Arctic Butterflies: Testing a new paradigm for polar atmospheric dynamics

The Arctic is warming faster than anywhere else on Earth and uncertainty over future climate change has severe consequences for decision making in the Arctic and mid-latitudes. Increased human activity in the region, partly due to the dramatically reducing summer sea-ice extent, increases vulnerability to high impact weather. Mitigating these risks demands better forecasts, but to make more confident predictions of both extreme weather and future climate change we need to address a critical foundational knowledge gap. While polar atmospheric dynamics is generally considered to be similar to that in mid-latitudes, our recent work challenges that assumption, highlighting several aspects of weather system dynamics that are fundamentally different, with implications for their inherent predictability and interaction with climate. Altogether, our recent work suggests a new paradigm in which polar dynamics is typically dominated by vortices interacting across a broad range of scales, contrasting the dominance of wave-like features existing on jet streams in mid-latitudes. Attention should be focused closely on the mechanisms of vortex evolution and interaction, such as the intriguing potential for frictional and diabatic processes to enhance the longevity of Arctic cyclones, as explored in our recent Arctic Summertime Cyclones field campaign. We hypothesise that two distinct dynamical regimes can occur: one in which the Arctic atmosphere is strongly coupled to mid-latitudes and a second in which it is isolated. In this second regime, vortices evolve and interact in close accordance with geostrophic turbulence theory, classically linked to an upscale energy cascade and an inherent limit to predictability as popularised by the butterfly effect in chaos theory (defined as a sensitive dependence to initial conditions). Our hypothesis is that shifts between these dynamical regimes can account for the much higher variations in weather predictability of the Arctic compared with mid-latitudes. If true, this paradigm has important implications not only for weather prediction in this region but also for the impact of climate change on aspects of variability such as the interaction of mid-latitude jet stream meanders with the Arctic. Here we propose to thoroughly test this paradigm from a range of different perspectives. A new very high resolution pan-Arctic reanalysis dataset, from our partner Met-Norway, provides a valuable opportunity, and a novel method to directly diagnose local upscale and downscale energy transfers will be applied to this. A suite of idealised model experiments will be performed to determine the sensitivity of the vortex dynamics to key physical parameters, and will allow us to connect with previous work in the field of planetary geophysical fluid dynamics. Arctic cyclone case studies will then be used to ensure relevance to the most extreme weather events and also to allow the best use to be made of the valuable field campaign observations. Once the role of turbulent vortex dynamics has been thoroughly quantified, we will proceed to apply this paradigm to explain the large variability in forecast skill in the Arctic. Working closely with the Met Office we will develop practical tools for assessing Arctic predictability and contribute to the development and evaluation of the new UK regional couped Arctic model. We ultimately aim to uncover the secrets of the elusive Arctic butterflies: what are the small-scale flow features that grow to disrupt forecasts across the Arctic, where do they form, how do they grow and under what conditions do they flourish?