Tuning an idealized ITCZ model to observations

The axisymmetric version of the second quasi-equilibrium tropical circulation model (QTCM2) is run over an SST profile derived from observations in the the eastern Pacific in northern summer. Analysis of the observed circulation and its energy transports suggests that the model, with a slab atmospheric boundary layer and two vertical modes in the free troposphere, simple moist atmospheric physics, and fully nonlinear dynamics, should have a good chance of capturing the basic dynamics of the intertropical convergence zone (ITCZ) in this region. Parameters are varied with an eye towards understanding the sensitivities of the model, and the reasons for agreement or disagreement with the observations. Of particular interest are factors controlling the intensity of the ITCZ and the presence or absence of a spurious precipitation maximum in the southern hemisphere. The strength of the trade winds is also of interest, and is positively influenced by the inclusion of a crude representation of eddy momentum fluxes due to midlatitude eddies.