How we forecast the behaviour of our oceans
We routinely run a number of ocean forecast computer models that help organisations, such as ferry operators, to plan their operations at sea, and allow accurate warnings of coastal flooding to be issued.
- Deep ocean - using ocean circulation analysis and forecast models.
- Shelf seas - using ocean circulation forecast models for the seas of the continental shelf that surrounds the UK.
- Wave forecast models
- A high-resolution sea-surface temperature analysis
- Coupled ecosystem forecast models that describe changes in the chemical and biological make-up of both deep ocean and UK shelf-seas
To further develop these capabilities we have established a National Centre for Ocean Forecasting (NCOF) in association with Proudman Oceanographic Laboratory, Plymouth Marine Laboratory, National Oceanography Centre, Southampton and the NERC Environmental Systems Science Centre. The aim of NCOF is to establish ocean forecasting as part of the national infrastructure, based on world-class research and development.
The deep ocean exerts an important influence on the weather we all experience. Understanding the processes of change of the deep ocean is also vital to improving our understanding of climate change.
We have run the global Forecasting Ocean Assimilation Model (FOAM) daily since 1997, forecasting three-dimensional ocean currents: temperature, salinity and sea-ice concentration, and thickness and velocity.
Each daily run uses observations from the previous 10 days, including:
- temperature and salinity profiles including data from Argo floats and moored instruments;
- sea-surface height data measured from earth orbiting satellites;
- ship, buoy and satellite sea-surface temperature observations;
- sea-ice concentration fields received from the Canadian Meteorological centre.
Mobile circulation patterns, such as ocean eddies, fronts and jets, are the ocean equivalent of the storm systems we recognise from weather charts. Model resolution is the key to ensuring that these features are properly captured. In order to do this, a number of high-resolution configurations, are nested within the global FOAM model.
Tides and storm surges have a major influence on the character of the regional seas around the UK, and predicting these correctly is of critical importance to mariners.
Following the catastrophic storm surge that flooded part of the south-east of England in 1953, the Met Office established a storm tides forecast service and now make daily runs of a storm surge model developed for the Environment Agency by the Proudman Oceanographic Laboratory.
The storm surge model is specifically designed to calculate changes in water level due to tide and surge. To forecast other key characteristics of our coastal seas, such as sea temperature the Proudman Oceanographic Laboratory Coastal Ocean Modelling System (POLCOMS) is used.
Both models are driven by tides (gravitational effects of the sun and moon) and forecasts of atmospheric parameters, including surface pressure. Close to the coastline the sea-bed becomes more complex, so a number of high-resolution configurations are used to represent the sea's response to this complexity as accurately as possible.
High seas are dangerous for mariners and bring the risk of coastal flooding.
Over the past two decades, we have run and maintained wave models to provide predictions of wave conditions, globally and around the UK.
Waves develop as a result of the wind blowing over the sea surface, leading to high 'wind-waves' developing during the strongest storms. Away from storm centres, wind-wave energy becomes more uniform and moves without further external influence - at this stage the waves are termed as swell. Wave energy is lost from the ocean when the waves break (e.g. white-capping in windy conditions) and due to friction as waves move through shallow water.
The Met Office model represents all these processes, including shallow-water physics and is driven by forecasts of surface winds.
Outputs from the models are used for a variety purposes, from predicting offshore vessel motion characteristics to forecasts of coastal waves and overtopping.
The Operational Sea Surface Temperature and Sea Ice Analysis (OSTIA) system produces a high-resolution (1/20°, approx. 5 km) daily analysis of the current sea-surface temperature (SST) for the global ocean. OSTIA uses satellite data provided by the Global High Resolution Sea Surface Temperature Pilot Project (GHRSST-PP), together with in-situ observations, to determine the sea-surface temperature.
Marine ecosystem modelling is of fundamental importance in understanding issues of water quality; environmental health, and maintaining sustainable ecologies. We are one of the first centres to run an operational forecast model.
Our models simulate the carbon-cycle and predict the biological and chemical make-up of both the open ocean and shelf seas. For example, in the shelf-seas around the UK we use models which separate the ecosystem into functional groups, including:
- one bacteria, four phytoplankton and three zooplankton functional groups
- a fully resolved diurnal cycle
- variable carbon to chlorophyll ratios
- independent nutrient pools for carbon, nitrogen, phosphorous and silicate