The role of the hydrologic cycle in atmospheric heat transport: experiments and tracer diagnostics with Isca

The atmosphere partially balances the difference between solar radiation at the equator and the poles through a poleward transport of heat. Traditionally this transport is partitioned into two different components: the transport of heat by dry air and the transport of latent heat by atmospheric moisture. However these two components are strongly linked through condensation, which removes moisture from the atmosphere and increases the thermal energy of the dry air. As a consequence, both the moist and dry components of atmospheric heat transport are connected to the hydrologic cycle, and so the total transport is in balance with surface evaporation. This connection can be studied by using Isca and perturbing the surface evaporation in different ways, all of which create a strong response in atmospheric heat transport.

To better understand the role of the hydrologic cycle in atmospheric heat transport, tagged tracers--passive tracers constructed to decompose another field between different processes--have been added to the Isca model. This talk will examine two examples of these tracers. The first, called "heat tags", uses passive tracers to track the heat transport of dry air, and shows how the warm air masses created by latent heating play an important role in atmospheric variability and heat transport. The second example, called "water tags", traces the source origins of water vapor as it moves through the atmosphere, and reveals that tropical and subtropical water makes up more of the high water vapor than extratropical water vapor.