Periodic Reporting for period 4 - WAAXT (Wave-modulated Arctic Air-sea eXchanges and Turbulence)
Reporting period: 2023-07-01 to 2024-12-31
Wave-modulated Arctic Air-sea eXchanges and Turbulence (WAAXT) was a project designed to improve our understanding of ocean boundary layer processes in a changing Arctic Ocean. Arctic sea ice is linked to atmospheric and oceanic processes at lower latitudes through complicated teleconnections, meaning that changes in Arctic sea ice cover can have (poorly understood) effects on the weather and climate in Europe. Sea ice extent in the Arctic Ocean has been decreasing since the beginning of the satellite era, and current projections (e.g. IPCC 2021) suggest that the central Arctic basin will likely experience ice-free summers by the end of the century. While historically the Arctic Ocean has been isolated from the atmosphere by sea ice, the transition to a seasonally ice-free ocean means that air-sea exchanges of energy, momentum, and mass will now be more direct. In open water, waves play a key role in modulating those exchanges. Furthermore, prior research has shown that as the area of open water in the Arctic Ocean increases, the wave energy becomes stronger - due to the effect of increased wave fetch. The presence of this new wave field will have several important effects, notably: 1) Modification and suppression of ice formation by wave motions and the associated near-surface turbulence. 2) Physical breakup of sea ice by wave motions, and the resulting modification of air-sea fluxes, upper-ocean structure, and melt rates. 3) Interactions between wave-driven turbulence, especially breaking and Langmuir circulations, with the unique salinity-based stratification in the Arctic basin. The net sum of these wave-ice feedback mechanism is a potentially significant contributor to future changes in sea ice cover.
WAAXT used a series of field campaigns to better understand the small-scale physical processes at the heart of wave-ice feedbacks. Autonomous, shipboard, and manually-sampled instrumentation measured the effects of wind/wave events over a range of scales; capturing both small-scale physical processes and their bulk effects.
Technological advances included the development of an autonomous surface vehicle capable of measuring the horizontal structure of turbulence in the upper-ocean and the lower atmosphere, and the effects thereof on sea ice formation. These in situ measurements were supported by measurements taken from a variety of drifting buoys, unmanned aerial vehicles (UAVs) with custom payloads, as well as a crewed aircraft.
Supported by these technical developments, WAAXT was able to pursue the scientific objectives during 4 field campaigns, two in the Lower St. Lawrence Estuary (Canada), and two in the Arctic (Canada, Denmark).
One challenge in modelling wave-ice feedbacks has been in quantifying the attenuation of waves in sea ice. WAAXT research showed that physical interactions within the ice pack, rather than under-ice turbulence is often the key driver for wave attenuation. Furthermore, that the mechanism for that attenuation varies significantly with ice type and ice floe density.
During the freeze up season, waves and wave-driven turbulence inhibit the formation of an ice layer that would isolate the atmosphere from the ocean. This means that more heat is transferred from the ocean to the atmosphere, and the ocean mixed layer cools more than it would if ice was present. By directly measuring ice formation, upper-ocean turbulence, and atmospheric forcing, WAAXT was able to show that wave-driven turbulence directly affects ice formation rates and was able to develop a metric for predicting the onset of ice formation. Numerical modelling was then used to show the seasonal effects of these processes.
Technological advances included the development of an autonomous surface vehicle capable of measuring the horizontal structure of turbulence in the upper-ocean and the lower atmosphere, and the effects thereof on sea ice formation. These in situ measurements were supported by measurements taken from a variety of drifting buoys, unmanned aerial vehicles (UAVs) with custom payloads, as well as a crewed aircraft.
Supported by these technical developments, WAAXT was able to pursue the scientific objectives during 4 field campaigns, two in the Lower St. Lawrence Estuary (Canada), and two in the Arctic (Canada, Denmark).
One challenge in modelling wave-ice feedbacks has been in quantifying the attenuation of waves in sea ice. WAAXT research showed that physical interactions within the ice pack, rather than under-ice turbulence is often the key driver for wave attenuation. Furthermore, that the mechanism for that attenuation varies significantly with ice type and ice floe density.
During the freeze up season, waves and wave-driven turbulence inhibit the formation of an ice layer that would isolate the atmosphere from the ocean. This means that more heat is transferred from the ocean to the atmosphere, and the ocean mixed layer cools more than it would if ice was present. By directly measuring ice formation, upper-ocean turbulence, and atmospheric forcing, WAAXT was able to show that wave-driven turbulence directly affects ice formation rates and was able to develop a metric for predicting the onset of ice formation. Numerical modelling was then used to show the seasonal effects of these processes.
WAAXT was able to provide a clearer understanding of the wave-modulated atmosphere-ice-ocean system, specifically:
- Momentum and heat fluxes in ice forming conditions.
- Ice streak formation mechanisms and their importance.
- Wave attenuation in sea ice as a function of ice type.
- The role of wave forcing on the mechanical thickening of sea ice.
- Ice breakup by waves.
- Sensitivity of sea ice cover and thickness to the timing, intensity, and duration of wind/wave events.
- Momentum and heat fluxes in ice forming conditions.
- Ice streak formation mechanisms and their importance.
- Wave attenuation in sea ice as a function of ice type.
- The role of wave forcing on the mechanical thickening of sea ice.
- Ice breakup by waves.
- Sensitivity of sea ice cover and thickness to the timing, intensity, and duration of wind/wave events.