Investigation of Convective Differences in the Pacific ITCZ

The intertropical convergence zone (ITCZ) is known to be important to tropical convection and the global climate system, yet there is still much that we do not know about the convection in the region. One specific area where we lack understanding is the relative importance of dynamics and thermodynamics in controlling the convection. An area in the eastern part of the Pacific ITCZ has convection that has more low-level convergence per unit rainfall compared to other parts of the ITCZ. The increase in low-level convergence can be seen in the shape of the vertical mass flux profiles being more bottom heavy. There are two different explanations for the increased precipitation efficiency: the first is an imprinting of local SST gradients onto the boundary layer in the form of pressure gradients. These pressure gradients combine with friction and lead to convergence in the lower levels. The other is a thermodynamic explanation in which lower moist convective instability allows for increased rainfall for a certain amount of surface fluxes. Using a limited area cloud resolving model with large scale dynamics parameterized by a spectral weak temperature gradient (SWTG) approximation, I will simulate two different regions of the ITCZ that have similar amounts of precipitation. One area from the eastern ITCZ with higher low-level convergence and the other area from the western ITCZ with normal low-level convergence. This will provide a good comparison of the thermodynamic interactions between the two different regions, and potentially show the importance of the thermodynamic mechanisms in regulating the strength and shape of convection in the ITCZ.