Different from previous versions, V2.2, by default, uses a ``nonlinear 
''
scheme for convective closure assumption. It is in principle
the same as the original Betts-Miller convective closure scheme but retains
the nonlinear Clausius-Clapeyron dependence of 
(the convective moisture
profile) on temperature in horizontal variations as well as vertical. In the
original scheme, linearization is used about a reference profile at each
level, which holds well through the tropics, but is beyond its range of
validity in mid-latitudes in winter.
The nonlinear scheme significantly reduces the excessive mid-latitude
precipitation shown in the original model and prevents occurrence of negative
humidity in mid-latitudes. The original linear scheme is commented out
in qtcm.F.
Another convective closure assumption implemented but
commented out in qtcm.F is called the
`unshifted- 
scheme' or `U- scheme',
which assumes that the convective temperature profile, , arises
following a moist adiabat from the boundary layer without the shift
used in the original Betts-Miller scheme to match the moisture sinks.
This condition is indeed applied to the moisture sink term.
It avoids explicitly specifying convective moisture profile.
Simulations with this scheme produce similar
results to the original linear scheme.