EGU2020-11872
https://doi.org/10.5194/egusphere-egu2020-11872
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Model and state dependence of the atmospheric response to Arctic sea-ice loss

Amber Walsh1, James Screen2, Adam Scaife2,3, Doug Smith3, and Rosie Eade2,3
Amber Walsh et al.
  • 1College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter, UK (a.l.walsh@exeter.ac.uk)
  • 2College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter, UK
  • 3Met Office, Exeter, UK

The climate response to Arctic sea-ice loss is highly uncertain. There exists considerable disagreement between observational and modelling studies, and between models, for reasons that remain poorly understood. To make progress, the Polar Amplification Model Intercomparison Project (PAMIP) was designed to provide coordinated experiments, with consistent sea-ice loss applied in multiple models. Results from the PAMIP are presented, focussing on the robustness of the atmospheric response to Arctic sea-ice loss across models and, within individual models, the dependence of the response on the mean state.

In the troposphere, the mid-latitude jet is either weakened and/or shifted towards the equator in all models, albeit with varying magnitudes. We hypothesise that the magnitude of the jet response is sensitive to the atmospheric model resolution. To test this, and to more broadly identify the aspects of the atmospheric response that are sensitive to model resolution, we compare like-for-like experiments with two versions of the HadGEM3 model at low (N96) and high (N216) horizontal resolution.

The stratospheric polar vortex response to Arctic sea-ice loss is not consistent between models, and appears to be influenced by both the size of the ensemble for each model and the phase of the Quasi-Biennial Oscillation (QBO). The possible modulating effect of the QBO is further explored using new simulations with background atmospheric states representing the easterly and westerly QBO phases.

A surprising early result from the PAMIP simulations were sizeable changes in the Southern Hemisphere in response to Arctic sea-ice loss and significant changes in the Northern Hemisphere in response to Antarctic sea-ice loss, even in atmosphere-only model experiments. The robustness of such apparent interhemispheric connections across models, ensemble sizes and mean states is investigated.

 

 

 

How to cite: Walsh, A., Screen, J., Scaife, A., Smith, D., and Eade, R.: Model and state dependence of the atmospheric response to Arctic sea-ice loss, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11872, https://doi.org/10.5194/egusphere-egu2020-11872, 2020

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Display material version 1 – uploaded on 05 May 2020
  • CC1: Comment on EGU2020-11872, Tetsu Nakamura, 05 May 2020

    Thank you for interesting results.

    In the abstarct you mentioned about interhemispheric connection.

    Does this interhemispheric connection also depends on QBO-phase, or robustly seen among models?

    • AC1: Reply to CC1, Amber Walsh, 05 May 2020

      Thanks for your question Tetsu. Since writing the abstract, it has become clear that the interhemispheric effects are limited to a small number of models so it appears they are not robust responses. For HadGEM3 which is the model I've used to compare QBO phase, there's little evidence of an interhemispheric effect. Initially HadGEM3 did show this effect, although when the ensemble size was increased it disappeared. 

      • CC2: Reply to AC1, Tetsu Nakamura, 06 May 2020

        Thank you for detail answer, Amber.

         

        Althoug it might be a casual result due to internal variability, it is interesting that both directions (N to S and S to N) are found.

         

        Only in the limited month, we have found interhemisoheric connection between AO and AAO in the reanalysis (doi:/10.1029/2018GL081002), so I thought it is interesting if the sea ice changes in both poles driven it.

         

        Thank you, again.