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Shiogama h 20150708_1730_upmc_jussieu_-_room_307

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Shiogama h 20150708_1730_upmc_jussieu_-_room_307

  1. 1. Hideo Shiogama1, Masahiro Watanabe2, Yukiko Imada3, Masato Mori2, Youichi Kamae1, Masayoshi Ishii3, and Masahide Kimoto2 Attribution of the June-July 2013 heat wave in the southwestern United States Shiogama et al. (2014, SOLA) 1Center for Global Environmental Research, National Institute for Environmental Studies, Tsukuba, Japan 2Atmosphere and Ocean Research Institute, the University of Tokyo, Kashiwa, Japan 3Meteorological Research Institute, Tsukuba, Japan
  2. 2. the June-July 2013 heat wave in the southwestern United States A severe heat wave occurred in the southwestern US during June and July 2013. • This heat wave was associated with the persistent positive Z500 anomalies. • The positive phase of the summertime AO lead to the positive Z500 anomalies over the southwestern US. Contours: Z500 anomalies Shading: Surface air temp anomalies Shading: Z500 anomalies
  3. 3. Questions 1. Was this atmospheric circulation pattern (the positive AO) deterministically controlled by the anthropogenic and natural boundary conditions? 2. Did the natural variability of SST+SIC and/or the human activity alter probabilities of atmospheric circulation regimes? 3. Have anthropogenic warming together with changes in atmospheric circulation increased the probability of heat wave?
  4. 4. Probabilistic Event Attribution Experiments using the MIROC5 AGCM (T85) ALL NAT1 NAT2 ALL-LNG Boundary conditions External Forcing HIST+RCP natural natural HIST+RCP SST sea ice HadISST a liner trend based on HadISST (1870 to 2012) is removed (Christidis and Stott 2014) ANT changes estimated from the CMIP5 historical runs are removed (Stone 2013) HadISST Ensemble size 100 100 100 10 Period 2009-2013 2009-2013 2009-2013 1949-2013 ANT changes in SST ANT changes in sea ice concentrations
  5. 5. Histograms of SAT anomalies averaged over the southwestern US • These PDFs have wide ranges spanning from negative to positive values due to stochastic behaviors of atmospheric circulations. • Human activities led to the rightward shift of the PDF. • Both human influences and the atmospheric natural variability contributed to the occurrence of the 2013 heat wave.
  6. 6. SAT and Z500 anomalies on June-July 2013 Z500anomalies • Whereas the ensemble average of the ALL runs did not capture the extremely high SAT anomaly in the southwestern US, a few ensemble members had large positive SAT anomalies and Z500 anomaly patterns similar to ERAI. • The observed Z500 anomaly pattern was not deterministically forced by the observed SST plus the external forcing factors. • Stochastic behaviors of atmospheric circulation were related to the observed Z500 pattern and the large positive SAT anomalies in the southwestern US Counter interval: 10 m Counter interval: 10 mCounter interval: 5 m Contours: Z500 anom Shading: SAT anom
  7. 7. The summertime AO • The summertime AO index of ERAI had a positive value in 2013. • PDFs of ALL, NAT1 and NAT2 show the rightward shift relative to the climatology. • There are no significant differences between ALL and NAT. • The natural variability of SST and SIC in 2013 increased the likelihood of the positive AO, whereas the human activity did not affect the circulation regime (the dynamic components). AO index Climatology
  8. 8. Anthropogenic SAT warming patters (the ensemble averaged SAT difference between ALL and NAT) These general warming patterns due to the human activity (thermodynamic component) are also important factors for the increased probabilities of heat wave.
  9. 9. Answers 1. The positive AO was not deterministically controlled by the anthropogenic and natural boundary conditions. 2. The natural variability of SST+SIC altered probabilities of atmospheric circulation regimes. Mechanisms are not clear yet. The human activity has not affected the circulation regime. 3. Anthropogenic warming together with non-anthropogenic changes in atmospheric circulation increased the probability of heat wave. Shiogama H, Watanabe M, Imada Y, Mori M, Kamae Y, Ishii M, Kimoto M (2014) Attribution of the June-July 2013 heat wave in the southwestern United States. SOLA, 10, 122−126 1. Was this atmospheric circulation pattern (the positive AO) deterministically controlled by the anthropogenic and natural boundary conditions? 2. Did the natural variability of SST+SIC and/or the human activity alter probabilities of atmospheric circulation regimes? 3. Have anthropogenic warming together with changes in atmospheric circulation increased probability of heat wave? Questions
  10. 10. Histograms of SAT anomalies averaged over the southwestern US • MIROC5A simulated well the distributions of inter-annual variations of SAT in the SW-US. • Therefore no bias corrections were applied. • The PDFs have wide ranges spanning from negative to positive values due to stochastic behaviors of atmospheric circulations. • Anthropogenic warming led to the rightward shift of the PDF. • Both human influences and the atmospheric natural variability contributed to the occurrence of the 2013 heat wave. PDFs during the 1980-2013 period PDFs during the June-July 2013
  11. 11. PCs of Z500 during 1980-2013 for ERAI and ALL-Long Both the indices of these two modes had positive values for the June-July 2013 mean of ERAI, connecting to the positive Z500 anomalies over the Southwestern US.
  12. 12. Histograms of Modes #1 and #2 for ALL, NAT1 and NAT2 DottedlinesaretheALL-Long runsduring1980-2013. The natural variability of SST and SIC in 2013 increased the likelihood of positive phase M1, in part contributing to the occurrence of heat wave. By contrast, the human activity did not largely affect phases of M1. The histograms of M2 were not skewed for ALL, NAT1 and NAT2 compared to the histogram of the ALL-Long runs, indicating that neither the SST+SIC natural variability nor the human activity influenced phases of M2.

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