Aeolus is the first satellite mission to acquire profiles of Earth’s wind on a global scale.
Aeolus is the fifth in the family of ESA’s Earth Explorer missions, which address key scientific challenges identified by the science community and demonstrate breakthrough technology in observing techniques.
These near-realtime observations will improve the accuracy of numerical weather and climate prediction and advance our understanding of tropical dynamics and processes relevant to climate variability.
Aeolus – The Need
Many aspects of our lives are influenced by the weather. It goes without saying that accurate forecasts are important for commercial undertakings such as farming, fishing, construction and transport – and in general make it easier to plan the days ahead.
In extreme circumstances, knowing what the weather will bring can also help save lives and protect property.
Although weather forecasts have advanced considerably in recent years, meteorologists urgently need reliable wind-profile data to improve accuracy further.
Aeolus wind mission will demonstrate that measuring global wind-profiles from space, using laser technology, can meet this requirement.
Named after Aeolus, who in Greek mythology was appointed ‘keeper of the winds’ by the Gods, this novel mission will not only provide much-needed data to improve the quality of weather forecasts, but also contribute to long-term climate research.
The Aeolus satellite carries just one large instrument – a Doppler wind lidar called Aladin that will probe the lowermost 30 km of the atmosphere to measure the winds sweeping around our planet.
The lack of direct global wind measurements is one of the major deficits in the Global Observing System. This lack of measurements limits our understanding and the prediction of weather and climate.
Aeolus plays a key role in the quest to better understand the workings of our atmosphere, and to improve weather forecasting.
The wind forms the basis of atmospheric circulation, which governs the weather and climate.
Some areas of Earth receive more heat from the Sun than other areas. This leads to differences in air temperature, density and pressure, which in turn, cause the air to move – creating wind.
Wind transports heat away from equatorial regions towards the poles, and returns cooler air to the Tropics.
Rising warm air is associated with areas of low surface-pressure called cyclones, while areas of high surface-pressure, known as anticyclones, are associated with subsiding air. These pressure differences are balanced by air motion – wind.
Since Earth rotates and is spherical, winds to not move directly from high to low pressure areas. The greater the difference in air pressure between two regions, the stronger the wind will be. The wind continues to blow until the pressure difference changes.
The Coriolis force explains why winds generally blow perpendicular to the direction of the pressure difference.
The force acts at right angles to the direction of motion, so as to cause deflection to the right in the northern hemisphere and to the left in the southern hemisphere. The force increases from zero at the equator to a maximum at the poles. Winds are therefore deflected relatively little at low latitudes and at higher latitudes the degree of deflection is much larger.
In order to improve numerical weather prediction so that we can benefit from better weather forecasting, there is an urgent need for detailed near-realtime observations of global wind-fields at all scales. This is something meteorologists have needed for some time.
Aeolus has been developed to fulfil this need. The mission will generate about a 100 wind profiles an hour, which will give meteorologists better information to predict the weather.
Aeolus will be able to provide wind profiles for the entire planet, including remote areas lacking ground-based weather stations.
It will be the first space mission to acquire profiles of the wind on a global scale and pave the way for future operational wind missions.
Aeolus – Objective
The main objective of the Aeolus mission is to address the lack of global wind profiles in the Global Observing System (GOS).
Established under the auspices of the World Meteorological Organization, GOS is a coordinated system of methods and facilities for making meteorological and environmental observations on a global scale. Atmospheric measurements are used for weather forecast models worldwide.
However, direct global profile measurements of wind fields are lacking, representing one of the largest deficiencies in GOS and limiting improvements to numerical weather predictions and climate models.
Currently, most direct observations of the wind come from radiosondes that are launched every day from stations, most of which are in the Northern Hemisphere. Wind-field information in remote regions, over the oceans, in the tropics and Southern Hemisphere is largely indirect.
Different types of observations currently come from:
Surface data: from land stations, ships and buoys, and also from scatterometers on satellites. They are all single level data, and cannot provide any information on atmospheric profiles.
Single-level air data: mainly from aircraft at cruise altitude and cloud-motion winds derived from geostationary satellite imagery. Aircraft observations of wind and temperature are also made during ascent and descent, and are therefore ‘multi-level’ around airports.
Multi-level air data: mainly from radiosondes, wind profilers and polar-orbiting sounder data. Satellite sounders provide global coverage of radiance measurements, which can only be used indirectly.
Reliable and timely wind profiles are needed to improve our understanding of atmospheric dynamics, transport and cycling of energy, water, aerosols, chemicals and other airborne materials.
The Aeolus mission will:
- Measure global wind profiles (along a single line-of-sight) up to an altitude of 30 km
- Measure wind to an accuracy of 1 m/s in the planetary boundary layer (up to an altitude of 2 km)
- Measure wind to an accuracy of 2 m/s in the free troposphere (up to an altitude of 16 km)
- Determine the average wind velocity over 100 km tracks
- Measure 100 wind profiles per hour
Aeolus – Mission
The central aim of the Aeolus mission is to further our knowledge of the Earth’s atmosphere and weather systems. By recording and monitoring the weather in different parts of the world, Aeolus will allow scientists to build complex models of our environment, which can then be used to help predict how that environment will behave in the future.
These predictions will be useful in the short-term, since they can be applied to Numerical Weather Prediction in order to make forecasts more accurate. The Aeolus mission will thus improve our knowledge of all sorts of weather phenomena, from global warming to the effects of pollution.
Aeolus will fly in a rather low Sun-synchronous orbit of 320 km and will always be in the dusk or dawn position. The wind will be measured at 90 degrees to the satellite ground track on the night side of the Earth.
Aeolus will provide global observation of wind profiles from space. The main aim is to further our knowledge of Earth’s atmosphere and weather systems.
The mission will provide global observations of wind profiles from space to improve the quality of weather forecasts and advance our understanding of atmospheric dynamics and climate processes.
By demonstrating new laser technology, Aeolus is seen as a pre-operational mission that will pave the way for future meteorological satellites to measure wind. Aeolus carries breakthrough technology in the form of an innovative instrument called Aladin – an atmospheric laser Doppler instrument. It uses ‘light scattering’ and the Doppler Effect to gather data on wind.
Data are sent to a ground station in Svalbard, Norway, every orbit.