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Title: Role of Equatorial Cold Tongue in Central Pacific Double-ITCZ Bias in the NCAR CESM1.2

Journal Article · · Journal of Climate
 [1];  [1]
  1. Scripps Inst. of Oceanography, La Jolla, CA (United States)

Warm SST bias underlying the spurious southern ITCZ has long been recognized as one of the main causes for double-ITCZ bias in coupled GCMs in the central Pacific. This study demonstrates that the NCAR CESM1.2 can still simulate significant double-ITCZ bias even with cold SST bias in the southern ITCZ region, indicating that warm SST bias is not a necessary condition for double-ITCZ bias in the central Pacific. Further analyses suggest that the equatorial cold tongue (ECT) biases play important roles in the formation of double-ITCZ bias in the central Pacific. The severe cold SST biases in the ECT region in the central Pacific may enhance the SST gradient between the ECT and southern ITCZ region, strengthening the lower troposphere dynamical convergence and hence convection in the southern ITCZ region. The formation mechanism of excessive ECT bias is further investigated. It is shown that the cold SST biases in the ECT region can be largely attributed to the anomalous cooling tendency produced by the upper ocean zonal advection due to overly strong zonal currents. In the ECT region, the westward ocean surface zonal current is driven by the equatorial easterly surface winds. In this work, it is shown that convection bias simulated by the atmospheric model in the equatorial Amazon region may lead to easterly wind bias in the downwind side (west) of convection region. Finally, the mean Walker circulation transports these easterly wind momentum anomalies downward and westward to the surface, resulting in the overly strong surface easterly wind in the central equatorial Pacific.

Research Organization:
Univ. of California, San Diego, CA (United States). Scripps Inst. of Oceanography
Sponsoring Organization:
USDOE Office of Science (SC), Biological and Environmental Research (BER); National Science Foundation (NSF)
Grant/Contract Number:
SC0016504; SC0019373; AGS-1549259
OSTI ID:
1657518
Journal Information:
Journal of Climate, Vol. 33, Issue 24; Related Information: Song, X., and G. J. Zhang, 2019: Culprit of the eastern Pacific double-ITCZ bias in the NCAR CESM1.2, J. Climate, 32, 6349-6364.; ISSN 0894-8755
Publisher:
American Meteorological SocietyCopyright Statement
Country of Publication:
United States
Language:
English

References (36)

Regional and seasonal variations of the double-ITCZ bias in CMIP5 models journal September 2017
The Version-2 Global Precipitation Climatology Project (GPCP) Monthly Precipitation Analysis (1979–Present) journal December 2003
On the Relationship between SST Gradients, Boundary Layer Winds, and Convergence over the Tropical Oceans journal August 2009
An Improved Coupled Model for ENSO Prediction and Implications for Ocean Initialization. Part I: The Ocean Data Assimilation System journal April 1998
Sensitivities of the hydrologic cycle to model physics, grid resolution, and ocean type in the aquaplanet C ommunity A tmosphere M odel journal May 2017
The ERA-Interim reanalysis: configuration and performance of the data assimilation system journal April 2011
The Tropical Eastern Pacific Seasonal Cycle: Assessment of Errors and Mechanisms in IPCC AR4 Coupled Ocean–Atmosphere General Circulation Models journal June 2008
An Ocean Analysis System for Seasonal to Interannual Climate Studies journal February 1995
NCEP–DOE AMIP-II Reanalysis (R-2) journal November 2002
A Framework to Decompose Wind-Driven Biases in Climate Models Applied to CCSM/CESM in the Eastern Pacific journal November 2017
Tropical Biases in CMIP5 Multimodel Ensemble: The Excessive Equatorial Pacific Cold Tongue and Double ITCZ Problems journal February 2014
The Double-ITCZ Problem in IPCC AR4 Coupled GCMs: Ocean–Atmosphere Feedback Analysis journal September 2007
On the Role of Sea Surface Temperature Gradients in Forcing Low-Level Winds and Convergence in the Tropics journal September 1987
An Investigation of the Initial Development of the Double-ITCZ Warm SST Biases in the CCSM journal January 2012
Peruvian Stratus Clouds and the Tropical Pacific Circulation: A Coupled Ocean-Atmosphere GCM Study journal July 1996
The Seasonal Cycle over the Tropical Pacific in Coupled Ocean–Atmosphere General Circulation Models journal September 1995
The Seasonal Heat Budget of the North Pacific: Net Heat Flux and Heat Storage Rates (1950–1990) journal March 1998
The double ITCZ bias in CMIP5 models: interaction between SST, large-scale circulation and precipitation journal January 2015
Global analyses of sea surface temperature, sea ice, and night marine air temperature since the late nineteenth century journal January 2003
Role of Troposphere-Convection-Land Coupling in the Southwestern Amazon Precipitation Bias of the Community Earth System Model Version 1 (CESM1) journal August 2018
Tropical Pacific SST and ITCZ Biases in Climate Models: Double Trouble for Future Rainfall Projections? journal February 2019
Effects of Southeastern Pacific Sea Surface Temperature on the Double-ITCZ Bias in NCAR CESM1 journal October 2016
Convection Parameterization, Tropical Pacific Double ITCZ, and Upper-Ocean Biases in the NCAR CCSM3. Part I: Climatology and Atmospheric Feedback journal August 2009
Culprit of the Eastern Pacific Double-ITCZ Bias in the NCAR CESM1.2 journal August 2019
The Double‐ITCZ Bias in CMIP3, CMIP5, and CMIP6 Models Based on Annual Mean Precipitation journal April 2020
The Surface-Layer Heat Balance in the Equatorial Pacific Ocean. Part I: Mean Seasonal Cycle* journal August 1999
Predicting the severity of spurious “double ITCZ” problem in CMIP5 coupled models from AMIP simulations journal February 2017
Ocean–Atmosphere Interaction in the Making of the Walker Circulation and Equatorial Cold Tongue journal February 1998
How well can CMIP5 simulate precipitation and its controlling processes over tropical South America? journal November 2012
Links between Annual Variations of Peruvian Stratocumulus Clouds and of SST in the Eastern Equatorial Pacific journal November 1999
Double ITCZs journal June 2001
Sensitivity of climate simulations to the parameterization of cumulus convection in the Canadian climate centre general circulation model journal September 1995
Convection Parameterization, Tropical Pacific Double ITCZ, and Upper-Ocean Biases in the NCAR CCSM3. Part II: Coupled Feedback and the Role of Ocean Heat Transport journal February 2010
Toward understanding the double Intertropical Convergence Zone pathology in coupled ocean-atmosphere general circulation models journal January 2007
Double ITCZ in Coupled Ocean-Atmosphere Models: From CMIP3 to CMIP5: DOUBLE ITCZ IN CMIP3 AND CMIP5 AOGCMS journal October 2015
Excessive ITCZ but Negative SST Biases in the Tropical Pacific Simulated by CMIP5/6 Models: The Role of the Meridional Pattern of SST Bias journal June 2020