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1

Electronic Resource

The seasonal cycle in coupled ocean-atmosphere general circulation models (2000)

Covey, C. ; Abe-Ouchi, A. ; Boer, G. J. ; [et al.]

Springer

Climate dynamics 16 (2000), S. 775-787

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ISSN: 1432-0894

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences , Physics

Notes: Abstract We examine the seasonal cycle of near-surface air temperature simulated by 17 coupled ocean-atmosphere general circulation models participating in the Coupled Model Intercomparison Project (CMIP). Nine of the models use ad hoc “flux adjustment” at the ocean surface to bring model simulations close to observations of the present-day climate. We group flux-adjusted and non-flux-adjusted models separately and examine the behavior of each class. When averaged over all of the flux-adjusted model simulations, near-surface air temperature falls within 2 K of observed values over the oceans. The corresponding average over non-flux-adjusted models shows errors up to ∼6 K in extensive ocean areas. Flux adjustments are not directly applied over land, and near-surface land temperature errors are substantial in the average over flux-adjusted models, which systematically underestimates (by ∼5 K) temperature in areas of elevated terrain. The corresponding average over non-flux-adjusted models forms a similar error pattern (with somewhat increased amplitude) over land. We use the temperature difference between July and January to measure seasonal cycle amplitude. Zonal means of this quantity from the individual flux-adjusted models form a fairly tight cluster (all within ∼30% of the mean) centered on the observed values. The non-flux-adjusted models perform nearly as well at most latitudes. In Southern Ocean mid-latitudes, however, the non-flux-adjusted models overestimate the magnitude of January-minus-July temperature differences by ∼5 K due to an overestimate of summer (January) near-surface temperature. This error is common to five of the eight non-flux-adjusted models. Also, over Northern Hemisphere mid-latitude land areas, zonal mean differences between July and January temperatures simulated by the non-flux-adjusted models show a greater spread (positive and negative) about observed values than results from the flux-adjusted models. Elsewhere, differences between the two classes of models are less obvious. At no latitude is the zonal mean difference between averages over the two classes of models greater than the standard deviation over models. The ability of coupled GCMs to simulate a reasonable seasonal cycle is a necessary condition for confidence in their prediction of long-term climatic changes (such as global warming), but it is not a sufficient condition unless the seasonal cycle and long-term changes involve similar climatic processes. To test this possible connection, we compare seasonal cycle amplitude with equilibrium warming under doubled atmospheric carbon dioxide for the models in our data base. A small but positive correlation exists between these two quantities. This result is predicted by a simple conceptual model of the climate system, and it is consistent with other modeling experience, which indicates that the seasonal cycle depends only weakly on climate sensitivity.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s003820000081

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2

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Sea-ice effects on climate model sensitivity and low frequency variability (2000)

Meehl, G. A. ; Arblaster, J. M. ; Strand Jr, W. G.

Springer

Climate dynamics 16 (2000), S. 257-271

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ISSN: 1432-0894

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences , Physics

Notes: Abstract A change in a sea-ice parameter in a global coupled climate model results in a reduction in amplitude (of about 60%) and a shortening of the predominant period of decadal low frequency variability in the time series of globally averaged surface air temperature. These changes are global in extent and also are reflected in time series of area-averaged SSTs in the equatorial eastern Pacific Ocean, the principal components of the first EOFs of global surface air temperature and sea level pressure, Asian monsoon precipitations and other quantities. Coupled ocean-atmosphere-sea ice processes acting on a global scale are modified to produce these changes. Global climate sensitivity is reduced when ice albedo feedback is weakened due to the change in sea ice that makes it more difficult to melt. The changes in the amplitude and time scale of the low frequency variability in the model are traced to changes in the base state of the climate simulations as affected by modifications associated with the changes in sea ice. Making sea ice more difficult to melt results in increased sea-ice area, colder high latitudes, increased meridional surface temperature gradients, and, to a first order, stronger surface winds in most regions which strengthen near-surface currents, particularly in the Northern Hemisphere, and decreases the advection time scale in the upper ocean gyres. Additionally, in the North Atlantic there is enhanced meridional overturning due to increased density mainly in the Greenland Sea region. This also contributes to an intensified North Atlantic gyre. The changes in base state due to the sea ice change result in a more predominant decadal time scale of near 14 years and significantly reduced contributions from lower frequencies in the range of 15–40 year periods.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s003820050326

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3

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Intercomparsion of regional biases and doubled CO2-sensitivity of coupled atmosphere-ocean general circulation model experiments (1997)

Kittel, T. G. F. ; Giorgi, F. ; Meehl, G. A.

Springer

Climate dynamics 14 (1997), S. 1-15

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ISSN: 1432-0894

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences , Physics

Notes: Abstract We compared regional biases and transient doubled CO2 sensitivities of nine coupled atmosphere-ocean general circulation models (GCMs) from six international climate modeling groups. We evaluated biases and responses in winter and summer surface air temperatures and precipitation for seven subcontinental regions, including those in the 1990 Intergovernmental Panel on Climate Change (IPCC) Scientific Assessment. Regional biases were large and exceeded the variance among four climatological datasets, indicating that model biases were not primarily due to uncertainty in observations. Model responses to altered greenhouse forcing were substantial (average temperature change=2.7±0.9 °C, range of precipitation change =−35 to +120% of control). While coupled models include more climate system feedbacks than earlier GCMs implemented with mixed-layer ocean models, inclusion of a dynamic ocean alone did not improve simulation of long-term mean climatology nor increase convergence among model responses to altered greenhouse gas forcing. On the other hand, features of some of the coupled models including flux adjustment (which may have simply masked simulation errors), high horizontal resolution, and estimation of screen height temperature contributed to improved simulation of long-term surface climate. The large range of model responses was partly accounted for by inconsistencies in forcing scenarios and transient-simulation averaging periods. Nonetheless, the models generally had greater agreement in their sensitivities than their controls did with observations. This suggests that consistent, large-scale response features from an ensemble of model sensitivity experiments may not depend on details of their representation of present-day climate.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s003820050204

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4

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Tropical air-sea interaction in general circulation models (1992)

Neelin, J D ; Latif, M ; Allaart, M A F ; [et al.]

Springer

Climate dynamics 7 (1992), S. 73-104

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ISSN: 1432-0894

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences , Physics

Notes: Abstract An intercomparison is undertaken of the tropical behavior of 17 coupled ocean-atmosphere models in which at least one component may be termed a general circulation model (GCM). The aim is to provide a taxonomy—a description and rough classification—of behavior across the ensemble of models, focusing on interannual variability. The temporal behavior of the sea surface temperature (SST) field along the equator is presented for each model, SST being chosen as the primary variable for intercomparison due to its crucial role in mediating the coupling and because it is a sensitive indicator of climate drift. A wide variety of possible types of behavior are noted among the models. Models with substantial interannual tropical variability may be roughly classified into cases with propagating SST anomalies and cases in which the SST anomalies develop in place. A number of the models also exhibit significant drift with respect to SST climatology. However, there is not a clear relationship between climate drift and the presence or absence of interannual oscillations. In several cases, the mode of climate drift within the tropical Pacific appears to involve coupled feedback mechanisms similar to those responsible for El Niño variability. Implications for coupled-model development and for climate prediction on seasonal to interannual time scales are discussed. Overall, the results indicate considerable sensitivity of the tropical coupled ocean-atmosphere system and suggest that the simulation of the warm-pool/cold-tongue configuration in the equatorial Pacific represents a challenging test for climate model parameterizations.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00209610

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5

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Parallel climate model (PCM) control and transient simulations (2000)

Washington, W. M. ; Weatherly, J. W. ; Meehl, G. A. ; [et al.]

Springer

Climate dynamics 16 (2000), S. 755-774

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ISSN: 1432-0894

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences , Physics

Notes: Abstract The Department of Energy (DOE) supported Parallel Climate Model (PCM) makes use of the NCAR Community Climate Model (CCM3) and Land Surface Model (LSM) for the atmospheric and land surface components, respectively, the DOE Los Alamos National Laboratory Parallel Ocean Program (POP) for the ocean component, and the Naval Postgraduate School sea-ice model. The PCM executes on several distributed and shared memory computer systems. The coupling method is similar to that used in the NCAR Climate System Model (CSM) in that a flux coupler ties the components together, with interpolations between the different grids of the component models. Flux adjustments are not used in the PCM. The ocean component has 2/3° average horizontal grid spacing with 32 vertical levels and a free surface that allows calculation of sea level changes. Near the equator, the grid spacing is approximately 1/2° in latitude to better capture the ocean equatorial dynamics. The North Pole is rotated over northern North America thus producing resolution smaller than 2/3° in the North Atlantic where the sinking part of the world conveyor circulation largely takes place. Because this ocean model component does not have a computational point at the North Pole, the Arctic Ocean circulation systems are more realistic and similar to the observed. The elastic viscous plastic sea ice model has a grid spacing of 27 km to represent small-scale features such as ice transport through the Canadian Archipelago and the East Greenland current region. Results from a 300 year present-day coupled climate control simulation are presented, as well as for a transient 1% per year compound CO2 increase experiment which shows a global warming of 1.27 °C for a 10 year average at the doubling point of CO2 and 2.89 °C at the quadrupling point. There is a gradual warming beyond the doubling and quadrupling points with CO2 held constant. Globally averaged sea level rise at the time of CO2 doubling is approximately 7 cm and at the time of quadrupling it is 23 cm. Some of the regional sea level changes are larger and reflect the adjustments in the temperature, salinity, internal ocean dynamics, surface heat flux, and wind stress on the ocean. A 0.5% per year CO2 increase experiment also was performed showing a global warming of 1.5 °C around the time of CO2 doubling and a similar warming pattern to the 1% CO2 per year increase experiment. El Niño and La Niña events in the tropical Pacific show approximately the observed frequency distribution and amplitude, which leads to near observed levels of variability on interannual time scales.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s003820000079

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6

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Vulnerability of freshwater resources to climate change in the tropical pacific region (1996)

Meehl, G. A.

Springer

Water, air & soil pollution 92 (1996), S. 203-213

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ISSN: 1573-2932

Keywords: Australasia ; Pacific island nations ; water resources ; El Nino ; drought

Source: Springer Online Journal Archives 1860-2000

Topics: Energy, Environment Protection, Nuclear Power Engineering

Notes: Abstract El Nino events and associated droughts adversely affect freshwater resources on islands in the tropical Pacific region. Particularly vulnerable are low-lying atolls because rainwater collection is the main freshwater source on such islands. During El Nino-related droughts, water can be drawn only from the limited freshwater lenses beneath the islands. If drought conditions such as these intensify, the depletion of freshwater resources could affect the habitability of atolls. Average climate change inthe Pacific region from increased anthropogenic carbon dioxide in a global coupled climate model resembles present-day El Nino conditions as well as the decadal time-scale sea surface temperature and precipitation anomalies observed during the 1980s and early 1990s. These anomalies are a consequence of greater warming of sea surface temperatures in the eastern equatorial Pacific than over the western Pacific warm pool with increased carbon dioxide in the climate model. Attendant increases in precipitation in the central equatorial Pacific are also accompanied by precipitation decreases in the northern and southern tropical Pacific (roughly 5 °N to 15°N and 5°S to 15°S), as well as in the Australasian and eastern Indian Ocean regions. Associated effects in the midlatitude North Pacific also resemble El Nino conditions and the decadal time-scale signals from the 1980s. Future possible increases of drought conditions in certain tropical Pacific regions, as indicated by the climate model results, could limit the sustainability of atoll populations in those regions, causing migration and increased urbanization, with all the attendant problems, on larger high islands with more stable water supplies.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00175566

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7

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Projections of Future Climate Change (2001)

Cubasch, U. ; Meehl, G. A. ; Boer, G. J. ; [et al.]

In: EPIC3, in: J.T Houghton, Y. Ding, D.J. Griggs, M. Noguer, P.J. Van der Linden, X. Dai, K. Maskell, and C.A. Johnson (eds.): Climate Change 2001: The Scientific Basis: Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel, pp. 526-582

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Publication Date: 2019-07-17

Repository Name: EPIC Alfred Wegener Institut

Type: Book , peerRev

Format: application/pdf

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Quantifying Progress Across Different CMIP Phases With the ESMValTool (2021)

Bock, L. ; Lauer, A. ; Schlund, M. ; [et al.]

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Publication Date: 2021-07-04

Description: More than 40 model groups worldwide are participating in the Coupled Model Intercomparison Project Phase 6 (CMIP6), providing a new and rich source of information to better understand past, present, and future climate change. Here, we use the Earth System Model Evaluation Tool (ESMValTool) to assess the performance of the CMIP6 ensemble compared to the previous generations CMIP3 and CMIP5. While CMIP5 models did not capture the observed pause in the increase in global mean surface temperature between 1998 and 2013, the historical CMIP6 simulations agree well with the observed recent temperature increase, but some models have difficulties in reproducing the observed global mean surface temperature record of the second half of the twentieth century. While systematic biases in annual mean surface temperature and precipitation remain in the CMIP6 multimodel mean, individual models and high‐resolution versions of the models show significant reductions in many long‐standing biases. Some improvements are also found in the vertical temperature, water vapor, and zonal wind speed distributions, and root‐mean‐square errors for selected fields are generally smaller with reduced intermodel spread and higher average skill in the correlation patterns relative to observations. An emerging property of the CMIP6 ensemble is a higher effective climate sensitivity with an increased range between 2.3 and 5.6 K. A possible reason for this increase in some models is improvements in cloud representation resulting in stronger shortwave cloud feedbacks than in their predecessor versions.

Description: Key Points: Temperature, water vapor, and zonal wind speed show improvements in CMIP6 with amplitudes of many long‐standing biases smaller than CMIP3/5. High‐resolution models show significant improvements in their historical CMIP6 simulations for temperature and precipitation mean biases. Spread in effective climate sensitivity in CMIP6 is larger than in previous phases.

Description: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347

Description: National Center for Atmospheric Research (NCAR) http://dx.doi.org/10.13039/100005323

Description: U.S. Department of Energy (DOE) http://dx.doi.org/10.13039/100000015

Description: European Space Agency (ESA) http://dx.doi.org/10.13039/501100000844

Description: German Federal Ministry of Education and Research (BMBF)

Description: PRIMAVERA

Description: Coordinated Research in Earth Systems and Climate: Experiments, kNowledge, Dissemination and Outreach (CRESCENDO)

Description: European Union's Framework Programme Horizon 2020 for Research and Innovation

Keywords: 551.6 ; climate model ; evaluation ; CMIP

Type: article

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