Discovering a hidden driver of extreme moist heatwaves

Intense sun at sunset. Credit: Pixabay

A new study in Nature Geoscience examines how the movement of dry air drives moist heatwaves, which pose serious risks to human health through the combination of humidity and high temperatures. Scientists supported by the Climate Program Office’s Modeling, Analysis, Predictions, and Projections (MAPP) program discovered that contrary to prior assumptions, dry air entrainment, the mixing of dry air from higher altitudes into the moist air below, plays a key role in the formation of moist heatwaves. Using reanalysis data, climate models, and experiments, they found that dry air in the lower-free troposphere (the layer of the atmosphere about 1-3 kilometers above the surface) can limit the upward movement of warm, moist air that usually cools the surface. The suppression of this movement leads to higher temperatures and humidity near the ground. As the climate warms, the increasing dryness of the lower-free troposphere could lead to more frequent and intense moist heatwaves, exacerbating health risks and economic impacts, particularly in densely populated tropical and subtropical areas.