Is the Brewer-Dobson Circulation driven by tropospheric baroclinic waves or high latitude, upper stratospheric planetary waves?

Studies based on TEM downward control diagnostics as applied to tropical upwelling at the 100 hPa level emphasize the role of low latitude, lower stratospheric planetary and synoptic scale waves in driving the time-mean Brewer-Dobson Circulation and the seasonal and nonseasonal variations about the mean. In contrast, statistical analysis of reanalysis datasets and model simulations show that the breaking of high latitude planetary waves in the upper stratosphere exerts a strong influence on tropical lower stratospheric temperature, which is presumably a measure of upwelling. Key elements in reconciling these seemingly contradictory interpretations are (a) recognizing the different character of the Lagrangian mean meridional circulation below and above 70 hPa and (b) extending the analysis high enough into the stratosphere to be able to resolve the equatorward extension of the momentum fluxes at 20 hPa and above.