A quasi-equilibrium tropical circulation model - Implementation and simulation

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.