“We have investigated the details about how rain showers are becoming intensive and we discovered that cloud build up is not just decided by large-scale atmospheric movements. There is also an internal self-organisation in cumulus clouds, which over the course of a day leads to less – but more enduring – rain showers,” explains Peter Berg, researcher within precipitation and climate at SMHI.
Previous studies have shown that powerful precipitation becomes intensified from increasing temperatures compared to more vast areas of rain. Now researchers are able to show that the self-organisation in cumulus clouds is increased with higher temperatures.
Influenced by the atmosphere's “memory”
“Simulations clearly showed that the atmosphere “remembers” previous rain showers that are stored in steam, amongst other things. This influences both the build-up of individual rain showers and the distribution of rain showers over a larger area,” says Peter Berg.
Researchers have created simulations in an area equivalent to a typical grid square of a global climate model. Using a very high-resolution atmospheric model, they can show the highly detailed important processes for the way rain showers are influenced by external factors and how they influence each other.
Extremely detailed model conditions
The simulations were created at the Max Planck Institute in Hamburg. They have a resolution of around 200 metres, which is very high when compared to a global climate model that typically has a resolution of several hundred kilometres.
Researchers studied rain showers under various idealised conditions and increasing temperatures. Due to the coarse-resolution, modern climate models are unable to provide the same high level of detail and continued development is necessary for them to provide usable information about climate change in short, intensive rain showers.
Parts of the research team have previously studied weather station readings and high temporal resolution radar where they have also been able to separate the different background processes for precipitation build-up. Previous studies have shown that powerful precipitation becomes intensified from increasing temperatures compared to more vast areas of rain. The new results provide further pieces of the puzzle that is understanding the origins of rainfall and extreme precipitation.