How Rising Air Plumes Help Spike Moist Heat
When dry air mixes with warm, moist air carried aloft by currents from the surface, it can contribute to rising wet-bulb temperatures near Earth’s surface.
Climate change has brought about more frequent extreme heat events worldwide, making moist heat metrics like wet-bulb temperature more significant. Wet-bulb temperature merges temperature and humidity, and when both heat and humidity are elevated, it poses a threat to human health. Researchers Jha and Byrne analyzed moist heat extremes on extratropical continents using data from the European Centre for Medium-Range Weather Forecasts' ERA5 reanalysis and the CESM2 global climate model.
They focused on the impact of dry air mixing into warm, moist air plumes that rise from Earth's surface to the upper troposphere. This process, called entrainment, significantly impacts moist heat extremes outside of the tropics. Entrainment alters the connection between stored energy in near-surface air and higher levels in the troposphere.
When dry air is mixed into rising plumes, it makes near-surface air more energetic due to increased humidity and temperature, resulting in more severe moist heat events. Using simulations, the researchers discovered that as the climate warms and the lower atmosphere becomes drier, the entrainment process will keep raising wet-bulb temperatures at the surface, potentially creating even more intense moist heat events.
Future research examining the effects of global warming on dry-air entrainment rates in rising plumes will help better predict how wet-bulb temperatures will rise in the future, the authors conclude.
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