Processes Leading to Double Intertropical Convergence Zone Bias in CESM1/CAM5

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Please use this identifier to cite or link to this item: https://irlib.pccu.edu.tw/handle/987654321/30752

Title:	Processes Leading to Double Intertropical Convergence Zone Bias in CESM1/CAM5
Authors:	Wang, Chia-Chi Lee, Wei-Liang Chen, Yu-Luen Hsu, Huang-Hsiung
Contributors:	Dept Atmospher Sci
Keywords:	COMMUNITY ATMOSPHERE MODEL SHALLOW MERIDIONAL CIRCULATION TROPICAL EASTERN PACIFIC DOUBLE-ITCZ PROBLEM SEASONAL CYCLE CLIMATE MODELS COUPLED OCEAN PART I CONVECTION PARAMETERIZATION
Date:	2015-04
Issue Date:	2015-10-30 13:35:44 (UTC+8)
Abstract:	The double intertropical convergence zone (ITCZ) bias in the eastern Pacific in the Community Earth System Model version 1 with Community Atmosphere Model version 5 (CESM1/CAM5) is diagnosed. In CAM5 standalone, the northern ITCZ is associated with inertial instability and the southern ITCZ is thermally forced. After air-sea coupling, the processes on both hemispheres are switched because the spatial pattern of sea surface temperature (SST) is changed. Biases occur during boreal spring in both CAM5 and the ocean model. In CAM5 alone, weaker-than-observed equatorial easterly in the tropical eastern South Pacific leads to weaker evaporation and an increase in local SST. The shallow meridional circulation overly converges in the same region in the CAM5 standalone simulation, the planetary boundary layer and middle troposphere are too humid, and the large-scale subsidence is too weak at the middle levels. These biases may result from excessive shallow convection behavior in CAM5. The extra moisture would then fuel stronger convection and a higher precipitation rate in the southeastern Pacific. In the ocean model, the South Equatorial Current is underestimated and the North Equatorial Countercurrent is located too close to the equator, causing a warm SST bias in the southeastern Pacific and a cold bias in the northeastern Pacific. These SST biases feed back to the atmosphere and further influence convection and the surface wind biases in the coupled simulation. When the convection in the tropical northeastern Pacific becomes thermally forced after coupling, the northern ITCZ is diminished due to colder SST, forming the so-called alternating ITCZ bias.
Relation:	JOURNAL OF CLIMATE 卷: 28 期: 7 頁碼: 2900-2915
Appears in Collections:	[Department of Atmospheric Sciences & Graduate Institute of Earth Science / Atmospheric Science ] journal articles

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