Cirrus and water vapor transport in the tropical tropopause layer – Part 1: A specific case modeling study Department of Atmospheric Sciences, University of Washington, Seattle, Washington 98195, USA
29 Oct 2012
Received: 31 Mar 2012 – Published in Atmos. Chem. Phys. Discuss.: 25 Apr 2012Abstract. In a simulation of a tropical-tropopause-layer (TTL) cirrus forced by a
large-scale equatorial Kelvin wave, the radiatively induced mesoscale dynamics
of the cloud actively contributes to the transport of water vapor in the
Revised: 06 Sep 2012 – Accepted: 18 Sep 2012 – Published: 29 Oct 2012
In a typical TTL cirrus, the heating that results from absorption of radiation
by ice crystals induces a mesoscale circulation. Advection of water vapor by the
radiatively induced circulation leads to upward advection of the cloudy air.
Upward advection of the cloudy air is equivalent to upward transport of water
vapor when the air above the cloud is drier than the cloudy air. On the other
hand, ice nucleation and depositional growth, followed by sedimentation and
sublimation lead to downward transport of water vapor.
Under the conditions specific to our simulation, the upward
transport of water vapor by the mesoscale circulation dominates the downward
transport by microphysical processes. The net result is upward transport of
water vapor, which is equivalent to hydration of the lower stratosphere.
Sensitivity to model conditions and parameters will be discussed in a follow-up
Citation: Dinh, T., Durran, D. R., and Ackerman, T.: Cirrus and water vapor transport in the tropical tropopause layer – Part 1: A specific case modeling study, Atmos. Chem. Phys., 12, 9799-9815, doi:10.5194/acp-12-9799-2012, 2012.