Impact of Resolution on the Tropical Pacific Circulation in a Matrix of Coupled Models

Abstract Results are presented from a matrix of coupled model integrations, using atmosphere resolutions of 135 and 90 km, and ocean resolutions of 1° and 1/3°, to study the impact of resolution on simulated climate. The mean state of the tropical Pacific is found to be improved in the models with a higher ocean resolution. Such an improved mean state arises from the development of tropical instability waves, which are poorly resolved at low resolution; these waves reduce the equatorial cold tongue bias. The improved ocean state also allows for a better simulation of the atmospheric Walker circulation. Several sensitivity studies have been performed to further understand the processes involved in the different component models. Significantly decreasing the horizontal momentum dissipation in the coupled model with the lower-resolution ocean has benefits for the mean tropical Pacific climate, but decreases model stability. Increasing the momentum dissipation in the coupled model with the higher-resolution ocean degrades the simulation toward that of the lower-resolution ocean. These results suggest that enhanced ocean model resolution can have important benefits for the climatology of both the atmosphere and ocean components of the coupled model, and that some of these benefits may be achievable at lower ocean resolution, if the model formulation allows.

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Decadal Modulation of ENSO in a Hybrid Coupled Model

Journal of Climate ◽

10.1175/2008jcli1933.1 ◽

2008 ◽

Vol 21 (21) ◽

pp. 5482-5500 ◽

Cited By ~ 19

Author(s):

Robert J. Burgman ◽

Paul S. Schopf ◽

Ben P. Kirtman

Keyword(s):

Time Scales ◽

Low Frequency ◽

Coupled Model ◽

Tropical Pacific ◽

Stochastic Forcing ◽

Decadal Modulation ◽

The Mean ◽

Frequency Changes ◽

Mean State ◽

The Tropical Pacific

Abstract Decadal variations in the amplitude of El Niño and the Southern Oscillation have been the subject of great interest in the literature for the past decade. One theory suggests that ENSO is best described as a stable system driven by linear dynamics and that stochastic atmospheric forcing is responsible for the development and modulation of ENSO on interannual as well as decadal time scales. Another theory suggests that ENSO is driven by strong nonlinear coupled feedbacks between the ocean and atmosphere and low frequency changes in ENSO amplitude are driven by decadal changes in the tropical Pacific mean state. Unfortunately, the observed record is too short to collect reliable statistics for such low frequency behavior. A hybrid coupled model composed of a simple statistical atmosphere coupled to the Poseidon isopycnal ocean model has been developed for the study of ENSO decadal variability. The model simulates realistic ENSO variability on interannual and decadal time scales with negligible climate drift over 1000 years. Through analysis and experimentation the authors show that low frequency changes in the atmospheric “weather noise” drive changes in the tropical Pacific mean state leading to changes in the amplitude of ENSO on decadal time scales. Additional model simulations suggest that, while predictability is limited by the presence of atmospheric noise, there are extended periods when the coupled instability, strengthened by changes in the mean state, is insensitive to noise on interannual time scales. The relationship between decadal modulation of ENSO and mean state changes resides somewhere between the linear damped stochastically forced theory and the strongly unstable theory. Unlike the strongly unstable system, changes in ENSO amplitude on longer time scales are determined by the stochastic forcing. The stochastic forcing is not necessary in this model to sustain ENSO; however, its presence is crucial for low frequency changes in the mean state of the tropical Pacific. The strong relationship between the mean state and ENSO amplitude modulation in the model is in opposition to the linear damped stochastically forced theory. The fact that changes in the tropical Pacific mean state lead directly to changes in ENSO amplitude and predictability has positive implications for predictability.

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The impact of resolving the Rossby radius at mid-latitudes in the ocean: results from a high-resolution version of the Met Office GC2 coupled model

Geoscientific Model Development ◽

10.5194/gmd-9-3655-2016 ◽

2016 ◽

Vol 9 (10) ◽

pp. 3655-3670 ◽

Cited By ~ 33

Author(s):

Helene T. Hewitt ◽

Malcolm J. Roberts ◽

Pat Hyder ◽

Tim Graham ◽

Jamie Rae ◽

...

Keyword(s):

High Resolution ◽

Coupled Model ◽

Ocean Model ◽

The Body ◽

Western Boundary ◽

Coupled Models ◽

Technical Developments ◽

Enhanced Resolution ◽

Circumpolar Current ◽

The Impact

Abstract. There is mounting evidence that resolving mesoscale eddies and western boundary currents as well as topographically controlled flows can play an important role in air–sea interaction associated with vertical and lateral transports of heat and salt. Here we describe the development of the Met Office Global Coupled Model version 2 (GC2) with increased resolution relative to the standard model: the ocean resolution is increased from 1/4 to 1/12° (28 to 9 km at the Equator), the atmosphere resolution increased from 60 km (N216) to 25 km (N512) and the coupling period reduced from 3 hourly to hourly. The technical developments that were required to build a version of the model at higher resolution are described as well as results from a 20-year simulation. The results demonstrate the key role played by the enhanced resolution of the ocean model: reduced sea surface temperature (SST) biases, improved ocean heat transports, deeper and stronger overturning circulation and a stronger Antarctic Circumpolar Current. Our results suggest that the improvements seen here require high resolution in both atmosphere and ocean components as well as high-frequency coupling. These results add to the body of evidence suggesting that ocean resolution is an important consideration when developing coupled models for weather and climate applications.

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The impact of resolving the Rossby radius at mid-latitudes in the ocean: results from a high-resolution version of the Met Office GC2 coupled model

10.5194/gmd-2016-87 ◽

2016 ◽

Cited By ~ 2

Author(s):

Helene T. Hewitt ◽

Malcolm J. Roberts ◽

Pat Hyder ◽

Tim Graham ◽

Jamie Rae ◽

...

Keyword(s):

High Resolution ◽

Coupled Model ◽

Ocean Model ◽

The Body ◽

Coupled Models ◽

Surface Ocean ◽

Technical Developments ◽

Enhanced Resolution ◽

Circumpolar Current ◽

The Impact

Abstract. There is mounting evidence that resolving mesoscale eddies and boundary currents in the surface ocean field can play an important role in air-sea interaction associated with vertical and lateral transports of heat and salt. Here we describe the development of the Met Office Global Coupled Model version 2 (GC2) with increased resolution relative to the standard model: the ocean resolution is increased from 1/4° to 1/12° (28 km to 9 km at the Equator), the atmosphere resolution increased from 60 km (N216) to 25 km (N512) and the coupling frequency increased from 3-hourly to hourly. The technical developments that were required to build a version of the model at higher resolution are described as well as results from a 20 year simulation. The results demonstrate the key role played by the enhanced resolution of the ocean model: reduced Sea Surface Temperature biases, improved ocean heat transports, deeper and stronger overturning circulation and a stronger Antarctic Circumpolar Current. Our results suggest that the improvements seen here require high resolution in both atmosphere and ocean components as well as high frequency coupling. These results add to the body of evidence suggesting that ocean resolution is an important consideration when developing coupled models for weather and climate applications.

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Introduction to A Regional Coupled Forecasting System

10.5194/egusphere-egu2020-12626 ◽

2020 ◽

Author(s):

Mingkui Li ◽

Shaoqing Zhang

Keyword(s):

National Laboratory ◽

Coupled Model ◽

Ocean Model ◽

Asia Pacific ◽

Model Resolution ◽

Coupled Models ◽

Regional Ocean Model System ◽

Extended Range ◽

Coupled Data Assimilation ◽

The Impact

<p>A regional coupled prediction system for the Asia-Pacific area (AP-RCP) has been established. The AP-RCP system consists of WRF-ROMS (Weather Research and Forecast and Regional Ocean Model System) coupled models combined with local observing information through dynamically downscaling coupled data assimilation. The system generates 18-day atmospheric and oceanic environment forecasts on a daily quasi-operational schedule at Qingdao Pilot National Laboratory for Marine Science and Technology (QNLM). The AP-RCP system mainly includes 2 different coupled model resolutions: 27km WRF coupled with 9km ROMS, and 9km WRF coupled with 3km ROMS. This study evaluates the impact of enhancing coupled model resolution on the extended-range forecasts, focusing on forecasts of typhoon onset, and improved precipitation and typhoon intensity forecasts. Results show that enhancing coupled model resolution is a necessary step to realize the extended-range predictability of the atmosphere and ocean environmental conditions that include a plenty of local details. The next challenges include improving the planetary boundary physics and the representation of air-sea and air-land interactions when the model can resolve the kilometer or sub-kilometer processes.</p>

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Regional impacts of ocean color on tropical Pacific variability

Ocean Science Discussions ◽

10.5194/osd-6-243-2009 ◽

2009 ◽

Vol 6 (1) ◽

pp. 243-275 ◽

Cited By ~ 8

Author(s):

W. Anderson ◽

A. Gnanadesikan ◽

A. Wittenberg

Keyword(s):

El Niño ◽

El Nino ◽

Pure Water ◽

Ocean Color ◽

Tropical Pacific ◽

Shortwave Radiation ◽

Penetration Length ◽

The Mean ◽

Mean State ◽

The Tropical Pacific

Abstract. The role of the penetration length scale of shortwave radiation into the surface ocean and its impact on tropical Pacific variability is investigated with a fully coupled ocean, atmosphere, land and ice model. Previous work has shown that removal of all ocean color results in a system that tends strongly towards an El Niño state. Results from a suite of surface chlorophyll perturbation experiments show that the mean state and variability of the tropical Pacific is highly sensitive to the concentration and distribution of ocean chlorophyll. Setting the near-oligotrophic regions to contain optically pure water warms the mean state and suppresses variability in the western tropical Pacific. Doing the same above the shadow zones of the tropical Pacific also warms the mean state but enhances the variability. It is shown that increasing penetration can both deepen the pycnocline (which tends to damp El Niño) while shifting the mean circulation so that the wind response to temperature changes is altered. Depending on what region is involved this change in the wind stress can either strengthen or weaken ENSO variability.

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The response of the Peruvian Upwelling Ecosystem to centennial-scale global change during the last two millennia

Climate of the Past ◽

10.5194/cp-10-715-2014 ◽

2014 ◽

Vol 10 (2) ◽

pp. 715-731 ◽

Cited By ~ 35

Author(s):

R. Salvatteci ◽

D. Gutiérrez ◽

D. Field ◽

A. Sifeddine ◽

L. Ortlieb ◽

...

Keyword(s):

Walker Circulation ◽

Tropical Pacific ◽

Warm Period ◽

Ice Age ◽

Global Changes ◽

Marine Productivity ◽

Peruvian Upwelling Ecosystem ◽

Mean State ◽

The Walker Circulation ◽

The Tropical Pacific

Abstract. The tropical Pacific ocean–atmosphere system influences global climate on interannual, decadal, as well as longer timescales. Given the uncertainties in the response of the tropical Pacific to increasing greenhouse gasses, it is important to assess the role of the tropical Pacific climate variability in response to past global changes. The Peruvian Upwelling Ecosystem (PUE) represents an ideal area to reconstruct past changes in the eastern tropical Pacific region because productivity and subsurface oxygenation are strongly linked to changes in the strength of the Walker circulation. Throughout the last 2000 years, warmer (the Roman Warm Period – RWP; the Medieval Climate Anomaly – MCA; and the Current Warm Period – CWP), and colder (the Dark Ages Cold Period – DACP – and Little Ice Age – LIA) intervals were identified in the Northern Hemisphere (NH). We use a multi-proxy approach including organic and inorganic proxies in finely laminated sediments retrieved off Pisco (~14° S), Peru to reconstruct the PUE response to these climatic periods. Our results indicate that the centennial-scale changes in precipitation are associated with changes in the Intertropical Convergence Zone (ITCZ) meridional displacements and expansion/contraction of the South Pacific Sub-tropical High (SPSH). Additionally, during the NH cold periods, the PUE exhibited an El Niño-like mean state, characterized by a weak oxygen minimum zone (OMZ), and low marine productivity. In contrast, during the RWP, the last stage of the MCA and the CWP, the PUE exhibited a La Niña-like mean state, characterized by an intense OMZ and high marine productivity. Comparing our results with other relevant paleoclimatic reconstructions revealed that changes in the Walker circulation strength and the SPSH expansion/contraction controlled marine productivity and OMZ intensity changes during the past two millennia.

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Regional impacts of ocean color on tropical Pacific variability

Ocean Science ◽

10.5194/os-5-313-2009 ◽

2009 ◽

Vol 5 (3) ◽

pp. 313-327 ◽

Cited By ~ 28

Author(s):

W. Anderson ◽

A. Gnanadesikan ◽

A. Wittenberg

Keyword(s):

El Niño ◽

El Nino ◽

Pure Water ◽

Ocean Color ◽

Tropical Pacific ◽

Shortwave Radiation ◽

Penetration Length ◽

The Mean ◽

Mean State ◽

The Tropical Pacific

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ENSO Amplitude Changes due to Climate Change Projections in Different Coupled Models

Journal of Climate ◽

10.1175/jcli4001.1 ◽

2007 ◽

Vol 20 (2) ◽

pp. 203-217 ◽

Cited By ~ 37

Author(s):

Sang-Wook Yeh ◽

Ben P. Kirtman

Keyword(s):

Climate Change ◽

Tropical Pacific ◽

Skewed Distribution ◽

Geophysical Fluid Dynamics Laboratory ◽

Coupled Models ◽

Climate Change Projections ◽

State Changes ◽

The Mean ◽

Gfdl Model ◽

Mean State

Abstract Four climate system models are chosen here for an analysis of ENSO amplitude changes in 4 × CO2 climate change projections. Despite the large changes in the tropical Pacific mean state, the changes in ENSO amplitude are highly model dependant. To investigate why similar mean state changes lead to very different ENSO amplitude changes, the characteristics of sea surface temperature anomaly (SSTA) variability simulated in two coupled general circulation models (CGCMs) are analyzed: the Meteorological Research Institute (MRI) and Geophysical Fluid Dynamics Laboratory (GFDL) models. The skewed distribution of tropical Pacific SSTA simulated in the MRI model suggests the importance of nonlinearities in the ENSO physics, whereas the GFDL model lies in the linear regime. Consistent with these differences in ENSO regime, the GFDL model is insensitive to the mean state changes, whereas the MRI model is sensitive to the mean state changes associated with the 4 × CO2 scenario. Similarly, the low-frequency modulation of ENSO amplitude in the GFDL model is related to atmospheric stochastic forcing, but in the MRI model the amplitude modulation is insensitive to the noise forcing. These results suggest that the understanding of changes in ENSO statistics among various climate change projections is highly dependent on whether the model ENSO is in the linear or nonlinear regime.

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Robust Strengthening and Westward Shift of the Tropical Pacific Walker Circulation during 1979–2012: A Comparison of 7 Sets of Reanalysis Data and 26 CMIP5 Models

Journal of Climate ◽

10.1175/jcli-d-15-0398.1 ◽

2016 ◽

Vol 29 (9) ◽

pp. 3097-3118 ◽

Cited By ~ 37

Author(s):

Shuangmei Ma ◽

Tianjun Zhou

Keyword(s):

Vertical Section ◽

Coupled Model ◽

Walker Circulation ◽

Reanalysis Data ◽

Tropical Pacific ◽

La Niña ◽

Cmip5 Models ◽

La Nina ◽

Independent Observations ◽

The Tropical Pacific

Abstract In this study, the zonal mass streamfunction Ψ, which depicts intuitively the tropical Pacific Walker circulation (PWC) structure characterized by an enclosed and clockwise rotation cell in the zonal–vertical section over the equatorial Pacific, was used to study the changes of PWC spatial structure during 1979–2012. To examine the robustness of changes in PWC characteristics, the linear trends of PWC were evaluated and compared among the current seven sets of reanalysis data, along with a comparison to the trends of surface climate variables. The spatial pattern of Ψ trend exhibited a strengthening and westward-shifting trend of PWC in all reanalysis datasets, with the significantly positive Ψ dominating the western Pacific and negative Ψ controlling the eastern Pacific. This kind of change is physically in agreement with the changes of the sea level pressure (SLP), surface winds, and precipitation derived from both the reanalyses and independent observations. Quantitative analyses of the changes in the PWC intensity and western edge, defined based on the zonal mass streamfunction, also revealed a robust strengthening and westward-shifting trend among all reanalysis datasets, with a trend of 15.08% decade−1 and 3.70° longitude decade−1 in the ensemble mean of seven sets of reanalysis data, with the strongest (weakest) intensification of 17.53% decade−1 (7.96% decade−1) in the Twentieth Century Reanalysis (NCEP-2) and largest (smallest) westward shift of −4.68° longitude decade−1 (−2.55° longitude decade−1) in JRA-55 (JRA-25). In response to the recent observed La Niña–like anomalous SST forcing, the ensemble simulations from phase 5 of the Coupled Model Intercomparison Project (CMIP5), with 26 models in the ensemble, reasonably reproduced the observed strengthening and westward-shifting trend of PWC, implying the dominant forcing of the La Niña–like SST anomalies to the recent PWC change.

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Interactive Feedback between the Tropical Pacific Decadal Oscillation and ENSO in a Coupled General Circulation Model

Journal of Climate ◽

10.1175/2009jcli2782.1 ◽

2009 ◽

Vol 22 (24) ◽

pp. 6597-6611 ◽

Cited By ~ 47

Author(s):

Jung Choi ◽

Soon-Il An ◽

Boris Dewitte ◽

William W. Hsieh

Keyword(s):

General Circulation ◽

Circulation Model ◽

Tropical Pacific ◽

Thermocline Depth ◽

Coupled General Circulation Model ◽

The Mean ◽

The Stability ◽

Interactive Feedback ◽

Mean State ◽

The Tropical Pacific

Abstract The output from a coupled general circulation model (CGCM) is used to develop evidence showing that the tropical Pacific decadal oscillation can be driven by an interaction between the El Niño–Southern Oscillation (ENSO) and the slowly varying mean background climate state. The analysis verifies that the decadal changes in the mean states are attributed largely to decadal changes in ENSO statistics through nonlinear rectification. This is seen because the time evolutions of the first principal component analysis (PCA) mode of the decadal-varying tropical Pacific SST and the thermocline depth anomalies are significantly correlated to the decadal variations of the ENSO amplitude (also skewness). Its spatial pattern resembles the residuals of the SST and thermocline depth anomalies after there is uneven compensation from El Niño and La Niña events. In addition, the stability analysis of a linearized intermediate ocean–atmosphere coupled system, for which the background mean states are specified, provides qualitatively consistent results compared to the CGCM in terms of the relationship between changes in the background mean states and the characteristics of ENSO. It is also shown from the stability analysis as well as the time integration of a nonlinear version of the intermediate coupled model that the mean SST for the high-variability ENSO decades acts to intensify the ENSO variability, while the mean thermocline depth for the same decades acts to suppress the ENSO activity. Thus, there may be an interactive feedback consisting of a positive feedback between the ENSO activity and the mean state of the SST and a negative feedback between the ENSO activity and the mean state of the thermocline depth. This feedback may lead to the tropical decadal oscillation, without the need to invoke any external mechanisms.

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