The ENSO signal in atmospheric composition fields: emission-driven versus dynamically induced changes

A Inness,M Parrington,J W Kaiser,A Benedetti,S Remy,J Flemming,V Huijnen

doi:10.5194/acp-15-9083-2015

Abstract

Abstract. The El Niño–Southern Oscillation (ENSO) not only affects meteorological fields but also has a large impact on atmospheric composition. Atmospheric composition fields from the Monitoring Atmospheric Composition and Climate (MACC) reanalysis are used to identify the ENSO signal in tropospheric ozone, carbon monoxide, nitrogen oxide and smoke aerosols, concentrating on the months October to December. During El Niño years, all of these fields have increased concentrations over maritime South East Asia in October. The MACC Composition Integrated Forecasting System (C-IFS) model is used to quantify the relative magnitude of dynamically induced and emission-driven changes in the atmospheric composition fields. While changes in tropospheric ozone are a combination of dynamically induced and emission-driven changes, the changes in carbon monoxide, nitrogen oxides and smoke aerosols are almost entirely emission-driven in the MACC model. The ozone changes continue into December, i.e. after the end of the Indonesian fire season while changes in the other fields are confined to the fire season.

Highlights

The El Niño–Southern Oscillation (ENSO) is the dominant mode of variability in the tropics (e.g. Allan et al, 1996)
In this paper we show that the Monitoring Atmospheric Composition and Climate (MACC) reanalysis shows the ENSO-induced anomalies in O3, carbon monoxide (CO), nitrogen oxides (NOx) and aerosols described in earlier studies
Between September and November 2006 the Global Fire Assimilation System (GFAS) v1.0 fire emissions used in BASE lead to an increased CO burden, which reaches values up to 21 Tg, almost double the values seen in CLIM

Summary

Introduction

The El Niño–Southern Oscillation (ENSO) is the dominant mode of variability in the tropics (e.g. Allan et al, 1996). Tosca et al (2010) used satellite data and modelling studies and found that the aerosol optical depth (AOD) over Indonesia had a large IAV that was driven by wild fires during periods of El Niño-induced droughts. We use MACC’s Composition Integrated Forecasting System (C-IFS) model (Flemming et al, 2015) to quantify the relative impact of the dynamics and the biomass burning emissions on the ENSO signal in the O3, CO, NOx and smoke aerosol fields.

The MACC reanalysis

ENSO anomalies

Experiment setup

Results of the C-IFS experiments

Conclusions and outlook