共查询到20条相似文献，搜索用时 31 毫秒
1.
R. Bintanja 《Theoretical and Applied Climatology》1997,56(1-2):1-24
Summary In this paper a simple climate model is presented which is used to perform some sensitivity experiments. The atmospheric part is represented by a vertically and zonally averaged layer in which the surface air temperature, radiative fluxes at the surface and at the top of the atmosphere, the turbulent fluxes between atmosphere and surface and the snow cover are calculated. This atmospheric layer is coupled to a two-dimensional advection-diffusion ocean model in which the zonal overturning pattern is prescribed. The ocean model evaluates the temperature distribution, the amount of sea-ice and the meridional and vertical heat fluxes. The present-day climate simulated by the model compares reasonably well with observations of the seasonal and latitudinal distribution of temperature, radiation, surface alebdo, sea-ice and snow cover and meridional energy fluxes. Then, the sensitivity of the model-simulated present-day climate to perturbations in the incident solar radiation at the top of the atmosphere is investigated. The temperature response displays large latitudinal and seasonal variations, which is in qualitative agreement with results obtained with other climate models. It is found that the seasonal variation of sea-ice cover (and hence, the effective oceanic heat capacity) is one of the most important elements determining seasonal variations in climate sensitivity. Differences in sensitivity between the seasonal and annual mean version of the model are discussed. Finally, the equilibrium response to perturbations in some selected model variables is presented; these variables include meridional diffusion coefficients, drag coefficient, sea-ice thickness, atmospheric CO2-concentration and cloud optical thickness.With 13 Figures 相似文献
2.
In the present paper the effect of an abrupt change of the atmospheric radiative forcing is investigated by means of a global climate model that includes a mixed layer ocean. In assessing if, under such a change, the model response has a bifurcation point, the steady solution is studied for a sudden decrease of CO2 concentration from its actual value. It is found that there is a critical threshold for CO2 content below which the model ends up to a snowball Earth. It occurs for a few percentage changes of CO2 concentration around the threshold because the model strongly depends on the relationship among atmospheric temperature, water vapor content and the sudden ice-albedo feedback activation, even in the subtropical regions. Moreover, results suggest that the transition to ice-covered Earth is clearly favoured when Q-flux corrections (i.e. the parameterization of ocean heat transports) are removed. 相似文献
3.
The increase of atmospheric CO2 concentrations due to anthropogenic activities is substantially damped by the ocean, whose CO2 uptake is determined by the state of the ocean, which in turn is influenced by climate change. We investigate the mechanisms of the ocean’s carbon uptake within the feedback loop of atmospheric CO2 concentration, climate change and atmosphere/ocean CO2 flux. We evaluate two transient simulations from 1860 until 2100, performed with a version of the Max Planck Institute Earth System Model (MPI-ESM) with the carbon cycle included. In both experiments observed anthropogenic CO2 emissions were prescribed until 2000, followed by the emissions according to the IPCC Scenario A2. In one simulation the radiative forcing of changing atmospheric CO2 is taken into account (coupled), in the other it is suppressed (uncoupled). In both simulations, the oceanic carbon uptake increases from 1 GT C/year in 1960 to 4.5 GT C/year in 2070. Afterwards, this trend weakens in the coupled simulation, leading to a reduced uptake rate of 10% in 2100 compared to the uncoupled simulation. This includes a partial offset due to higher atmospheric CO2 concentrations in the coupled simulation owing to reduced carbon uptake by the terrestrial biosphere. The difference of the oceanic carbon uptake between both simulations is primarily due to partial pressure difference and secondary to solubility changes. These contributions are widely offset by changes of gas transfer velocity due to sea ice melting and wind changes. The major differences appear in the Southern Ocean (?45%) and in the North Atlantic (?30%), related to reduced vertical mixing and North Atlantic meridional overturning circulation, respectively. In the polar areas, sea ice melting induces additional CO2 uptake (+20%). 相似文献
4.
The OSU global coupled atmosphere-ocean general circulation model has been used to investigate a 2xCO2-induced climate change. A previous analysis of the simulated 2xCO2–1xCO2 temperature differences showed that the CO2-induced warming penetrated into the ocean and thereby caused a delay in the equilibration of the climate system with an estimatede-folding time of 50–75 years. The objective of the present study is to determine by what pathways and through which physical processes the simulated ocean general circulation produces the penetration of the CO2-induced warming into the ocean.A global-mean oceanic heat budget analysis shows that the ocean gains heat at a rate of 3 W/m2 due to the CO2 doubling, and that this heat penetrates downward into the ocean predominantly through the reduction in the convective overturning. A zonal-mean oceanic heat budget analysis shows that the surface warming increases from the tropics toward the midlatitudes of both hemispheres and gradually penetrated into the deeper ocean, with a greater penetration in the subtropics and midlatitudes than in the equatorial region. The zonal-mean heat budget analysis also shows that the CO2-induced warming of the ocean occurs predominantly through the down-ward transport of heat, with the meridional heat flux being only of secondary importance. In the tropics the penetration of the CO2-induced heating is minimized by the upwelling of cold water. In the subtropics the heating is transported down-ward more readily by the downwelling existing there. In the high latitudes the suppressed convection plays the dominant role in the downward penetration of the CO2-induced heating. The latter result should be considered as tentative, however, as the ocean component of the coupled model employed a prescribed surface salinity field and did not include the mechanism of brine rejection when sea water freezes into sea ice. 相似文献
5.
Parametrisations of meridional energy and moisture transport used in zonally averaged climate models are validated using
reanalysis data and results from a doubling CO2-experiment from a general circulation model. Global meridional fluxes of moisture and sensible heat are calculated by integrating
surface and top-of-the-atmosphere vertical fluxes from one pole to the other. The parametrisations include an eddy-diffusion
term, representing down-gradient transport of specific humidity and temperature due to the transient atmospheric eddies at
mid- and high latitudes, and simple representations of the mean meridional circulation. Qualitative and quantitative agreement
between the increased hydrological cycle in the 2×CO2-run from the GCM and the parametrisation is found. The performance for the sensible heat flux shows larger differences to
the GCM results, particularly at low latitudes. Seasonal variations of the moisture and sensible heat transport are well captured
by parametrisations including the influence of the mean meridional circulation. Interannual variability cannot be simulated.
An examination of the parametrisations on different spatial scales suggests that they should not be used for small scales.
Furthermore, two closures for the zonal distribution of precipitation were examined. They are used in zonally averaged atmosphere
models coupled to an ocean model with different ocean basins at one latitudinal belt. An assessment of both the reanalysis
data and the GCM results shows that both closures exhibit very similar behaviour and are valid in the long-term mean and seasonal
cycle. Interannual variability is not captured well. They become invalid for spatial scales smaller than 10∘.
Received: 30 November 1998 / Accepted: 4 July 1999 相似文献
6.
The meridional energy flux modelled by the Bureau of Meteorology Research Centre general circulation model is examined. It is divided into atmospheric and oceanic components, and the resolved atmospheric components in turn into mean and eddy circulations. Comparison with observations shows the modelled total planetary meridional energy transport to be low, but shows better agreement for the resolved atmospheric component alone. The overall patterns of the individual circulation and energy components of the model also agree well, although strengths and locations do show some discrepancies. The doubled CO2 climate change is analyzed in terms of the changes in each of the circulation and energy components. It is found that the changes are the relatively small residual of larger, and generally opposing changes in sensible heat and potential energy fluxes. Despite the general decrease in poleward energy flux, the poleward latent heat flux is found to increase. The reduction in poleward transport is found to be dominated by changes in the mean meridional circulation at low southern latitudes, and changes in both mean circulations and eddy fluxes elsewhere. 相似文献
7.
James R. Miller Gary L. Russell Lie-Ching Tsang 《Dynamics of Atmospheres and Oceans》1983,7(2):95-109
Mean annual estimates of the oceanic poleward energy transport are obtained using a global atmospheric general circulation model. The computations are carried out by using the atmospheric model to determine the net annual heat flux into the ocean on an 8° × 10° grid. Assuming no net annual heat storage, the annual surface heat fluxes into any zonal band must be accompanied by a corresponding meridional heat transport in the ocean. Heat is transported northward at all latitudes in the Atlantic Ocean and is transported poleward in both hemispheres in the Pacific Ocean. To account for the net northward transport throughout the Atlantic, heat is transported into the Atlantic from the Indian and Pacific basins. The results are compared with several recent direct and indirect calculations of oceanic meridional heat transports. 相似文献
8.
A three-dimensional, coupled atmosphere-ocean general circulation model is developed and effects of the seasonal variation
on forming a steady-state coupled atmosphere-ocean system are studied. Case studies are carried out for a basin of idealized
geometry by changing the period of the seasonal variation in the solar forcing. The coupled system shows significant differences
depending on the existence of the seasonal variation, where the heat transport by the oceanic circulation plays a central
role. For the regular seasonal variation, a stronger oceanic meridional circulation, which accompanies larger poleward heat
transport, is realized compared with that for the annual-mean solar forcing. The stronger meridional circulation is associated
with a larger wintertime meridional gradient of the sea surface temperature. The meridional gradient of the annual-mean sea
surface temperature is smaller for the regular seasonal variation, which results in a smaller atmospheric poleward heat transport.
In consequence, the total of the atmospheric and the oceanic poleward heat transport is almost identical for the two cases.
Cases with the seasonal variation of the doubled period and with the time-filtered flux exchange between the atmosphere and
the ocean are also studied, showing that the system is not sensitive to those factors. 相似文献
9.
S. L. Weber 《Climate Dynamics》1998,14(3):201-212
The sensitivity of a coupled model to the oceanic vertical diffusion coefficient κ
v
is examined. This is compared to the sensitivity of an ocean-only model forced by mixed boundary conditions (BC). The atmospheric
component of the coupled model is a moist energy balance model. The ocean component is a 12-level geostrophic model, defined
on a midlatitude β-plane. Atmosphere and ocean are coupled through the fluxes of heat and moisture at their interface. The
coupled model contains a number of feedback processes which are not represented in the ocean-only model. This results in a
temperature and salinity response to κ
v
which is stronger in the coupled model than in the ocean-only model. On the other hand, there is a weaker response in oceanic
processes such as meridional heat transport, deep-water formation at high latitudes, etc. Ocean-only sensitivity experiments
were also performed with modified BCs, which parametrise the feedback processes included in the coupled model. These are the
modified thermal BC of Rahmstorf and Willebrand and a modified freshwater BC proposed in the present study. Large-scale features
of the response in oceanic surface fields are well represented with modified BCs. However, the sensitivity of the deep ocean
temperature is only partly captured due to local differences in the surface response. The scaling behavior of the zonal overturning
stream function was found to depend on the surface BCs. In contrast to this, the meridional overturning stream function basically
scales with κ0.5
v
in all sensitivity experiments. Differences in the heat transport response among the experiments are thus primarily related
to differences in the temperature response.
Received: 28 February 1997/Accepted: 12 September 1997 相似文献
10.
The uptake and storage of anthropogenic carbon in the North Atlantic is investigated using different configurations of ocean
general circulation/carbon cycle models. We investigate how different representations of the ocean physics in the models,
which represent the range of models currently in use, affect the evolution of CO2 uptake in the North Atlantic. The buffer effect of the ocean carbon system would be expected to reduce ocean CO2 uptake as the ocean absorbs increasing amounts of CO2. We find that the strength of the buffer effect is very dependent on the model ocean state, as it affects both the magnitude
and timing of the changes in uptake. The timescale over which uptake of CO2 in the North Atlantic drops to below preindustrial levels is particularly sensitive to the ocean state which sets the degree
of buffering; it is less sensitive to the choice of atmospheric CO2 forcing scenario. Neglecting physical climate change effects, North Atlantic CO2 uptake drops below preindustrial levels between 50 and 300 years after stabilisation of atmospheric CO2 in different model configurations. Storage of anthropogenic carbon in the North Atlantic varies much less among the different
model configurations, as differences in ocean transport of dissolved inorganic carbon and uptake of CO2 compensate each other. This supports the idea that measured inventories of anthropogenic carbon in the real ocean cannot
be used to constrain the surface uptake. Including physical climate change effects reduces anthropogenic CO2 uptake and storage in the North Atlantic further, due to the combined effects of surface warming, increased freshwater input,
and a slowdown of the meridional overturning circulation. The timescale over which North Atlantic CO2 uptake drops to below preindustrial levels is reduced by about one-third, leading to an estimate of this timescale for the
real world of about 50 years after the stabilisation of atmospheric CO2. In the climate change experiment, a shallowing of the mixed layer depths in the North Atlantic results in a significant
reduction in primary production, reducing the potential role for biology in drawing down anthropogenic CO2. 相似文献
11.
We analyze the sensitivity of the oceanic thermohaline circulation (THC) regarding perturbations in fresh water flux for a range of coupled oceanic general circulation — atmospheric energy balance models. The energy balance model (EBM) predicts surface air temperature and fresh water flux and contains the feedbacks due to meridional transports of sensible and latent heat. In the coupled system we examine a negative perturbation in run-off into the southern ocean and analyze the role of changed atmospheric heat transports and fresh water flux. With mixed boundary conditions (fixed air temperature and fixed surface fresh water fluxes) the response is characterized by a completely different oceanic heat transport than in the reference case. On the other hand, the surface heat flux remains roughly constant when the air temperature can adjust in a model where no anomalous atmospheric transports are allowed. This gives an artificially stable system with nearly unchanged oceanic heat transport. However, if meridional heat transports in the atmosphere are included, the sensitivity of the system lies between the two extreme cases. We find that changes in fresh water flux are unimportant for the THC in the coupled system. 相似文献
12.
A global, flux-corrected climate model is employed to predict the surface wind stress and associated wind-driven oceanic circulation
for climate states corresponding to a doubling and quadrupling of the atmospheric CO2 concentration in a simple 1% per year CO2 increase scenario. The model indicates that in response to CO2 increase, the position of zero wind stress curl in the mid-latitudes of the Southern Hemisphere shifts poleward. In addition,
the wind stress intensifies significantly in the mid-latitudes of the Southern Hemisphere. As a result, the rate of water
circulation in the subpolar meridional overturning cell in the Southern Ocean increases by about 6 Sv (1 Sv=106 m3 s−1) for doubled CO2 and by 12 Sv for quadrupled CO2, implying an increase of deep water upwelling south of the circumpolar flow and an increase of Ekman pumping north of it.
In addition, the changes in the wind stress and wind stress curl translate into changes in the horizontal mass transport,
leading to a poleward expansion of the subtropical gyres in both hemispheres, and to strengthening of the Antarctic Circumpolar
Current. Finally, the intensified near-surface winds over the Southern Ocean result in a substantial increase of mechanical
energy supply to the ocean general circulation. 相似文献
13.
Using a global carbon cycle model (GLOCO) that considers seven terrestrial biomes, surface and deep ocean layers based on the HILDA model and a single mixed atmosphere, we analyzed the response of atmospheric CO2 concentration and oceanic DIC and DOC depth profiles to additions of carbon to the atmosphere and ocean. The rate of transport of carbon to the deepest oceanic layers is rather insensitive to the atmosphereic-ocean surface gas exchange coefficient over a wide range, hence discrepancies between researchers on the precise global average value of this coefficient do not significantly affect predictions of atmospheric response to anthropogenic inputs. Upwelling velocity, on the other hand, amplifies oceanic response by increasing primary production in the upper ocean layers, resulting in a larger flux into DOC and sediments and increased carbon storage; experiments to reduce the uncertainty in this parameter would be valuable.The location of the carbon addition, whether it is released in the atmosphere or in the middle of the oceanic thermocline, has a significant impact on the maximum atmospheric CO2 concentration (pCO2) subsequently reached, suggesting that oceanic burial of a significant fraction of carbon emissions (e.g. via clathrate hydrides) may be an important management option for limiting pCO2 buildup. Our analysis indicates that the effectiveness of ocean burial decreases asymptotically below about 1000 m depth. With a constant emissions scenario (at 1990 levels), pCO2 at year 2100 is reduced from 501 ppmv considering all emissions go to the atmosphere, to 422 ppmv with ocean burial at a depth of 1000 m of 50% of the fossil fuel emissions. An alternative scenario looks at stabilizing pCO2 at 450 ppmv; with no ocean burial of fossil fuel emissions, the rate of emissions has to be cut drastically after the year 2010, whereas oceanic burial of 2 GtC/yr allows for a smoother transition to alternative energy sources. 相似文献
14.
A two-dimensional carbon cycle model is divided into three zones representing equatorial, middle and high latitude regions. The three zones are coupled together by a deep ocean meridional convective cell and atmospheric transport terms. The model is applied to the calculation of the dispersion of radiocarbon and tritium from nuclear weapons tests, to the calculation of the atmospheric record of bomb radiocarbon and to the calculation of the Mauna Loa record of atmospheric CO2. Calibrating on the basis of the Northern hemisphere bomb test data yields a model which has approximately twice the CO2 ocean uptake of the one-dimension box diffusion models calibrated on the basis of deep water equilibrium carbon 14.Work performed under the auspices of the U.S. Department of Energy by the Lawrence Livermore Laboratory under contract No. W-7405-ENG-78. 相似文献
15.
16.
T. M. Lenton M. S. Williamson N. R. Edwards R. Marsh A. R. Price A. J. Ridgwell J. G. Shepherd S. J. Cox 《Climate Dynamics》2006,26(7-8):687-711
A new Earth system model, GENIE-1, is presented which comprises a 3-D frictional geostrophic ocean, phosphate-restoring marine biogeochemistry, dynamic and thermodynamic sea-ice, land surface physics and carbon cycling, and a seasonal 2-D energy-moisture balance atmosphere. Three sets of model climate parameters are used to explore the robustness of the results and for traceability to earlier work. The model versions have climate sensitivity of 2.8–3.3°C and predict atmospheric CO2 close to present observations. Six idealized total fossil fuel CO2 emissions scenarios are used to explore a range of 1,100–15,000 GtC total emissions and the effect of rate of emissions. Atmospheric CO2 approaches equilibrium in year 3000 at 420–5,660 ppmv, giving 1.5–12.5°C global warming. The ocean is a robust carbon sink of up to 6.5 GtC year−1. Under ‘business as usual’, the land becomes a carbon source around year 2100 which peaks at up to 2.5 GtC year−1. Soil carbon is lost globally, boreal vegetation generally increases, whilst under extreme forcing, dieback of some tropical and sub-tropical vegetation occurs. Average ocean surface pH drops by up to 1.15 units. A Greenland ice sheet melt threshold of 2.6°C local warming is only briefly exceeded if total emissions are limited to 1,100 GtC, whilst 15,000 GtC emissions cause complete Greenland melt by year 3000, contributing 7 m to sea level rise. Total sea-level rise, including thermal expansion, is 0.4–10 m in year 3000 and ongoing. The Atlantic meridional overturning circulation shuts down in two out of three model versions, but only under extreme emissions including exotic fossil fuel resources. 相似文献
17.
J. Bendtsen 《Climate Dynamics》2002,18(7):595-609
A simple coupled ocean, atmosphere and sea-ice model is presented. The idealised model consists of a zonally averaged land and ocean strip of constant angular width extending from pole to pole. The meridional energy transport in the ocean is modelled by contributions from the large scale thermohaline overturning cells and from horizontal diffusive fluxes. The atmospheric meridional energy transports are parametrised as diffusive fluxes in addition to advective transports in the Hadley domain. This parametrisation resolves the equatorward moisture transport as well as the poleward transport of potential energy in the upper branch of the Hadley circulation. The model reproduces the annual averaged meridional energy transports in the climate system with a small number of free model parameters. The basic feedbacks between the three climatic components are studied by investigating the model's sensitivity towards reductions in the solar insolation. It is found that the meridional energy transport in the ocean does not amplify the ice albedo feedback. This has important implications for modelling the climate sensitivity in atmosphere-only models, as these would exaggerate the sensitivity to changes in the solar insolation if their parametrisations of the meridional energy transport are constrained by surface temperatures. The role of the dependence of the atmospheric transports on the meridional temperature gradient is shown to have a significant influence on the sensitivity on the coupled model, and the inclusion of seasonal cycles greatly increase the models sensitivity. The Hadley circulation does significantly alter the strength of the ice-albedo feedback in the coupled model. The idealised configuration of the model makes it a useful tool for studying the feedbacks in the ocean-atmosphere-sea ice system in the context of the "Snowball Earth" hypothesis. 相似文献
18.
In this study we investigate the role of heat, freshwater and momentum fluxes in changing the oceanic climate and thermohaline
circulation as a consequence of increasing atmospheric CO2 concentration. Two baseline integrations with a fully coupled ocean atmosphere general circulation model with either fixed
or increasing atmospheric CO2 concentrations have been performed. In a set of sensitivity experiments either freshwater (precipitation, evaporation and
runoff from the continents) and/or momentum fluxes were no longer simulated, but prescribed according to one of the fully
coupled baseline experiments. This approach gives a direct estimate of the contribution from the individual flux components.
The direct effect of surface warming and the associated feedbacks in ocean circulation are the dominant processes in weakening
the Atlantic thermohaline circulation in our model. The relative contribution of momentum and freshwater fluxes to the total
response turned out to be less than 25%, each. Changes in atmospheric water vapour transport lead to enhanced freshwater input
into middle and high latitudes, which weakens the overturning. A stronger export of freshwater from the Atlantic drainage
basin to the Indian and Pacific ocean, on the other hand, intensifies the Atlantic overturning circulation. In total the modified
freshwater fluxes slightly weaken the Atlantic thermohaline circulation. The contribution of the modified momentum fluxes
has a similar magnitude, but enhances the formation of North Atlantic deep water. Salinity anomalies in the Atlantic as a
consequence of greenhouse warming stem in almost equal parts from changes in net freshwater fluxes and from changes in ocean
circulation caused by the surface warming due to atmospheric heat fluxes. Important effects of the momentum fluxes are a poleward
shift of the front between Northern Hemisphere subtropical and subpolar gyres and a southward shift in the position of the
Antarctic circumpolar current, with a clear signal in sea level.
Received: 3 May 1999 / Accepted: 11 December 1999 相似文献
19.
Gary L. Russell James R. Miller Lie-Ching Tsang 《Dynamics of Atmospheres and Oceans》1985,9(3):253-271
Seasonal estimates of the oceanic poleward heat transport are obtained using a climate model that is a global atmospheric general circulation model on an 8° × 10° grid. The climate model is used to calculate the surface heat flux into each ocean grid point for each day of the year. The rate of ocean heat storage is calculated using climatological surface temperatures, mixed layer depths, and ice amounts. By assuming that the rate of change of heat storage in the deep ocean is spatially constant, the horizontal transports are calculated from the vertical fluxes and the upper ocean storage rates. The oceanic meridional transport for each latitude and for each ocean basin are derived, and results are compared with other calculations of the seasonal transports. In the Northern Hemisphere, comparisons between the simulated seasonal transports indicate that the annual variation is much greater in the Pacific than in the Atlantic. 相似文献
20.
S. J. Kim 《Climate Dynamics》2004,22(6-7):639-651
The role of reduced atmospheric CO2 concentration and ice sheet topography plus its associated land albedo on the LGM climate is investigated using a coupled atmosphere-ocean-sea ice climate system model. The surface cooling induced by the reduced CO2 concentration is larger than that by the ice sheet topography plus other factors by about 30% for the surface air temperature and by about 100% for the sea surface temperature. A large inter-hemispheric asymmetry in surface cooling with a larger cooling in the Northern Hemisphere is found for both cases. This asymmetric inter-hemispheric temperature response is consistent in the ice sheet topography case with earlier studies using an atmospheric model coupled with a mixed-layer ocean representation, but contrasts with these results in the reduced CO2 case. The incorporation of ocean dynamics presumably leads to a larger snow and sea ice feedback as a result of the reduction in northward ocean heat transport, mainly as a consequence of the decrease in the North Atlantic overturning circulation by the substantial freshening of the North Atlantic convection regions. A reversed case is found in the Southern Ocean. Overall, the reduction in atmospheric CO2 concentration accounts for about 60% of the total LGM climate change. 相似文献