The Origin of Stratospheric Water Vapor and Resolving the Stratospheric Isotope Paradox

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The Origin of Stratospheric Water Vapor and
Resolving the Stratospheric Isotope Paradox
J. A. Smith, A. S. Ackerman, E. J. Jensen, and O.
B. Toon
Aura Validation Workshop, September 20, 2005
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Outline

• Dehydration of stratospheric air and H2O
  isotopologues
• Simulations of deep convection
• Troposphere-stratosphere exchange

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Dehydration of Tropical Air Entering the
Stratosphere
Overshooting and Mixing
Gradual Ascent
Both mechanisms are consistent with water vapor
mixing ratio
Use water isotopologues to distinguish the two
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Stable Isotopologues of Water

• Standard Mean
• Ocean Water
• (SMOW)
• HDO H2O
• 3 104
• RSMOW 3.1 x 10-4

H2O
HDO
Heavy hydrogen has 1 extra neutron
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Equilibrium Isotopic Fractionation Factor
H2O
HDO
a(T) gt 1.05 - 1.4

• HDO is less volatile
• Condensate is richer in HDO than vapor
• Every condensation event depletes vapor

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Rayleigh Distillation

• Pseudo-adiabatic parcel
• Maintain equilibrium
• Sediment condensate

Rv - RSMOW
d
X 1000
RSMOW
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Stratospheric Isotope Paradox

• The stratosphere is underdepleted for its
  humidity
• Ice lofting in deep convection is responsible for
  underdepletion

Stratosphere
qv
dHDO ()

• Moyer et al., 1996

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Observations of Ice

• ALIAS measurements during CRYSTAL/FACE field
  campaign
• Lofted ice is rich in HDO

Webster and Heymsfield, 2003
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Deep Convection Simulation
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DHARMA
Coupling of CARMA to an LES
(Ackerman and Stevens)
LES Generates Additional Buoyancy From Latent
Heat And A Cumulonimbus Develops
CARMA Grows Droplets And Releases Latent Heat
Supersaturate, CARMA Activates CCN
Add Heat, LES Produces Rising Thermals
Time
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CARMA
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Microphysics
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Kinetic Fractionation
Condensational Growth (stratified)
Evaporate (mixed)
Exchange (mixed)
H2O
HDO
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Water Vapor Isotope Distribution
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Bootstrapping
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Comparison to ATMOS Data
Kuang et al., GRL 30, doi10.1029/2003GL017023,
2003
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Detrainment and Cirrus Dehydration
60 Supersaturation
Equilibrium
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Conclusions Implications for Stratospheric
Entry of Air

• Rayleigh fractionation is invalid for deep
  convection

Convective injection is consistent with
observations
Slow ascent of detrained air is also consistent
with observations