scholarly journals Robust Warming Pattern of Global Subtropical Oceans and Its Mechanism

2015 ◽  
Vol 28 (21) ◽  
pp. 8574-8584 ◽  
Author(s):  
Guihua Wang ◽  
Shang-Ping Xie ◽  
Rui Xin Huang ◽  
Changlin Chen
Keyword(s):  
General Circulation ◽  
Coupled Model ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Thermocline Depth ◽  
Surface Warming ◽  
Ocean Response ◽  
Subsurface Ocean ◽  
Subtropical Oceans ◽  
The Tropics

Abstract The subsurface ocean response to anthropogenic climate forcing remains poorly characterized. From the Coupled Model Intercomparison Project (CMIP), a robust response of the lower thermocline is identified, where the warming is considerably weaker in the subtropics than in the tropics and high latitudes. The lower thermocline change is inversely proportional to the thermocline depth in the present climatology. Ocean general circulation model (OGCM) experiments show that sea surface warming is the dominant forcing for the subtropical gyre change in contrast to natural variability for which wind dominates, and the ocean response is insensitive to the spatial pattern of surface warming. An analysis based on a ventilated thermocline model shows that the pattern of the lower thermocline change can be interpreted in terms of the dynamic response to the strengthened stratification and downward heat mixing. Consequently, the subtropical gyres become intensified at the surface but weakened in the lower thermcline, consistent with results from CMIP experiments.

The Freshening of Surface Waters in High Latitudes: Effects on the Thermohaline and Wind-Driven Circulations

2007 ◽  
Vol 37 (4) ◽  
pp. 896-907 ◽  
Author(s):  
Alexey Fedorov ◽  
Marcelo Barreiro ◽  
Giulio Boccaletti ◽  
Ronald Pacanowski ◽  
S. George Philander
Keyword(s):  
Surface Waters ◽  
General Circulation ◽  
Thermohaline Circulation ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Critical Parameters ◽  
High Latitudes ◽  
Oceanic Circulation ◽  
Meridional Overturning ◽  
The Tropics

Abstract The impacts of a freshening of surface waters in high latitudes on the deep, slow, thermohaline circulation have received enormous attention, especially the possibility of a shutdown in the meridional overturning that involves sinking of surface waters in the northern Atlantic Ocean. A recent study by Fedorov et al. has drawn attention to the effects of a freshening on the other main component of the oceanic circulation—the swift, shallow, wind-driven circulation that varies on decadal time scales and is closely associated with the ventilated thermocline. That circulation too involves meridional overturning, but its variations and critical transitions affect mainly the Tropics. A surface freshening in mid- to high latitudes can deepen the equatorial thermocline to such a degree that temperatures along the equator become as warm in the eastern part of the basin as they are in the west, the tropical zonal sea surface temperature gradient virtually disappears, and permanently warm conditions prevail in the Tropics. In a model that has both the wind-driven and thermohaline components of the circulation, which factors determine the relative effects of a freshening on the two components and its impact on climate? Studies with an idealized ocean general circulation model find that vertical diffusivity is one of the critical parameters that affect the relative strength of the two circulation components and hence their response to a freshening. The spatial structure of the freshening and imposed meridional temperature gradients are other important factors.

scholarly journals Influence of Surface Topography on the Critical Carbon Dioxide Level Required for the Formation of a Modern Snowball Earth

2018 ◽  
Vol 31 (20) ◽  
pp. 8463-8479 ◽  
Author(s):  
Yonggang Liu ◽  
W. Richard Peltier ◽  
Jun Yang ◽  
Yongyun Hu
Keyword(s):  
Sea Ice ◽  
General Circulation Model ◽  
Land Surface ◽  
General Circulation ◽  
Coupled Model ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Ocean Model ◽  
Snowball Earth ◽  
Ice Dynamics

The influence of continental topography on the initiation of a global glaciation (i.e., snowball Earth) is studied with both a fully coupled atmosphere–ocean general circulation model (AOGCM), CCSM3, and an atmospheric general circulation model (AGCM), CAM3 coupled to a slab ocean model. It is found that when the climate is very cold, snow cover over the central region of the Eurasian continent decreases when the atmospheric CO2 concentration ( pCO2) is reduced. In the coupled model, this constitutes a negative feedback due to the reduction of land surface albedo that counteracts the positive feedback due to sea ice expansion toward the equator. When the solar insolation is 94% of the present-day value, Earth enters a snowball state when pCO2 is ~35 ppmv. On the other hand, if the continents are assumed to be flat topographically (with the global mean elevation as in the more realistic present-day case), Earth enters a snowball state more easily at pCO2 = ~60 ppmv. Therefore, the presence of topography may increase the stability of Earth against descent into a snowball state. On the contrary, a snowball Earth is found to form much more easily when complex topography is present than when it is not in CAM3. This happens despite the fact that the mid- to high-latitude climate is much warmer (by ~10°C) when topography is present than when it is not. Analyses show that neglecting sea ice dynamics in this model prevents the warming anomaly in the mid- to high latitudes from being efficiently transmitted into the tropics.

scholarly journals Influence of XBT Temperature Bias on Decadal Climate Prediction with a Coupled Climate Model

2011 ◽  
Vol 24 (20) ◽  
pp. 5303-5308 ◽  
Author(s):  
Sayaka Yasunaka ◽  
Masayoshi Ishii ◽  
Masahide Kimoto ◽  
Takashi Mochizuki ◽  
Hideo Shiogama
Keyword(s):  
General Circulation ◽  
Climate Model ◽  
Initial Conditions ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Climate Prediction ◽  
Temperature Bias ◽  
Subsurface Ocean ◽  
Decadal Climate ◽  
Decadal Climate Prediction

Abstract The influence of the expendable bathythermograph (XBT) depth bias correction on decadal climate prediction is presented by using a coupled atmosphere–ocean general circulation model called the Model for Interdisciplinary Research on Climate 3 (MIROC3). The global mean subsurface ocean temperatures that were simulated by the model with the prescribed anthropogenic and natural forcing are consistent with bias-corrected observations from the mid-1960s onward, but not with uncorrected observations. The latter is reflected by biases in subsurface ocean temperatures, particularly along thermoclines in the tropics and subtropics. When the correction is not applied to XBT observations, these biases are retained in data assimilation results for the model’s initial conditions. Hindcasting past Pacific decadal oscillations (PDOs) is more successful in the experiment with the bias-corrected observations than that without the correction. Improvement of skill in predicting 5-yr mean vertically average ocean subsurface temperature is also seen in the tropical and the central North Pacific where PDO-related signals appear large.

scholarly journals Natural variability contributes to model–satellite differences in tropical tropospheric warming

2021 ◽  
Vol 118 (13) ◽  
pp. e2020962118
Author(s):  
Stephen Po-Chedley ◽  
Benjamin D. Santer ◽  
Stephan Fueglistaler ◽  
Mark D. Zelinka ◽  
Philip J. Cameron-Smith ◽  
...  
Keyword(s):  
Climate Sensitivity ◽  
General Circulation ◽  
Climate Model ◽  
Coupled Model ◽  
General Circulation Models ◽  
Satellite Observations ◽  
Sea Surface ◽  
Eastern Pacific ◽  
Surface Warming ◽  
The Tropics

A long-standing discrepancy exists between general circulation models (GCMs) and satellite observations: The multimodel mean temperature of the midtroposphere (TMT) in the tropics warms at approximately twice the rate of observations. Using a large ensemble of simulations from a single climate model, we find that tropical TMT trends (1979–2018) vary widely and that a subset of realizations are within the range of satellite observations. Realizations with relatively small tropical TMT trends are accompanied by subdued sea-surface warming in the tropical central and eastern Pacific. Observed changes in sea-surface temperature have a similar pattern, implying that the observed tropical TMT trend has been reduced by multidecadal variability. We also assess the latest generation of GCMs from the Coupled Model Intercomparison Project Phase 6 (CMIP6). CMIP6 simulations with muted warming over the central and eastern Pacific also show reduced tropical tropospheric warming. We find that 13% of the model realizations have tropical TMT trends within the observed trend range. These simulations are from models with both small and large climate sensitivity values, illustrating that the magnitude of tropical tropospheric warming is not solely a function of climate sensitivity. For global averages, one-quarter of model simulations exhibit TMT trends in accord with observations. Our results indicate that even on 40-y timescales, natural climate variability is important to consider when comparing observed and simulated tropospheric warming and is sufficiently large to explain TMT trend differences between models and satellite data.

scholarly journals Importance of Ocean Dynamics for the Skewness of the Indian Ocean Dipole Mode*

2013 ◽  
Vol 26 (7) ◽  
pp. 2145-2159 ◽  
Author(s):  
Tomomichi Ogata ◽  
Shang-Ping Xie ◽  
Jian Lan ◽  
Xiaotong Zheng
Keyword(s):  
Indian Ocean ◽  
General Circulation ◽  
Model Simulation ◽  
Heat Budget ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Ocean Dynamics ◽  
Thermocline Depth ◽  
Indian Ocean Dipole Mode ◽  
Budget Analysis

Abstract Interannual anomalies of sea surface temperature (SST), wind, and cloudiness in the southeastern tropical Indian Ocean (SE-TIO) show negative skewness. In this research, asymmetry between warm and cold episodes in the SE-TIO and the importance of ocean dynamics are investigated. A coupled model simulation and observations show an asymmetric relationship between SST and the thermocline depth in the SE-TIO where SST is more sensitive to an anomalous shoaling than to deepening of the thermocline. This asymmetric thermocline feedback on SST is a result of a deep mean thermocline. Sensitivity experiments with an ocean general circulation model (OGCM) show that a negative SST skewness arises in response to sinusoidal zonal wind variations that are symmetric between the westerly and easterly phases. Heat budget analysis with an OGCM hindcast also supports the importance of ocean dynamics for SST skewness off Sumatra and Java.

scholarly journals Importance of ocean salinity for climate and habitability

2016 ◽  
Vol 113 (16) ◽  
pp. 4278-4283 ◽  
Author(s):  
Jodie Cullum ◽  
David P. Stevens ◽  
Manoj M. Joshi
Keyword(s):  
Ocean Circulation ◽  
General Circulation ◽  
Circulation Model ◽  
Deep Ocean ◽  
Ocean General Circulation Model ◽  
Warm Water ◽  
Polar Regions ◽  
Ocean Salinity ◽  
Meridional Overturning ◽  
The Tropics

Modeling studies of terrestrial extrasolar planetary climates are now including the effects of ocean circulation due to a recognition of the importance of oceans for climate; indeed, the peak equator-pole ocean heat transport on Earth peaks at almost half that of the atmosphere. However, such studies have made the assumption that fundamental oceanic properties, such as salinity, temperature, and depth, are similar to Earth. This assumption results in Earth-like circulations: a meridional overturning with warm water moving poleward at the surface, being cooled, sinking at high latitudes, and traveling equatorward at depth. Here it is shown that an exoplanetary ocean with a different salinity can circulate in the opposite direction: an equatorward flow of polar water at the surface, sinking in the tropics, and filling the deep ocean with warm water. This alternative flow regime results in a dramatic warming in the polar regions, demonstrated here using both a conceptual model and an ocean general circulation model. These results highlight the importance of ocean salinity for exoplanetary climate and consequent habitability and the need for its consideration in future studies.

scholarly journals Coupled Climate Simulation by Constraining Ocean Fields in a Coupled Model with Ocean Data

2009 ◽  
Vol 22 (20) ◽  
pp. 5541-5557 ◽  
Author(s):  
Yosuke Fujii ◽  
Toshiyuki Nakaegawa ◽  
Satoshi Matsumoto ◽  
Tamaki Yasuda ◽  
Goro Yamanaka ◽  
...  
Keyword(s):  
Data Assimilation ◽  
General Circulation ◽  
Coupled Model ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
The Philippines ◽  
Ocean Model ◽  
Climate Simulation ◽  
Philippine Sea ◽  
Estimation System

Abstract The authors developed a system for simulating climate variation by constraining the ocean component of a coupled atmosphere–ocean general circulation model (CGCM) through ocean data assimilation and conducted a climate simulation [Multivariate Ocean Variational Estimation System–Coupled Version Reanalysis (MOVE-C RA)]. The monthly variation of sea surface temperature (SST) is reasonably recovered in MOVE-C RA. Furthermore, MOVE-C RA has improved precipitation fields over the Atmospheric Model Intercomparison Project (AMIP) run (a simulation of the atmosphere model forced by observed daily SST) and the CGCM free simulation run. In particular, precipitation in the Philippine Sea in summer is improved over the AMIP run. This improvement is assumed to stem from the reproduction of the interaction between SST and precipitation, indicated by the lag of the precipitation change behind SST. Enhanced (suppressed) convection tends to induce an SST drop (rise) because of cloud cover and ocean mixing in the real world. A lack of this interaction in the AMIP run leads to overestimating the precipitation in the Bay of Bengal in summer. Because it is recovered in MOVE-C RA, the overestimate is suppressed. This intensifies the zonal Walker circulation and the monsoon trough, resulting in enhanced convection in the Philippine Sea. The spurious positive correlation between SST and precipitation around the Philippines in the AMIP run in summer is also removed in MOVE-C RA. These improvements demonstrate the effectiveness of simulating ocean interior processes with the ocean model and data assimilation for reproducing the climate variability.

scholarly journals Retrospective Forecasts of Interannual Sea Surface Temperature Anomalies from 1982 to Present Using a Directly Coupled Atmosphere–Ocean General Circulation Model

2005 ◽  
Vol 133 (10) ◽  
pp. 2972-2995 ◽  
Author(s):  
David G. DeWitt
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
General Circulation Model ◽  
General Circulation ◽  
Coupled Model ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Sea Surface ◽  
Initial Condition ◽  
Ocean General Circulation

Abstract A large number of ensemble hindcasts (or retrospective forecasts) of tropical Pacific sea surface temperature (SST) have been made with a coupled atmosphere–ocean general circulation model (CGCM) that does not employ flux correction in order to evaluate the potential skill of the model as a seasonal forecasting tool. Oceanic initial conditions are provided by an ocean data assimilation system. Ensembles of seven forecasts of 6-month length are made starting each month in the 1982 to 2002 period. Skill of the coupled model is evaluated from both a deterministic and a probabilistic perspective. The skill metrics are calculated using both the bulk method, which includes all initial condition months together, and as a function of initial condition month. The latter method allows a more objective evaluation of how the model has performed in the context in which forecasts are actually made and applied. The deterministic metrics used are the anomaly correlation and the root-mean-square error. The coupled model deterministic skill metrics are compared with those from persistence and damped persistence reference forecasts. Despite the fact that the coupled model has a large cold bias in the central and eastern equatorial Pacific this coupled model is shown to have forecast skill that is competitive with other state-of-the-art forecasting techniques. Potential skill from probabilistic forecasts made using the coupled model ensemble members are evaluated using the relative operating characteristics method. This analysis indicates that for most initial condition months this coupled model has more skill at forecasting cold events than warm or neutral events in the central Pacific. In common with other forecasting systems, the coupled model forecast skill is found to be lowest for forecasts passing through the Northern Hemisphere (NH) spring. Diagnostics of this so-called spring predictability barrier in the context of this coupled model indicate that two factors likely contribute to this predictability barrier. First, the coupled model shows a too-weak coupling of the surface and subsurface temperature anomalies during NH spring. Second, the coupled-model-simulated signal-to-noise ratio for SST anomalies is much lower during NH spring than at other times of the year, indicating that the model’s potential predictability is low at this time.

scholarly journals The Climate of the MIS-13 Interglacial according to HadCM3

2013 ◽  
Vol 26 (23) ◽  
pp. 9696-9712 ◽  
Author(s):  
Helene Muri ◽  
André Berger ◽  
Qiuzhen Yin ◽  
Mehdi Pasha Karami ◽  
Pierre-Yves Barriat
Keyword(s):  
Summer Monsoon ◽  
General Circulation ◽  
Southern Oscillation ◽  
Asian Summer Monsoon ◽  
Coupled Model ◽  
Circulation Model ◽  
Stationary Wave ◽  
Ocean General Circulation Model ◽  
The Sea Of Japan ◽  
The North

The climate of the Marine Isotopic Stage 13 (MIS-13) is explored in the fully coupled atmosphere–ocean general circulation model the Hadley Centre Coupled Model, version 3 (HadCM3). It is found that the strong insolation forcing at the time imposed a strengthened land–ocean thermal contrast, resulting in an intensified summer monsoon over Asia. The addition of land ice over North America and Eurasia results in a stationary wave feature across the Eurasian continent. This leads to a high pressure anomaly over the Sea of Japan with increased advection of warm moist air onto the Chinese landmasses. This in turn reinforces the East Asian summer monsoon (EASM), highlighting the counterintuitive notion that, depending on the background insolation and its size, ice can indeed contribute to strengthening the EASM. The modeling results support the geological record indication of a strong EASM 500 000 years ago. Furthermore, Arctic Oscillation, El Niño–Southern Oscillation, and Indian Ocean dipole–like teleconnection features are discussed in the MIS-13 environment. It is shown that the change in the tropical Pacific sea surface temperature has the potential to impact the North Atlantic climate through an atmospheric “bridge.”

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