**
Water vapor and atmospheric heat engines
**

**
Abstract
**

Many atmospheric phenomena, from convection to hurricanes to the global circulation are often described as heat engines. By this, we refer to the fact that these atmospheric flows can convert internal energy into kinetic energy by transporting heat from the warm Earth surface to the colder troposphere.

In this talk, I will first review the concept of a heat engine and discuss how the presence of water vapor can greatly reduce the work produced by a given thermodynamic cycle. I will then show how these thermodynamic concepts can be used to study atmospheric flows using a new technique, the Mean Air Flow As Lagrangian Dynamics Approximation (MAFALDA). This technique uses the standard output from a numerical model to build a set of idealized parcel trajectories in thermodynamic space, which can then be analyzed as thermodynamic cycles.

In doing so, we will contrast the thermodynamic cycles associated with deep convection and with hurricanes.