Atmospheric Chemistry and Physics, vol. 12, issue 20 (2012) pp. 9799-9815
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 vertical direction.
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 paper.
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