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Researchers integrate gravity waves into prediction models

German meteorologists are developing a way to incorporate the influence of gravity waves in weather prediction models.

Gravity waves form in the atmosphere as a result of destabilizing processes, for example at weather fronts, during storms or when air masses stroke over mountain ranges. They can occasionally be seen in the sky as bands of cloud. However, most of the time they are not accounted for in weather forecasts and climate models because of their short wavelength.

Measuring gravity waves

Research led by Goethe University Frankfurt has successfully developed parameterizations that are now being tested in the second phase of the MS-GWaves project. Although gravity waves have comparatively short wavelengths of between just a few hundred meters and several hundred kilometers, at times they influence the transport of water vapor as well as large-scale winds and temperature distributions to a considerable degree.

This effect is strongest in the upper layers of the atmosphere. These, in turn, have such a strong effect on the lower layers that a realistic modeling of weather and climate in the atmosphere is impossible without giving due consideration to gravity waves.

Gravity waves also play a significant role for air traffic in predicting turbulence and are an important factor in weather extremes, such as heavy rain or storms.

In the first phase of the MS-GWaves projects, 10 research institutes documented the formation of gravity waves in one of the largest measuring campaigns ever undertaken, using radar, high-performance lasers, rockets and research planes as well as laboratory tests.

The researchers also refined the hypothesis on the formation and dispersion of gravity waves to such an extent that their development can now be reproduced much more reliably in high-resolution numerical models too.

Modeling

In the next step of the research – which is being led by Professor Ulrich Achatz of the Department of Atmospheric and Environmental Sciences at Goethe University Frankfurt – the findings will be used to improve parameterizations, which serve to describe the influence of gravity waves, in weather and climate models with typically coarser resolution.

Researchers have so far refined the weather and climate model ICON, which is used by Germany's National Meteorological Service and the Max Planck Institute for Meteorology.

The new model, UA-ICON, allows for more precise predictions for the upper atmosphere and can be operated with different resolutions, so that gravity waves can either be simulated in it for test purposes or parameterized in the operational mode. Advanced parameterizations are now being integrated in this model and tested.

The project will also focus on the impacts on weather prediction and climate modeling. An important aspect in this context is a better description of the interaction between gravity waves and ice clouds (cirrus), undertaken in cooperation with the University of Mainz.

- September 2017

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