How does moisture impact the storm tracks?

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Marguerite Brown just submitted a very insightful paper on the role of moisture in the mid-latitude circulation to JAS! She builds on a pioneering work by Lapeyre and Held to use a moist 2-layer quasi-geostrophic model to tease out the competing roles of moisture and temperature in driving the midlatitude atmosphere.

The effect of moist processes, especially the impact of latent heating associated with condensation, on the size and strength of mid-latitude storms is not well understood. Such insight is particularly needed in the context of global warming, as we expect moisture to play a more important role in a warmer world. In this study, we provide intuition into how including condensation can result in mid-latitude storms that grow faster and have features on both larger and smaller scales than their dry counterparts. We provide a framework for quantifying these changes and verify it for the special case where it is raining everywhere. These findings can be extended to the more realistic situation where it is only raining locally.