Dehydration in the Tropical Tropopause Layer of a Cloud- Resolving Model University of Reading, Department of Meteorology * DLR Oberpfaffenhofen, Institut für Physik der Atmosphäre Thomas Birner Christoph Küpper, John Thuburn, George Craig * Küpper et al. 2004, JGR

Dehydration Scenarios e.g. Jensen et al. 1996, Holton & Gettelman 2001 e.g. Danielsen 1982 e.g. Sherwood & Dessler 2000 thin cirrus dehydration no dehydration CP

The Cloud-Resolving Model (LEM) anelastic fully interactive radiation scheme complex bulk microphysics: prognostic variables for mass mixing ratios q l, q r, q i, q s, q g, and n i doubly periodic (96 km  96 km, 2 km resolution) 30 km deep, rigid lid, 90 levels, 300 m vertical resolution in TTL relaxation layer in top 5 km initial conditions: SST = 300 K, q v (surface) = 17 mg/g, q v (stratosphere) = 1.6 μg/g, CP at 16 km

Initial Conditions moist stratosphere experiment (μg/g)

Imposed Mean Ascent (w ma ) ERA, Jan ERA, July convective, this work ρ w ma

Control Simulation

Temporal Evolution at the Cold Point: Temperature T i,sat

Temporal Evolution at the Cold Point: Temperature T i,sat

Mean Profiles in Statistical Equilibrium T T min T ERA CPTTL Definition: q > µg/g

conv.  non-conv. conv.  total thermal solar total matching level Mean Profiles in Statistical Equilibrium TTL

conv.  non-conv. conv.  total thermal solar total matching level Mean Profiles in Statistical Equilibrium TTL convective: |w / | > 1 m/s

precip. outside conv. conv. adv. + precip. qvqv qiqi q i,sat Mean Profiles in Statistical Equilibrium convective mean asc. TTL

Mean Profiles in Statistical Equilibrium T std. dev. T i,sat TTL Potter & Holton 1995

conv.  non-conv. conv.  total total dyn. total rad. mean asc. microphys. Mean Profiles in Statistical Equilibrium TTL

Moist Stratosphere Experiment

Initial Conditions moist stratosphere experiment (μg/g)

Mean Profiles in Statistical Equilibrium T T min T ERA CPTTL Control Run

Mean Profiles in Statistical Equilibrium T T min T ERA CPTTL

Difference to Control Simulation T T min

precip. outside conv. conv. adv. + precip. qvqv qiqi q i,sat Mean Profiles in Statistical Equilibrium convective mean asc. TTL

precip. outside conv. conv. adv. + precip. qvqv qiqi q i,sat Mean Profiles in Statistical Equilibrium convective mean asc. TTL Control Run

Tape Recorder Mote et al. 1996

Further Results convection, in our simulation, hydrates the TTL additionally imposed wave perturbations typical for Kelvin waves lead to further dehydration allowing supersaturations up to 50% does not change results qualitatively

Summary cloud-resolving simulations of the mass and moisture transport into the tropical stratosphere mass and moisture transport through cold point dominated by mean ascent (see also Küpper et al., JGR 2004) dynamical heating rate in TTL dominated by mean ascent mean water vapor subsaturated at CP in control run final stage of dehydration in convectively generated buoyancy waves thin cirrus at CP sensitive to initialized stratospheric moisture

Outlook microphysics parameter sensitivity continental conditions (CAPE) more realistically imposed wave perturbations