Organic particles can be crucial to induce heavy rains, suggest climatologists

The clouds form on the particles existing in the atmosphere and extreme weather events such as floods and snowstorms are linked to the production of large amounts of ice in the clouds.

Organic particles such as pollen, bacteria, spores and plant material floating in air are particularly good for promoting the formation of ice in clouds, and EPFL climatologists show that the concentrations of these particles evolve as temperatures increase and decrease. The results are published in NPJ climate and atmospheric sciences.

“Biological particles are very effective in forming ice in the clouds, and the formation of ice is responsible for most of the precipitation that the planet receives worldwide, because ice falls very quickly from the sky. Intense ice formation is also associated with extreme weather conditions,” explains Thanos (Athanasios) born from the EPFL laboratory of atmospheric processor and their impacts Postdoctoral postdoctoral.

“Given our results, weather and climatic models must absolutely take into account organic particles, especially since biological particles should be present in larger quantities in the atmosphere while the climate warms up.”

Indeed, current meteorological and climatic models do not consider the effects of biological particles or their cyclic nature, which means that they potentially lack important modulators of clouds and precipitation engines in current and future climatic forecasts.

Mount Helmos, a case study for alpine regions

The study takes into account the air samples and their biological content collected in Mount Helmos, an Alpine zone located in Greece. The mountain reaches an altitude of 2,350 m, has a frequent cloud cover throughout the year and is influenced by the biological emissions of the Alpine forest below.

As temperatures increase throughout the day, pollen, bacteria, fungal spores and plant material are released from the Alpine forest, culminating at noon when the sun is at its highest level and reaches stockings during the night.

“We note that the number of particles which can nucle the ice coincides with the number of counts of organic particles and that they both show a strongly correlated diurnal periodicity, and the increase in biological particles can contribute to the formation of clouds which can make them precipitate”, concludes the GAO.

Nenes, who participated in the IPCC framing meeting in Malaysia to help define the chapters and shape the content of the 7th IPCC assessment report, says: “The result comes with a perfect moment.”

As a scientific coordinator of the great European project Cleancloud, Nenes is currently carrying out a second campaign at Mount Helmos, called Chopin, which benefits from an even more instrumentation to help identify the types of organic particles present in the atmosphere that induce clouds of clouds and ice formation.

A full sequence of cloudy radars, aerosol, UAV lidars, attached balloons and direct air sampling (with and without clouds) is used to characterize – with unprecedented details – how each biological particle contributes to the formation of clouds, and those most effective to do so, to improve weather and climatic predictions.

Nenes adds: “The data collected will not only be used for understanding the processes and improving the model, but also to improve or develop new algorithms used by satellites and soil remote sensing to study aerosols and clouds.

“We and the CleanCloud Consortium as a whole will work with the European Space Agency and our Sister Consortia Certainty and Airsense to help make the best use of the Earthcare satellite recently launched in the ultimate goal of understanding the role of aerosols on clouds and precipitation in a post-fossil world.”