Theory for the description of the effect of short-wavelength waves in weather and climate models

What is it about?

Gravity waves are atmospheric waves with oscillations in wind, temperature, pressure etc that are emitted by heavy weather like thunderstorms, weather fronts etc, but also by winds blowing over mountains. Their wavelengths are so short (down to a few km) that present-day weather and climate models cannot resolve all of them with their coarse grids. Yet their impact on weather and climate is important. Atmospheric models must describe the dynamics and effects of gravity waves without resolving them explicitly, by modules called parameterizations, in order to get weather forecasts and climate simulations right. By now we understand that the traditional construction of gravity-wave parameterizations is too simple in several regards. This limits especially the reliability of climate-change simulations. The paper outlines a generalized theory to be used for gravity-wave parameterizations and it describes a numerical approach how it can be used in models. This potentielly also has applications to other interactions of waves and mean flows, e.g. in accoustics, plasma physics, general relativity, and quantum mechanics.

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Why is it important?

We describe how to better describe the effect of small-scale waves in slowly varying media, with an application to atmospheric gravity waves. Recent findings indicate that the way this issue is presently approached in numerical climate models is critically limiting their reliability. Our extended approach will help solving this problem.

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