The response of the equatorial tropospheric ozone to the Madden–Julian Oscillation in TES satellite observations and CAM-chem model simulation
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.