[PAOCQ] Yi Zhang (New York University)

“Atmospheric Limits on Heat Extremes”

How hot can a heatwave get? And what about humidity that makes the heat more dangerous? Much research has focused on the drivers of extreme heat, such as blocking highs. Here, we examine the physical process that limits temperature and humidity. Like a pot of water on a stove, where hot water rises and cooler water sinks, convection in the atmosphere prevents heat from accumulating indefinitely near the surface. We use this principle to derive theoretical upper bounds on surface temperature and wet-bulb temperature, expressed as functions of free-tropospheric temperature. These bounds enabled a successful seasonal forecast of tropical wet-bulb temperature extremes following the 2023 El Niño and provide a physically grounded framework for reassessing CMIP6 projections. The dependence of the upper bound on free-tropospheric temperature naturally raises the question: what controls free-tropospheric temperature and its distribution? In the tropics, this distribution is narrow due to the weak Coriolis effect. With warming, we show that these weak temperature gradients become even weaker, due to a slowdown in clear-sky subsidence. I will conclude by discussing how the bounded nature of heat extremes (given a certain free-tropospheric temperature distribution) could reshape risk assessment and help constrain uncertainty in future projections.

PAOC Colloquium —

Interdisciplinary seminar series that brings together the whole PAOC (Program in Atmospheres, Oceans, and Climate) community. Seminar topics include all research concerning the physics, chemistry, and biology of the atmospheres, oceans and climate, as well as talks about societal impacts of climatic processes.

Contact: paoc-colloquium-comm@mit.edu