Towering cumulus clouds often loom over the southern Great Plains of the United States, particularly when warm, moist air rises from the soil during summer months. New research that tracked cumulus cloud formation over the course of a day demonstrates that much of the complex variation in the clouds derives from local variations in soil moisture, combined with pockets of cold air in the atmosphere.
Fast et al. used observational data from Oklahoma and Kansas collected on 30 August 2016 through the Holistic Interactions of Shallow Clouds, Aerosols, and Land-Ecosystems (HI-SCALE) campaign, which studied interactions between land, vegetation, and the atmosphere. During the morning, rainless, shallow clouds formed over southeast Oklahoma, then spread northwest into southern Kansas. By early afternoon, what was a fairly uniform field of clouds became more complex—some regions became cloudless, whereas others saw bigger, rain-laden clouds form.
The team attempted to recreate those patterns in a computer simulation, using an algorithm that tracks thousands of individual cumulus clouds at once. The researchers could faithfully represent the HI-SCALE observational data in the model only by including detailed soil moisture data from across the region. Later in the day, after about 1:00 p.m., regions of colder air surrounded by warm air, called cold pools, also played an important role, they found. The new study suggests that to accurately predict how clouds will behave, climate and weather models must account for soil conditions. (Journal of Advances in Modeling Earth Systems (JAMES), https://doi.org/10.1029/2019MS001727, 2019)
—Emily Underwood, Freelance Writer