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1. Walker circulation response to extratropical radiative forcing

   https://doi.org/10.1126/sciadv.abd3021  

   Kang, Sarah M. ; Xie, Shang-Ping ; Shin, Yechul ; Kim, Hanjun ; Hwang, Yen-Ting ; Stuecker, Malte F. ; Xiang, Baoqiang ; Hawcroft, Matt ( November 2020 , Science Advances)

   null (Ed.)

   Walker circulation variability and associated zonal shifts in the heating of the tropical atmosphere have far-reaching global impacts well into high latitudes. Yet the reversed high latitude–to–Walker circulation teleconnection is not fully understood. Here, we reveal the dynamical pathways of this teleconnection across different components of the climate system using a hierarchy of climate model simulations. In the fully coupled system with ocean circulation adjustments, the Walker circulation strengthens in response to extratropical radiative cooling of either hemisphere, associated with the upwelling of colder subsurface water in the eastern equatorial Pacific. By contrast, in the absence of ocean circulation adjustments, the Walker circulation response is sensitive to the forcing hemisphere, due to the blocking effect of the northward-displaced climatological intertropical convergence zone and shortwave cloud radiative effects. Our study implies that energy biases in the extratropics can cause pronounced changes of tropical climate patterns. 

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2. The contrasting response of outlet glaciers to interior and ocean forcing

   https://doi.org/10.5194/tc-14-2515-2020  

   Christian, John Erich ; Robel, Alexander A. ; Proistosescu, Cristian ; Roe, Gerard ; Koutnik, Michelle ; Christianson, Knut ( January 2020 , The Cryosphere)

   Abstract. The dynamics of marine-terminating outlet glaciers are of fundamental interest in glaciology and affect mass loss from ice sheets in a warming climate. In this study, we analyze the response of outlet glaciers to different sources of climate forcing. We find that outlet glaciers have a characteristically different transient response to surface-mass-balance forcing applied over the interior than to oceanic forcing applied at the grounding line. A recently developed reduced model represents outlet-glacier dynamics via two widely separated response timescales: a fast response associated with grounding-zone dynamics and a slow response of interior ice. The reduced model is shown to emulate the behavior of a more complex numerical model of ice flow. Together, these models demonstrate that ocean forcing first engages the fast, local response and then the slow adjustment of interior ice, whereas surface-mass-balance forcing is dominated by the slow interior adjustment. We also demonstrate the importance of the timescales of stochastic forcing for assessing the natural variability in outlet glaciers, highlighting that decadal persistence in ocean variability can affect the behavior of outlet glaciers on centennial and longer timescales. Finally, we show that these transient responses have important implications for attributing observed glacier changes to natural or anthropogenic influences; the future change already committed by past forcing; and the impact of past climate changes on the preindustrial glacier state, against which current and future anthropogenic influences are assessed. 

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3. The contrasting response of outlet glaciers to interior and ocean forcing

   https://doi.org/doi.org/10.5194/tc-2019-301  

   Christian, J.E. ( December 2019 , The cryosphere discussions)

   The dynamics of marine-terminating outlet glaciers are of fundamental interest in glaciology, and affect mass loss from ice sheets in a warming climate. In this study, we analyze the response of outlet glaciers to different sources of climate forcing. We find that outlet glaciers have a characteristically different transient response to surface-mass-balance forcing applied over the interior than to oceanic forcing applied at the grounding line. A recently developed reduced model represents outlet glacier dynamics via two widely-separated response timescales: a fast response associated with grounding-zone dynamics, and a slow response of interior ice. The reduced model is shown to emulate the behavior of a more complex numerical model of ice flow. Together, these models demonstrate that ocean forcing first engages the fast, local response, and then the slow adjustment of interior ice, whereas surface-mass-balance forcing is dominated by the slow interior adjustment. We also demonstrate the importance of the timescales of stochastic forcing for assessing the natural variability of outlet glaciers, highlighting that decadal persistence in ocean variability can affect the behavior of outlet glaciers on centennial and longer timescales. Finally, we show that these transient responses have important implications for: attributing observed glacier changes to natural or anthropogenic influences; the future change already committed by past forcing; and the impact of past climate changes on the preindustrial glacier state, against which current and future anthropogenic influences are assessed. 

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4. The response of surface buoyancy flux-driven convection to localized mechanical forcing

   https://doi.org/10.1007/s00348-019-2722-5  

   Matusik, Katarzyna E. ; Llewellyn Smith, Stefan G. ( May 2019 , Experiments in Fluids)

   null (Ed.)
5. Arctic Amplification: A Rapid Response to Radiative Forcing

   https://doi.org/10.1029/2020GL089933  

   Previdi, Michael ; Janoski, Tyler P. ; Chiodo, Gabriel ; Smith, Karen L. ; Polvani, Lorenzo M. ( September 2020 , Geophysical Research Letters)

   Arctic amplification (AA) of surface warming is a prominent feature of anthropogenic climate change with important implications for human and natural systems. Despite its importance, the underlying causes of AA are not fully understood. Here, analyzing coupled climate model simulations, we show that AA develops rapidly (within the first few months) following an instantaneous quadrupling of atmospheric CO₂. This rapid AA response—which occurs before any significant loss of Arctic sea ice—is produced by a positive lapse rate feedback over the Arctic. Sea ice loss is therefore not needed to produce polar‐amplified warming, although it contributes significantly to this warming after the first few months. Our results provide new and compelling evidence that AA owes its existence, fundamentally, to fast atmospheric processes.

    

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