Can reducing the incoming energy flux over the Southern Ocean in a CGCM improve its simulation of tropical climate?

Mechoso, Carlos R.; Losada, Teresa; Koseki, Shunya; Mohíno, Elsa; Keenlyside, Noel; Castaño-Tierno, Antonio; Myers, Timothy A.; Fonseca, Belén Rodríguez de; Toniazzo, Thomas

doi:10.1002/2016gl071150

Cited by 45 publications

(57 citation statements)

References 29 publications

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“…Among the aforementioned limitations, we address the issue of partitioning between atmosphere and ocean energy transports. Some recent studies that incorporate fully coupled models indicate that tropical rainfall is not as sensitive to extratropical forcings [53][54][55][56]61,62 as suggested by studies that disregard ocean dynamics. We propose that developing a hierarchy of ocean models is a step toward resolving the issue.…”

Section: Discussionmentioning

confidence: 99%

“…We demonstrate that an inclusion of Ekman advection completely damps or reverses the tropical rainfall response, as in the fully coupled model experiments mentioned previously. [53][54][55][56]61,62 Our results suggest that ocean Ekman advection can play a critical role in the coupled climate system. Complications arise from the competing effects of the tropical and the extratropical components of Ekman-driven heating.…”

Section: ∂Ts ∂φmentioning

confidence: 99%

“…57 In response to a reduction of solar flux over the Southern Ocean, the UCLA CGCM produces a significant ITCZ shift whereas a much weaker ITCZ response is obtained in the NorESM model. 56 These studies that employ fully coupled models suggest a large inter-model spread in the degree by which the ocean circulation modulates the tropical response to extratropical forcing. In general, extratropical energy perturbations are not as effective at forcing the ITCZ shift as predicted by the energetics framework with a slab ocean.…”

Section: Limitations and Ways Forwardmentioning

confidence: 99%

“…This may partly explain a large multi-model spread of the partitioning of the energy transport adjustments between atmosphere and ocean. [53][54][55][56]61,62 The partitioning is also expected to be sensitive to the location of the prescribed forcing because of large differences among ocean basins in the mean jet latitude, as well as the relative importance between the thermohaline and wind-driven circulation in transporting energy. Moreover, the climatological jet location is sensitive to the strength of transient eddy fluxes, 82 which controls the communication between the extratropics and the HC.…”

Section: ∂Ts ∂φmentioning

confidence: 99%

“…Recently, fully coupled models with a dynamical ocean are employed to examine the ITCZ response to high-latitude energy perturbation. [53][54][55][56][57] In response to modified Southern Ocean albedo, the changes in cross-equatorial energy transport are dominated by ocean adjustments, and the ITCZ response is muted with a persistent double-ITCZ problem 53,54 in some models (CESM-CAM5 58 and HadGEM2-ES 59 ). Similarly, when the model (CCSM4 60 ) is forced by the projected Arctic sea ice loss, the climate response exhibits a high degree of hemispheric symmetry with little ITCZ shift, as the energy transport is mostly accomplished by the ocean in the equatorial region.…”

Section: Limitations and Ways Forwardmentioning

confidence: 99%

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Extratropical forcing and tropical rainfall distribution: energetics framework and ocean Ekman advection

2018

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Intense tropical rainfall occurs in a narrow belt near the equator, called the inter-tropical convergence zone (ITCZ). In the past decade, the atmospheric energy budget has been used to explain changes in the zonal-mean ITCZ position. The energetics framework provides a mechanism for extratropics-to-tropics teleconnections, which have been postulated from paleoclimate records. In atmosphere models coupled with a motionless slab ocean, the ITCZ shifts toward the warmed hemisphere in order for the Hadley circulation to transport energy toward the colder hemisphere. However, recent studies using fully coupled models show that tropical rainfall can be rather insensitive to extratropical forcing when ocean dynamics is included. Here, we explore the effect of meridional Ekman heat advection while neglecting the upwelling effect on the ITCZ response to prescribed extratropical thermal forcing. The tropical component of Ekman advection is a negative feedback that partially compensates the prescribed forcing, whereas the extratropical component is a positive feedback that amplifies the prescribed forcing. Overall, the tropical negative feedback dominates over the extratropical positive feedback. Thus, including Ekman advection reduces the need for atmospheric energy transport, dampening the ITCZ response. We propose to build a hierarchy of ocean models to systematically explore the full dynamical response of the coupled climate system.

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Section: Discussionmentioning

confidence: 99%

Section: ∂Ts ∂φmentioning

confidence: 99%

Section: Limitations and Ways Forwardmentioning

confidence: 99%

Section: ∂Ts ∂φmentioning

confidence: 99%

Section: Limitations and Ways Forwardmentioning

confidence: 99%

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Extratropical forcing and tropical rainfall distribution: energetics framework and ocean Ekman advection

2018

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Assessing extratropical impact on the tropical bias in coupled climate model with regional coupled data assimilation

Liu

Zhang

et al. 2017

Geophysical Research Letters

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The tropical bias of double‐Intertropical Convergence Zone (ITCZ) has been a persistent feature in global climate models. It remains unclear how much of it is attributed to local and remote processes, respectively. Here we assess the extratropical influence on the tropical bias in a coupled general circulation model dynamically, systematically, and quantitatively using the Regional Coupled Data Assimilation (RCDA) method. RCDA experiments show that the model's double‐ITCZ bias is improved systematically when sea surface temperature, air temperature, and wind are corrected toward real‐world data from the extratropics into the tropics progressively. Quantitatively, the tropical asymmetry bias in precipitation and surface temperature is reduced by 40% due to extratropical impact from outside of ~25°. Coupled dynamics, as well as atmospheric and oceanic processes, play important roles in this extratropical‐to‐tropical teleconnection. Energetic analysis of cross‐equatorial atmospheric energy transport and equatorial net energy input are used to explain the changes in the precipitation bias.

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Sensitivity of Coupled Tropical Pacific Model Biases to Convective Parameterization in CESM1

Woelfle

Bretherton

et al. 2018

J Adv Model Earth Syst

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Six month coupled hindcasts show the central equatorial Pacific cold tongue bias development in a GCM to be sensitive to the atmospheric convective parameterization employed. Simulations using the standard configuration of the Community Earth System Model version 1 (CESM1) develop a cold bias in equatorial Pacific sea surface temperatures (SSTs) within the first two months of integration due to anomalous ocean advection driven by overly strong easterly surface wind stress along the equator. Disabling the deep convection parameterization enhances the zonal pressure gradient leading to stronger zonal wind stress and a stronger equatorial SST bias, highlighting the role of pressure gradients in determining the strength of the cold bias. Superparameterized hindcasts show reduced SST bias in the cold tongue region due to a reduction in surface easterlies despite simulating an excessively strong low‐level jet at 1‐1.5 km elevation. This reflects inadequate vertical mixing of zonal momentum from the absence of convective momentum transport in the superparameterized model. Standard CESM1simulations modified to omit shallow convective momentum transport reproduce the superparameterized low‐level wind bias and associated equatorial SST pattern. Further superparameterized simulations using a three‐dimensional cloud resolving model capable of producing realistic momentum transport simulate a cold tongue similar to the default CESM1. These findings imply convective momentum fluxes may be an underappreciated mechanism for controlling the strength of the equatorial cold tongue. Despite the sensitivity of equatorial SST to these changes in convective parameterization, the east Pacific double‐Intertropical Convergence Zone rainfall bias persists in all simulations presented in this study.

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Can reducing the incoming energy flux over the Southern Ocean in a CGCM improve its simulation of tropical climate?

Cited by 45 publications

References 29 publications

Extratropical forcing and tropical rainfall distribution: energetics framework and ocean Ekman advection

Extratropical forcing and tropical rainfall distribution: energetics framework and ocean Ekman advection

Assessing extratropical impact on the tropical bias in coupled climate model with regional coupled data assimilation

Sensitivity of Coupled Tropical Pacific Model Biases to Convective Parameterization in CESM1

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