The Impact of Changing Meteorological Variables to Be Assimilated into GCM on Ozone Simulation with MRI CTM

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  • Impact of Changing Meteorological Variables to Be Assimilated into GCM on Ozone Simulation with MRI CTM

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Abstract

To reanalyze ozone field with the MRI Chemical Transport Model (CTM) driven by the nudged General Circulation Model (GCM), we investigated the impact of changing meteorological variables of the ERA40 data to be nudged into a GCM. Two experiments were performed: one nudges only horizontal wind (mechanical nudging), and the other nudges both horizontal wind and temperature (mechanical and thermal nudging). The reanalyzed ozone field produced by the two experiments is different, due to the difference in the meridional circulation of the nudged GCM simulation. This may be related to the cold bias of MRI-GCM, which is commonly found in many GCMs. Mechanical nudging causes weaker meridional circulation in the lower stratosphere and a stronger circulation in the troposphere, compared to ERA40 due to the temperature bias of the GCM. Thermal nudging systematically creates a spurious heat source in the GCM, which makes the meridional circulation stronger in the lower stratosphere and weaker in the troposphere. As a result, thermal nudging decreases ozone in the tropical lower stratosphere and increases it in the mid-latitudes upper troposphere and lower stratosphere. The meridional circulation of the nudged GCM depends on the relaxation time for the thermal nudging. It may be possible to optimize the relaxation time to obtain a realistic meridional circulation.

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