Xin Kai Lee

I added a `ParticleAdvectionForcing` that behaves similarly to `dynamics(particles, model, Δt)` which allows user to specify any velocities it wishes to add to the model by passing in `NonHydrostaticModel(..., advective_forcing...

I am thinking that perhaps we should start with temperature first, then move on to doing buoyancy flux after temperature is done. Also I think John's intention is to train...

There is an example here where I used `--buoyancy-flux 3e-8 --momentum-flux 0`, something odd is going on with a positive buoyancy flux as well. https://user-images.githubusercontent.com/50624521/119718892-0da53200-be60-11eb-9e38-ffb4bfdf8346.mp4