Watching the weather

Measuring wind

Like all of ESA’s Earth Explorer missions, Aeolus responds to one of the most urgent Earth-science questions of our time. This novel mission has been designed to address the lack of global wind profiles in the Global Observing System.

Established under the auspices of the World Meteorological Organization, the Global Observing System 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 the observing system 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.

Aeolus measurement geometry

Different types of observations currently come from:

Surface data: from land stations, ships and buoys, and also from scatterometer instruments on satellites. They are all single-level data and cannot provide 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 multilevel around airports.

Multilevel 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 from Aeolus will 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

However, being such a dynamic and relatively invisible aspect of Earth’s environment, it is extremely difficult to make global measurements of the wind in clear air from space. It took many years to develop the technology to do this – but Aeolus will profile the world’s winds by probing the atmosphere using a highly sophisticated Doppler wind lidar – a completely new approach to measuring the wind from space.

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