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Title: Culprit of the Eastern Pacific Double-ITCZ Bias in the NCAR CESM1.2

Abstract

The eastern Pacific double-ITCZ bias has long been attributed to the warm bias of SST in the southeastern Pacific and associated local air–sea interaction. In this study, we conducted two simulations using the NCAR CESM1.2.1 to demonstrate that significant double-ITCZ bias can still form in the eastern Pacific through air–sea coupled feedback even when there is cold SST bias in the southeastern Pacific, indicating that other nonlocal culprits and mechanisms should be responsible for the double-ITCZ bias in the eastern Pacific. Further analyses show that the oversimulated convection in the northern ITCZ region and Central America in boreal winter may result in biases in the surface wind fields in the tropical northeastern Pacific in the atmospheric model, which favor the cooling of the ocean mixed layer through enhancement of latent heat flux and Ekman upwelling. Furthermore, these biases are passed into the ocean model in coupled simulations and result in a severe cold bias of SST in the northern ITCZ region. The overly cold SST bias persists in the subsequent spring, leading to the suppression of convection in the northern ITCZ region. The enhanced low-level cross-equatorial northerly wind strengthens the wind convergence south of the equator and transports abundant watermore » vapor to the convergence zone, strengthening the southern ITCZ convection. All these processes lead to the disappearance of the northern ITCZ and the enhancement of the southern ITCZ in boreal spring, forming a seasonally alternating double-ITCZ bias. This study suggests that convection biases in the northern ITCZ region and Central America in boreal winter may be a culprit for the double-ITCZ bias in the eastern Pacific.« less

Authors:
 [1];  [1]
  1. Scripps Institution of Oceanography, La Jolla, California (United States).
Publication Date:
Research Org.:
Univ. of California, San Diego, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC); National Science Foundation (NSF)
OSTI Identifier:
1558840
Alternate Identifier(s):
OSTI ID: 1803009
Grant/Contract Number:  
SC0016504; AGS-1549259
Resource Type:
Published Article
Journal Name:
Journal of Climate
Additional Journal Information:
Journal Volume: 32; Journal Issue: 19; Journal ID: ISSN 0894-8755
Publisher:
American Meteorological Society
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; Meteorology & Atmospheric Sciences; Pacific Ocean; Atmosphere-ocean interaction; Climate models; Coupled models; Model errors; Seasonal cycle

Citation Formats

Song, Xiaoliang, and Zhang, Guang J. Culprit of the Eastern Pacific Double-ITCZ Bias in the NCAR CESM1.2. United States: N. p., 2019. Web. doi:10.1175/jcli-d-18-0580.1.
Song, Xiaoliang, & Zhang, Guang J. Culprit of the Eastern Pacific Double-ITCZ Bias in the NCAR CESM1.2. United States. https://doi.org/10.1175/jcli-d-18-0580.1
Song, Xiaoliang, and Zhang, Guang J. Tue . "Culprit of the Eastern Pacific Double-ITCZ Bias in the NCAR CESM1.2". United States. https://doi.org/10.1175/jcli-d-18-0580.1.
@article{osti_1558840,
title = {Culprit of the Eastern Pacific Double-ITCZ Bias in the NCAR CESM1.2},
author = {Song, Xiaoliang and Zhang, Guang J.},
abstractNote = {The eastern Pacific double-ITCZ bias has long been attributed to the warm bias of SST in the southeastern Pacific and associated local air–sea interaction. In this study, we conducted two simulations using the NCAR CESM1.2.1 to demonstrate that significant double-ITCZ bias can still form in the eastern Pacific through air–sea coupled feedback even when there is cold SST bias in the southeastern Pacific, indicating that other nonlocal culprits and mechanisms should be responsible for the double-ITCZ bias in the eastern Pacific. Further analyses show that the oversimulated convection in the northern ITCZ region and Central America in boreal winter may result in biases in the surface wind fields in the tropical northeastern Pacific in the atmospheric model, which favor the cooling of the ocean mixed layer through enhancement of latent heat flux and Ekman upwelling. Furthermore, these biases are passed into the ocean model in coupled simulations and result in a severe cold bias of SST in the northern ITCZ region. The overly cold SST bias persists in the subsequent spring, leading to the suppression of convection in the northern ITCZ region. The enhanced low-level cross-equatorial northerly wind strengthens the wind convergence south of the equator and transports abundant water vapor to the convergence zone, strengthening the southern ITCZ convection. All these processes lead to the disappearance of the northern ITCZ and the enhancement of the southern ITCZ in boreal spring, forming a seasonally alternating double-ITCZ bias. This study suggests that convection biases in the northern ITCZ region and Central America in boreal winter may be a culprit for the double-ITCZ bias in the eastern Pacific.},
doi = {10.1175/jcli-d-18-0580.1},
journal = {Journal of Climate},
number = 19,
volume = 32,
place = {United States},
year = {2019},
month = {8}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record
https://doi.org/10.1175/jcli-d-18-0580.1

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Cited by: 9 works
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