Impact of Tropical SSTs in the North Atlantic and Southeastern Pacific on the Eastern Pacific ITCZ

Song, Fengfei; Zhang, Guang J.

doi:10.1175/JCLI-D-16-0310.1

Title: Impact of Tropical SSTs in the North Atlantic and Southeastern Pacific on the Eastern Pacific ITCZ

Abstract

During boreal spring, observations show a double ITCZ over the eastern Pacific, with the northern ITCZ stronger than the southern ITCZ. However, it is opposite in most climate models. It is also evident that there exists a cold bias in tropical North Atlantic (TNA) sea surface temperature (SST) and a warm bias in southeastern Pacific (SEP) SST. In this study, the influences of TNA and SEP SSTs on the double-ITCZ bias are investigated by prescribing the observed SST in these regions in the NCAR CESM1. Results show that when TNA SST is prescribed, the northern ITCZ is substantially enhanced and the southern ITCZ is moderately reduced, although the SST response in these regions is small. When the SEP SST is prescribed, the southern ITCZ is reduced considerably. When both TNA and SEP SSTs are prescribed, the double-ITCZ bias is reduced by ~68%. Moisture budget analysis suggests that dynamics, mainly the low-level convergence change, determines the above precipitation changes. Based on a mixed layer model, changes in low-level convergence are shown to be determined by surface pressure P_s changes. With prescribed TNA/SEP SSTs, SST gradients change the P_s in the region directly via the Lindzen–Nigam mechanism. The corresponding low-level circulation changesmore »« less

Authors:

Song, Fengfei ^[1]; Zhang, Guang J. ^[1]

Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California

Publication Date:: Wed Feb 01 00:00:00 EST 2017

Research Org.:: Univ. of California, San Diego, CA (United States)

Sponsoring Org.:: USDOE Office of Science (SC), Biological and Environmental Research (BER)

OSTI Identifier:: 1341938

Alternate Identifier(s):: OSTI ID: 1537013

Grant/Contract Number:: SC0016504

Resource Type:: Published Article

Journal Name:: Journal of Climate

Additional Journal Information:: Journal Name: Journal of Climate Journal Volume: 30 Journal Issue: 4; Journal ID: ISSN 0894-8755

Publisher:: American Meteorological Society

Country of Publication:: United States

Language:: English

Subject:: 54 ENVIRONMENTAL SCIENCES; Meteorology & Atmospheric Sciences

Citation Formats


                    Song, Fengfei, and Zhang, Guang J. Impact of Tropical SSTs in the North Atlantic and Southeastern Pacific on the Eastern Pacific ITCZ.  United States: N. p., 2017. 
Web.  doi:10.1175/JCLI-D-16-0310.1.

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                    Song, Fengfei, & Zhang, Guang J. Impact of Tropical SSTs in the North Atlantic and Southeastern Pacific on the Eastern Pacific ITCZ.  United States.  https://doi.org/10.1175/JCLI-D-16-0310.1

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                    Song, Fengfei, and Zhang, Guang J. Wed .  
"Impact of Tropical SSTs in the North Atlantic and Southeastern Pacific on the Eastern Pacific ITCZ".  United States.  https://doi.org/10.1175/JCLI-D-16-0310.1.

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@article{osti_1341938,

  title        = {Impact of Tropical SSTs in the North Atlantic and Southeastern Pacific on the Eastern Pacific ITCZ},

  author       = {Song, Fengfei and Zhang, Guang J.},

  abstractNote = {During boreal spring, observations show a double ITCZ over the eastern Pacific, with the northern ITCZ stronger than the southern ITCZ. However, it is opposite in most climate models. It is also evident that there exists a cold bias in tropical North Atlantic (TNA) sea surface temperature (SST) and a warm bias in southeastern Pacific (SEP) SST. In this study, the influences of TNA and SEP SSTs on the double-ITCZ bias are investigated by prescribing the observed SST in these regions in the NCAR CESM1. Results show that when TNA SST is prescribed, the northern ITCZ is substantially enhanced and the southern ITCZ is moderately reduced, although the SST response in these regions is small. When the SEP SST is prescribed, the southern ITCZ is reduced considerably. When both TNA and SEP SSTs are prescribed, the double-ITCZ bias is reduced by ~68%. Moisture budget analysis suggests that dynamics, mainly the low-level convergence change, determines the above precipitation changes. Based on a mixed layer model, changes in low-level convergence are shown to be determined by surface pressure Ps changes. With prescribed TNA/SEP SSTs, SST gradients change the Ps in the region directly via the Lindzen–Nigam mechanism. The corresponding low-level circulation changes affect the 850-hPa thermodynamic state in a wider region, which in turn not only strengthens the SST-induced Ps change locally but also leads to Ps changes remotely, including the northern ITCZ region. Furthermore, the low-level convergence changes the vertical structure of moist static energy, altering the atmospheric stability and modulating precipitation distribution.},

  doi          = {10.1175/JCLI-D-16-0310.1},

  journal      = {Journal of Climate},

  number       = 4,

  volume       = 30,

  place        = {United States},

  year         = {Wed Feb 01 00:00:00 EST 2017},

  month        = {Wed Feb 01 00:00:00 EST 2017}

}

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Works referencing / citing this record:

Alleviated Double ITCZ Problem in the NCAR CESM1: A New Cloud Scheme and the Working Mechanisms
journal, September 2018

Qin, Yi; Lin, Yanluan
Journal of Advances in Modeling Earth Systems, Vol. 10, Issue 9
DOI: 10.1029/2018ms001343

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Similar Records

Title: Impact of Tropical SSTs in the North Atlantic and Southeastern Pacific on the Eastern Pacific ITCZ

Abstract

Citation Formats

Alleviated Double ITCZ Problem in the NCAR CESM1: A New Cloud Scheme and the Working Mechanisms journal, September 2018

Alleviated Double ITCZ Problem in the NCAR CESM1: A New Cloud Scheme and the Working Mechanisms
journal, September 2018