Over deep convective regions, high cloud tops associated with strong convection would increase gross dry stability, and thus gross moist stability, because of increased thickness of cloudy layers. In v2.3, this cloud top effect is included by a crude parameterization based on strong correlation of boundary layer moisture and convective activity in the atmosphere. Comparing to the constant GMs used in previous versions, GMs takes the following form in v2.3,
where GMsq is the coefficient of gross
dry stability dependence on moisture. We use the value of GMqp for GMsq
such that the gross moist stability M would be constant over moist regions.
Observational evidence shows that these two parameters are similar. We choose
them equal for simplicity. The threshold value of surface moisture is
decided by looking at model output and picking the typical value of
moisture in warm SST regions. The default is set to be 19 g 
.
The inclusion of cloud-top effect on GMs helps to prevent gross moist stability from decreasing lower than minimum value typical of the reference profile region. It also helps numerical stability. Without this, it is typical that one has to raise GMsr for numerical reasons.