Cirrus and water vapor transport in the tropical tropopause layer – Part 1: A specific case modeling study

摘要

In a simulation of a tropical-tropopause-layer (TTL) cirrus forced by alarge-scale equatorial Kelvin wave, the radiatively induced mesoscale dynamicsof the cloud actively contributes to the transport of water vapor in thevertical direction.In a typical TTL cirrus, the heating that results from absorption of radiationby ice crystals induces a mesoscale circulation. Advection of water vapor by theradiatively induced circulation leads to upward advection of the cloudy air.Upward advection of the cloudy air is equivalent to upward transport of watervapor when the air above the cloud is drier than the cloudy air. On the otherhand, ice nucleation and depositional growth, followed by sedimentation andsublimation lead to downward transport of water vapor.Under the conditions specific to our simulation, the upwardtransport of water vapor by the mesoscale circulation dominates the downwardtransport by microphysical processes. The net result is upward transport ofwater vapor, which is equivalent to hydration of the lower stratosphere.Sensitivity to model conditions and parameters will be discussed in a follow-uppaper.