More sophisticated PBL scheme (PBL height)

[bertjebertjek]

Newly added convection schemes (BMJ, NSAS) require PBL height as an input. The current 'simple' PBL scheme does not compute this.
Currently the PBL height input to the above-mentioned convection schemes is fixed at an arbitrary value (hard-coded in cu_driver.f90).

First, we should see how sensitive these schemes actually are to this hard-coded PBL value by varying the value and analyzing the output. If this is negligible, the need for PBL improvement may be small. If it turns out that this is significant, then two possible ways forward exist:

1. include a more sophisticated scheme that calculates PBL height. YSU is a logical choice, since it is already partially implemented.
2. Expanding the existing scheme based on Hong and Pan 1996 could be expanded to calculate the PBL height.