scholarly journals Freshwater Flux (FWF)-Induced Oceanic Feedback in a Hybrid Coupled Model of the Tropical Pacific

2009 ◽  
Vol 22 (4) ◽  
pp. 853-879 ◽  
Author(s):  
Rong-Hua Zhang ◽  
Antonio J. Busalacchi
Keyword(s):  
Heat Flux ◽  
Interannual Variability ◽  
Coupled Model ◽  
Tropical Pacific ◽  
Freshwater Flux ◽  
Atmosphere System ◽  
Ocean Atmosphere ◽  
Hybrid Coupled Model ◽  
Sst Anomalies ◽  
The Tropical Pacific

Abstract The impacts of freshwater flux (FWF) forcing on interannual variability in the tropical Pacific climate system are investigated using a hybrid coupled model (HCM), constructed from an oceanic general circulation model (OGCM) and a simplified atmospheric model, whose forcing fields to the ocean consist of three components. Interannual anomalies of wind stress and precipitation minus evaporation, (P − E), are calculated respectively by their statistical feedback models that are constructed from a singular value decomposition (SVD) analysis of their historical data. Heat flux is calculated using an advective atmospheric mixed layer (AML) model. The constructed HCM can well reproduce interannual variability associated with ENSO in the tropical Pacific. HCM experiments are performed with varying strengths of anomalous FWF forcing. It is demonstrated that FWF can have a significant modulating impact on interannual variability. The buoyancy flux (QB) field, an important parameter determining the mixing and entrainment in the equatorial Pacific, is analyzed to illustrate the compensating role played by its two contributing parts: one is related to heat flux (QT) and the other to freshwater flux (QS). A positive feedback is identified between FWF and SST as follows: SST anomalies, generated by El Niño, nonlocally induce large anomalous FWF variability over the western and central regions, which directly influences sea surface salinity (SSS) and QB, leading to changes in the mixed layer depth (MLD), the upper-ocean stability, and the mixing and the entrainment of subsurface waters. These oceanic processes act to enhance the SST anomalies, which in turn feedback to the atmosphere in a coupled ocean–atmosphere system. As a result, taking into account anomalous FWF forcing in the HCM leads to an enhanced interannual variability and ENSO cycles. It is further shown that FWF forcing is playing a different role from heat flux forcing, with the former acting to drive a change in SST while the latter represents a passive response to the SST change. This HCM-based modeling study presents clear evidence for the role of FWF forcing in modulating interannual variability in the tropical Pacific. The significance and implications of these results are further discussed for physical understanding and model improvements of interannual variability in the tropical Pacific ocean–atmosphere system.

Midlatitude Excitation of Tropical Variability in the Pacific: The Role of Thermodynamic Coupling and Seasonality*

2009 ◽  
Vol 22 (3) ◽  
pp. 518-534 ◽  
Author(s):  
Daniel J. Vimont ◽  
Michael Alexander ◽  
Abigail Fontaine
Keyword(s):  
Heat Flux ◽  
Temporal Structure ◽  
Surface Wind ◽  
Coupled Model ◽  
Tropical Pacific ◽  
Boreal Winter ◽  
Wes Feedback ◽  
Thermodynamic Coupling ◽  
Sst Anomalies ◽  
The Tropical Pacific

Abstract A set of ensemble model experiments using the National Center for Atmospheric Research Community Atmospheric Model version 3.0 (CAM3) is run to investigate the tropical Pacific response to midlatitude atmospheric variability associated with the atmospheric North Pacific Oscillation (NPO). Heat flux anomalies associated with the NPO are used to force a set of model simulations during boreal winter (when the NPO is most energetic), after which the forcing is switched off and the coupled model evolves on its own. Sea surface temperature (SST) and wind anomalies continue to amplify in the tropical Pacific after the imposed forcing has been shut off, indicating that coupled ocean–atmosphere interactions in the tropical Pacific alter the spatial and temporal structure of variability associated with midlatitude forcing. The tropical circulation evolves through feedbacks between the surface wind, evaporation, and SST (the WES feedback), as well as through changes in the shortwave radiative heat flux (caused by changes in convection). Sensitivity experiments are run to investigate how thermodynamic coupling and seasonality affect the tropical response to NPO-related forcing. Seasonality is found to affect the WES feedback through (i) altering the sensitivity of surface evaporation to changes in the low-level wind field and (ii) altering the structure and strength of the lower-level wind response to SST anomalies. Thermodynamic coupling causes an equatorward and westward development of SST anomalies and an associated equatorward shift in the lower-level zonal wind anomalies.

Separating freshwater flux effects on ENSO in a hybrid coupled model of the tropical Pacific

2020 ◽  
Vol 54 (11-12) ◽  
pp. 4605-4626 ◽  
Author(s):  
Chuan Gao ◽  
Rong-Hua Zhang ◽  
Kristopher B. Karnauskas ◽  
Lei Zhang ◽  
Feng Tian
Keyword(s):  
Coupled Model ◽  
Tropical Pacific ◽  
Freshwater Flux ◽  
Hybrid Coupled Model ◽  
The Tropical Pacific

Interannual Biases Induced by Freshwater Flux and Coupled Feedback in the Tropical Pacific

2010 ◽  
Vol 138 (5) ◽  
pp. 1715-1737 ◽  
Author(s):  
Rong-Hua Zhang ◽  
Guihua Wang ◽  
Dake Chen ◽  
A. J. Busalacchi ◽  
E. C. Hackert
Keyword(s):  
Interannual Variability ◽  
Large Scale ◽  
Climate Modeling ◽  
Coupled Model ◽  
Tropical Pacific ◽  
Freshwater Flux ◽  
Feedback Effects ◽  
Sst Variability ◽  
Interannual Anomaly ◽  
The Tropical Pacific

Abstract Freshwater flux (FWF) forcing–induced feedback has not been represented adequately in many coupled ocean–atmosphere models of the tropical Pacific. Previously, various approximations have been made in representing the FWF forcing in climate modeling. In this article, using a hybrid coupled model (HCM), sensitivity experiments are performed to examine the extent to which this forcing and related feedback effects can contribute to tropical biases in interannual simulations of the tropical Pacific. The total FWF into the ocean, represented by precipitation (P) minus evaporation (E), (P − E), is separated into its climatological part and interannual anomaly part: FWFTotal = (P − E)clim + FWFinter. The former can be prescribed (seasonally varying); the latter can be captured using an empirical model linking with large-scale sea surface temperature (SST) variability. Four cases are considered with different FWFinter specifications: interannual (P − E) forcing [FWFinter = (P − E)inter], interannual P forcing (FWFinter = Pinter), interannual E forcing (FWFinter = −Einter), and climatological (P − E) forcing (FWFinter = 0.0), respectively. The HCM-based experiments indicate that different FWFinter approximations can modulate interannual variability in a substantial way. The HCM with the interannual (P − E) forcing, in which a positive SST − (P − E)inter feedback is included explicitly, has a reasonably realistic simulation of interannual variability. When FWFinter is approximated in some ways, the simulated interannual variability can be modulated significantly: it is weakened with the climatological (P − E) forcing and is even more damped with the interannual E forcing, but is exaggerated with the interannual P forcing. Quantitatively, taking the interannual (P − E) forcing run as a reference, the Niño-3 SST variance can be reduced by about 12% and 26% in the climatological (P − E) forcing run and interannual E forcing run, respectively, but overestimated by 11% in the Pinter forcing run. It is demonstrated that FWF can be a clear bias source for coupled model simulations in the tropical Pacific.

Westerly Wind Events in the Tropical Pacific and their Influence on the Coupled Ocean-Atmosphere System: A Review

2013 ◽  
pp. 49-69 ◽  
Author(s):  
Matthieu Lengaigne ◽  
Jean-Philippe Boulanger ◽  
Christophe Menkes ◽  
Pascale Delecluse ◽  
Julia Slingo
Keyword(s):  
Tropical Pacific ◽  
Westerly Wind ◽  
System A ◽  
Atmosphere System ◽  
Ocean Atmosphere ◽  
Wind Events ◽  
Westerly Wind Events ◽  
The Tropical Pacific

scholarly journals Response of ENSO and the Mean State of the Tropical Pacific to Extratropical Cooling and Warming: A Study Using the IAP Coupled Model

2009 ◽  
Vol 22 (22) ◽  
pp. 5902-5917 ◽  
Author(s):  
Y. Yu ◽  
D-Z. Sun
Keyword(s):  
Climate Change ◽  
Climate Modeling ◽  
Coupled Model ◽  
Tropical Pacific ◽  
Equatorial Region ◽  
Upper Ocean ◽  
Central Pacific ◽  
Intergovernmental Panel ◽  
Ocean Atmosphere ◽  
The Tropical Pacific

Abstract The coupled model of the Institute of Atmospheric Physics (IAP) is used to investigate the effects of extratropical cooling and warming on the tropical Pacific climate. The IAP coupled model is a fully coupled GCM without any flux correction. The model has been used in many aspects of climate modeling, including the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) climate change and paleoclimate simulations. In this study, the IAP coupled model is subjected to cooling or heating over the extratropical Pacific. As in an earlier study, the cooling and heating is imposed over the extratropical region poleward of 10°N–10°S. Consistent with earlier findings, an elevated (reduced) level of ENSO activity in response to an increase (decrease) in the cooling over the extratropical region is found. The changes in the time-mean structure of the equatorial upper ocean are also found to be very different between the case in which ocean–atmosphere is coupled over the equatorial region and the case in which the ocean–atmosphere over the equatorial region is decoupled. For example, in the uncoupled run, the thermocline water across the entire equatorial Pacific is cooled in response to an increase in the extratropical cooling. In the corresponding coupled run, the changes in the equatorial upper-ocean temperature in the extratropical cooling resemble a La Niña situation—a deeper thermocline in the western and central Pacific accompanied by a shallower thermocline in the eastern Pacific. Conversely, with coupling, the response of the equatorial upper ocean to extratropical cooling resembles an El Niño situation. These results ascertain the role of extratropical ocean in determining the amplitude of ENSO. The results also underscore the importance of ocean–atmosphere coupling in the interaction between the tropical Pacific and the extratropical Pacific.

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