New research has unveiled a significant discovery about congestus clouds, a major cloud type that plays a pivotal but little-understood role in the Earth’s climate system. Led by Francisco Spaulding-Astudillo, a postdoctoral scholar in UCLA’s department of Earth, Planetary, and Space Sciences, and professor Jonathan Mitchell, the research provides new insights into why these clouds form at specific heights in the atmosphere and their potential impact on climate prediction models.
Congestus clouds, often described as “cauliflower-like” formations due to their towering and bulging structure, have long puzzled scientists. They are notoriously difficult to simulate in climate models, and observations have often conflicted on the reasons behind their formation. However, this study has advanced a novel explanation based on the interaction between water molecules and infrared radiation.
“We know water interacts with infrared radiation, and radiation, in turn, influences atmospheric circulation,” said Spaulding-Astudillo. “What we discovered is that the ability of water molecules to absorb and interact with radiation varies with altitude. This interaction creates an energy imbalance that pulls air out of clouds, offering a compelling explanation for the prominence of cloud cover at around 5-6 kilometers in the atmosphere.”
The findings reveal that an eccentric spectral property of water vapor in the mid-troposphere causes a decrease in the local cooling rate with height. This results in clear air being exported from where the cooling decreases, which, to maintain balance, draws in air from nearby clouds. This process is advanced as a key explanation for the prevalence of congestus clouds in tropical regions.
A Fundamental Discovery for Climate Science
The study addresses a central question in climate science: How do clouds organize themselves, and how does this influence the climate? In particular, the authors demonstrate that clouds are, to a remarkable degree, shaped by processes occurring within the clear air surrounding them.
The work also contributes to resolving an ambiguity in the relationship between humidity and cloud formation. Researchers demonstrated that the distribution of humidity with height supports the formation of congestus cloud tops. This adds support to the long-held idea that wetter conditions favor deep convective clouds, while drier conditions lead to mid-level clouds.
The Role of Congestus Clouds in a Warming Climate
Understanding the behavior of congestus clouds is crucial for improving climate models, as their radiative properties are poorly understood. Unlike low clouds, which cool the planet, and high clouds, which warm it, the net effect of congestus clouds on global temperature remains uncertain.
“Our ability to predict the future climate is hindered by uncertainties in cloud behavior,” Spaulding-Astudillo explained. “Our findings provide a framework to determine whether congestus clouds will have a net warming or cooling effect as the planet warms at an unprecedented rate.”
Historical Context and Future Impact
Congestus clouds were first documented in studies as early as 1962 by Malkus and Riehl, who noted their distinct structure over the tropical Pacific Ocean. Defined by the World Meteorological Organization as cumulus clouds with significant vertical growth, congestus clouds have remained a focus of curiosity for decades.
This new research helps to push the boundaries of modern climate science. By improving the representation of congestus clouds in climate models, the findings promise to enhance predictions of how the Earth’s climate will evolve in the coming decades.