UTLS Workshop Boulder, Colorado October , 2009 UTLS Workshop Boulder, Colorado October , 2009 Characterizing the Seasonal Variation in Position and Depth of the Mixing Layer in the UTLS Based on Observations from the ACE- FTS and TES Satellite Instruments Dave MacKenzie 1, D. B. A. Jones 1, M. Hegglin 1, J. Worden 2, C. D. Boone 3, K. A. Walker 1,3, P. F. Bernath 3,4, C. Carouge 5, L. Murray 5 1 University of Toronto, 2 Jet Propulsion Laboratory, 3 University of Waterloo, 4 University of York, 5 Harvard University

Motivation: TES Observations over Central Asia in Summer TES shows enhanced O3 in the middle and upper troposphere over central Asia This feature is robust and is observed each summer (see poster by John Worden) Enhanced O3 over central Asia may reflect the influence of mixing of stratospheric ozone into the troposphere TES shows enhanced O3 in the middle and upper troposphere over central Asia This feature is robust and is observed each summer (see poster by John Worden) Enhanced O3 over central Asia may reflect the influence of mixing of stratospheric ozone into the troposphere TES O 3 at 464 hPa, July Longitude [Worden et al. 2009] TES O 3 at 464 hPa, July 2007

Description of Data and Model  Tropospheric Emission Spectrometer (TES)  Instrument on AURA satellite  Measurements made in nadir (5.3km x 8.3km footprint)  Sun-synchronous orbit with 1:43pm ascending node  Vertical resolution is ~6-7km  Atmospheric Chemistry Experiment (ACE)  Fourier Transform Spectrometer (FTS) instrument on SCISAT-I satellite  Solar occultation during sunrise/sunset  Covers 85S - 85N and km altitude  Effective vertical resolution in UTLS ~1km  GEOS-Chem Model (GEOS5 v )  Chemistry Transport Model (CTM)  Driven by assimilated GMAO meteorological fields  4° latitude by 5° longitude, 47 vertical levels (top level ~0.01hPa)  Vertical resolution in UTLS ~1.1km  Linearized ozone (LINOZ) chemistry in stratosphere

Using CO/O 3 Correlations to Characterize Mixing 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 (fwhm) and peak (mode) Mixing widths are sensitive to the method used to define stratospheric and tropospheric end members 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 (fwhm) and peak (mode) Mixing widths are sensitive to the method used to define stratospheric and tropospheric end members Altitude - TP Height [km] CO [ppbv] O 3 [ppbv] Number of Data Lat=[30N,50N], Lon=[0,175E], July 2007 Stratospheric air (CO < 30 ppb) Tropospheric air (O3 < 100 ppb) Mixed layer Tropopause

GEOS-Chem - ACE Mixing Layer Width Comparison Zonally averaged, 10° latitude bins, seasonal quasi-climatology Tropical data sparse for satellite Model mixing width similar to satellite with largest difference in northern hemisphere subtropics Smallest (largest) width in northern mid-latitudes in fall (spring) in GEOS- Chem; mixing widths are also large is summer in ACE-FTS data Zonally averaged, 10° latitude bins, seasonal quasi-climatology Tropical data sparse for satellite Model mixing width similar to satellite with largest difference in northern hemisphere subtropics Smallest (largest) width in northern mid-latitudes in fall (spring) in GEOS- Chem; mixing widths are also large is summer in ACE-FTS data Mixing Width [km] Latitude [degrees north] GEOS-Chem Zonal Mixing Layer Width ACE Zonal Mixing Layer Width Mixing Width [km] Zonal Mixing Layer Widths

GEOS-Chem - ACE Mixing Layer Peak Comparison ACE-FTS mixing layer found slightly above tropopause; GEOS- Chem mixing layer is below (above) tropopause in subtropics (extratropics) Mixing layer consistently lower in summer months ACE-FTS mixing layer found slightly above tropopause; GEOS- Chem mixing layer is below (above) tropopause in subtropics (extratropics) Mixing layer consistently lower in summer months Mixing Peak [km from trop] Latitude [degrees north] GEOS-Chem Zonal Mixing Layer Peak ACE Zonal Mixing Layer Peak Mixing Peak [km from trop] Zonal Mixing Layer Peaks Tropopause

Regional Mixing Layer in GEOS-Chem July 2007 Enhanced mixing over Eastern Europe and central Asia Most mixing occurs in extratropics, just poleward of subtropical jet The mixing widths will depend on the definition of the stratospheric and tropospheric end members, but the spatial distribution and the relative mixing widths will be preserved Enhanced mixing over Eastern Europe and central Asia Most mixing occurs in extratropics, just poleward of subtropical jet The mixing widths will depend on the definition of the stratospheric and tropospheric end members, but the spatial distribution and the relative mixing widths will be preserved Mixing layer is lowest over the eastern Mediterranean Low mixing layer over eastern Atlantic and central Asia may indicate downward transport from the stratosphere Mixing layer is lowest over the eastern Mediterranean Low mixing layer over eastern Atlantic and central Asia may indicate downward transport from the stratosphere Mixing Layer Width [km], July 2007 Mixing Layer Peak [km from trop], July

Evidence of Stratospheric Influence Low CO and high O3 located equatorward of the regions with enhanced mixing widths and in the vicinity of the region with the lowest mixing peak

Meteorological Conditions for July Pressure tendencies indicate strong descent over the eastern Mediterranean and southeast of the Caspian Sea where the mixing peak is low These regions of descent are linked to the heating in the Asian monsoon region [Rodwell and Hoskins, 1996] GEOS-Chem (GEOS-5) potential vorticity (PV) for July 2007 indicates stratospheric PV values (PV > 2 PVU) near these regions of descent (1 PVU = 1.0x10 -6 K m 2 kg -1 s -1 )

Contribution of the stratosphere to total ozone GEOS-Chem total ozone [ppb] in the upper troposphere GEOS-Chem stratospheric ozone tracer [ppb] in the upper troposphere Ozone from the stratosphere contributes as much as 45% to the total ozone over Turkey and central Asia

Summary There is good agreement between mixing layer widths and peaks estimated from GEOS-Chem and ACE-FTS data GEOS-Chem has a smaller mixing layer in the subtropics, but otherwise there is small difference between the two Larger differences are seen when comparing the location of the peak of the mixing layer with the greatest differences seen at high latitudes The mixing layer in GEOS-Chem appears smallest (largest) in fall (spring) and lowest with respect to the tropopause in summer Enhanced region of mixing found near the Mediterranean and central Asia, poleward of the subtropical jet in summer Omega and PV fields suggest downward and equatorward transport from the stratosphere in this region TES observes high O 3 in the middle and upper troposphere in over central Asia in summer and GEOS-Chem suggests that as much as 45% of this O 3 could be from the stratosphere There is good agreement between mixing layer widths and peaks estimated from GEOS-Chem and ACE-FTS data GEOS-Chem has a smaller mixing layer in the subtropics, but otherwise there is small difference between the two Larger differences are seen when comparing the location of the peak of the mixing layer with the greatest differences seen at high latitudes The mixing layer in GEOS-Chem appears smallest (largest) in fall (spring) and lowest with respect to the tropopause in summer Enhanced region of mixing found near the Mediterranean and central Asia, poleward of the subtropical jet in summer Omega and PV fields suggest downward and equatorward transport from the stratosphere in this region TES observes high O 3 in the middle and upper troposphere in over central Asia in summer and GEOS-Chem suggests that as much as 45% of this O 3 could be from the stratosphere