Impact of Infrared Atmospheric Sounding Interferometer (IASI) thermal infrared measurements on global ozone reanalyses

Emanuele Emili,Mohammad El Aabaribaoune

doi:10.5194/gmd-14-6291-2021

Abstract

Abstract. The information content of thermal infrared measurements for tropospheric ozone (O3) estimation has already been well demonstrated. However, the impact of such measurements to constrain modelled O3 distributions within global assimilation systems is not yet unequivocal. A new tropospheric O3 reanalysis is computed for the year 2010 by means of assimilating measurements from the Infrared Atmospheric Sounding Interferometer (IASI) within the MOdéle pour la Chimie Á Grande Echelle (MOCAGE) chemical transport model. The objective is to evaluate the impact of recent methodological improvements of the data assimilation scheme on the O3 distribution. The new O3 reanalysis (named IASI-r) and its precursor (IASI-a) have been validated against ozonesondes, and compared to independent estimations of tropospheric O3 and to results from two state-of-the-art products based on detailed tropospheric chemistry (the Goddard Earth Observing System with a coupled chemistry–climate model, GEOS-CCM, and the Copernicus Atmosphere Monitoring Service, CAMS, reanalysis). The main difference between IASI-r and IASI-a concerns the treatment of IASI observations, with radiances being assimilated directly in IASI-r instead of intermediate Level 2 O3 retrievals. IASI-r is found to correct major issues with IASI-a, such as the neutral or negative impact of IASI assimilation in the extra-tropics and the presence of residual biases in the tropics. IASI-r also compares relatively well to the CAMS reanalysis, which is based on a more comprehensive chemical mechanism and the assimilation of several ultraviolet (UV) and microwave measurements.

Highlights

Tropospheric ozone (O3) contributes to global warming with a net positive effect in the upper troposphere–lower stratosphere (UTLS) at tropical and subtropical latitudes (Stevenson et al, 2013)
The new O3 reanalysis fundamentally inherits the methodology from Infrared Atmospheric Sounding Interferometer (IASI)-a (Emili et al, 2014; Peiro et al, 2018) and includes the recent developments discussed by Emili et al (2019) and El Aabaribaoune et al (2021) concerning the direct assimilation of IASI Level 1 (L1) radiances
Most aspects of the system were kept unchanged with respect to IASI-a in order to primarily evaluate the impact of the radiances assimilation

Summary

Introduction

Tropospheric ozone (O3) contributes to global warming with a net positive effect in the upper troposphere–lower stratosphere (UTLS) at tropical and subtropical latitudes (Stevenson et al, 2013). The complexity of O3 processes (sources, sinks, and transport patterns) and the scarcity of direct O3 measurements in the UTLS (Cooper et al, 2014) make the use of atmospheric composition models necessary for the estimation of the O3 radiative forcing (Gauss et al, 2006). The background error covariance B has been slightly improved with respect to previous studies, which prescribed O3 error profiles based on a single and fixed tropopause height (Emili et al, 2014; Peiro et al, 2018; Emili et al, 2019; El Aabaribaoune et al, 2021). Horizontal and vertical error correlations have been kept the same as in Emili et al (2019)

Objectives

Methods

Results

Conclusion