Atmospheric waves skew forecasts

Clive Cookson, Financial Times, p 15, 19 March 2004

Basic flaws in mathematical models are not the only factor undermining the accuracy of weather forecasts (see article on right). Physicists at the University of Oxford have discovered that small-scale fluctuations in the atmosphere, known as inertia-gravity waves, are causing significant forecasting errors.

These waves, so called because they are sustained by a combination of inertial and gravitational forces, can sometimes be seen as stripy features in clouds. Meteorologists have always assumed that they do not interact significantly with weather systems such as warm and cold fronts.

According to the Oxford scientists, this assumption is wrong. They tested it, using laboratory experiments and a computer model to simulate inertia-gravity waves, and found that the waves had an unexpectedly strong impact on the system. The results are published in Nonlinear Processes in Geophysics.

It is impossible to add inertia-gravity waves directly to forecasting models, because their wavelengths are too small. Instead, the Oxford researchers suggest that the effect of the waves can be simulated by adding random noise to the model.

"More research is needed to find out exactly how bad the forecast error [due to ignoring inertia-gravity waves] might be, but the preliminary results are very exciting," says Paul Williams, one of the researchers. "It sounds bizarre to suggest that adding random noise to a forecast might help to improve it, but science is always full of surprises."