Weather prediction model skill during rapid solar fluctuation events

Name of applicant

Jacob Svensmark


Postdoctoral Fellow


University of Oxford


DKK 1,334,473



Type of grant

Reintegration Fellowships


Coronal mass ejections from the sun can significantly suppress the cosmic ray flux through Earth's atmosphere. Satellite observations of Earths cloud cover show that in the days following such events, the global cloud cover appears to be similarly lowered. This project aims to test whether the apparent cloud response to such rapid cosmic ray fluctuations is predicted by established weather forecasting models, or whether the the cosmic ray-cloud signal really stems from a physical mechanism not included in such models, such as a sensitivity of aerosol production and clouds to ionization rates caused by cosmic rays.


Clouds provide a net cooling effect of Earths climate. If cosmic rays are indeed affecting atmospheric aerosol concentrations and cloud cover, then that effect is not taken into account in current climate and weather prediction models. Aerosols and cloud interactions currently provide the largest uncertainty of our understanding the radiation budget of our climate, and any mechanism which can impact this is therefore potentially very important. This project provides a simple yet powerful test of the existence of a cosmic ray-cloud mechanism in the context of rapid cosmic ray fluctuation events.


The European Centre for Medium-Range Weather Forecasts (ECMWF) provides an assimilation of a large and diverse set of weather observations into a reanalysis product: A 3D state of the atmosphere, every 12 hours. Within the ERA-Interim data set, at each reanalysis step, the weather is then forecasted 10 days ahead. The skill of this forecast is the difference between the reanalysis and the forecast for a given observable quantity. The forecasting skill can then be analysed for relevant atmospheric parameters during times of rapid cosmic ray fluctuations, such as those caused by coronal mass ejections or rotating sunspots on earths surface. Doing so will then uncover whether the apparent cloud signal is due to natural meteorological variability or whether the cosmic rays are causing the cloud response signal.

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