Seasonal Variations in the Mixing Layer in the UTLS

1
Seasonal Variations in the Mixing Layer in the
UTLS

• Dave MacKenzie
• davem_at_atmosp.physics.utoronto.ca
• University of Toronto
• GEOS-Chem Meeting April 2009

• GEOS-Chem (GEOS4 v8-01-01)
• 4 latitude by 5 longitude, 30 vertical levels
  (top level 0.01hPa)
• Linearized ozone (LINOZ) chemistry in
  stratosphere
• Global Modeling Initiative (GMI Combo)
• 2 latitude by 2.5 longitude, 42 vertical levels
  (top level 0.01hPa)
• Has 117 chemical species, including a complete
  stratospheric chemistry
• Model transport driven by assimilated met fields
  from NASA GMAO
• Chemistry Transport Models (CTMs)

Altitude km
Pressure hPa
Pole Equator
Adapted from figure 1 of Stohl et al., 2003
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Background CO/O3 Correlation

• High CO (flat) indicates tropospheric air high
  O3 (steep) is stratospheric
• Points in between indicate a region of mixing
• Distribution of mixing data with altitude
  relative to tropopause gives mixing layer width
  and central position
• Figures from Hoor et al., 2002 (top) and Pan et
  al., 2004 (bottom)

Number of Data
O3 ppbv
Number of Data
Altitude - TP Height km
CO Mixing Ratio ppbv
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Improvement with New TPCORE

• GEOS-Chem (GEOS4 v7-02-04) had excessive
  scatter in CO/O3 correlations which was greatly
  reduced with new TPCORE
• New TPCORE increased agreement between
  GEOS-Chem and GMI
• Mixing layer width decreased from 7.5 km to
  6.5 km (5 km in GMI)

Northern Hemisphere Jan 2006
Northern Hemisphere Mixing Width Jan May 2006
GEOS-Chem old TPCORE GEOS-Chem new TPCORE GMI
GEOS-Chem old TPCORE GEOS-Chem new TPCORE GMI
Mixing Layer Width km
O3 ppbv
CO ppbv
Time months
4
CO/O3 Correlations at Three NH Locations

• Scatter varies across longitudes

• Both models agree on shape and central position
  of mixing data distribution
• Mixing layer center 0-1km below tropopause in Jun

Tropospheric air (O3 150 ppb)
Stratospheric air (CO 30 ppb)
North Am Jun 2006
Europe Jun 2006
Asia Jun 2006
GEOS-Chem GMI
GEOS-Chem GMI
GEOS-Chem GMI
Mixed layer
O3 ppbv
O3 ppbv
O3 ppbv
CO ppbv
CO ppbv
CO ppbv
Asia Jun 2006
North Am Jun 2006
Europe Jun 2006
GEOS-Chem GMI
GEOS-Chem GMI
GEOS-Chem GMI
Number of Data
Number of Data
Number of Data
Altitude - Tpause km
Altitude - Tpause km
Altitude - Tpause km
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Time Series of Mixing Layer Widths and Centers

• Longitudinal differences in mixing layer width
  lots of monthly variability
• Seasonal max in winter and min in summer,
  centered 0-1km below tropopause
• Only major discrepancy between models over Asia

5 km width
North America 2004 - 2006
Europe 2004 - 2006
Asia 2004 - 2006
GEOS-Chem GMI
GEOS-Chem GMI
GEOS-Chem GMI
Mixing Width km
Mixing Width km
Mixing Width km
Time months
Time months
Time months
North America 2004 - 2006
Europe 2004 - 2006
Asia 2004 - 2006
GEOS-Chem GMI
GEOS-Chem GMI
GEOS-Chem GMI
Tropopause
Mixing Center km
Mixing Center km
Mixing Center km
Time months
Time months
Time months
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Summary and Future Work

• Summary
• New TPCORE improves CO/O3 correlations
• There is good agreement between GEOS-Chem and GMI
  COMBO model, except over Asia where GEOS-Chem
  produces larger mixing depths
• Over North America and Europe the mixing layer
  depth varies seasonally, whereas the center of
  the mixing layer does not over Asia both the
  mixing layer depth and layer center show strong
  seasonal variations, which could be linked to the
  Asian monsoon
• Larger mixing width in winter than summer
• Mixing layer centered at 0-1km below the
  tropopause

• Future Work
• Apply other techniques and compare to
  observations (satellites/aircraft)
• Compare CTM results to GCM (CMAM) to evaluate
  influence of assimilation
• Determine the relative influence of mixing
  processes on the mixing layer