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Impact of Seasonal Variation of Long-Range Transport on the Middle Eastern O3 Maximum

Jane Liu, Dylan B. Jones, Mark Parrington, Jay Kar

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University of Toronto

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The 3rd GEOS-CHEM Users’ Meeting at Harvard University

11-13 April 2007

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Introduction

  • Objectives and motivations
  • Approaches
    • GEOS-CHEM (Chemical Transport Model),

version: v7-02-04, Meteorological fields: GEOS-4

    • Satellite data: TES, MOPITT
    • CO, Ozone…
  • A transport pathway in the summer from Asia to the North Atlantic through the upper troposphere
  • The Middle Eastern ozone maximum

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The Middle Eastern Ozone Maximum

GEOS4 Ozone 2000/07, Monthly Mean, ~350hPa (7.8 km)

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Mean Vertical Ozone Profiles in the Middle East (2001-2006)

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O3 Sounding Data in the Middle East (Isfahan [32.5N, 51.7E])

Red line: ozonesonde

Black solid line: LINOZ

Blue dash line: SYNOZ

Assimilation 18 Aug 2005

Without assimilation 18 Aug 2005

Assimilation 13 Sept 2005

  • GEOS-CHEM reproduces the maximum ozone abundances (compared to sounding data), but overestimates the ozone in the upper troposphere
  • With Linoz the overestimate is exacerbated, suggesting that transport from the stratosphere is contributes to the ozone build-up
  • Assimilating TES ozone with Linoz significantly reduces the overestimate of ozone in the upper troposphere

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Monthly Mean O3 in GEOS-CHEM at ~350 hPa, ~8 km

May 2005

June 2005

July 2005

Aug 2005

Sept 2005

Oct 2005

  • The ozone maximum is confined to a narrow altitude layer in the upper troposphere, where TES is most sensitive
  • Ozone accumulation is seasonal, peaking during June-August

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Time Series of Modelled O3 over Middle East (20-40N,30-60 E)

  • Ozone in the Middle East decreases rapidly from September to December, and increase over late winter and spring
  • In July – August (2005 and 2006), the assimilation (with LINOZ) reduces maximum slightly, due to the overestimate in the model in the upper troposphere

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Budget Analysis, 500-300 hPa, in the Middle East

2005

2006

  • Transport of ozone into the region is the dominant source for the increase of ozone during spring
  • In summer, both vertical and horizontal transport provides a source for ozone in the region

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Monthly Mean Horizontal Ozone Flux

2005/05, 7.8 km L10, ~350 hPa

2005/06

2005/07

2005/08

2005/09

2005/10

  • Ozone accumulation in the Middle East is liked to convergence associated with the Arabian anticyclone in the upper troposphere
  • In September, ozone is reduced as the anticyclone weakens

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Conclusions

  • Although long-range transport and in situ chemical production both contribute to the formation ozone maximum, transport appears to be the predominant source.
  • Accumulation of ozone in the region is strongly related to the location and movement of the northern Arabian anticyclone.
  • GEOS-CHEM captures the ozone maximum in the middle troposphere, but overestimates ozone in the upper troposphere. This could be due to errors in the tropopause heights, excessive STE, or errors in the long-range transport in the upper troposphere.
  • Assimilation of TES data with LINOZ reduced the bias in the upper troposphere and provides a better description of the ozone maximum.

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