Atmosphere Ocean Science Colloquium

---

The Mesoscale Dynamics of Cirrus Clouds in the Tropical Tropopause Layer

Speaker: Tra Dinh, Princeton University

Location: Warren Weaver Hall 1302

Date: Wednesday, December 4, 2013, 3:30 p.m.

Synopsis:

Cirrus clouds in the tropical tropopause layer (TTL) have an important impact in controlling the distribution of water vapor in the TTL, and transport of water vapor into the stratosphere. TTL cirrus are warmed through the absorption of infrared radiation. The radiative heating induces a mesoscale circulation in the atmosphere around the clouds. I show in numerical simulations that this thermally induced mesoscale circulation offers explanations for the persistence and large horizontal extent of real-world TTL cirrus. Furthermore, water vapor is advected upwards by the mesoscale circulation. In some cases this effect outweighs downward transport of water by ice sedimentation. This means that TTL cirrus can lead to hydration of the lower stratosphere. This result contrasts with the conventional view that associates these clouds with dehydration only. The effect of the mesoscale dynamics is persistent even when the cirrus clouds response to the external forcing of a large-scale equatorial Kelvin wave. This work emphasizes the dynamics in cirrus clouds, which is often overlooked compared with microphysical processes in cloud-resolving models.