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Updated: May 13, 2026
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Published on: June 13, 2020
Link between the double-Intertropical Convergence Zone problem and cloud biases over the Southern Ocean
Yen-Ting Hwang1, Dargan M W Frierson
1Department of Atmospheric Sciences, University of Washington, Seattle, WA 98195-1640, USA. yting@atmos.washington.edu
Summary
Global climate models often show excessive rain in the Southern Hemisphere tropics, a bias linked to energy imbalances. Cloud biases over the Southern Ocean are a key factor driving this double-Intertropical Convergence Zone (ITCZ) problem.
Area of Science:
- Climate modeling
- Atmospheric science
- Earth system science
Background:
- The double-Intertropical Convergence Zone (ITCZ) problem is a persistent bias in global climate models, characterized by excessive precipitation in the Southern Hemisphere tropics.
- This bias creates an unrealistic atmospheric circulation pattern, with a stronger ITCZ in the Northern Hemisphere.
Purpose of the Study:
- To investigate the extratropical causes of the double-ITCZ problem.
- To analyze the relationship between global energy budget and ITCZ biases in climate models.
Main Methods:
- Performed a global energetic analysis using historical simulations from multiple global climate models.
- Compared model results with satellite observations of the Earth's energy budget.
Main Results:
- Models with greater energy flux into the Southern Hemisphere atmosphere exhibit a stronger double-ITCZ bias.
- Cloud biases over the Southern Ocean significantly contribute to model-to-model variations in Southern Hemisphere precipitation.
- These Southern Ocean cloud biases are identified as a primary driver of the double-ITCZ problem in many models.
Conclusions:
- Extratropical factors, particularly Southern Ocean cloud biases, play a crucial role in the double-ITCZ problem.
- Addressing cloud biases in climate models is essential for improving the simulation of tropical precipitation and ITCZ dynamics.
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