2. What is the origin of vertical diffusion ?

The vertical diffusion of 1D model is correspond to meridional circulation, breaking of thermal tide, ...

We focus on gravity wave generated by thermal convection.
Mixing due to gravity wave breaking may contribute to the large turbulent diffusion.

The result of 2D model simulation shows that gravity wave is generated by penetration of convective plume to stratosphere (Odaka, et al. 2001).