Observing the ocean
14 August 2020
Information from the ocean is a vital input for the weather and marine forecasts that support safe navigation at sea. The ocean also holds the key to predicting larger-scale influences on our climate. But the ocean is vast, inhospitable and very deep. So how do we keep track of what's happening above and below the sea?
How are the ocean and atmosphere connected?
Oceans cover over 70% of the Earth's surface and have a close relationship with the atmosphere.
Oceans help moderate temperature by absorbing heat from the sun. They distribute this stored heat energy around the globe via currents.
Oceans also influence the weather. Climate drivers such as El Nino and La Nina, which are caused by temperatures in the tropical Pacific oceans, affect large areas of the planet.
Observing the state of the oceans and atmosphere enables us to predict the weather and detect how the climate varies and changes over time.
A global system of observations
We gather marine observations in different ways. Some come from equipment on board ships and others from equipment in the sea, such as buoys.
While satellites now give a wealth of information about ocean conditions, observations from the sea are still the only way to gather some types of data. They also help in confirming and checking satellite observations.
Meteorology is a global science. What happens in the atmosphere or oceans in one part of the world can affect the weather in other regions. That's why the UN coordinates several programs that our marine observations contribute to. These are the Global Ocean Observing System, the Global Observing System and Global Climate Observing System.
Our data are used:
- nationally – in weather forecasting on land and at sea
- internationally – contributing to large-scale weather and ocean prediction schemes
- globally – in climate monitoring, research and prediction, including the prediction of events such as El Niño and La Niña in the Pacific.
Animation: Our network of marine observing systems
Observations from ships
Australia takes part in the World Meteorological Organization's Voluntary Observing Ship scheme. It maintains a national fleet of ships that record and report weather observations at sea. Most of these are for temperature, barometric pressure, waves, wind speed and direction, sea surface temperature and visibility. The Australian Voluntary Observing Fleet consists of around 50 Australian and foreign-owned merchant, research, passenger, fishing and private vessels. These ships record observations close to Australia. They often also launch meteorological drifting buoys (more about those below).
We also take part in the Ship of Opportunity Programme. Our fleet is made up of five volunteer ships that drop probes every four hours on selected global shipping routes. These measure the temperature of the ocean at the surface and down to 800 m depth. The sampling is performed using a probe known as an expendable bathythermograph (XBT for short). Some of these routes have been continuously sampled for over 20 years.
Observations from buoys
We also take observations from a fleet of buoys and floats. They send back data from the depths as well as the ocean surface.
Meteorological drifting buoys record atmospheric pressure and sea surface temperature from all ocean areas. From tracking their path we can also measure water movement. This uses a technique called Lagrangian current, which measures the path of a water particle over a long time. These buoys are often released by volunteer ships along common trading routes.
Argo profiling floats drift at depths of 1–2 km and return to the surface every 10 days. They measure temperature and salinity at different levels as they rise. Our profiling floats contribute to Argo Australia, part of a global array of these profiling floats.
Animation: The cycle of an Argo float
Wave buoys give us a variety of wave characteristics, including height, direction and period (the time between waves). We operate two wave buoys and receive data from other networks operated in New South Wales, Queensland, Victoria and Western Australia by state government agencies.
Tsunami warning buoys are deep-ocean moored buoys used to detect and measure tsunami waves. These waves are caused by earthquakes or underwater landslides. We established a network of tsunami warning buoys as part of the Australian Tsunami Warning System following the Indian Ocean Tsunami on Boxing Day 2004. Three pairs of buoys are moored in significant locations in the Indian Ocean, Coral Sea and Tasman Sea.
Animation: The Australian tsunami detection system
What's next in marine observations?
Our buoys and floats have been extremely reliable over the years. As technology improves so does the information we receive from them. They're continuously being upgraded to measure more environmental variables through the addition of new sensors, increased sampling depth and extended operating life. Observations from ships also benefit from technological improvements. Increased automation allows for more frequent observations in data-sparse areas of the oceans.
Small image at top left: The launch of a tsunami buoy.