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1.
Sensitivity of the thermohaline circulation and climate to ocean exchanges in a simple coupled model 总被引：2，自引：0，他引：2
A new simple, coupled climate model is presented and used to investigate the sensitivity of the thermohaline circulation
and climate to ocean vertical and horizontal exchange. As formulated, the model highlights the role of thin, ocean surface
layers in the communication between the atmosphere and the subsurface ocean. Model vertical exchange is considered to be an
analogue to small-scale, diapycnal mixing and convection (when present) in the ocean. Model horizontal exchange is considered
to be an analogue to the effects of the wind-driven circulation. For small vertical exchange in the ocean, the model exhibits
only one steady-state solution: a relatively cold, mid-high-latitude climate associated with a weak, salinity-driven circulation
(“off ” mode). For large vertical and horizontal exchange in the ocean, the model also exhibits only one steady-state solution:
a relatively warm, mid-high-latitude climate associated with a strong, thermally-driven circulation (“on” mode). For sufficiently
weak horizontal exchange but large enough vertical exchange, both modes are possible stable, steady-state solutions. When
model parameters are calibrated to fit tracer distributions of the modern ocean-atmosphere system, only the “on” mode is possible
in this standard case. This suggests that the wind-driven circulation in consort with diapycnal mixing suppresses the “off ”
mode in the modern ocean-atmosphere system. Since both diapycnal mixing and the wind-driven circulation would be expected
to increase in a cold climate with greater meridional temperature gradients and enhanced winds, vertical and horizontal exchange
in the ocean are probably associated with strong negative feedbacks which tend to stabilize climate. These results point to
the need to resolve ocean wind-driven circulation and to greatly improve the treatment of ocean diapycnal mixing in more complete
models of the climate system.
Received: 16 November 1999 / Accepted: 19 June 2000 相似文献
2.
Coupled ocean-atmosphere models with flux correction 总被引：11，自引：3，他引：11
A method is proposed for removing the drift of coupled atmosphere-ocean models, which in the past has often hindered the application of coupled models in climate response and sensitivity experiments. The ocean-atmosphere flux fields exhibit inconsistencies when evaluated separately for the individual sub-systems in independent, uncoupled mode equilibrium climate computations. In order to balance these inconsistencies a constant ocean-atmosphere flux correction field is introduced in the boundary conditions coupling the two sub-systems together. The method ensures that the coupled model operates at the reference climate state for which the individual model subsystems were designed without affecting the dynamical response of the coupled system in climate variability experiments. The method is illustrated for a simple two component box model and an ocean general circulation model coupled to a two layer diagnostic atmospheric model. 相似文献
3.
Gerald A. Meehl 《Climate Dynamics》1990,5(1):19-33
It has long been believed that a climate model capable of realistically simulating many features of global climate, variability, and climate change must interactively represent the major components of the dynamically coupled climate system, particularly the atmosphere, ocean, and cryosphere. This effort traditionally has been constrained by computing power, our understanding of the observed system, and climate modeling capability. With the advent of supercomputers, improved understanding of global climate processes, and computationally efficient general circulation climate models, we have witnessed a rapid increase in the simulation of global climate by coupling together various representations of atmosphere, ocean, and sea ice. Beginning in the late 1960s and continuing through the early 1980s, general circulation models (GCMs) of the atmosphere, ocean, and sea ice were coupled and run asynchronously to produce credible simulations of the global climate. Systematic errors in these component models later led some modeling groups to use flux correction or flux adjustment, whereby either one or several of the variables at the air-sea interface are adjusted to bring the simulations in closer agreement with observations. Further advances in computing power and climate modeling techniques in the past few years have allowed global coupled ocean-atmosphere GCMs to be run synchronously (i.e., atmosphere and ocean communicate at least once each model day). Computing constraints, combined with the need for multidecadal climate integrations, still only allow relatively coarse-grid ocean GCMs to be coupled to correspondingly coarse-grid atmospheric models (on the order of 500 km × 500 km). However, results from this current generation of global, coupled GCMs have revealed interesting characteristics associated with ocean dynamics and global climate in experiments with gradual increases of carbon dioxide. Another somewhat surprising aspect of the global-coupled GCM simulations is the appearance of some features associated with the El Niño-Southern Oscillation. Along with concurrent efforts with other types of limited-domain, dynamical coupled models, this has led to the realization that inherent unstable coupled modes exist in the climate system that are the unique product of the interactive coupling of the atmosphere and the ocean. All of these efforts are leading to the next generation of coupled ocean-atmosphere GCMs. These models will run on even faster and larger-memory computers and will have higher-resolution atmosphere and ocean components, more accurate sea-ice formulations, improved cloud-radiation schemes, and increasingly realistic land-surface processes.This paper was presented at the International Conference on Modelling of Global Climate Change and Variability, held in Hamburg 11–15 September 1989 under the auspices of the Meteorological Institute of the University of Hamburg and the Max Planck Institute for Meteorology. Guest Editor for these papers is Dr. L. DümenilThe National Center for Atmospheric Research is sponsored by the National Science Foundation 相似文献
4.
We report the analysis of two 20-year simulations performed with the low resolution version of the IPSL coupled ocean-atmosphere
model, with no flux correction at the air-sea interface. The simulated climate is characterized by a global sea surface temperature
warming of about 4 °C in 20 years, driven by a net heat gain at the top of the atmosphere. Despite this drift, the circulation
is quite realistic both in the ocean and the atmosphere. Several distinct periods are analyzed. The first corresponds to an
adjustment during which the heat gain weakens both at the top of the atmosphere and at the ocean surface, and the tropical
circulation is slightly modified. Then, the surface warming is enhanced by an increase of the greenhouse feedback. We show
that the mechanisms involved in the model share common features with sensitivity experiments to greenhouse gases or to SST
warming. At the top of the atmosphere, most of the longwave trapping in the atmosphere is driven by the tropical circulation.
At the surface, the reduction of longwave cooling is a direct response to increased temperature and moisture content at low
levels in the atmospheric model. During the last part of the simulation, a regulation occurs from evaporation at the surface
and longwave cooling at TOA. Most of the model drift is attributed to a too large heating by solar radiation in middle and
high latitudes. The reduction of the north–south temperature gradient, and the related changes in the meridional equator-to-pole
ocean heat transport lead to a warming of equatorial and subtropical regions. This is also well demonstrated by the difference
between the two simulations which differ only in the parametrization of sea-ice. When the sea-ice cover is not restored to
climatology the model does not maintain sea-ice at high latitudes. The climate warms more rapidly and the water vapor and
clouds feedback occurs earlier.
Received: 24 May 1996 / Accepted: 29 November 1996 相似文献
5.
A high-resolution tropical Pacific general circulation model (GCM) coupled to a global atmospheric GCM is described in this paper. The atmosphere component is the 5°×4°global general circulation model of the Institute of Atmospheric Physics (IAP) with 9 levels in the vertical direction. The ocean component with a horizontal resolution of 0.5°, is based on a low-resolution model (2°×1°in longitude-latitude).Simulations of the ocean component are first compared with its previous version. Results show that the enhanced ocean horizontal resolution allows an improved ocean state to be simulated; this involves (1) an apparent decrease in errors in the tropical Pacific cold tongue region, which exists in many ocean models,(2) more realistic large-scale flows, and (3) an improved ability to simulate the interannual variability and a reduced root mean square error (RMSE) in a long time integration. In coupling these component models, a monthly "linear-regression" method is employed to correct the model's exchanged flux between the sea and the atmosphere. A 100-year integration conducted with the coupled GCM (CGCM) shows the effectiveness of such a method in reducing climate drift. Results from years 70 to 100 are described.The model produces a reasonably realistic annual cycle of equatorial SST. The large SSTA is confined to the eastern equatorial Pacific with little propagation. Irregular warm and cold events alternate with a broad spectrum of periods between 24 and 50 months, which is very realistic. But the simulated variability is weaker than the observed and is also asymmetric in the sense of the amplitude of the warm and cold events. 相似文献
6.
A global hybrid coupled model is developed, with the aim of studying the effects of ocean-atmosphere feedbacks on the stability of the Atlantic meridional overturning circulation. The model includes a global ocean general circulation model and a statistical atmosphere model. The statistical atmosphere model is based on linear regressions of data from a fully coupled climate model on sea surface temperature both locally and hemispherically averaged, being the footprint of Atlantic meridional overturning variability. It provides dynamic boundary conditions to the ocean model for heat, freshwater and wind-stress. A basic but consistent representation of ocean-atmosphere feedbacks is captured in the hybrid coupled model and it is more than 10 times faster than the fully coupled climate model. The hybrid coupled model reaches a steady state with a climate close to the one of the fully coupled climate model, and the two models also have a similar response (collapse) of the Atlantic meridional overturning circulation to a freshwater hosing applied in the northern North Atlantic. 相似文献
7.
An acceleration scheme is proposed in a coupled ocean-atmosphere model for the simulation of long term climate evolutions forced by climate forcing of longer than millennia time scales. In this coordinated acceleration scheme, both the surface forcing and the deep ocean are accelerated simultaneously by the same factor. The acceleration scheme is evaluated in a 3-dimensional ocean general circulation model and in a coupled ocean-atmosphere model of intermediate complexity. For millennial climate evolution, our acceleration scheme produces reasonably good simulations with an acceleration factor of about 5. For climate evolution of even longer time scales, the acceleration factor can be increased further. 相似文献
8.
Stefan Rahmstorf 《Climate Dynamics》1995,11(8):447-458
A very simple, diffusive energy balance atmosphere is coupled to the GFDL ocean circulation model. This provides a useful tool for analyzing climate drift in the ocean model after coupling, and may be used to assess various schemes for minimizing such drift. In the experiment reported here, the atmosphere is constructed in such a way that it provides the ocean model at the moment of coupling with the same fluxes as during spinup. The experiment is therefore equivalent to coupling a perfectly flux-corrected atmosphere model, and is used to investigate the response of the ocean model under these conditions. In spite of the steady, passive, flux-corrected atmosphere, the ocean model drifts to a new equilibrium state after coupling. The transition takes about 2000 years; the new state is characterized by different sites of deep convection and resulting changes in high-latitude SST and global deep temperatures. The mechanism for the transition is an instability of the oceanic convection patterns under the new feedback, felt after coupling. A similar state transition of the ocean model may be triggered by the coupling shock in fully coupled GCMs. If this is so, the transition would contaminate the results of climate scenario experiments, and it would explain part of the residual drift observed in coupled models in spite of the use of flux corrections. 相似文献
9.
CMIP1 evaluation and intercomparison of coupled climate models 总被引：10，自引：1，他引：10
The climates simulated by 15 coupled atmosphere/ocean climate models participating in the first phase of the Coupled Model
Intercomparison Project (CMIP1) are intercompared and evaluated. Results for global means, zonal averages, and geographical
distributions of basic climate variables are assembled and compared with observations. The current generation of climate models
reproduce the major features of the observed distribution of the basic climate parameters, but there is, nevertheless, a considerable
scatter among model results and between simulated and observed values. This is particularly true for oceanic variables. Flux
adjusted models generally produce simulated climates which are in better accord with observations than do non-flux adjusted
models; however, some non-flux adjusted model results are closer to observations than some flux adjusted model results. Other
model differences, such as resolution, do not appear to provide a clear distinction among model results in this generation
of models. Many of the systematic differences (those differences common to most models), evident in previous intercomparison
studies are exhibited also by the CMIP1 group of models although often with reduced magnitudes. As is characteristic of intercomparison
results, different climate variables are simulated with different levels of success by different models and no one model is
“best” for all variables. There is some evidence that the “mean model” result, obtained by averaging over the ensemble of
models, provides an overall best comparison to observations for climatological mean fields. The model deficiencies identified
here do not suggest immediate remedies and the overall success of the models in simulating the behaviour of the complex non-linear
climate system apparently depends on the slow improvement in the balance of approximations that characterize a coupled climate
model. Of course, the results of this and similar studies provide only an indication, at a particular time, of the current
state and the moderate but steady evolution and improvement of coupled climate models.
Received: 26 January 2000 / Accepted: 9 June 2000 相似文献
10.
Z. Liu R. G. Gallimore J. E. Kutzbach W. Xu Y. Golubev P. Behling R. Selin 《Climate Dynamics》1999,15(5):325-340
The use of the equilibrium asynchronous coupling (EAC) scheme is proposed as a strategy to better understand long-term climate
changes in a fully coupled ocean-atmosphere general circulation model. The EAC scheme requires each component model to be
integrated to its equilibrium before being coupled to the other component. Use of this scheme has the distinct advantage of
being able to clarify the nature of the coupling between the ocean and atmosphere, because each asynchronous iteration takes
the form of a sensitivity experiment. Basic features of the EAC scheme are first studied in an energy balance model. It is
found that the convergence rate of the EAC scheme is proportional to the damping rate in the atmosphere or surface ocean,
but is inversely proportional to the coupling strength between the ocean and atmosphere. Furthermore, the seasonal cycle response
converges much faster than the annual mean response. Using realistic parameters, the seasonal cycle response should converge
in a few iterations. The EAC scheme is further applied to a coupled ocean-atmosphere general circulation model to study the
tropical monsoon climate of the early Holocene. The convergence behavior of the sea surface temperature is found to agree
with the theory derived from the energy balance model study. The EAC scheme is further used to investigate the role of ocean-atmosphere
feedback in modifying the response of monsoons to orbital forcings in the early Holocene. It is found that the ocean exerts
a positive feedback on the North African monsoon, but a negative feedback on the Indian monsoon.
Received: 16 March 1998 / Accepted: 24 December 1998 相似文献
11.
A Coupled General Circulation Model for the Tropical Pacific Ocean and Global Atmosphere 总被引：3，自引：0，他引：3
On the basis of Zeng’s theoretical design, a coupled general circulation model (CGCM) is developed with its characteristics different from other CGCMs such as the unified vertical coordinates and subtraction of the standard stratification for both atmosphere and ocean, available energy consideration, and so on. The oceanic component is a free surface tropical Pacific Ocean GCM between 30oN and 30oS with horizontal grid spacing of 1o in latitude and 2o in longitude, and with 14 vertical layers. The atmospheric component it a global GCM with low-resolution of 4o in latitude and 5o in longitude, and two layers or equal man in the vertical between the surface and 200 hPa. The atmospheric GCM includes comprehensive physical processes. The coupled model is subjected to seasonally-varying cycle. Several coupling experiments, ranging from straight forward coupling without flux correction to one with flux correction, and to so-called predictor-corrector monthly coupling (PCMC), are conducted to show the existence and final controlling of the climate drift in the coupled system. After removing the climate drift with the PCMC scheme, the coupled model is integrated for more than twenty years. The results show reasonable simulations of the annual mean and its seasonal cycle of the atmospheric and oceanic circulation. The model also produces the coherent interannual variations of the climate system, manifesting the observed El Ni?o / Southern Oscillation (ENSO). 相似文献
12.
Climate drift is a common and serious problem in most state-of-the-art coupled atmosphere-ocean-sea ice models. We consider the nature of climate drift in such a model, and in particular address the question of whether or not climate drift is inherent to the model, or whether the drift can be averted by a suitable choice of initial conditions or coupling procedure. The synchronous approach to coupling was adopted in which the ocean, atmosphere and sea ice models were spun-up independently to equilibrium using climatological forcing fields. The models were then coupled and integrated forward in time. Several experiments were performed which were designed to assess the impact of different coupling methodologies and changes in the initial conditions of the component models on the climate drift of the system. The results of our experiments indicate that climate drift is a problem inherent to the coupled model in that systematic errors in the components lead to incompatibilities in the surface fluxes required by the component models to maintain realistic climatologies. We conclude that climate drift can be averted only if the parameterizations of certain important physical processes are improved which should have the effect of reducing or eliminating these incompatibilities. 相似文献
13.
We describe a coupled climate model of intermediate complexity designed for use in global warming experiments. The atmospheric component is a two-dimensional (zonally averaged) statistical-dynamical model based on the Goddard Institute for Space Study's atmospheric general circulation model (GCM). In contrast with energy-balance models used in some climate models of intermediate complexity, this model includes full representation of the hydrological and momentum cycles. It also has parameterizations of the main physical processes, including a sophisticated radiation code. The ocean component is a coarse resolution ocean GCM with simplified global geometry based on the Geophysical Fluid Dynamics Laboratory modular ocean model. Because of the simplified geometry the resolution in the western boundary layers can be readily increased compared to conventional coarse resolution models, without increasing the model's computational requirements in a significant way. The ocean model's efficiency is also greatly increased by using a moderate degree of asynchronous coupling between the oceanic momentum and tracer fields. We demonstrate that this still allows an accurate simulation of transient behavior, including the seasonal cycle. A 100 years simulation with the model requires less than 8 hours on a state-of the art workstation. The main novelty of the model is therefore a combination of computational efficiency, statistical-dynamical atmosphere and 3D ocean. Long-term present-day climate simulations are carried out using the coupled model with and without flux adjustments, and with either the Gent-McWilliams (GM) parametrization scheme or horizontal diffusion (HD) in the ocean. Deep ocean temperatures systematically decrease in the runs without flux adjustment. We demonstrate that the mismatch between heat transports in the uncoupled states of two models is the main cause for the systematic drift. In addition, changes in the circulation and sea-ice formation also contribute to the drift. Flux adjustments in the freshwater fluxes are shown to have a stabilizing effect on the thermohaline circulation in the model, whereas the adjustments in the heat fluxes tend to weaken the global "conveyor". To evaluate the model's response to transient external forcing global warming simulations are also carried out with the flux-adjusted version of the coupled model. The coupled model reproduces reasonably well the behavior of more sophisticated coupled GCMs for both current climate and for the global warming scenarios. 相似文献
14.
In this study the global coupled atmosphere-ocean general circulation model ECHAM2/OPYC and its performance in simulating the present-day climate is presented. The model consists of the T21-spectral atmosphere general circulation model ECHAM2 and the ocean general circulation model OPYC with a resolution corresponding to a T42 Gaussian grid, with increasing resolution towards the equator. The sea-ice is represented by a dynamic thermodynamic sea-ice model with rheology. Both models are coupled using the flux correction technique. With the coupled model ECHAM2/OPYC a 210-year integration under present-day greenhouse gas conditions has been performed. The coupled model simulates a realistic mean climate state, which is close to the observations. The model generates several ENSO events without external forcing. Using traditional and advanced (POP-technique) methods these ENSO events have been analyzed. The results are consistent with the delayed action oscillator theory. The model simulates both a tropical and an extra-tropical response to ENSO, which are in good agreement with observations. 相似文献
15.
The climatology of the OPA/ARPEGE-T21 coupled general circulation model (GCM) is presented. The atmosphere GCM has a T21
spectral truncation and the ocean GCM has a 2°×1.5° average resolution. A 50-year climatic simulation is performed using the OASIS coupler, without flux correction techniques.
The mean state and seasonal cycle for the last 10 years of the experiment are described and compared to the corresponding
uncoupled experiments and to climatology when available. The model reasonably simulates most of the basic features of the
observed climate. Energy budgets and transports in the coupled system, of importance for climate studies, are assessed and
prove to be within available estimates. After an adjustment phase of a few years, the model stabilizes around a mean state
where the tropics are warm and resemble a permanent ENSO, the Southern Ocean warms and almost no sea-ice is left in the Southern
Hemisphere. The atmospheric circulation becomes more zonal and symmetric with respect to the equator. Once those systematic
errors are established, the model shows little secular drift, the small remaining trends being mainly associated to horizontal
physics in the ocean GCM. The stability of the model is shown to be related to qualities already present in the uncoupled
GCMs used, namely a balanced radiation budget at the top-of-the-atmosphere and a tight ocean thermocline.
Received: 1 February 1996 / Accepted: 1 August 1996 相似文献
16.
W. M. Connolley 《Climate Dynamics》1997,13(10):745-756
Using a hierarchy of climate models together with observations from gridded analyses, I examine the atmosphere-only and coupled
ocean-atmosphere variability in the general circulation for the region south of 40 °S. The variability in mean sea level pressure
(MSLP) is well simulated by the coupled models. A complication is that the difference between the two analyses used for verification
is comparable to the analysis-model differences. An increase in variability is seen within the hierarchy of model runs although
even a model without interannual variations in sea surface temperatures (SSTs) captures most of the observed variability.
The temporal variation in MSLP in southern high latitudes has a white spectrum consistent with “random” forcing by weather
events and a decoupling from oceanic “integration”. In contrast, the spatial pattern of MSLP variability shows large-scale
structure that is consistent between observations and various models, even without interannual variation in SSTs. This shows
that the models are sufficiently skillful to reproduce the pattern of observed variability and suggests that the pattern of
variability is a characteristic of the land-sea distribution and topography.
Received: 18 December 1996/Accepted: 23 May 1997 相似文献
17.
Impacts of shortwave radiation forcing on ENSO: a study with a coupled tropical ocean-atmosphere model 总被引：2，自引：0，他引：2
We describe a coupled tropical ocean-atmosphere model that represents a new class of models that fill the gap between anomaly
coupled models and fully coupled general circulation models. Both the atmosphere and ocean are described by two and half layer
primitive equation models, which emphasize the physical processes in the oceanic mixed layer and atmospheric boundary layer.
Ocean and atmosphere are coupled through both momentum and heat flux exchanges without explicit flux correction. The coupled
model, driven by solar radiation, reproduces a realistic annual cycle and El Nino-Southern Oscillation (ENSO). In the presence
of annual mean shortwave radiation forcing, the model exhibits an intrinsic mode of ENSO. The oscillation period depends on
the mean forcing that determines the coupled mean state. A perpetual April (October) mean forcing prolongs (shortens) the
oscillation period through weakening (enhancing) the mean upwelling and mean vertical temperature gradients. The annual cycle
of the solar forcing is shown to have fundamental impacts on the behavior of ENSO cycles through establishing a coupled annual
cycle that interacts with the ENSO mode. Due to the annual cycle solar forcing, the single spectral peak of the intrinsic
ENSO mode becomes a double peak with a quasi-biennial and a low-frequency (4–5 years) component; the evolution of ENSO becomes
phase-locked to the annual cycle; and the amplitude and frequency of ENSO become variable on an interdecadal time scale due
to interactions of the mean state and the two ENSO components. The western Pacific monsoon (the annual shortwave radiation
forcing in the western Pacific) is primarily responsible for the generation of the two ENSO components. The annual march of
the eastern Pacific ITCZ tends to lock ENSO phases to the annual cycle. The model's deficiencies, limitations, and future
work are also discussed.
Received: 15 June 1999 / Accepted: 11 December 1999 相似文献
18.
Fundamental framework and experiments of the third generation of IAP / LASG world ocean general circulation model 总被引：36，自引：8，他引：28
A new generation of the IAP / LASG world ocean general circulation model is designed and presented based on the previous 20-layer model, with enhanced spatial resolutions and improved parameterizations. The model uses a triangular-truncated spectral horizontal grid system with its zonal wave number of 63 (T63) to match its atmospheric counterpart of a T63 spectral atmosphere general circulation model in a planned coupled ocean-atmosphere system. There are 30 layers in vertical direction, of which 20 layers are located above 1000 m for better depicting the permanent thermocline. As previous ocean models developed in IAP / LASG, a free surface (rather than “rigid-lid” approximation) is included in this model. Compared with the 20-layer model, some more detailed physical parameterizations are considered, including the along / cross isopycnal mixing scheme adapted from the Gent-MacWilliams scheme. The model is spun up from a motionless state. Initial conditions for temperature and salinity are taken from the three-dimensional distributions of Levitus’ annual mean observation. A preliminary analysis of the first 1000-year integration of a control experiment shows some encouraging improvements compared with the twenty-layer model, particularly in the simulations of permanent thermocline, thermohaline circu?lation, meridional heat transport, etc. resulted mainly from using the isopycnal mixing scheme. However, the use of isopycnal mixing scheme does not significantly improve the simulated equatorial thermocline. A series of numerical experiments show that the most important contribution to the improvement of equatori?al thermocline and the associated equatorial under current comes from reducing horizontal viscosity in the equatorial regions. It is found that reducing the horizontal viscosity in the equatorial Atlantic Ocean may slightly weaken the overturning rate of North Atlantic Deep Water. 相似文献
19.
Studies of climate change 6,000 years before present using atmospheric general circulation models (AGCMs) suggest the enhancement
and northward shift of the summer Asian and African monsoons in the Northern Hemisphere. Although enhancement of the African
monsoonal precipitation by ocean coupling is a common and robust feature, contradictions exist between analyses of the role
of the ocean in the strength of the Asian monsoon. We investigated the role of the ocean in the Asian monsoon and sought to
clarify which oceanic mechanisms played an important role using three ocean coupling schemes: MIROC, an atmosphere–ocean coupled
general circulation model [C]; an AGCM extracted from MIROC coupled with a mixed-layer ocean model [M]; and the same AGCM,
but with prescribed sea surface temperatures [A]. The effect of “ocean dynamics” is quantified through differences between
experiments [C] and [M]. The effect of “ocean thermodynamics” is quantified through differences between experiments [M] and
[A]. The precipitation change for the African and Asian monsoon area suggested that the ocean thermodynamics played an important
role. In particular, the enhancement of the Asian monsoonal precipitation was most vigorous in the AGCM simulations, but mitigated
in early summer in ocean coupled cases, which were not significantly different from each other. The ocean feedbacks were not
significant for the precipitation change in late summer. On the other hand, in Africa, ocean thermodynamics contributed to
the further enhancement of the precipitation from spring to autumn, and the ocean dynamics had a modest impact in enhancing
precipitation in late summer. 相似文献
20.
Simulated Spatiotemporal Response of Ocean Heat Transport to Freshwater Enhancement in North Atlantic and Associated Mechanisms 
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下载免费PDF全文 The Atlantic Meridional Overturning Circulation(AMOC)transports a large amount of heat to northern high latitudes,playing an important role in the global climate change.Investigation of the freshwater perturbation in North Atlantic(NA)has become one of the hot topics in the recent years.In this study,the mechanism and pathway of meridional ocean heat transport(OHT)under the enhanced freshwater input to the northern high latitudes in the Atlantic are investigated by an ocean-sea ice-atmosphere coupled model.The results show that the anomalous OHT in the freshwater experiment(FW)is dominated by the meridional circulation kinetic and ocean thermal processes.In the FW,OHT drops down during the period of weakened AMOC while the upper tropical ocean turns warmer due to the retained NA warm currents.Conversely,OHT recovers as the AMOC recovers,and the mechanism can be generalized as:1)increased ocean heat content in the tropical Southern Ocean during the early integration provides the thermal condition for the recovery of OHT in NA;2)the OHT from the Southern Ocean enters the NA through the equator alongthe deep Ekman layer;3)in NA,the recovery of OHT appears mainly along the isopycnic layers of 24.70-25.77 below the mixing layer.It is then transported into the mixing layer from the "outcropping points"innorthern high latitudes,and finally released to the atmosphere by the ocean-atmosphere heat exchange. 相似文献