9:45 AM - 10:00 AM
[AAS01-04] Characteristics of the Brewer-Dobson circulation diagnosed from the JRA3Q reanalysis and the impact of a global model of the data assimilation system.
Keywords:Brewer-Dobson circulation, tropical upwelling, reanalysis, data assimilation system
The Brewer-Dobson circulation (BD circulation) is a meridional circulation in the stratosphere that transports atmospheric trace substances that affect radiation, such as water vapour, ozone and aerosols, from the troposphere to the stratosphere. The integrated tropical upwelling mass flux in the lower stratosphere is widely used as a standard (scalar) indicator to quantify the overall strength of the BD circulation. We compared climatological mean tropical upwelling mass fluxes diagnosed from reanalysis datasets and investigate the reasons for the differences in the strength of the BD circulation among reanalysis datasets. The climatological tropical upwelling in Japanese Reanalysis for Three Quarters of a Century (JRA-3Q) is weaker than that in JRA-55 and ERA5, and the difference between JRA-3Q and JRA-55 is almost constant throughout the reanalysis period. To investigate why the BD circulation in JRA-3Q is weaker than in JRA-55, the impact of differences of the global atmospheric model in the data assimilation system that produces the reanalysis data on the structure of the BD circulation and the intensity of tropical upwelling is investigated through data assimilation system experiments. It was found that differences in the diabatic heating profiles shown by the atmospheric models, in particular differences in condensation thermal heating, mainly affect the differences in the tropical upwelling intensity of the BD circulation in the reanalysis. On the other hand, it was also found that the adoption of the non-orographic gravity wave scheme is not the reason for the weaker upwelling intensity of JRA-3Q than JRA-55, as it has the effect of strengthening the tropical upwelling intensity of the BD circulation.