Two maps of the tropical Pacific Ocean showing difference in precipitation between a control model and observations (top panel) and a model with elevated Central American orography (bottom panel).
The difference of March-April-May mean precipitation over the tropical Pacific between the observation and the control model (upper panel) and between the model with elevated Central American orography and the control model (lower panel). Credit: Baldwin et al. [2021], Figure 5b and 5h
Source: AGU Advances

Global Climate Models (GCMs) suffer from the tropical rainfall bias, with double peaks on both sides of the equator rather than just north of the equator, known as the double Inter-Tropical Convergence Zone (ITCZ) bias. The tropical mean state bias limits the fidelity of GCMs in projecting the future climate. Much effort has gone into improving this double ITCZ bias, but it has not been alleviated since the early days of model development.

Baldwin et al. [2021] suggest that a significant portion of the double ITCZ bias originates from low biases in Central American orography in models. Orographic peaks are often smoothed out in models that use observed orography averaged onto model grid. Elevation of Central American orography is demonstrated to reduce the double ITCZ bias as the northeastern tropical Pacific becomes warmer owing to blocked easterlies. The study offers a simple and computationally inexpensive yet physically based method for improving pervasive double ITCZ bias.

Citation: Baldwin, J., Atwood, A., Vecchi, G. and Battisti, D. [2021]. Outsize Influence of Central American Orography on Global Climate. AGU Advances, 2, e2020AV000343.

Text © 2021. The authors. CC BY-NC-ND 3.0
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