Understanding & Predicting the Ocean Surface Boundary Layer
Exchanges of heat, water, carbon and nutrients between deep ocean and atmosphere are mediated through the ocean surface boundary layer (OSBL), and recent evidence links OSBL processes to weather and climate variations on timescales from a few days (eg organised tropical convection) to centuries (eg supply of nutrient to photic zone and links to the global carbon cycle).
Both the Met Office and the European Centre for Medium-range Weather Forecasts (ECMWF) are currently investigating the value of coupling ocean models to their existing weather models to improve the quality of extended range weather and climate forecasts.
While atmospheric boundary layer models are relatively mature, some fundamental physical processes determining ocean boundary layer dynamics and mixing are poorly understood; for example Langmuir circulations, interaction of inertial waves with shear at the mixed layer base, and horizontal and vertical fluxes into the boundary layer by submesoscale eddies and filaments.
There is a need to develop a more well-founded quantitative understanding of boundary layer processes that takes account of fundamental scaling relationships in order to give parameterisations that are valid over a wide range of dynamical regimes.
The overarching objective of the Ocean Surface Boundary Layer programme is:
"To build on recent UK scientific and technological advances to develop a fundamental improvement in weather and climate prediction on timescales from a few days to centuries."
In particular, the goal of this programme is to develop improved parameterisations of the physical processes that control transport and exchange of heat, water and biogeochemical tracers within and across the OSBL.
The parameterisations must be based on fundamental physical understanding and observation, and be suitable for global predictive Earth system modelling on timescales of days to decades. Parameterisations must be implemented and their performance evaluated in global ocean and Earth system models.
A number of scientific and technological building blocks for such an approach have been developed in recent years in the UK community, but an integrated approach to prediction of ocean boundary layer processes does not yet exist.
Recent advances have provided several key scientific tools to tackle the OSBL problem, including:
- Intensive process-based observations.
- Large Eddy Simulations (LES) that resolve the dynamics of the boundary layer and submesoscale processes.
- Large scale observations and modelling. The Argo buoy programme is now delivering a near global dataset of temperature and salinity profiles that captures boundary layer variability on timescales from 10 days to inter-annual.
This programme will contribute to several climate system theme challenges by delivering fundamental improvements to predictive models, based for example on novel process observations and on the new global Argo dataset.
These advances are likely to be fundamental to the UK's ability to deliver climate services, because of the increasing evidence that ocean boundary layer interactions are a key element in predictability on timescales from extended range Numerical Weather Prediction (10 days) through to seasons and decades.
The programme contributes to Earth system science challenges on ocean processes and their interaction with the Earth system, since boundary layer processes strongly influence nutrient supply to the photic zone and hence ecosystem development and carbon cycling.
It may also contribute to the technologies challenge on intelligent field sensors, by developing the potential of new technologies for intensive study of the ocean sub-mesoscale.