Disentangling the effect of regional surface heat flux bias on the double-ITCZ problem

• Main Author: Lee, Jiheun
• Other Authors: Kang, Sarah M.
• Format: Master Thesis
• Language: English
• Published: Ulsan National Institute of Science and Technology 2021
• Subjects: Pacific; Southern Ocean
• Online Access: https://scholarworks.unist.ac.kr/handle/201301/53663; http://unist.dcollection.net/common/orgView/200000505550

Department of Urban and Environmental Engineering (Environmental Science and Engineering) Despite substantial advances in climate modeling over the past several decades, state-of-the-art coupled general circulation models continue to suffer from a long-standing bias in the representation of regional tropical precipitation. Since the error is so entangled, quantifying the origin still remains a challenge. This study investigates the causes of the double intertropical convergence zone (ITCZ) bias???in which the ITCZ in the models straddles the equator with two maximum rain bands??? by disentangling the individual contribution of regional surface heat flux biases. A previously suggested Southern Ocean warm bias effect in displacing the zonal-mean ITCZ southward is diminished by the southern midlatitude cold bias effect. The northern extratropical cold bias turns out to be most responsible for a southward-displaced zonal-mean precipitation, but the zonal-mean diagnostics poorly represents longitudinal pattern of the tropical Pacific response. Examination of longitude-latitude structure indicates that the overall spatial pattern of tropical precipitation bias is largely shaped by the local surface heat flux bias, while extratropical origin renders only a weak compensating effect to the existing double-ITCZ. The southeastern tropical Pacific wet bias is driven by warm bias along the west coast of South America with negligible influence from the Southern Ocean warm bias. Our model experiments shed light on where the focus should be applied in model development to correct the certain features of tropical precipitation bias. open