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Found 3 results

  1. Centennial Trend and Decadal-to-Interdecadal Variability of Atmospheric Angular Momentum in CMIP3 and CMIP5 Simulations Authors: Houk Paek and Huei-Ping Huang First Published: 26th November, 2012 Published on line: 31st May, 2013 Abstract: The climatology and trend of atmospheric angular momentum from the phase 3 and the phase 5 Climate Model Intercomparison Project (CMIP3 and CMIP5, respectively) simulations are diagnosed and validated with the Twentieth Century Reanalysis (20CR). It is found that CMIP5 models produced a significantly smaller bias in the twentieth-century climatology of the relative MR and omega MΩ angular momentum compared to CMIP3. The CMIP5 models also produced a narrower ensemble spread of the climatology and trend of MR and MΩ. Both CMIP3 and CMIP5 simulations consistently produced a positive trend in MR and MΩ for the twentieth and twenty-first centuries. The trend for the twenty-first century is much greater, reflecting the role of greenhouse gas (GHG) forcing in inducing the trend. The simulated increase in MR for the twentieth century is consistent with reanalysis. Both CMIP3 and CMIP5 models produced a wide range of magnitudes of decadal and interdecadal variability of MRcompared to 20CR. The ratio of the simulated standard deviation of decadal or interdecadal variability to its observed counterpart ranges from 0.5 to over 2.0 for individual models. Nevertheless, the bias is largely random and ensemble averaging brings the ratio to within 18% of the reanalysis for decadal and interdecadal variability for both CMIP3 and CMIP5. The twenty-first-century simulations from both CMIP3 and CMIP5 produced only a small trend in the amplitude of decadal or interdecadal variability, which is not statistically significant. Thus, while GHG forcing induces a significant increase in the climatological mean of angular momentum, it does not significantly affect its decadal-to-interdecadal variability in the twenty-first century. Link to Paper: https://journals.ametsoc.org/doi/pdf/10.1175/JCLI-D-12-00515.1
  2. Bring Back 1962-63

    Causes of Antarctic Change - A Discussion

    Causes of Antarctic Change - A Discussion Workshop Presentation: Aspen Global Change Institute, Aspen, Colorado Workshop Programme: “Understanding the Causes and Consequences of Polar Amplification” - June 12th -16th, 2017 Workshop Discussion: Relating to their presentations (on the same afternoon) Presenters: John C Fyfe, Baek-Min Kim, Lorenzo Polvani, David Schneider, Karen L Smith, Laurent Terray and Xiangdong Zhang Presentation Date: 13th June, 2017 Link to full discussion (27 minute video): https://www.agci.org/lib/17s1/part-iv-discussion-causes-antarctic-change Link to full agenda and presentations: https://www.agci.org/event/17s1
  3. The MJO‐SSW Teleconnection: Interaction Between MJO‐Forced Waves and the Midlatitude Jet Authors: Wanying Kang and Eli Tziperman Published: 19th April, 2018 Abstract: The Madden‐Julian Oscillation (MJO) was shown to affect both present‐day sudden stratospheric warming (SSW) events in the Arctic and their future frequency under global warming scenarios, with implications to the Arctic Oscillation and midlatitude extreme weather. This work uses a dry dynamic core model to understand the dependence of SSW frequency on the amplitude and longitudinal range of the MJO, motivated by the prediction that the MJO will strengthen and broaden its longitudinal range in a warmer climate. We focus on the response of the midlatitude jets and the corresponding generated stationary waves, which are shown to dominate the response of SSW events to MJO forcing. Momentum budget analysis of a large ensemble of spinup simulations suggests that the climatological jet response is driven by the MJO‐forced meridional eddy momentum transport. The results suggest that the trends in both MJO amplitude and longitudinal range are important for the prediction of the midlatitude jet response and for the prediction of SSWs in a future climate. Plain Language Summary: Sudden stratospheric warming (SSW) events occur in the Arctic stratosphere during winter approximately every other year, featuring an abrupt warming and a breakdown of the polar vortex. These events affect midlatitude extreme weather events and are therefore of a societal relevance, making it important to be able to predict a change in their frequency in a future climate change scenario. In the present climate, these events seem to be only weakly influenced by the Madden‐Julian Oscillation (MJO), the dominant intraseasonal variability in the tropics. The authors have previously shown that a strengthening of the MJO, which is expected in a warmer future climate, may lead to more frequent SSW events. The mechanism behind such enhanced future SSW frequency is shown here to involve a nonlinear interaction of MJO‐forced atmospheric waves with the midlatitude tropospheric jet. The waves make the midlatitude jet more asymmetric in longitude, therefore causing it to emit stronger stationary waves that reach the polar Arctic stratosphere, therefore leading to the more frequent occurrence of SSW events. This motivates studying this teleconnection between the tropical MJO and the Arctic SSW events using more detailed models, to increase our confidence in the prediction of future climate and weather regimes. Link to full paper: https://www.seas.harvard.edu/climate/eli/reprints/Kang-Tziperman-2018b-preprint.pdf
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