Supervisors: Ronan Fablet, Bertrand Chapron, Valentin Resseguier
Funding: ERC STUOD
Start date: November 2023
Summary: Ocean surface waves have been demonstrated to be an important component of coupled earth system models. They affect atmosphere-ocean momentum transfer, break ice floes, alter CO2 fluxes, and impact mixed-layer depth through Langmuir turbulence. In contrast to the goals of third-generation spectral models, the wave information needed for mixing, air-sea, and wave-ice-coupling is much less than a full directional wave spectrum. All present parametrizations – for wave-induced mixing, surface drag, floe fracture, or sea spray – use primarily the wave spectrum's dominant frequency, direction, and energy or quantities that can be estimated from these such as Stokes drift and bending moments. Modest errors in sea state do not strongly affect the impacts of these parametrizations.
This minimal data and accuracy need starkly contrasts with the computational costs of spectral wave models as a component of next-generation Earth System Models (ESM). Can an alternative, cost-efficient wave modeling framework for air-sea interaction be developed to enable the routine use of sea state-dependent air-sea flux parametrization in ESMs?
In the proposed study, the Particle-in-Cell for Efficient Swell Wave Model (PiCLES) will be considered and constructed for coupled atmosphere-ocean-sea ice modeling. Combining Lagrangian wave growth solutions with the Particle-In-Cell method is expected to lead to a periodically meshing wave model on an arbitrary grid that scales in an embarrassingly parallel manner. Also anticipated, the set of equations solves for the growth and propagation of a parametric wave spectrum's peak wave number and total wave energy, which reduces the state vector size by a factor of 50-200 compared to spectral models.
The development of PiCLES shall thus aim to only require a fraction of the cost of established wave models with sufficient accuracy for ESMs--rivaling that of spectral models in the open ocean. The goal will be then to develop and test PiCLES against WaveWatch III in efficiency and accuracy, and consider extensions to analyze propagation properties of ocean surface swells in interaction with random surface currents.