Scientists develop detailed representation of clouds in weather and climate models

A team of climate researchers and computational experts has developed an innovative method to study cloud dynamics in unprecedented detail in weather and climate models.

Publication date: 16-09-2019

Climate researchers and computational experts have developed an innovative method to study cloud dynamics in unprecedented detail in weather and climate models. The method employs comprehensive three-dimensional cloud simulations to replace the traditional approximations of cloud processes currently used in global climate models. The coupling of these simulations to global models is done with the help of software technology originally developed for astrophysical research.

The project is led by Daan Crommelin at CWI, together with Pier Siebesma at the Delft University of Technology and KNMI. The team’s method and initial findings are published in the Journal of Advances in Modeling Earth Systems.

Notoriously difficult
It is notoriously difficult for climate modelers to accurately depict cloud processes. Cloud dynamics act on scales from millimeters to several kilometers, but present-day global climate models typically operate on scales from 100 km and coarser. To overcome this scale gap in the models, researchers have traditionally used approximate formulae, known as parameterizations, to represent cloud physics. Parameterizations are simplified numerical representations of physical processes based on measurements and physical understanding.

In their paper, the team presents a computationally attractive alternative. They have replaced the parameterizations of clouds in a global-scale model developed by the European Centre for Medium-Range Weather Forecasts (ECMWF) with a turbulence-resolving model (in technical terms a large-eddy simulation) developed by the Royal Netherlands Meteorological Institute (KNMI) and Dutch universities.

Increased reliability
This approach of replacing parameterizations by explicit simulations, called superparameterization, has the advantage that all the relevant processes for the formation and development of clouds are actually resolved and represented in the model. This will increase the reliability of the simulations by, for example, improved predictions of cloud cover, cloud amount and cloud top heights.

Gaining a huge understanding
"It is incredible that we can now represent clouds so realistically in global weather and climate models", says lead author Dr Fredrik Jansson from CWI. “It is still a big computation to resolve clouds globally, but by applying our method to the regions where traditional approximations fail, I think we can gain a huge understanding of the role of clouds in the present and future climate."

Improvements in weather prediction
The authors plan to apply their method to quantify the response of the global model to the changes in cloud representation, which will allow improvements in weather prediction with respect to rainfall and ultimately quantify the global role of clouds in the future warming earth climate.

The research team is comprised of researchers from the Royal Netherlands Meteorological Institute (KNMI), Delft University of Technology, the Centrum Wiskunde & Informatica (CWI) and the Netherlands eScience Center.