As climate has warmed in response to increasing greenhouse gases, the distribution of Arctic sea ice has changed dramatically, becoming thinner over large portions of the Arctic Ocean basin in summer with a prominent reduction of the September minimum in sea ice extent. A consequence is that the ice is more mobile and responds more easily to wind forcing. On the flip side, the expanding marginal ice zone (where ice cover is broken) is rougher and is hypothesized to influence Arctic cyclones and therefore feedback on the winds. Understanding of the physical processes that couple the atmosphere, ocean and sea ice is incomplete and the new frontier in prediction is to model this coupled system with fidelity and skill. Centres striving to improve capability in this area are our project partners: the Met Office, ECMWF and Met Norway.

Arctic cyclones are the dominant type of hazardous weather system affecting the Arctic environment in summer. They can also have critical impacts on sea-ice movement, sometimes resulting in ‘Very Rapid Ice Loss Events’ (timescale days to weeks) which present a major challenge to coupled forecasts of the Arctic environment from days out to a season ahead. Arctic cyclones also play an important role in the climate of the Arctic and through the field experiment we aim to deduce the dominant physical processes and mechanisms for two-way interaction between the Arctic cyclones and sea ice.

Our proposed observational experiment will be the first focusing on summer-time Arctic cyclones and taking the measurements required to investigate the influence of sea-ice conditions on their development. New observations are needed comprising of turbulent near-surface fluxes of momentum, heat and moisture measured simultaneously with the sea ice or ocean surface beneath the aircraft track and along cyclone-scale transects. These fluxes dictate the impact of the surface on the development of weather systems. We will operate from Svalbard (Norwegian Arctic) in August 2021, using the British Antarctic Survey’s Twin Otter low-flying aircraft equipped to measure turbulence at flight level and the surface properties through infrared and lidar remote sensing.

Our collaborators from the USA and France, have designed an observational experiment, called THINICE, looking downwards on Arctic cyclone structure from an aircraft flying near the tropopause (about 10 km above ground). Our projects are co-designed that the observations from the Twin Otter will form a bridge between measurements from above using the French SAFIRE Falcon aircraft, combined with satellite data, and the properties of the surface fluxes and sea ice beneath.