Multi-year assimilation of IASI and MLS ozone retrievals: Variability of tropospheric ozone over the tropics in response to ENSO

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Abstract

The Infrared Atmospheric Sounder Instrument (IASI) allows global coverage with very high spatial resolution and its measurements are promising for long-term ozone monitoring. In this study, the Microwave Limb Sounder (MLS) and IASI are assimilated in a chemistry transport model to produce 6-hourly analyses of tropospheric ozone during six years (2008&amp;ndash;2013). We have compared and evaluated the IASI-MLS analysis and the MLS analysis to assess the added value of IASI measurements. <br><br> The global chemical transport model MOCAGE (MOdèle de Chimie Atmosphérique à Grande Echelle) has been used with a linear ozone chemistry scheme and meteorological forcing fields from ERA-Interim (ECMWF global reanalysis). An horizontal resolution of 2&amp;thinsp;°&amp;thinsp;x&amp;thinsp;2&amp;thinsp;° and 60 sigma-hybrid vertical levels extending from the ground to the upper stratosphere have been used. MLS and IASI O<sub>3</sub> retrievals have been assimilated with a 4D-VAR variational algorithm to constrain stratospheric and tropospheric ozone respectively. The ozone analyses are validated against ozonesoundings and Tropospheric Column Ozone (TCO) from the OMI-MLS residual method. In addition, an Ozone ENSO Index (OEI) is computed from the analysis to validate the TCO variability during the ENSO events. <br><br> We show that the assimilation of IASI reproduces correctly the variability of tropospheric ozone during the period understudy. The variability deduced from the IASI-MLS analysis and the OMI-MLS measurements are similar for the whole period. IASI-MLS analysis can reproduce the extreme oscillation of tropospheric ozone caused by ENSO events over the tropical Pacific Ocean. However, a correction is required to reduce a constant bias present in the IASI-MLS analysis.

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APA

Peiro, H., Emili, E., Cariolle, D., Barret, B., & Le Flochmoën, E. (2018). Multi-year assimilation of IASI and MLS ozone retrievals: Variability of tropospheric ozone over the tropics in response to ENSO. Atmospheric Chemistry and Physics, 18(9), 6939–6958. https://doi.org/10.5194/acp-18-6939-2018

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