scholarly journals A study of predictability of coupled ocean–atmosphere system using attractor radius and global attractor radius

2021 ◽  
Author(s):  
Haoran Zhao ◽  
Shaoqing Zhang ◽  
Jianping Li ◽  
Youwei Ma
Keyword(s):  
Coupled Model ◽  
Lower Troposphere ◽  
Deep Ocean ◽  
Coupled System ◽  
Climate Simulation ◽  
Forecast System ◽  
Initial Value ◽  
Coupled Models ◽  
Atmosphere System ◽  
Ocean Atmosphere

AbstractWhile ocean–atmosphere coupled models play an increasingly important role in weather-climate simulation and prediction, the predictability theory based on an atmosphere-only model has significant limitations in interpreting prediction results and guiding predictability studies. Here we use a conceptual ocean–atmosphere coupled model that describes the typical interactions of a synoptic-scale atmosphere with a seasonally-interannually varying upper ocean as well as a deep ocean that varies on decadal timescales to systematically study the predictability of a coupled system. Moving from an atmosphere-only system to an ocean–atmosphere coupled system, the initial-value predictability problem becomes a joint initial-value and boundary-value problem. Although the coupling process increases the uncertainties of the boundary, ocean signals with longer timescales are added to the atmosphere system, thus increasing its predictability. We then investigate the predictability characteristics of the National Centers for Environmental Prediction coupled Climate Forecast System (CFS) and the uncoupled Global Ensemble Forecast System (GEFS). In the coupled CFS system, the practical predictability limit of the lower troposphere is significantly longer than in the uncoupled GEFS due to the contribution of low-frequency boundary signals from air-sea interactions. While further deep and thorough examination is necessary for understanding ocean predictability in the climate system, a preliminary discussion for the predictability of the upper and deep oceans within a coupled ocean–atmosphere framework is also presented in this study.

scholarly journals Constraints on ocean circulation at the Paleocene–Eocene Thermal Maximum from neodymium isotopes

2016 ◽  
Vol 12 (4) ◽  
pp. 837-847 ◽  
Author(s):  
April N. Abbott ◽  
Brian A. Haley ◽  
Aradhna K. Tripati ◽  
Martin Frank
Keyword(s):  
Ocean Circulation ◽  
Deep Water ◽  
Deep Ocean ◽  
Isotopic Data ◽  
Carbon Isotopic ◽  
Deep Waters ◽  
Atmosphere System ◽  
Thermal Maximum ◽  
Ocean Atmosphere ◽  
Deep Ocean Circulation

Abstract. Global warming during the Paleocene–Eocene Thermal Maximum (PETM)  ∼  55 million years ago (Ma) coincided with a massive release of carbon to the ocean–atmosphere system, as indicated by carbon isotopic data. Previous studies have argued for a role of changing ocean circulation, possibly as a trigger or response to climatic changes. We use neodymium (Nd) isotopic data to reconstruct short high-resolution records of deep-water circulation across the PETM. These records are derived by reductively leaching sediments from seven globally distributed sites to reconstruct past deep-ocean circulation across the PETM. The Nd data for the leachates are interpreted to be consistent with previous studies that have used fish teeth Nd isotopes and benthic foraminiferal δ13C to constrain regions of convection. There is some evidence from combining Nd isotope and δ13C records that the three major ocean basins may not have had substantial exchanges of deep waters. If the isotopic data are interpreted within this framework, then the observed pattern may be explained if the strength of overturning in each basin varied distinctly over the PETM, resulting in differences in deep-water aging gradients between basins. Results are consistent with published interpretations from proxy data and model simulations that suggest modulation of overturning circulation had an important role for initiation and recovery of the ocean–atmosphere system associated with the PETM.

scholarly journals Millennial scale feedbacks determine the shape and rapidity of glacial termination

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Stephen Barker ◽  
Gregor Knorr
Keyword(s):  
Sea Level ◽  
Late Pleistocene ◽  
Large Amplitude ◽  
Climate Simulation ◽  
Glacial Cycles ◽  
Major Transitions ◽  
Atmosphere System ◽  
Ocean Atmosphere ◽  
Recent Developments ◽  
Abrupt Shifts

AbstractWithin the Late Pleistocene, terminations describe the major transitions marking the end of glacial cycles. While it is established that abrupt shifts in the ocean/atmosphere system are a ubiquitous component of deglaciation, significant uncertainties remain concerning their specific role and the likelihood that terminations may be interrupted by large-amplitude abrupt oscillations. In this perspective we address these uncertainties in the light of recent developments in the understanding of glacial terminations as the ultimate interaction between millennial and orbital timescale variability. Innovations in numerical climate simulation and new geologic records allow us to highlight new avenues of research and identify key remaining uncertainties such as sea-level variability.

An intermediate coupled model for the tropical ocean-atmosphere system

2018 ◽  
Vol 61 (12) ◽  
pp. 1859-1874 ◽  
Author(s):  
Xunshu Song ◽  
Dake Chen ◽  
Youmin Tang ◽  
Ting Liu
Keyword(s):  
Coupled Model ◽  
Tropical Ocean ◽  
Atmosphere System ◽  
Ocean Atmosphere ◽  
Intermediate Coupled Model

scholarly journals Southern High-Latitude Ocean Climate Drift in a Coupled Model

1999 ◽  
Vol 12 (1) ◽  
pp. 132-146 ◽  
Author(s):  
Wenju Cai ◽  
Hal B. Gordon
Keyword(s):  
Sea Ice ◽  
High Latitude ◽  
Coupled Model ◽  
Coupled System ◽  
Subsurface Water ◽  
Initial Increase ◽  
Surface Boundary ◽  
Surface Mixed Layer ◽  
Coupled Models ◽  
Climate Drift

Abstract Climate drift in coupled models affects the response of the coupled system to an external forcing. In most existing coupled models that employ flux adjustments, the southern high latitudes, in particular, are still affected by some climate drift. In the CSIRO coupled model, within 100 years following coupling, the Antarctic Circumpolar Current (ACC) intensifies by about 30 Sv (Sv ≡ 106 m3 s−1). This happens despite the use of flux adjustments. Many other model fields such as sea ice, surface albedo, and heat fluxes of the coupled system also experience drift from the precoupled spinup states. It is therefore important to study the processes that give rise to these drifts. The primary cause of drift in the CSIRO model is due to changes in the pattern of convection in the Southern Ocean relative to the spinup steady state. Upon coupling, the pattern of convection alters systematically regardless of surface boundary conditions. Consequently, overturning at shallow to intermediate depths (from the surface to about 2000 m) weakens, while that below these depths intensifies. The decline of overturning at shallow to intermediate depths leads to reduced surface temperatures because a lesser amount of warm subsurface water is mixed up into the colder surface mixed layer. The cooler surface temperature leads to an initial increase in sea ice, which is exacerbated by a significant albedo–temperature–sea ice feedback. The resulting increase in sea ice formation at the higher southern latitudes leads to increased brine rejection and a general increase in salinity throughout much of the high-latitude water column. This increase in salinity intensifies deep convection and bottom water formation, driving a stronger ACC. Several additional experiments are performed to trace various oceanic and ocean–atmosphere feedbacks that give the drift its character. It is demonstrated that the feedbacks significant to the drift in the present model are the positive albedo–temperature–sea ice feedback and a negative feedback between sea ice and overturning. The role of these two feedbacks in the interconnection between the drifts in various model fields is discussed.

scholarly journals Wind–Mixed Layer–SST Feedbacks in a Tropical Air–Sea Coupled System: Application to the Atlantic

2019 ◽  
Vol 32 (13) ◽  
pp. 3865-3881 ◽  
Author(s):  
Takahito Kataoka ◽  
Masahide Kimoto ◽  
Masahiro Watanabe ◽  
Hiroaki Tatebe
Keyword(s):  
Mixed Layer ◽  
Mixed Layer Depth ◽  
Coupled Model ◽  
Coupled System ◽  
Shortwave Radiation ◽  
Coupled Models ◽  
Trade Winds ◽  
Tropical Oceans ◽  
Thermodynamic Coupling ◽  
Sst Anomalies

Abstract The ocean–atmosphere feedback associated with the thermodynamic coupling among wind speed, evaporation, and sea surface temperature (SST), called the wind–evaporation–SST (WES) feedback, contributes to the cross-equatorial SST gradient over the tropical oceans. By conducting an eigenanalyses of simple linear air–sea coupled models, it is shown that two additional feedback processes are present when the variable oceanic mixed layer depth (MLD) is considered. The horizontal structures of the leading modes are similar to the WES mode, which shows a meridional dipole in the SST anomalies straddling the equator with cross-equatorial wind anomalies that represent the weakening/strengthening of the trade winds over the warm/cool SST anomalies. The coupling of the variable MLD with winds and SST more than doubles the growth rate of the WES mode and enhances the equatorward propagation of the coupled disturbances. The identified feedbacks operate as follows: The weaker winds associated with warm SST anomalies shoal the mixed layer through suppressed turbulent mixing, which causes the mixed layer to be more sensitive to the climatological shortwave radiation and amplifies the initial positive SST anomalies. Likewise, deepening of the mixed layer due to stronger winds acts to maintain the negative SST anomaly on the other side of the dipole. The MLD anomalies can also be generated by the buoyancy flux anomaly related to the wind-induced latent heat flux anomaly. The antiphase relationship between the SST and MLD anomalies seen in the simple model bears some resemblance to that which is observed in the observations and a state-of-the-art coupled model during the Atlantic meridional mode.

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.

scholarly journals A regional coupled ocean–atmosphere modeling framework (MITgcm–WRF) using ESMF/NUOPC: description and preliminary results for the Red Sea

2018 ◽  
Author(s):  
Rui Sun ◽  
Aneesh Subramanian ◽  
Art Miller ◽  
Matt Mazloff ◽  
Ibrahim Hoteit ◽  
...  
Keyword(s):  
Red Sea ◽  
System Modeling ◽  
Coupled Model ◽  
Reanalysis Data ◽  
Ocean Model ◽  
Modeling Framework ◽  
Coupled Models ◽  
Ocean Atmosphere ◽  
Atmosphere Model ◽  
Regional Coupled Model

Abstract. A new regional coupled ocean–atmosphere model is developed to study air–sea feedbacks. The coupled model is based on two open-source community model components: (1) MITgcm ocean model; (2) Weather Research and Forecasting (WRF) atmosphere model. The coupling between these components is performed using ESMF (Earth System Modeling Framework) and implemented according to National United Operational Prediction Capability (NUOPC) consortium. The regional coupled model allows affordable simulation where oceanic mixed layer heat and momentum interact with atmospheric boundary layer dynamics at mesoscale and higher resolution. This can capture the feedbacks which are otherwise not well-resolved in coarse resolution global coupled models and are absent in regional uncoupled models. To test the regional coupled model, we focus on a series of heat wave events that occurred on the eastern shore of the Red Sea region in June 2012 using a 30-day simulation. The results obtained using the coupled model, along with those in forced uncoupled ocean or atmosphere model simulations, are compared with observational and reanalysis data. All configurations of coupled and uncoupled models have good skill in modeling variables of interest in the region. The coupled model shows improved skill in temperature and circulation evaluation metrics. In addition, a scalability test is performed to investigate the parallelization of the coupled model. The results indicate that the coupled model scales linearly for up to 128 CPUs and sublinearly for more processors. In the coupled simulation, the ESMF/NUOPC interface also scales well and accounts for less than 10 % of the total computational resources compared with uncoupled models. Hence this newly developed regional model scales efficiently for a large number of processors and can be applied for high-resolution coupled regional modeling studies.

A Coupled Model for Evaluating Surface and Subsurface Flow-MODHMS

2014 ◽  
Vol 1073-1076 ◽  
pp. 1716-1719
Author(s):  
Tian Yuan Zou ◽  
Jing Zhang
Keyword(s):  
Surface Water ◽  
Subsurface Flow ◽  
Coupled Model ◽  
Coupled System ◽  
Research Progress ◽  
Coupled Models ◽  
Advantages And Disadvantages ◽  
Surface Water And Groundwater ◽  
The Impact ◽  
Surface And Subsurface Flow

Surface water and ground water always influence each other in nature, both of which constitute an organic unity. Because of the gradual understanding of the impact of this interaction, surface water and groundwater coupled models are mostly used for the simulation and analysis of the process and its impact. This article concludes the research progress and focuses the coupled system of surface and subsurface flow to describe. However, the interaction between surface water and groundwater is still hot and difficult in today's research, because the interaction law is very complex. The application of MODHMS which is a coupled model for evaluating surface and subsurface flow is used for simulating non-point source pollution. Advantages and disadvantages of the model are analyzed for the future hydrology application.

scholarly journals Constraints on ocean circulation at the Paleocene–Eocene Thermal Maximum from neodymium isotopes

2015 ◽  
Vol 11 (3) ◽  
pp. 2557-2583 ◽  
Author(s):  
A. N. Abbott ◽  
B. A. Haley ◽  
A. K. Tripati ◽  
M. Frank
Keyword(s):  
Ocean Circulation ◽  
Deep Water ◽  
Deep Ocean ◽  
Published Data ◽  
Isotopic Data ◽  
Carbon Isotopic ◽  
Atmosphere System ◽  
Thermal Maximum ◽  
Ocean Atmosphere ◽  
Deep Ocean Circulation

Abstract. Global warming during the Paleocene Eocene Thermal Maximum (PETM) ~55 million years ago (Ma) coincided with a massive release of carbon to the ocean–atmosphere system, as indicated by carbon isotopic data. Previous studies have argued for a role for changing ocean circulation, possibly as a trigger or response to climatic changes. We use neodymium (Nd) isotopic data to reconstruct short high-resolution records of deep-water circulation across the PETM. These records are derived by reductively leaching sediments from seven globally distributed sites and comparing data with published data from fossil fish debris to reconstruct past deep ocean circulation across the PETM. The Nd data for the leachates are interpreted to be consistent with previous studies that have used fish teeth and benthic foraminiferal δ13C to constrain regions of convection. There is some evidence from combining Nd isotope and δ13C records that the three major ocean basins may not have had substantial exchanges of deep waters. If the isotopic data are interpreted within this framework, then the observed pattern may be explained if the strength of overturning in each basin varied distinctly over the PETM, resulting in differences in deep-water aging gradients between basins. Results are consistent with published interpretations from proxy data and model simulations that suggest modulation of overturning circulation had an important role for global recovery of the ocean–atmosphere system after the PETM.

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