Assimilation of TES O 3 data in GEOS-Chem

1. Assimilation of TES O3 data in GEOS-Chem Mark Parrington, Dylan Jones, Dave MacKenzieUniversity of Toronto Kevin Bowman Jet Propulsion LaboratoryCalifornia Institute of Technology

2. TES Global Survey Observations, July 4-31, 2005 TES O3 464.16 hPa ppb • Enhanced O3 abundances from central Asia, across the Middle East, and over the subtropical Atlantic • High O3 over the southeastern USA

3. GEOS-Chem ozone, 500hPa, July 26 2005 GEOS-Chem, no assimilation GEOS-Chem, with TES assimilation ppb Percent difference • TES ozone profiles assimilated from 4 July 2005 through to 31 August 2006. • GEOS-Chem captures the dominant features seen in the TES data, although it tends to underestimate the summer-time abundance. • Assimilation of TES data improves the simulated ozone abundance, which enables us to better quantify the processes controlling the distribution. %

4. Modelled O3 Over the Southeastern USA GEOS-Chem ozone (75°W, 12 GMT, July 26) • Assimilation increases the upper tropospheric maximum over the southeastern USA. • Assimilation produces a lower “ozone tropopause”, which reflects the broad averaging kernels of TES and the poor representation of stratospheric O3 in GEOS-Chem. Altitude (km) Latitude GEOS-Chem ozone analysis Altitude (km) Latitude ppb

5. Comparison of GEOS-Chem with Ozonesonde Data Sonde Assimilation GEOS-Chem Wallops (76°W, 38°N) 19 July 2005 Churchill (95°W, 58°N) 20 July 2005 Assimilation improves the O3 distribution in the UTLS region Pressure (hPa) Pressure (hPa) Ozone (ppb) Ozone (ppb) Wallops (76°W, 38°N) 26 July 2005 Eureka (85°W, 80°N) 20 July 2005 O3 plume is redistributed throughout column in assimilation Pressure (hPa) Pressure (hPa) Ozone (ppb) Ozone (ppb)

6. Stratospheric ozone distribution Wallops (76°W, 38°N) 26 July 2005 Linoz Synoz • The standard synthetic ozone, Synoz, parameterization of stratospheric ozone in GEOS-Chem can lead to uncertainties in the ozone analysis in the upper troposphere. • Over long model integrations, with assimilation, ozone can accumulate in the lower stratosphere with no sinks to remove it. • Due to the coarse vertical resolution of the TES data, this can lead to unrealistic ozone values being introduced into the analysis. • We have implemented the linearized ozone, Linoz, parameterization of stratospheric ozone into GEOS-Chem which gives a much improved distribution of ozone above the tropopause compared to Synoz. Sonde data Pressure (hPa) Ozone (ppb)

7. Timeseries of O3 over southeast USA Dash line: no assimilation, Solid line: O3 assimilation, Level: 500 hPa Ozone (ppb) Difference: assimilation - no assimilation Ozone difference (ppb) • With the Linoz in the stratosphere we can run the assimilation for extended periods. • O3 over the southeast is at a maximum in July-Sept and decreases into winter. The assimilation enhances the summer ozone maximum indicating possible issues with lightning NOx emissions in the model.

8. Linoz Sonde Synoz Comparison to Ozonesonde Profiles Boulder (40.3 N, 105.2 W), 21 July 2006 Wallops (76°W, 38°N) 26 July 2005 Pressure (hPa) Pressure (hPa) Ozone (ppb) Ozone (ppb) Trinidad Head (40.8 N, 124.2 W), 7 July 2006 Churchill (95°W, 58°N) 20 July 2005 Pressure (hPa) Pressure (hPa) Ozone (ppb) Ozone (ppb) • Over North America the impact of Linoz on O3 in the troposphere is small (compared to other regions where transport from the stratosphere is a more important in the ozone budget) • The improvement representation of the stratosphere by implementing Linoz provides a more realistic ozone distribution in the UTLS over North America (especially at high latitudes)

9. Assimilation performance at mid-latitudes • Residuals (TES - model, black line, and TES - assimilation, red line) time-series at 350 hPa from July 2005 to August 2006. • Area average over northern mid-latitudes: -180° to 180° W and 30° to 60° N. • The bias between the data and model is much reduced in the summer following the assimilation. • Negative bias in the winter due to stratospheric sudden warming in mid-January. O3 Difference (ppb)

10. High-latitude residuals time-series Upper troposphere: 350 hPa • Area average over -180° to 180° W and 60° to 80° N. • The bias between the data and model is much reduced in the summer following the assimilation, as also shown for North America. • In this case the stratospheric sudden warming is much more pronounced and the assimilation does not have much impact on the bias. • This time-series in the upper troposphere implies possible issues with tropopause height in GEOS-Chem and/or TES data? • The bias in the mid-troposphere is also negative but is not as pronounced as in the upper troposphere. O3 Difference (ppb) Mid troposphere: 500 hPa O3 Difference (ppb)

11. Conclusions • GEOS-Chem captures the dominant features in the distribution of tropospheric O3 as observed by TES, but the abundance is generally under-estimated with respect to these values. • The TES data has sufficient information to improve the ozone abundance in GEOS-Chem relative to ozonesonde profiles. • A linearized ozone chemistry scheme has been incorporated into GEOS-Chem which significantly improves the stratospheric ozone distribution. • This gives us more confidence in the assimilation of ozone in the troposphere where the width of the TES averaging kernels can smooth information from the stratosphere into the analysis. • In the Arctic, GEOS-Chem tends to overestimate the ozone abundance in the upper troposphere, which is reduced by the assimilation. • This could reflect errors in either the GEOS-Chem troposphere or the ozone tropopause in the TES retrievals in the Arctic. • A major sudden warming in the stratosphere in January 2006 enhanced ozone in the upper troposphere, beyond levels observed by TES. Simulation of O3 by the AM2 model (constrained by NCEP winds) does not produce a pronounced intrusion.