The influence of Arctic sea-ice loss on mid-latitude weather and climate: exploring sensitivities and mechanisms

• Main Author: McKenna, Christine
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: University of Cambridge 2019
• Subjects: Arctic sea-ice; climate change; climate variability; climate modelling; IGCM4; large-scale atmospheric circulation; stratosphere-troposphere coupling; teleconnections; Rossby waves; Arctic Oscillation; mid-latitudes; Arctic; Climate change; Sea ice
• Online Access: https://www.repository.cam.ac.uk/handle/1810/307132; https://doi.org/10.17863/CAM.54225

Over the past few decades, Arctic sea-ice extent has declined, while there has been an apparent increase in severe winter weather across some mid-latitude regions. This has led to much research into whether these trends are dynamically linked. It has been suggested that the link may involve the Arctic Oscillation (AO), which describes the observed oscillation in geopotential height anomalies between high and middle Northern Hemisphere latitudes. Sea-ice loss has been shown to excite the AO's negative phase, which is linked to colder conditions in key regions of mid-latitudes, through various tropospheric and stratospheric mechanisms. However, the nature of the response to Arctic sea-ice loss and the mechanisms involved remain uncertain. This is because it is difficult to disentangle the complex web of potential processes involved, the modelled response to sea-ice loss is small relative to internal climate variability, and modelling studies find contrasting climatological mean responses to imposed sea-ice loss. Since all climate models project a continuation of Arctic sea-ice loss during the 21st century in response to anthropogenic greenhouse gas forcing, it is important that the potential influence of this on the highly populated mid-latitudes is better understood. In this thesis, the issues of complexity and statistical robustness are partly addressed by conducting idealised numerical modelling experiments using an intermediate complexity global circulation model, IGCM4. Such models are useful because they are complex enough to simulate a variety of important processes, but are relatively simple and computationally fast compared to full complexity state-of-the-art climate models. This helps to disentangle different processes from one another and allows for several-century-long simulations, making a statistically robust response more attainable. To understand the contrasting results of past modelling studies, it is firstly investigated whether the response to sea-ice loss is sensitive to the loss region (the ...