What is the ITCZ?

Why we are researching the ITCZ
- Climate models struggle to correctly simulate the oceanic ITCZ (e.g., Adam et al., 2017), which has limited our ability to fully understand and communicate how the atmosphere and ocean will respond to climate change.
- Our group’s research is focused on better understanding the fundamental physics that explains the weather in and near the ITCZ through detailed examinations of observations, reanalyses, and models of varying complexity.
- Our ultimate goal is to improve the accuracy of climate models so that scientists can 1) improve subseasonal and seasonal forecasting and 2) better communicate the anticipated effects of climate change.
Project 1: Nonlinear Dynamics of boreal spring ITCZ shifts

Our recent work has shown that the ITCZ’s latitudinal location can be explained by an idealized two-dimensional (time & latitude) atmospheric model near Earth’s surface (e.g., Gonzalez et al., 2016). A key component to the model is the inclusion of nonlinear dynamical (velocity) terms that have often been left out of idealized tropical models. These nonlinear terms are particularly important for the eastern Pacific ITCZ, as shown in the figure to the right (Gonzalez and Schubert, 2019).
Project 2: Mitigating ITCZ climate model biases through hindcast simulations
ITCZ accuracy in climate models is typically assessed by computing monthly or seasonal averages, however, it is possible that model biases begin to develop at shorter timescales. This is particularly relevant for the eastern Pacific Ocean, whose ITCZ biases tend occur in the months surrounding February–April, which are the months when the ITCZ experiences to shifts or splits in observations.
We are investigating the submonthly variability of the eastern Pacific Ocean ITCZ in climate models by running them in “hindcast” mode. A hindcast is a forecast of past weather conditions using an updated (current) model. Running a climate model in hindcast mode is a relatively new concept as climate model simulations are typically not expected to accurately predict weather conditions (see Climate.gov article). With the idea that weather in and near the ITCZ actually matters to the average ITCZ behavior, hindcast simulations may be the best way to illustrate how and why ITCZ biases creep up.

Hindcast simulations using the Community Atmosphere Model (CAM) version 5.3 demonstrate how fast ITCZ biases develop for many ITCZ precipitation events, such as the February 23–28 ITCZ event shown above. There is a gradual development of southern hemisphere ITCZ precipitation (top right) and cross-equatorial wind speed (bottom right) over the 20 day hindcasts.