scholarly journals Interannual Atmospheric Variability Affects Continental Ice Sheet Simulations on Millennial Time Scales

2008 ◽  
Vol 21 (22) ◽  
pp. 5976-5992 ◽  
Author(s):  
Michael S. Pritchard ◽  
Andrew B. G. Bush ◽  
Shawn J. Marshall
Keyword(s):  
North American ◽  
General Circulation ◽  
Southern Oscillation ◽  
Ice Sheet ◽  
Sheet Thickness ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Equilibrium Geometry ◽  
Atmospheric Variability ◽  
Enso Teleconnections

Abstract To inform the ongoing development of earth system models that aim to incorporate interactive ice, the potential impact of interannual variability associated with synoptic variability and El Niño–Southern Oscillation (ENSO) at the Last Glacial Maximum (LGM) on the evolution of a large continental ice sheet is explored through a series of targeted numerical modeling experiments. Global and North American signatures of ENSO at the LGM are described based on a multidecadal paleoclimate simulation using an atmosphere–ocean general circulation model (AOGCM). Experiments in which a thermomechanical North American ice sheet model (ISM) was forced with persistent LGM ENSO composite anomaly maps derived from the AOGCM showed only modest ice sheet thickness sensitivity to ENSO teleconnections. In contrast, very high model sensitivity was found when North American climate variations were incorporated directly in the ISM as a looping interannual time series. Under this configuration, localized transient cold anomalies in the atmospheric record instigated substantial new ice formation through a dynamically mediated feedback at the ice sheet margin, altering the equilibrium geometry and resulting in a bulk 10% growth of the Laurentide ice sheet volume over 5 kyr.

Improved Climate Simulation by MIROC5: Mean States, Variability, and Climate Sensitivity

2010 ◽  
Vol 23 (23) ◽  
pp. 6312-6335 ◽  
Author(s):  
Masahiro Watanabe ◽  
Tatsuo Suzuki ◽  
Ryouta O’ishi ◽  
Yoshiki Komuro ◽  
Shingo Watanabe ◽  
...  
Keyword(s):  
Climate Sensitivity ◽  
General Circulation ◽  
Southern Oscillation ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Climate Simulation ◽  
Mean Fields ◽  
Equatorial Ocean ◽  
The Mean ◽  
The Difference

Abstract A new version of the atmosphere–ocean general circulation model cooperatively produced by the Japanese research community, known as the Model for Interdisciplinary Research on Climate (MIROC), has recently been developed. A century-long control experiment was performed using the new version (MIROC5) with the standard resolution of the T85 atmosphere and 1° ocean models. The climatological mean state and variability are then compared with observations and those in a previous version (MIROC3.2) with two different resolutions (medres, hires), coarser and finer than the resolution of MIROC5. A few aspects of the mean fields in MIROC5 are similar to or slightly worse than MIROC3.2, but otherwise the climatological features are considerably better. In particular, improvements are found in precipitation, zonal mean atmospheric fields, equatorial ocean subsurface fields, and the simulation of El Niño–Southern Oscillation. The difference between MIROC5 and the previous model is larger than that between the two MIROC3.2 versions, indicating a greater effect of updating parameterization schemes on the model climate than increasing the model resolution. The mean cloud property obtained from the sophisticated prognostic schemes in MIROC5 shows good agreement with satellite measurements. MIROC5 reveals an equilibrium climate sensitivity of 2.6 K, which is lower than that in MIROC3.2 by 1 K. This is probably due to the negative feedback of low clouds to the increasing concentration of CO2, which is opposite to that in MIROC3.2.

Interannual oscillations in an ocean general circulation model coupled to a simple atmosphere model

1989 ◽  
Vol 329 (1604) ◽  
pp. 189-205 ◽  
Keyword(s):  
El Niño ◽  
General Circulation ◽  
El Nino ◽  
Southern Oscillation ◽  
Circulation Model ◽  
Coupled System ◽  
General Circulation Models ◽  
Atmospheric Model ◽  
Ocean General Circulation Model ◽  
Coupled Oscillations

A model is being developed for tropical air-sea interaction studies that is intermediate in complexity between the large coupled general circulation models (GCMS) that are coming into use, and the simple two-level models with which pioneering El Nino Southern Oscillation studies were done. The model consists of a stripped-down tropical Pacific Ocean GCM, coupled to an atmospheric model that is sufficiently simple that steady-state solutions may be found for low-level flow and surface stress, given oceanic boundary conditions. This permits examination of the nature of interannual coupled oscillations in the absence of atmospheric noise. In preliminary tests of the model the coupled system is found to undergo a Hopf bifurcation as certain parameters are varied, giving rise to sustained three to four year oscillations. For stronger coupling, a secondary bifurcation yields six month coupled oscillations during the warm phase of the El Nino-period oscillation. Such variability could potentially affect the predictability of the coupled system.

scholarly journals Sources of holocene variability of oxygen isotopes in paleoclimate archives

2009 ◽  
Vol 5 (2) ◽  
pp. 1133-1162 ◽  
Author(s):  
A. N. LeGrande ◽  
G. A. Schmidt
Keyword(s):  
Water Vapor ◽  
General Circulation ◽  
Ice Sheet ◽  
Circulation Model ◽  
Ice Cores ◽  
Ocean General Circulation Model ◽  
Ocean Basin ◽  
Water Vapor Transport ◽  
Water Isotopes ◽  
Water Isotope

Abstract. Variability in water isotopes has been captured in numerous archives and used to infer climate change. Here we examine water isotope variability over the course of the Holocene using the water-isotope enabled, coupled atmosphere-ocean general circulation model, GISS ModelE-R. Eight Holocene time slices, mostly 1000 years apart are simulated using estimated changes in orbital configuration, greenhouse gases, and ice sheet extent. We find that water isotopes in the model match well with those captured in proxy climate archives in ice cores, ocean sediment cores, and speleothems. The climate changes associated with the water isotope changes, however, are more complex than simple modern analog interpretations. In particular, water isotope variability in Asian speleothems is linked to alterations in landward water vapor transport, not local precipitation, and ice sheet changes over North America lead to masking of temperature signals in Summit, Greenland. Salinity-seawater isotope variability is complicated by inter-ocean basin exchanges of water vapor. Water isotopes do reflect variability in the hydrologic cycle, but are better interpreted in terms of regional changes rather than local climate variables.

Predictability of Two Types of El Niño Assessed Using an Extended Seasonal Prediction System by MIROC

2015 ◽  
Vol 143 (11) ◽  
pp. 4597-4617 ◽  
Author(s):  
Yukiko Imada ◽  
Hiroaki Tatebe ◽  
Masayoshi Ishii ◽  
Yoshimitsu Chikamoto ◽  
Masato Mori ◽  
...  
Keyword(s):  
El Niño ◽  
Lead Time ◽  
General Circulation ◽  
El Nino ◽  
Southern Oscillation ◽  
Circulation Model ◽  
Seasonal Prediction ◽  
Ocean General Circulation Model ◽  
Prediction System ◽  
Central Pacific

Abstract Predictability of El Niño–Southern Oscillation (ENSO) is examined using ensemble hindcasts made with a seasonal prediction system based on the atmosphere and ocean general circulation model, the Model for Interdisciplinary Research on Climate, version 5 (MIROC5). Particular attention is paid to differences in predictive skill in terms of the prediction error for two prominent types of El Niño: the conventional eastern Pacific (EP) El Niño and the central Pacific (CP) El Niño, the latter having a maximum warming around the date line. Although the system adopts ocean anomaly assimilation for the initialization process, it maintains a significant ability to predict ENSO with a lead time of more than half a year. This is partly due to the fact that the system is little affected by the “spring prediction barrier,” because increases in the error have little dependence on the thermocline variability. Composite analyses of each type of El Niño reveal that, compared to EP El Niños, the ability to predict CP El Niños is limited and has a shorter lead time. This is because CP El Niños have relatively small amplitudes, and thus they are more affected by atmospheric noise; this prevents development of oceanic signals that can be used for prediction.

scholarly journals The Response of Ice Shelf Basal Melting to Variations in Ocean Temperature

2008 ◽  
Vol 21 (11) ◽  
pp. 2558-2572 ◽  
Author(s):  
Paul R. Holland ◽  
Adrian Jenkins ◽  
David M. Holland
Keyword(s):  
Ocean Circulation ◽  
General Circulation ◽  
Ice Sheet ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Flow Speed ◽  
Ocean Warming ◽  
Ocean Temperature ◽  
Ice Shelf ◽  
Ice Shelves

Abstract A three-dimensional ocean general circulation model is used to study the response of idealized ice shelves to a series of ocean-warming scenarios. The model predicts that the total ice shelf basal melt increases quadratically as the ocean offshore of the ice front warms. This occurs because the melt rate is proportional to the product of ocean flow speed and temperature in the mixed layer directly beneath the ice shelf, both of which are found to increase linearly with ocean warming. The behavior of this complex primitive equation model can be described surprisingly well with recourse to an idealized reduced system of equations, and it is shown that this system supports a melt rate response to warming that is generally quadratic in nature. This study confirms and unifies several previous examinations of the relation between melt rate and ocean temperature but disagrees with other results, particularly the claim that a single melt rate sensitivity to warming is universally valid. The hypothesized warming does not necessarily require a heat input to the ocean, as warmer waters (or larger volumes of “warm” water) may reach ice shelves purely through a shift in ocean circulation. Since ice shelves link the Antarctic Ice Sheet to the climate of the Southern Ocean, this finding of an above-linear rise in ice shelf mass loss as the ocean steadily warms is of significant importance to understanding ice sheet evolution and sea level rise.

Optimal Tropical Sea Surface Temperature Forcing of North American Drought

2010 ◽  
Vol 23 (14) ◽  
pp. 3907-3917 ◽  
Author(s):  
Sang-Ik Shin ◽  
Prashant D. Sardeshmukh ◽  
Robert S. Webb
Keyword(s):  
Time Series ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
North American ◽  
General Circulation ◽  
Southern Oscillation ◽  
Circulation Model ◽  
Sea Surface ◽  
Drought Severity ◽  
Sst Anomaly

Abstract The optimal anomalous sea surface temperature (SST) pattern for forcing North American drought is identified through atmospheric general circulation model integrations in which the response of the Palmer drought severity index (PDSI) is determined for each of 43 prescribed localized SST anomaly “patches” in a regular array over the tropical oceans. The robustness and relevance of the optimal pattern are established through the consistency of results obtained using two different models, and also by the good correspondence of the projection time series of historical tropical SST anomaly fields on the optimal pattern with the time series of the simulated PDSI in separate model integrations with prescribed time-varying observed global SST fields for 1920–2005. It is noteworthy that this optimal drought forcing pattern differs markedly in the Pacific Ocean from the dominant SST pattern associated with El Niño–Southern Oscillation (ENSO), and also shows a large sensitivity of North American drought to Indian and Atlantic Ocean SSTs.

scholarly journals Megadroughts in Southwestern North America in ECHO-G Millennial Simulations and Their Comparison to Proxy Drought Reconstructions*

2013 ◽  
Vol 26 (19) ◽  
pp. 7635-7649 ◽  
Author(s):  
Sloan Coats ◽  
Jason E. Smerdon ◽  
Richard Seager ◽  
Benjamin I. Cook ◽  
J. F. González-Rouco
Keyword(s):  
North American ◽  
General Circulation ◽  
Southern Oscillation ◽  
Circulation Model ◽  
Tropical Pacific ◽  
Drought Severity ◽  
The North ◽  
Hydroclimate Variability ◽  
And Control ◽  
The Tropical Pacific

Abstract Simulated hydroclimate variability in millennium-length forced transient and control simulations from the ECHAM and the global Hamburg Ocean Primitive Equation (ECHO-G) coupled atmosphere–ocean general circulation model (AOGCM) is analyzed and compared to 1000 years of reconstructed Palmer drought severity index (PDSI) variability from the North American Drought Atlas (NADA). The ability of the model to simulate megadroughts in the North American southwest is evaluated. (NASW: 25°–42.5°N, 125°–105°W). Megadroughts in the ECHO-G AOGCM are found to be similar in duration and magnitude to those estimated from the NADA. The droughts in the forced simulation are not, however, temporally synchronous with those in the paleoclimate record, nor are there significant differences between the drought features simulated in the forced and control runs. These results indicate that model-simulated megadroughts can result from internal variability of the modeled climate system rather than as a response to changes in exogenous forcings. Although the ECHO-G AOGCM is capable of simulating megadroughts through persistent La Niña–like conditions in the tropical Pacific, other mechanisms can produce similarly extreme NASW moisture anomalies in the model. In particular, the lack of low-frequency coherence between NASW soil moisture and simulated modes of climate variability like the El Niño–Southern Oscillation, Pacific decadal oscillation, and Atlantic multidecadal oscillation during identified drought periods suggests that stochastic atmospheric variability can contribute significantly to the occurrence of simulated megadroughts in the NASW. These findings indicate that either an expanded paradigm is needed to understand multidecadal hydroclimate variability in the NASW or AOGCMs may incorrectly simulate the strength and/or dynamics of the connection between NASW hydroclimate variability and the tropical Pacific.

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.”

scholarly journals Imprint of chaotic ocean variability on transports in the Southwest Pacific at interannual timescales

2020 ◽  
Author(s):  
Sophie Cravatte ◽  
Guillaume Serazin ◽  
Thierry Penduff ◽  
Christophe Menkes
Keyword(s):  
Interannual Variability ◽  
General Circulation ◽  
Large Scale ◽  
Southern Oscillation ◽  
Initial Perturbation ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Atmospheric Forcing ◽  
Southwest Pacific ◽  
Ocean Variability

Abstract. The Southwest Pacific Ocean sits at a bifurcation where southern subtropical waters are redistributed equatorward and poleward by different ocean currents. The processes governing the interannual variability of these currents are not completely understood. This issue is investigated using a probabilistic modeling strategy that allows disentangling the atmospherically-forced deterministic ocean variability and the chaotic intrinsic ocean variability. A large ensemble of 50 simulations performed with the same ocean general circulation model (OGCM) driven by the same realistic atmospheric forcing that only differ by a small initial perturbation is analyzed over 1980–2015. Our results show that, in the Southwest Pacific, the interannual variability of the transports is strongly dominated by chaotic ocean variability south of 20° S. In the tropics, while the interannual variability of transports and eddy kinetic energy modulation is largely deterministic and explained by El Nino Southern Oscillation (ENSO), ocean nonlinear processes still explain 10 to 20 % of their interannual variance at large-scale. Regions of strong chaotic variance generally coincide with regions of high mesoscale activity, suggesting that a spontaneous inverse cascade is at work from mesoscale toward lower frequencies and larger scales. The spatiotemporal features of the low-frequency oceanic chaotic variability are complex but spatially coherent within certain regions. In the Subtropical Countercurrent area, they appear as interannually-varying, zonally elongated alternating current structures, while in the EAC region, they are eddy-shaped. Given this strong imprint of large-scale chaotic oceanic fluctuations, our results question the attribution of interannual variability to the atmospheric forcing in the region from point-wise observations and one-member simulations.

scholarly journals Greenland Ice Sheet influence on Last Interglacial climate: global sensitivity studies performed with an atmosphere–ocean general circulation model

2015 ◽  
Vol 11 (2) ◽  
pp. 933-995 ◽  
Author(s):  
M. Pfeiffer ◽  
G. Lohmann
Keyword(s):  
General Circulation ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
High Latitudes ◽  
Last Interglacial ◽  
Proxy Records ◽  
Sensitivity Studies ◽  
The Impact

Abstract. During the Last Interglacial (LIG, 130–115 kiloyear before present), the northern high latitudes experienced higher temperatures than those of the late Holocene with a notably lower Greenland Ice Sheet (GIS). However, the impact of a reduced GIS on the global climate has not yet been well constrained. In this study, we quantify the contribution of the GIS to LIG warmth by performing various sensitivity studies, employing the Community Earth System Models (COSMOS), with a focus on height and extent of the GIS. In order to asses the effects of insolation changes over time and for a comparison of LIG climate with the current interglacial, we perform transient simulations covering the whole LIG and Holocene. We analyze surface air temperature (SAT) and separate the contribution of different forcings to LIG warmth. The strong Northern Hemisphere warming is mainly caused by increased summer insolation. Reducing the height and extent of the GIS leads to a warming of several degrees Celcius in the northern and southern high latitudes during local winter. In order to evaluate the performance of our LIG simulations, we additionally compare the simulated SAT anomalies with marine and terrestrial proxy-based LIG temperature anomalies. Our model results are in good agreement with proxy records with respect to the pattern, but underestimate the reconstructed temperatures. We are able to reduce the mismatch between model and data by taking into account the potential seasonal bias of the proxy record and the uncertainties in the dating of the proxy records for the LIG thermal maximum. The seasonal bias and the uncertainty of the timing are estimated from our own transient model simulations. We note however that our LIG simulations are not able to reproduce the full magnitude of temperature changes indicated by the proxies, suggesting a potential misinterpretation of the proxy records or deficits of our model.

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