Add alternative formulation of scavenging in convective clouds. about cam HOT 1 OPEN

I have looked at the code from Pengfei Yu, published in Geophysical Research Letters, 46,1061–1069.
What you should be aware of is that the the code does not change the scavenging, only the transport. I notice from old notes that I have seen this before although I did not fully understood the idea behind the parameterisation.

The deep convective transport in NorESM (and CESM) is expressed as the fraction of aerosols which is not being scavenged:
Transport fraction=1-stratiform scavenging - convective in-cloud scavenging
Transport mass = Transport fraction * interstitial concentration mass of entrainment into updraft
Convective in-coud scavenging: Convective cloud volumeassumed activated fraction of aerosols*(precipitation rate/in-cloud cloud-water)

The problem is that this assumes that the entrained mass = cloud volume independent of updraft speed. This creates a problem because the entrained mass-flux within one timestep is often higher than the mass within the convective cloud. The solution to this should have been to calculate the scavenging within the mass flux, but the mass flux is calculated after the scavenging. Also there has been attempts to replace the convective parameterisation for the last 15 years or so, so it is possible that no one has wanted to touch the problem.

The added parameterisation I still do not understand at least from a physical point of view. It looks like it is added a flux that is dependent on the thickness of the layer, so the deeper the layer the more added the mass is reduced, i.e. a thick layer is suppoosed to have much higher vertical velocity than a thinner layer

from cam.