The quasi-equilibrium tropical circulation model (QTCM1) is implemented and
tested. The formulation, described by Neelin and Zeng, uses a Galerkin fra
mework in the vertical, but with basis functions tailored to quasi-equilibr
ium deep convective physics via analytical solutions. QTCM1 retains a singl
e vertical structure of temperature and humidity. For a balanced treatment
of dynamics and subgrid-scale physics, a physics parameterization package o
f intermediate complexity is developed. This includes a linearized longwave
radiation scheme, a simple cloud prediction method, simple shortwave radia
tion schemes, and an intermediate land surface model.
The simulated climatology has a reasonable spatial pattern and seasonal evo
lution of the tropical convergence zones, including over land regions. Outg
oing longwave radiation and net surface heat Bur both appear satisfactory.
The Asian monsoon is slightly weak but depicts the northward progression of
the monsoon onset, and a monsoon wind shear index exhibits interannual var
iability associated with observed SST that is similar to general circulatio
n model (GCM) results. The extent and position of the main El Nino-Southern
Oscillation rainfall anomalies are simulated, as well as a number of the o
bserved tropical and subtropical teleconnections. The seasonal cycle and in
terannual variability of the Amazon water budget, including evapotranspirat
ion, interception loss, and surface and subsurface runoff, illustrate reaso
nable simulation of the hydrologic cycle. Sensitivity studies on effects of
topography, evaporation formulation, and land surface processes are also c
onducted. While the results are imperfect with respect to observations, man
y aspects are comparable to or better than GCMs of the previous generation.
Considering the complexity of these simulated phenomena, the model is comp
utationally light and easy to diagnose. It thus provides a useful tool fill
ing the niche between GCMs and simpler models.