Implementing Cloud Radiative Effect Denial Experiments into E3SM
Photo by Daniel Ramirez. Taken on 8 September 2013. Wikimedia CC BY-2.0
Clouds play a key role in controlling the Earth’s temperature by affecting how much sunlight reaches the surface and how much heat escapes back into space. These cloud radiative effects (CREs) play an important role in modulating the flow of energy through Earth’s atmosphere. Disabling, or turning off, aspects of these CREs in Earth system models allows scientists to test hypotheses related to how CREs impact features of the present-day climate as well as potential future climates. Researchers added seven new disabling experiments to the Energy Exascale Earth System Model (E3SM) model to study clouds more closely These experiments include both commonly used ones in the research community and new experiments. This work documents the code changes needed to produce these experiments as well as step-by-step instructions for how to run them. Researchers used these experiments to provide new insights into prior findings such as the role of CREs on monsoon rainfall, intensifying rain rates, and poleward expansion of the atmospheric circulations.
Understanding CREs helps us understand the current climate as well as cloud feedbacks, and it is critical to making predictions for Earth’s future. Experiments that selectively disable aspects of the CREs have been added to E3SM to enable new scientific hypothesis testing. These experiments help test new ideas by changing how we consider clouds’ impact. By changing how clouds are represented in the model, researchers can ask new questions, like how clouds affect seasonal rains or weather cycles.
Clouds play a big role in how energy moves through Earth’s climate, affecting temperatures and weather patterns. CRE modulates the flow of energy through the system. The mean CRE impacts surface and atmospheric temperatures as well as the distribution of rainfall. Researchers have introduced seven existing and new experiment types into the E3SM for modifying the simulation CRE, enabling new hypothesis testing and scientific discovery.
The experiments are broadly contained within two categories: one that disrupts the mean CRE; and one that disables the covariance of CRE with atmospheric circulations (covariance is a measure of how two processes interact). Disrupting the mean CRE allows scientists to examine questions related to how the mean CRE impacts present-day climate features. Disrupting the covariance between CRE and circulations not only allows for examination of how those covariances impact the present day but has also been shown previously to be the ideal method for examining cloud feedbacks on physical processes. The researchers demonstrated that by comparing experiment types, the role of individual aspects of the CRE on monsoon rainfall can be quantified. Also, the researchers proposed an alternative to the popular cloud-locking method that may open up new research pathways in the future. This addition to the E3SM model opens up new possibilities for understanding and predicting climate changes more precisely.