Abstract
Abstract. The Madden–Julian Oscillation (MJO) is the dominant form of the atmospheric intra-seasonal oscillation, manifested by slow eastward movement (about 5 m s−1) of tropical deep convection. This study investigates the MJO's impact on equatorial tropospheric ozone (10° N–10° S) in satellite observations and chemical transport model (CTM) simulations. For the satellite observations, we analyze the Tropospheric Emission Spectrometer (TES) level-2 ozone profile data for the period of January 2004 to June 2009. For the CTM simulations, we run the Community Atmosphere Model with chemistry (CAM-chem) driven by the Goddard Earth Observing System Model, Version 5 (GEOS-5)-analyzed meteorological fields for the same data period as the TES measurements. Our analysis indicates that the behavior of the total tropospheric column (TTC) ozone at the intra-seasonal timescale is different from that of the total column ozone, with the signal in the equatorial region comparable with that in the subtropics. The model-simulated and satellite-measured ozone anomalies agree in their general pattern and amplitude when examined in the vertical cross section (the average spatial correlation coefficient among the eight phases is 0.63), with an eastward propagation signature at a similar phase speed as the convective anomalies (5 m s−1). The model ozone anomalies on the intra-seasonal timescale are about 5 times larger when lightning emissions of NOx are included in the simulation than when they are not. Nevertheless, large-scale advection is the primary driving force for the ozone anomalies associated with the MJO. The variability related to the MJO for ozone reaches up to 47% of the total variability (ranging from daily to interannual), indicating that the MJO should be accounted for in simulating ozone perturbations in the tropics.
Highlights
Tropospheric ozone is key in governing the tropospheric oxidation capacity through its role in producing hydroxyl (OH) radicals (Lelieveld and Dentener, 2000), the primary chemical sink for many chemical pollutants
The tropical tropospheric ozone distribution and variability have not been well documented and characterized, especially on the intra-seasonal timescale (e.g., Thompson et al, 2003). This is true in the observations, as well as in model simulations, where the focus has been on the climatology or seasonal variation of the tropospheric total column ozone in the tropics
This study investigates the dominant form of the intra-seasonal oscillation, the Madden–Julian Oscillation’s (MJO) (Madden and Julian, 1972) impact on equatorial tropospheric ozone (10◦ N–10◦ S) in satellite observations and in chemical transport model (CTM) simulations
Summary
Tropospheric ozone is key in governing the tropospheric oxidation capacity through its role in producing hydroxyl (OH) radicals (Lelieveld and Dentener, 2000), the primary chemical sink for many chemical pollutants. We examine (C5H8), NOx (NO + NO2), carbon monoxide (CO) and hydrocarbons over polluted regions, convection significantly inthe response of tropospheric ozone to the MJO in the equatorial region and the factors that drive the response using recent creases these precursor concentrations, and ozone, in Tropospheric Emission Spectrometer (TES) ozone data and the mid- and upper troposphere at the expense of concen- a chemical transport model (CAM-chem). Since we are most interested in the model simulation of the tropospheric ozone variation given realistic dynamical forcing of the MJO (convection, precipitation and large-scale circulation), the CAM-chem was driven by Goddard Earth Observing System Model, Version 5 (GEOS-5)-analyzed meteorological fields for the period January 2004 to June 2009 with the first 8 months used as spin up. The advective algorithm (the flux form of the semi-Lagrangian scheme) does not readily allow the differentiation of advection into vertical and horizontal components
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