The other half of surface observations. Marine observations concerns data collection out at sea.
Observations of the weather over the oceans are particularly important for:
- Forecasts and warnings to help ships and other offshore operators to avoid severe weather conditions at sea;
- Input to computer models that predict the future state of the atmosphere; and
- Provision of meteorological information over the long term that aids our understanding of the global climate.
Atmospheric changes on timescales of months, decades and centuries are driven by the state of the oceans. Observations are required from below the surface to help us understand the ocean circulation and to provide the initial conditions for ocean modelling.
The Met Office gathers marine observations from five main sources:
- Marine automatic weather stations - moored buoys, light vessels, offshore installations etc.
- Voluntary observing ships - merchant ships which cross the world's oceans
- Shipbourne automatic weather stations - on suitable ships primarily operating in UK coastal waters
- Drifting buoys - small buoys which drift with the ocean current
- Argo floats - compact measuring devices which descend to the depths of the oceans
The Met Office requires marine observations, not just from the waters surrounding the UK, but also from the North Atlantic and the other ocean areas of the world. Those made and funded by the Met Office are part of an international effort co-ordinated by the World Meteorological Organisation (WMO), the International Maritime Organisation (IMO) and other regional bodies. Observations from observing ships, moored buoys and drifting buoys are also coordinated at the European level through the EUMETNET Surface Marine Programme.
The Met Office's network of Marine Automatic Weather Stations (MAWS) consists of 11 moored buoys and seven systems on lightships and islands. Three of the buoys are in coastal inshore waters, six are in open-ocean locations to the west of the British Isles and two, jointly owned with the French, are in the deep waters off the Bay of Biscay. These are supplemented by six moored buoys operated by Ireland and one by the Jersey Met Department.
Out of the water each buoy stands 6 m tall, measures 3 m in diameter, weighs 4.5 tonnes and has anchor cables several kilometres in length to moor it in the deep ocean off the continental shelf. It is deployed by a ship with heavy lifting gear and operates for up to two years between service visits. It measures air pressure; air temperature; sea temperature; humidity; wind speed, wind direction, wave height and wave period.
The buoys are designed to operate in the extreme environment of the north eastern Atlantic. They are solar powered using twin panels, but will run for around three months on batteries alone. All components of the observing system are duplicated to provide backup in the event of any system failures. The buoys have demonstrated their resilience very well over the last 10 years.
During winter 2007/8 our moored buoy network recorded several extreme wave events. In December the K3 buoy measured a significant wave height of 18.2 m and in March K2 measured a wave height of 17.6 m - the two highest wave events ever recorded by the network. The maximum wave heights (crest to trough) were probably several times higher than the significant wave height. Observations suggest the incidence of severe wave conditions in the north-east Atlantic is increasing and the buoy network provides the continuous stream of accurate measurements required to monitor these changes.
The stations transmit their observations hourly - 24 hours a day, 365 days a year. The data are currently used to help us:
- Produce forecasts;
- monitor developing weather conditions;
- provide information on the climatology of oceanic and coastal areas; and
- provide ground-truth for satellite observations.
Lightships are permanently-moored ships that have light beacons to aid navigation in busy sea routes. They offer a convenient platform for a Marine Automatic Weather Station. The lightship systems make the same range of measurements as the moored buoys, with the addition of visibility.
We also operate Automatic Weather Stations on two remote uninhabited Scottish Islands - Foula, and Sule Skerry. The island systems make most of the same measurements as the other systems, but because they are land based they do not measure sea temperature or waves.
Data from Foula is particularly useful for assessing the suitability of conditions to deploy pilots on to the oil supertankers prior to berthing at the Sullom Voe terminal on Shetland.
Observations from ships
Merchant ships and offshore oil platforms offer convenient sites for making meteorological observations in locations over the open ocean which would otherwise be devoid of data. The Met Office maintains an observing capability on more than 300 Voluntary Observing Ships (VOS) operating across the world's oceans. Officers and staff on recruited ships are encouraged to record and transmit weather observations in support of the World Meteorological Organisation's World Weather Watch and the JCOMM Voluntary Observing Ship Scheme (http://www.bom.gov.au/jcomm/vos/ ) . The recruitment of voluntary ships is also encouraged in the International Maritime Organisation's SOLAS (Safety of Life At Sea) Convention. Observations from ships are usually made every three to six hours, while at sea and transmitted back to the Met Office by satellite. About 50 percent of the UK's ship observations are from European waters and the North Atlantic, with the rest further afield.
VOS climate ships
More than 150 vessels from the UK observing fleet have been upgraded to report higher quality data for climate applications. This data is monitored to higher standard than the rest of the UK fleet and is accessible to climate researchers via the VOS Climate Project web site. VOSClim
The Met Office also acts as one of two Global Collecting Centre for Marine Climatological Data (alongside the German Met. Service DWD), with responsibility for basic quality control of ship data, and collection of those data not available in real-time The Met Office is also a lead centre for monitoring the real-time surface marine data from the VOS and drifting buoys.
Shipbourne Automatic Weather Station (AWS)
The level of automation on UK observing ships has increased significantly in recent years and this trend is expected to continue in the future. Automatic Weather Stations (AWS) have now been installed on a number of ferries, container ships and research vessels. They have the advantage that basic meteorological quantities can be automatically measured and transmitted at hourly intervals, rather than 3 or 6 hourly.
The Met Office has developed its own AWS system called AMOS ( Autonomous Marine Observing System) which measures pressure, temperature and humidity but which has the capacity to be extended to report additional parameters. The system reports via a built-in Iridium transmitter which also allows two-way communications.
Because it is an autonomous system it can be easily installed on a host ship in a matter of hours and because it is solar powered it is independent of the ships own systems.
Observations from Drifting Buoys
We use data from the global array of around 1,250 drifting buoys for both forecasting and climate studies. Drifting buoys, along with Voluntary Observing Ships, are the primary source of air pressure data over the oceans required by our weather forecasting models. They also provide measurements of sea temperature, which are vital for understanding the global climate.
What are drifting buoys?
Drifting buoys normally measure sea temperature and air pressure. By tracking their positions the surface currents can also be determined. Some also have sensors to measure wind and salinity. The buoys are battery powered and typically last for one to two years. Measurements are normally made hourly and the data are transmitted to satellite. Most drifting buoys use the Argo floats satellite system for data transmission and positioning, although new systems such as Iridium are currently being evaluated.
Met Office deployments
Over recent years the Met Office has deployed around 20 to 30 drifting buoys each year in the North Atlantic, co-ordinating its activities with its European partners. We also purchase about five each year for deployment in the South Atlantic and the Southern Ocean, as a contribution to the much larger Global Ocean Observing System (GOOS).