Understand the trends of the tropical lower stratospheric temperature over the past few decades

The long term trends of the tropical lower stratospheric temperature over the past few decades have been investigated with satellite-borned measurements, reanalyses data and Whole Atmosphere Community Climate Model (WACCM) simulations. We quantified the contribution to the tropical lower stratospheric temperature trends from radiative process due to changes in the trace gas constitutions, and the the contribution from dynamical process due to changes in the Brewer-Dobson circulation (BDC). The observed tropical lower stratospheric temperature trends have exhibited evident seasonality, which is mostly determined by the change of the BDC. The observed temperature trends also indicate a strengthening of the BDC since 1979, especially the southern cell. The WACCM simulated tropical lower stratospheric temperature trends show a similar seasonal dependence and radiative-dynamic partition as the observations, but the annual mean BDC strength shows weaker trends. To further understand the changes of the BDC, we diagnosed the wave propagation and dissipation in models using Eliassen-Palm flux, and compared with results from reanalyses data.