Dehydration in the Tropical Tropopause Layer of a Cloud- Resolving Model University of Reading, Department of Meteorology * DLR Oberpfaffenhofen, Institut

Dehydration in the Dehydration in the Tropical Tropopause Tropical Tropopause

Layer of a Cloud-Layer of a Cloud-Resolving ModelResolving Model

University of Reading, Department of Meteorology

*DLR Oberpfaffenhofen, Institut für Physik der Atmosphäre

Thomas BirnerThomas BirnerChristoph Küpper, John Thuburn, George Christoph Küpper, John Thuburn, George

CraigCraig**

Küpper et al. 2004, JGRKüpper et al. 2004, JGR

Dehydration ScenariosDehydration Scenarios

e.g. Jensen et al. 1996, Holton & Gettelman 2001

e.g. Danielsen 1982 e.g. Sherwood & Dessler 2000

thin cirrusdehydration

no dehydration

CPCP

The Cloud-Resolving Model (LEM)The Cloud-Resolving Model (LEM)

• anelastic

• fully interactive radiation scheme

• complex bulk microphysics: prognostic variables for

mass mixing ratios ql , qr , qi , qs , qg , and ni

• 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, qv (surface) = 17 mg/g,

qv (stratosphere) = 1.6 μg/g, CP at 16 km

Initial ConditionsInitial Conditions

moist stratosphereexperiment

(μg/g)

Imposed Mean Ascent (Imposed Mean Ascent (wwmama))

ERA, Jan

ERA, July

convective, this work

ρ wma

Control Control SimulationSimulation

Temporal Evolution at the Cold Point: Temporal Evolution at the Cold Point: TemperatureTemperature

Ti,sat

Temporal Evolution at the Cold Point: Temporal Evolution at the Cold Point: TemperatureTemperature

Ti,sat

Mean Profiles in Statistical EquilibriumMean Profiles in Statistical Equilibrium

TTmin

TERA

CPCPTTLTTL

Definition: q > 10-4 µg/g

conv.

non-conv.

conv.

total

thermal

solar

total

matching level


TTLTTL

conv.

non-conv.

conv.

total

thermal

solar

total

matching level


TTLTTLconvective:|w/| > 1 m/s

precip.

outside conv.

conv. adv. + precip.

qv

qi

qi,sat


convective

mean asc.

TTLTTL


Tstd. dev.Ti,sat

TTLTTL

Potter & Holton 1995Potter & Holton 1995

conv.

non-conv.

conv.

total

total dyn.total rad.mean asc.microphys.


TTLTTL

Moist Moist Stratosphere Stratosphere ExperimentExperiment

Initial ConditionsInitial Conditions

moist stratosphereexperiment

(μg/g)


TTmin

TERA

CPCPTTLTTL

Control Run


TTmin

TERA

CPCPTTLTTL

Difference to Control SimulationDifference to Control Simulation

TTmin

precip.

outside conv.


qv

qi

qi,sat


convective

mean asc.

TTLTTL

precip.

outside conv.


qv

qi

qi,sat


convective

mean asc.

TTLTTL

Control RunControl Run

Tape RecorderTape Recorder

Mote et al. 1996

Further ResultsFurther 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

SummarySummary• 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

OutlookOutlook

• microphysics parameter sensitivity

• continental conditions (CAPE)

• more realistically imposed wave perturbations

Documents

Dehydration in the Tropical Tropopause Layer of a Cloud- Resolving Model University of Reading, Department of Meteorology * DLR Oberpfaffenhofen, Institut