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2 Maintenance of tropical tropopause layer cirrus 3 T. P. Dinh,1

Summary: 2 Maintenance of tropical tropopause layer cirrus
3 T. P. Dinh,1
D. R. Durran,1
and T. P. Ackerman1
4 Received 25 June 2009; revised 30 August 2009; accepted 18 September 2009; published XX Month 2010.
5 [1] A two-dimensional cloud resolving model with explicit bin microphysics is used to
6 study the maintenance of tropical tropopause layer (TTL) cirrus. Numerical simulations
7 using this model show that a TTL cirrus with a maximum radiative heating rate of 3 K/day
8 is able to self-maintain for as long as 2 days if it contains ice crystals whose initial
9 mean radius is smaller than about 5 mm. The key to the maintenance of the cloud is the
10 circulation thermally forced by the cloud radiative heating. When the cloud layer is at ice
11 saturation and temperature decreases with height, advection of water vapor by the
12 thermally forced circulation results in water vapor flux convergence in the cloud. This
13 leads to growth of ice crystals despite the diabatic warming produced by the radiative
14 heating. The source of water vapor for the growth of ice crystals is outside the cloud
15 lateral edge, which is outside the vertical column that contains the initial cloud. The
16 conversion of water vapor into ice in the simulated TTL cirrus indicates its potential to
17 dehydrate the surrounding environment. This dehydration mechanism does not involve
18 adiabatic cooling associated with external large-scale uplift.
19 Citation: Dinh, T. P., D. R. Durran, and T. P. Ackerman (2010), Maintenance of tropical tropopause layer cirrus, J. Geophys. Res.,


Source: Ackerman, Thomas P. - Department of Atmospheric Sciences, University of Washington at Seattle


Collections: Geosciences; Environmental Sciences and Ecology