Moisture makes the atmosphere less efficient?

Marguerite Brown just published our work on On the Inefficiency of Moist Geostrophic Turbulence: A Theory for the Energetic Output under Subsaturated Conditions in JAS!

The impact of humidity on the strength of midlatitude storms is not well understood. Humidity will increase as the planet warms, but it is unclear whether storms will become stronger or weaker as a result. We use an idealized computer model to learn how humidity will impact the strength of storms. We focus on the effect of evaporation at the planet’s surface, with simulations ranging from a completely dry atmosphere to one with rain everywhere. In between these two limits, it is raining in only part of the atmosphere, and storms are much weaker than in the case with rain everywhere. Somewhat counterintuitively, moisture makes the atmosphere less efficient at creating storm activity, despite the fact that latent heating plays a key role in driving individual storms! We discuss how to connect these results to more complex models and real-world data.