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K. Wargan, S. Pawson , M. Olsen, J. Witte, A. Douglass

Assimilation of EOS-Aura Data in GEOS-5: Evaluation of ozone in the Upper Troposphere - Lower Stratosphere. K. Wargan, S. Pawson , M. Olsen, J. Witte, A. Douglass. Global Modeling and Assimilation Office (GMAO) Chemistry and Dynamics Branch NASA GSFC. A question.

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K. Wargan, S. Pawson , M. Olsen, J. Witte, A. Douglass

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  1. Assimilation of EOS-Aura Data in GEOS-5: Evaluation of ozone in the Upper Troposphere - Lower Stratosphere K. Wargan, S. Pawson, M. Olsen, J. Witte, A. Douglass Global Modeling and Assimilation Office (GMAO) Chemistry and Dynamics Branch NASA GSFC

  2. A question How much of the ozone that we see in the troposphere is of stratospheric origin? Models disagree on this quite dramatically

  3. Plan of Talk • Motivation – quantifying sources of tropospheric ozone • Ozone data and GEOS-5 Data Assimilation System • Results • Evaluation against ozonesonde data • Vertical structure of UTLS ozone fields We look at the lower stratosphere but the goal is to derive some information on tropospheric ozone as well

  4. Tropospheric Ozone 2010 boreal summer mean tropospheric ozone column [Dobson Units]

  5. Tropospheric Ozone Maxima along the subtropical jet streams. Summer, Northern Hemisphere higher 2010 boreal summer mean tropospheric ozone column [Dobson Units]

  6. Tropospheric Ozone Wave one pattern in the tropics Lightning Convection 2010 boreal summer mean tropospheric ozone column [Dobson Units]

  7. Tropospheric Ozone Tropical Pacific controlled by ENSO and MJO 2010 boreal summer mean tropospheric ozone column [Dobson Units]

  8. Tropospheric Ozone Very low over snow-covered Greenland and Antarctica 2010 boreal summer mean tropospheric ozone column [Dobson Units]

  9. Tropospheric Ozone - Sources • NOx / CO / Volatile Organic Compounds chemistry • Biomass burning • Fossil fuel burning • Lightning • Transport from the stratosphere • Spatial distribution closely tied to meteorology These mechanisms are well understood but quantitative attribution is not precise

  10. Constrain ozone in the Upper Troposphere – Lower Stratosphere (abundance, structure, variability) • Stratosphere-Troposphere Exchange • Separate tropospheric and stratospheric ozone columns • Accurate tropospheric ozone budget based on global observations • Assimilation can help achieve this • Model supplies information on dynamics • Vertical grid of a DAS can resolve features that data cannot

  11. GEOS-5 Data Assimilation System • Atmospheric General Circulation Model: • Horizontal resolution: flexible - 2.5° to ¼° • 72 layers from the surface to 0.01 hPa • Parameterized ozone chemistry (stratospheric P&L; dry deposition) • No representation of tropospheric ozone sources in the model • 3D-Var analysis: GridpointStatistical Interpolation • Observations: • Conventional (surface, sondes, radar, aircraft, MODIS-derived winds,…) • Satellite radiance data (TOVS/ATOVS, AIRS, IASI, SSM/I, GOES, GPS-RO) • Ozone data (OMI, MLS retrievals)

  12. Microwave Limb Sounder (MLS) on EOS Aura • Measures temperature and composition of the atmosphere from microwave emissions • Limb scanner • Vertical range: We assimilate profiles between ~260 hPa – 0.14 hPa • Vertical resolution: 2.5 – 6 km • 9 years and counting

  13. Ozone Monitoring Instrument (OMI) • Total ozone information derived from observations of backscattered UV radiation • Observes sun-lit atmosphere • Total Ozone Monitoring Instrument (TOMS) legacy • Operational 2004 - present • Sensitivity varies with altitude and local meteorology (no signal from below clouds). This is taken into account by weighting the signal by OMI’s efficiency factors (averaging kernels), ε We have 8 year long, 2°×2.5° assimilation run with this configuration, 2005 - 2008

  14. Results in the stratosphere • Time series of integrated stratospheric ozone column in three latitude bands • 60N – 90N: Winter-Spring maximum, interannual variability; “Arctic ozone hole” in 2011 • Tropics: Ozone controlled by the QBO • 90S – 60S: Austral Spring ozone holes • Realistic representation of temporal variability 60N -90N 10S -10N 90S -60S Year

  15. Vertically integrated Observation – Forecast statistics • Assimilation significantly reduces the O-Fs for both instruments • Negligible bias between analysis total ozone and OMI data • Stratospheric column biased low w.r.t. MLS observations but MLS likely overestimates ozone below 200 hPa

  16. Total ozone O-Fs and tropospheric response, June - August Analysis tendency in troposphere O-F 2009 2010 • Analysis tendencies/increments in the troposphere have similar pattern to total ozone O-Fs: OMI supplies tropospheric ozone information • O-Fs and increments positive over land and negative in regions of strong convection

  17. Total ozone O-Fs and tropospheric response, June - August Analysis tendency in troposphere O-F 2009 Biomass burning signal over the Amazon varies from year to year. Very low fire counts in 2009 result in lower ozone production Here, OMI makes up for the lack of explicit chemistry in the model 2010 • Analysis tendencies/increments in the troposphere have similar pattern to total ozone O-Fs: OMI supplies tropospheric ozone information • O-Fs and increments positive over land and negative in regions of strong convection

  18. Lower Stratosphere and Upper Troposphere; Comparison with ozonesondes Lower Stratosphere, tropopause – 50 hPa Sonde data are from the WOUDC, NDACC, and SHADOZ databases, 2005 - 2012 Upper Troposphere, 500 hPa - tropopause • Excellent agreement of lower stratospheric ozone with sonde data • Good agreement in the upper troposphere; assimilation is biased low by 1.4 Dobson Units – missing NOx chemistry in the model?

  19. Ozone in the lower stratosphere – assimilation vs. sondes Sonde data Assimilation Hohenpeissenberg (47.8N, 11E) Assimilation faithfully reproduces the annual cycle as well as day-to-day variability of ozone in the lower stratosphere at this location.

  20. Vertical structure – an example High and low ozone layers in the UTLS often form as a result oftransport of ozone poor air from low latitudes. Assimilation reproduces layered structure of this ozone profile as permitted by the vertical resolution of the DAS Sonde data Assimilation Hohenpeissenberg (47.8N, 11E) on May 4th 2005

  21. Capturing fine structures in the UTLS Satellite data Assimilation Theta [°K] Theta [°K] Latitude Latitude Combining observations with assimilated dynamics allows accurate representation of small-scale features unresolved by the data. We use along-track ozone profiles from High Resolution Dynamics Limb Sounder (HIRDLS) Vertical resolution is ~1 km for HIRDLS and ~2.5 – 3 km for MLS

  22. Summary • Eight year long record of global ozone was obtained by assimilating OMI and MLS observations into GEOS-5 • Very good agreement with ozonesondes in terms of vertically integrated ozone in the lower stratosphere • Good agreement in the upper troposphere as well. Low bias needs fixing – representation of sources in the model? • Good representation of shallow vertical structures in the UTLS • The product can be used to quantify stratosphere – troposphere exchange of ozone

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