The Arctic is being radically transformed by ongoing climate change. This has important effects on peoples lives, not just in the Arctic where people are now experiencing a climate very different to the one they have experienced throughout the 20th century, but also further afield as the changes in the Arctic may also affect the weather across Europe. This transformation is particularly visible in the shrinking sea ice cover. The ice is getting thinner and this makes it easier for it to be broken up by the action of wind and waves. While in the atmosphere the weather is also strongly affected by the presence of sea ice. If the sea ice is thin, then a passing storm can break up the sea ice, possibly causing it to melt faster. But the storm may also be affected by the breaking of the ice cover as it is then 'fed' with more heat from the ocean.
In ARIA we make use of a cutting-edge sea ice model driven by a regional atmospheric model to investigate the response of sea ice to the passage of cyclones in the Arctic. We have looked at rapid break-up events in the ice where large chunks of the sea ice break-off from the rest of the ice pack in quick secession, following the passage of a storm. And we have used an atmospheric model customised to simulate the dynamics of the harsh polar environment to drive the sea ice model.
We took a case study of a particularly large break-up event that occurred in the Beaufort Sea during February and March of 2013, and we have shown that this sea ice model is capable of realistically capturing the fracturing of sea ice. This is the first time that this kind of rapid break-up of sea ice has been captured in a model. We found that during these events there is a temporary increase in the sea ice volume in the Arctic as new sea ice forms in the gaps where the sea ice has been broken up by the storm. However, the sea ice also gets exported out of the Arctic more rapidly, leading to a reduction in the thick multi-year ice cover. So the net effect of these storms is to create a thinner and weaker sea ice cover, which may precondition earlier breakup in Spring and accelerate sea ice loss. Another important result from our work is that it is necessary to have a high quality and high-resolution atmospheric model to accurately simulate such breakup events.
Our next steps will be to investigate the importance of feedbacks between the ocean, sea ice, and atmosphere during these events. We will focus on how the breakup of sea ice affects the amount of heat coming from the ocean into the atmosphere and whether that has a significant effect on the lifecycle of the storms breaking up the ice.
By using these very detailed models to understand these processes we will then investigate how well these processes are captured in current climate models. A lot of the uncertainty around what the Arctic sea ice cover will look like in the near future is due to uncertainty in these dynamics, so by improving our understanding of these processes, we can reduce uncertainty in our climate projections.
Arctic cyclones can break up and reshape the Arctic sea-ice cover and can be expected to do so more readily as the ice grows thinner due to anthropogenic climate change. Processes driven by Arctic cyclones can enhance the rate of melting of the ice and increase its export out of the Arctic. The record minima in sea ice extent in 2012, which was partially attributed to the presence of an Arctic cyclone. However, despite their importance, Arctic cyclones have remained relatively un-examined. We hypothesise that surface coupling (interactions between the ocean, sea ice and atmosphere) play a crucial role in determining the life cycle of Arctic cyclones, and the effect they have on the sea ice.
In ARIA we will take an important step towards understanding the role of sea ice-atmosphere interactions during the passage of cyclones, and how they might be expected to change in the future. We will quantify the dynamical feedback between the sea ice and atmosphere using a cutting-edge sea-ice model and a state-of-the-art atmospheric model. We will then evaluate the latest generation of climate models (CMIP6) to determine how well they reproduce the underlying conditions, and what is lost in the climatology by failing to resolve these processes. In particular we will focus on the impact cyclones have on the sea-ice volume, both in the short-term response and how it affects the inter-annual variability and overall decline observed in recent decades. The project results will therefore directly contribute to addressing the World Climate Research Programme’s grand challenge on the melting cryosphere.