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Bring Back 1962-63 posted a topic in Research PortalAtmospheric Dynamics Feedback: Concept, Simulations, and Climate Implications Authors: Michael P. Byrne and Tapio Schneider First Published: January 12th, 2018 Published on line: March 26th, 2018 Abstract: The regional climate response to radiative forcing is largely controlled by changes in the atmospheric circulation. It has been suggested that global climate sensitivity also depends on the circulation response, an effect called the “atmospheric dynamics feedback.” Using a technique to isolate the influence of changes in atmospheric circulation on top-of-the-atmosphere radiation, the authors calculate the atmospheric dynamics feedback in coupled climate models. Large-scale circulation changes contribute substantially to all-sky and cloud feedbacks in the tropics but are relatively less important at higher latitudes. Globally averaged, the atmospheric dynamics feedback is positive and amplifies the near-surface temperature response to climate change by an average of 8% in simulations with coupled models. A constraint related to the atmospheric mass budget results in the dynamics feedback being small on large scales relative to feedbacks associated with thermodynamic processes. Idealized-forcing simulations suggest that circulation changes at high latitudes are potentially more effective at influencing global temperature than circulation changes at low latitudes, and the implications for past and future climate change are discussed. Link to Paper: https://pdfs.semanticscholar.org/8f29/8a8c3782fc69b576804e2ad9d037daf1df3f.pdf
Bring Back 1962-63 posted a topic in Research PortalFast and Slow Components of the Extratropical Atmospheric Circulation Response to CO2 Forcing Authors: Paulo Ceppi, Giuseppe Zappa, Theodore G. Shepherd and Jonathan M. Gregory First Published: September 15th, 2017 Published on line: January 19th, 2018 Abstract: Poleward shifts of the extratropical atmospheric circulation are a common response to CO2 forcing in global climate models (GCMs), but little is known about the time dependence of this response. Here it is shown that in coupled climate models, the long-term evolution of sea surface temperatures (SSTs) induces two distinct time scales of circulation response to steplike CO2 forcing. In most GCMs from phase 5 of the Coupled Model Intercomparison Project as well as in the multimodel mean, all of the poleward shift of the midlatitude jets and Hadley cell edge occurs in a fast response within 5–10 years of the forcing, during which less than half of the expected equilibrium warming is realized. Compared with this fast response, the slow response over subsequent decades to centuries features stronger polar amplification (especially in the Antarctic), enhanced warming in the Southern Ocean, an El Niño–like pattern of tropical Pacific warming, and weaker land–sea contrast. Atmosphere-only GCM experiments demonstrate that the SST evolution drives the difference between the fast and slow circulation responses, although the direct radiative effect of CO2 also contributes to the fast response. It is further shown that the fast and slow responses determine the long-term evolution of the circulation response to warming in the representative concentration pathway 4.5 (RCP4.5) scenario. The results imply that shifts in midlatitude circulation generally scale with the radiative forcing, rather than with global-mean temperature change. A corollary is that time slices taken from a transient simulation at a given level of warming will considerably overestimate the extratropical circulation response in a stabilized climate. Link to Paper: https://journals.ametsoc.org/doi/pdf/10.1175/JCLI-D-17-0323.1
Bring Back 1962-63 posted a topic in Research PortalMultiple Drivers of Arctic Amplification - Presentation Workshop Presentation: Aspen Global Change Institute, Aspen, Colorado Workshop Programme: “Understanding the Causes and Consequences of Polar Amplification” - June 12th -16th, 2017 Presenters: Laurent Terray and Clara Deser Presentation Date: 13th June, 2017 Abstract: None Link to full video presentation (31 minutes): https://www.agci.org/lib/17s1/multiple-drivers-arctic-amplification Link to presentation (slides and charts only): https://www.agci.org/sites/default/files/pdfs/lib/main/Aspen_terray_2017.pdf Link to full agenda and presentations: https://www.agci.org/event/17s1