On the mechanisms in a tropical ocean-global atmosphere coupled general circulation model. Part II: interannual variability and its relation to the seasonal cycle

Abstract. This study aims to determine the role of the tropical ocean dynamics in the response of the climate to extratropical thermal forcing. We analyse and compare the outcomes of coupling an atmospheric general circulation model (AGCM) with two ocean models of different complexity. In the first configuration the AGCM is coupled with a slab ocean model while in the second a reduced gravity ocean (RGO) model is additionally coupled in the tropical region. We find that the imposition of extratropical thermal forcing (warming in the Northern Hemisphere and cooling in the Southern Hemisphere with zero global mean) produces, in terms of annual means, a weaker response when the RGO is coupled, thus indicating that the tropical ocean dynamics oppose the incoming remote signal. On the other hand, while the slab ocean coupling does not produce significant changes to the equatorial Pacific sea surface temperature (SST) seasonal cycle, the RGO configuration generates strong warming in the central-eastern basin from April to August balanced by cooling during the rest of the year, strengthening the seasonal cycle in the eastern portion of the basin. We hypothesize that such changes are possible via the dynamical effect that zonal wind stress has on the thermocline depth. We also find that the imposed extratropical pattern affects El Niño–Southern Oscillation, weakening its amplitude and low-frequency behaviour.

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Internal variability in a coupled general circulation model in radiative-convective equilibrium

Geophysical Research Letters ◽

10.1002/2017gl073658 ◽

2017 ◽

Vol 44 (10) ◽

pp. 5142-5149 ◽

Cited By ~ 20

Author(s):

David Coppin ◽

Sandrine Bony

Keyword(s):

General Circulation Model ◽

General Circulation ◽

Circulation Model ◽

Internal Variability ◽

Coupled General Circulation Model

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Sensitivity of the tropical climate to an interhemispheric thermal gradient: the role of tropical ocean dynamics

10.5194/esd-2017-113 ◽

2017 ◽

Author(s):

Stefanie Talento ◽

Marcelo Barreiro

Keyword(s):

Seasonal Cycle ◽

General Circulation ◽

Southern Oscillation ◽

Circulation Model ◽

Ocean Dynamics ◽

Thermocline Depth ◽

Thermal Forcing ◽

Tropical Ocean ◽

Slab Ocean

Abstract. This study aims to determine the role of the tropical ocean dynamics in the response of the climate to an extratropical thermal forcing. We analyse and compare the outcomes of coupling an atmospheric general circulation model (AGCM) with two ocean models of different complexity. In the first configuration the AGCM is coupled with a slab ocean model while in the second a Reduced Gravity Ocean (RGO) model is additionally coupled in the tropical region. We find that the imposition of an extratropical thermal forcing (warming in the Northern Hemisphere and cooling in the Southern Hemisphere with zero global mean) produces, in terms of annual means, a weaker response when the RGO is coupled, thus indicating that the tropical ocean dynamics opposes the incoming remote signal. On the other hand, while the slab ocean coupling does not produce significant changes to the equatorial Pacific sea surface temperature (SST) seasonal cycle, the RGO configuration generates a strong warming in the centre-east of the basin from April to August balanced by a cooling during the rest of the year, strengthening the seasonal cycle in the eastern portion of the basin. We hypothesize that such changes are possible via the dynamical effect that zonal wind stress has on the thermocline depth. We also find that the imposed extratropical pattern affects El Niño Southern Oscillation, weakening its amplitude and low-frequency behaviour.

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Coupled Ocean–Atmosphere Response to Seasonal Modulation of Ocean Color: Impact on Interannual Climate Simulations in the Tropical Pacific

Journal of Climate ◽

10.1175/jcli3958.1 ◽

2007 ◽

Vol 20 (2) ◽

pp. 353-374 ◽

Cited By ~ 39

Author(s):

J. Ballabrera-Poy ◽

R. Murtugudde ◽

R-H. Zhang ◽

A. J. Busalacchi

Keyword(s):

Solar Radiation ◽

Interannual Variability ◽

Seasonal Cycle ◽

General Circulation ◽

Ocean Color ◽

Circulation Model ◽

Enso Events ◽

Ocean Atmosphere ◽

Atmosphere Model ◽

The Impact

Abstract The ability to use remotely sensed ocean color data to parameterize biogenic heating in a coupled ocean–atmosphere model is investigated. The model used is a hybrid coupled model recently developed at the Earth System Science Interdisciplinary Center (ESSIC) by coupling an ocean general circulation model with a statistical atmosphere model for wind stress anomalies. The impact of the seasonal cycle of water turbidity on the annual mean, seasonal cycle, and interannual variability of the coupled system is investigated using three simulations differing in the parameterization of the vertical attenuation of downwelling solar radiation: (i) a control simulation using a constant 17-m attenuation depth, (ii) a simulation with the spatially varying annual mean of the satellite-derived attenuation depth, and (iii) a simulation accounting for the seasonal cycle of the attenuation depth. The results indicate that a more realistic attenuation of solar radiation slightly reduces the cold bias of the model. While a realistic attenuation of solar radiation hardly affects the annual mean and the seasonal cycle due to anomaly coupling, it significantly affects the interannual variability, especially when the seasonal cycle of the attenuation depth is used. The seasonal cycle of the attenuation depth interacts with the low-frequency equatorial dynamics to enhance warm and cold anomalies, which are further amplified via positive air–sea feedbacks. These results also indicate that interannual variability of the attenuation depths is required to capture the asymmetric biological feedbacks during cold and warm ENSO events.

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