Seasonal Variations in the Mixing Layer in the UTLS Dave MacKenzie University of Toronto GEOS-Chem Meeting April 2009 Dave MacKenzie University of Toronto GEOS-Chem Meeting April 2009 [Adapted from figure 1 of Stohl et al., 2003] Pressure [hPa] Pole Equator Altitude [km]  GEOS-Chem (GEOS4 v )  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)

Background: CO/O 3 Correlation High CO (flat) indicates tropospheric air; high O 3 (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) High CO (flat) indicates tropospheric air; high O 3 (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 Altitude - TP Height [km] CO Mixing Ratio [ppbv] O 3 [ppbv] Number of Data

Improvement with New TPCORE CO [ppbv] O 3 [ppbv] Northern Hemisphere Jan 2006 GEOS-Chem old TPCORE GEOS-Chem new TPCORE GMI GEOS-Chem (GEOS4 v ) had excessive scatter in CO/O 3 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) Time [months] Mixing Layer Width [km] Northern Hemisphere Mixing Width Jan – May 2006 GEOS-Chem old TPCORE GEOS-Chem new TPCORE GMI

CO/O 3 Correlations at Three NH Locations CO [ppbv] O 3 [ppbv] North Am Jun 2006 CO [ppbv] O 3 [ppbv] Europe Jun 2006 CO [ppbv] O 3 [ppbv] Asia Jun 2006 Stratospheric air (CO ~ 30 ppb) Tropospheric air (O3 ~ 150 ppb) Mixed layer  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 Altitude - Tpause [km] Number of Data Asia Jun 2006 Altitude - Tpause [km] Number of Data North Am Jun 2006 Altitude - Tpause [km] Number of Data Europe Jun 2006 GEOS-Chem GMI GEOS-Chem GMI GEOS-Chem GMI GEOS-Chem GMI GEOS-Chem GMI GEOS-Chem GMI

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 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 Mixing Width [km] Time [months] North America km width GEOS-Chem GMI Mixing Width [km] Time [months] Europe GEOS-Chem GMI Mixing Width [km] Time [months] Asia GEOS-Chem GMI Mixing Center [km] Time [months] North America Tropopause GEOS-Chem GMI Mixing Center [km] Time [months] Europe GEOS-Chem GMI Mixing Center [km] Time [months] Asia GEOS-Chem GMI

Summary and Future Work Summary New TPCORE improves CO/O 3 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 Summary New TPCORE improves CO/O 3 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 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