Energetic and dynamical constraints on the width of the ITCZ

The intertropical convergence zone (ITCZ) has been the focus of considerable research in recent years, with much of this work focusing on how the latitude of maximum tropical precipitation responds to natural climate variability and to radiative forcing. The width of the ITCZ, however, has received little attention despite its importance for regional climate and for our understanding of tropical dynamics. Here we examine the width of the ITCZ in simulations with an idealized general circulation model. In response to increases in longwave optical thickness, the ITCZ width (defined as the latitude nearest to the equator where precipitation minus evaporation, P-E, is zero) increases at a rate of approximately 1%/K. This sensitivity of ITCZ width to variations in climate is shown to be related to an offset between changes in P-E and changes in the curvature of the energy input at the center of the ITCZ. We also explore dynamical constraints on the ITCZ width related to the subcloud-layer moist entropy distribution. Our results may be useful for analyzing biases in ITCZ width in more complex climate models and for understanding past and future climate change in the Tropics.