UTLS Chemical Structure, ExTL

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UTLS Chemical Structure, ExTL

• Summary of the talks
• Data sets
• Coordinates
• Thickness of the ExTL (tracers based)
• Outstanding questions
• Discussion

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Key results (1/2)

• Hegglin et al., ACE satellite measurements of of
  ozone versus CO and ozone versus H2O in UTLS
  region are consistent with SPURT aircraft
  measurements, providing a broader global picture
  of the ExTL related to mixing between
  stratosphere and troposphere.
• deltaZ from Tp
• Mackenzie et al., Enhanced ozone observed by TES
  at latitudes near 50 degrees North over Central
  Asia are consistent with large mixing layer depth
  at these latitudes. Using the GEOS-Chem model for
  analysis, up to 45 of ozone can be attributed to
  stratospheric air over Central Asia.
• deltaZ from Tp
• Manney et al. Ozone distributions in UTLS are
  related to jet structure. Transport and mixing
  processes related to the jets are captured in
  many instances by MLS.
• Jet Core coordinates

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Key results (2/2)

• Brioude et al. MOZAIC data are used to
  characterized ozone and CO distributions in the
  mixing layer and relate them to PV within upper
  level troughs. Seasonal and regional differences
  are assessed. MOZAIC CO over Asia is much higher
  in UTLS region with peak values in the spring.
• PV coordinates
• Pisso et al. Research aircraft data. Increased
  thickness of the Extratropical Tropopause Layer
  with increasing latitude, from 0 at 20 to 30 K
  at 60.
• Equivalent latitude and delta theta
• Pan et al. Theta coordinates and equivalent
  latitudes well describe stratospheric processes
  but do not characterize tropospheric ones.
  Disadvantage Equivalent latitude coordinates are
  derived from re-analysis which do not have the
  same fine-scale resolution as the observations
  analyzed this way.
• Neu et al. Problem thermal, dynamical, and
  ozone tropopause definitions cannot simply be
  used for comparison with numerical simulations
  It was proposed to use E90 tracer which defines
  the tropopause as a mixing barrier to better
  define the tropopause height in CTMs. This
  tracer leads to good comparisons of ozone at
  extratropics but the model has problem with ozone
  in tropics.

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Thickness of the ExTL ?
- Hegglin dz from Tp
Upper and lower boundary of the ExTL as distance
from the thermal tropopause derived from ACE-FTS
H2O-O3 and CO-O3 correlations.

• The ExTL in the Southern Hemisphere is thinner
  by 1 km.
• The ExTL depth increases with latitude.
• The ExTL depth varies when using different
  tracer-pairs.

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Thickness of the ExTL

• Pisso O3, CO,CO2, H20 ? 0K at 20, 30K at
  60-70
• Brioude O3-CO ? 2-6 pvu (up to 8 pvu in summer)
  for NH mid-latitudes in 2003
• MacKenzie O3-CO ? 4-6 km

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Are authors happy with the 1-2 summary sentences ?

• If no, come to see me
• If yes, but want to complete, come to see me as
  well

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Outstanding questions? - Are we all understand
the mixing layer and ExTL the same way (common
understanding ? Physical boundaries ?) - Is there
a unified view of how to define the mixing layer
(observational data set, coordinates, tracers
based, units for thickness) and exchange
processes between stratosphere and troposphere
(vertical vs isentropic mixing) ? The answer
probably depends on what are such analyses made
for Needed - What is the impact of
stratosphere on tropospheric ozone budget / How
do we quantify reversible versus irreversible
transport (horizontal advection) ? - Validation
of CCMs for examining impacts of climate
variability on chemistry and their feedbacks. -
Process studies for how extra-tropical UTLS is
related to jet structure. (dynamical issues
todays session)
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Integral view ?
Chemical structure of the lowermost
stratosphere - transition layer which extending
around the tropopause - the vertical depth 2-4
km relative to the tropopause 25-30 K
above 2 PVU tracer
dependency, tropopause - chemical transition
layer marks a change in transport time from the
lower troposphere to the LMS - strong seasonality
above the transition layer - 'young' air in
summer and autumn - rapid 'flushing' from late
spring to summer - strong coupling to the TTL and
tropical lower stratosphere
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Challenges

• Which dynamical processes are most important for
  the observed chemical structure, particularly the
  strong coupling to the tropics?
• What is the role of transport and mixing in
  maintaining the dynamical structure of UTLS?
• Are there feedbacks between dynamical structure
  and composition ?
• How robust are the estimated budgets?
• Do we have enough data ? What kind of data and
  where ? High resolution, polar, SH,