future changes in tropical SSTs prescribed in GEOS-CCMà might explain lack of changes in PNJ 10
Changes in tropospheric forcing: causes Changes in climatological SSTs (Future-minus-past) CNRM-CCM (SSTs from CNRM) EMAC (SSTs from HadGEM) K - General warming in CNRM-CCM - Predominant change in prescribed SSTs in EMAC: warming of the North Pacific + a slight warming of the equatorial Pacific 11
Changes in tropospheric forcing: causes Why are the results of RCP6.0 and SCN-B2d runs of EMAC different? RCP6.0 (SSTs from HadGEM) SCN-B2d (SSTs from ECHAM/MPIOM) The prescribed SSTs come from different AOGCMs and show differencies in the response to global warming (i.e., El Niño-like pattern is only present in SCN-B2d) K 12
Conclusions No statistically significant future changes in the mean frequency of MSWs are found in general in the analyzed CCMI models. Three groups of models are found in terms of future seasonal changes in the intensity of the PNJ: 1. Models with a future weakening (strengthening) and an increased (reduced) variability of the polar stratosphere and an enhanced (reduced) tropospheric forcing in midwinter (early winter) (CCSRIES-MIROC3.2 & NIWA-UKCA) 2. Models with a future strengthening (weakening) and a reduced (enhanced) variability of PNJ and a reduced or unchanged (enhanced) tropospheric forcing in midwinter (early winter) (CNRM-CCM & EMAC) 3. Models that do not show any statistically significant changes of the polar vortex in the future (GEOS-CCM) Differences in the response of SSTs to global warming can be at least partly responsible for these differences in the future polar stratosphere among models. 13
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Changes in tropospheric forcing: causes Changes in SSTs (El Niño 3.4 index ) CCSRNIES-MIROC3.2 CNRM-CCM NIWA-UKCA EMAC GEOS-CCM The evolution of El Niño index confirms the stronger warming of the equatorial Pacific in the future in models with a mid-winter weakening of the polar vortex than in the other models. 15
Distribution of MSWs & polar vortex state CCSRNIES-MIROC 3.2 GEOS-CCM 4 4 Events/Decade 3 2 1 Past Future Events/Decade 3 2 1 Past Future 0 Nov Dec Jan Feb Mar 0 Nov Dic Ene Feb Mar 4 NIWA-UKCA 4 CNRM-CCM Events/Decade 3 2 1 Past Future Events/Decade 3 2 1 Past Future 0 Nov Dic Ene Feb Mar 0 Nov Dic Ene Feb Mar 16