共查询到20条相似文献,搜索用时 31 毫秒
1.
The stability properties of a seasonal, one dimensional energy balance climate model are examined. The model contains idealized landsea geography, an interactive moving snowline and high space-time resolution. For a polar land cap surrounded by ocean we find a bifurcation in the seasonal cycle solutions as a function of solar constant leading to qualitatively different climate regimes: one with continental snow-free summers and the other with perennial snow cover over a large area surrounding the pole. In the parameterspace neighborhood of a bifurcation an infinitesimal change in any radiation budget parameter can cause the transition from one state to the other. Of special interest to those planning more elaborate numerical experiments (GCMs) is the result that 10s of seasonal cycles may be necessary for the model to damp out transient effects before settling upon a repeating seasonal cycle if parameter values are such that the solution is near a bifurcation. This latter finding is unexpected, since the longest time scale in the linear version of the energy balance model is about 5 years. 相似文献
2.
Much work has gone into deciphering the causes of the large scale glacial/interglacial variations in the climate system over the last 900 000 years. While variations on the 41 thousand year (ky) and 23 ky time scales seem to be linearly linked to the variations in the distribution of solar radiation at the top of the atmosphere, Milankovitch solar radiation variations, the causes of the dominant 100 ky cycle in the geologic record are still unknown. One of the aspects of this cycle that is not well understood is how large scale ice sheet growth is initiated. Here we describe the mechanisms by which large scale ice sheet growth may have been initiated by the changes in the seasonal and latitudinal distribution of solar radiation over the past 160 ky. This is done through the use of a coupled energy balance climate-thermodynamic sea ice model that includes a hydrologic cycle which computes precipitation, and a land surface energy balance which determines the net accumulation of snow and ice. Results indicate that the initiation of ice sheet growth is possible during times of extremely low summer solstice solar radiation as a result of a large decrease in ablation during the critical melt season. 相似文献
3.
L. D. Danny Harvey 《Climatic change》1988,13(2):191-224
A seasonal energy balance climate model containing a detailed treatment of surface and planetary albedo, and in which seasonally varying land snow and sea ice amounts are simulated in terms of a number of explicit physical processes, is used to investigate the role of high latitude ice, snow, and vegetation feedback processes. Feedback processes are quantified by computing changes in radiative forcing and feedback factors associated with individual processes. Global sea ice albedo feedback is 5–8 times stronger than global land snowcover albedo feedback for a 2% solar constant increase or decrease, with Southern Hemisphere cryosphere feedback being 2–5 times stronger than Northern Hemisphere cryosphere feedback.In the absence of changes in ice extent, changes in ice thickness in response to an increase in solar constant are associated with an increase in summer surface melting which is exactly balanced by increased basal winter freezing, and a reduction in the upward ocean-air flux in summer which is exactly balanced by an increased flux in winter, with no change in the annual mean ocean-air flux. Changes in the mean annual ocean-air heat flux require changes in mean annual ice extent, and are constrained to equal the change in meridional oceanic heat flux convergence in equilibrium. Feedback between ice extent and the meridional oceanic heat flux obtained by scaling the oceanic heat diffusion coefficient by the ice-free fraction regulates the feedback between ice extent and mean annual air-sea heat fluxes in polar regions, and has a modest effect on model-simulated high latitude temperature change.Accounting for the partial masking effect of vegetation on snow-covered land reduces the Northern Hemisphere mean temperature response to a 2% solar constant decrease or increase by 20% and 10%, respectively, even though the radiative forcing change caused by land snowcover changes is about 3 times larger in the absence of vegetational masking. Two parameterizations of the tundra fraction are tested: one based on mean annual land air temperature, and the other based on July land air temperature. The enhancement of the mean Northern Hemisphere temperature response to solar constant changes when the forest-tundra ecotone is allowed to shift with climate is only 1/3 to 1/2 that obtained by Otterman et al. (1984) when the mean annual parameterization is used here, and only 1/4 to 1/3 as large using the July parameterization.The parameterized temperature dependence of ice and snow albedo is found to enhance the global mean temperature response to a 2% solar constant increase by only 0.04 °C, in sharp contrast to the results of Washington and Meehl (1986) obtained with a mean annual model. However, there are significant differences in the method used here and in Washington and Meehl to estimate the importance of this feedback process. When their approach is used in a mean annual version of the present model, closer agreement to their results is obtained. 相似文献
4.
For over twenty years it has been known that energy balance models (EBMs) with snow-albedo feedback are characterized by unstable behavior in some areas of parameter space. This behavior leads to rapid changes in snow area due to small changes in forcing, and has been termed the small ice cap instability (SICI). It has never been clarified whether this behaviour reflects a real feature of the climate system or a limitation in EBMs. In this study we demonstrate that evidence for similar unstable behavior can also be found in an atmospheric general circulation model (GCM), using a realistic set of boundary conditions for the Carboniferous (300 Ma), one of the most extensive periods of glaciation in Earth history. When solar luminosity is sequentially lowered to near values appropriate for the Carboniferous, there is a discontinuous increase in summer snow area. The instability occurs in approximately the same area of parameter space as one previously found in an EBM. Analysis of selected fields indicates that the circulation is primarily affected in the area of snow increase; far-field effects are minimal. There is good agreement between model-generated summer snowcover and one reconstruction of Carboniferous ice cover. Although more work is required on this topic, our results provide increased support for the possibility that the snowline instability represents a real feature of the climate system, and that it may help explain some cases of glacial inception and abrupt transitions in Earth history. 相似文献
5.
Stephen G. Warren 《Climatic change》1982,4(4):329-340
The growth and decay of ice sheets are driven by forces affecting the seasonal cycles of snowfall and snowmelt. The external forces are likely to be variations in the earth's orbit which cause differences in the solar radiation received. Radiational control of snowmelt is modulated by the seasonal cycles of snow albedo and cloud cover. The effects of orbital changes can be magnified by feedbacks involving atmospheric CO2 content, ocean temperatures and desert areas. Climate modeling of the causes of the Pleistocene ice ages involves modeling the interactions of all components of the climate system; snow, sea ice, glacier ice, the ocean, the atmosphere, and the solid earth. Such modeling is also necessary for interpreting oxygen isotope records from ice and ocean as paleoclimatic evidence. 相似文献
6.
Sea ice formed over shallow Arctic shelves often entrains sediments resuspended from the sea floor. Some of this sediment-laden ice advects offshore into the Transpolar Drift Stream and the Beaufort Gyre of the Arctic Basin. Through the processes of seasonal melting at the top surface, and the freezing of clean ice on the bottom surface, these sediments tend, over time, to concentrate at the top of the ice where they can affect the surface albedo, and thus the absorbed solar radiation, when the ice is snow free. Similarly, wind-blown dust can reduce the albedo of snow. The question that is posed by this study is what is the impact of these sediments on the seasonal variation of sea ice, and how does it then affect climate? Experiments were conducted with a coupled energy balance climate-thermodynamic sea ice model to examine the impact of including sediments in the sea ice alone and in the sea ice and overlying snow. The focus of these experiments was the impact of the radiative and not the thermal properties of the sediments. The results suggest that if sea ice contains a significant amount of sediments which are covered by clean snow, there is only a small impact on the climate system. However, if the snow also contains significant sediments the impact on sea ice thickness and surface air temperature is much more significant. 相似文献
7.
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
8.
Solar radiation cycles, earth-orbital changes, and continental drift drive long to very long term (103–106 years) climatic changes. Lin and North used the stationary solutions of a simple energy balance model (EBM) to study the equilibrium climatic stages. In this paper, we study time dependent solutions and, in particular, transition processes. We make use of two time scales: a seasonal cycle (fast variation) and a long term time change (slow variation). Variations over short time scales are solved using a Fourier transform in time and long term variations are studied using a 4th order Runge-Kutta method. The energy balance equation is a parabolic type equation and it is well posed. Climate changes depend mainly on external forcing and the state of the climate is determined by the slow time scale forcing. In other words, transitions from one climate stage (snow-covered) to another (snow-free) at bifurcation points are monotonic, despite 20% to 50% shortperiod random fluctuations in the solar energy. This smooth transition is especially noticeable when the land bands lie close to the north pole (70° N to 90° N) or at high latitudes (50° N to 75° N).Now at Applied Physics Laboratory, The Johns Hopkins University, Laurel, MD 20723, USA 相似文献
9.
CLIMBER-2: a climate system model of intermediate complexity. Part I: model description and performance for present climate 总被引:10,自引:5,他引:5
V. Petoukhov A. Ganopolski V. Brovkin M. Claussen A. Eliseev C. Kubatzki S. Rahmstorf 《Climate Dynamics》2000,16(1):1-17
A 2.5-dimensional climate system model of intermediate complexity CLIMBER-2 and its performance for present climate conditions
are presented. The model consists of modules describing atmosphere, ocean, sea ice, land surface processes, terrestrial vegetation
cover, and global carbon cycle. The modules interact through the fluxes of momentum, energy, water and carbon. The model has
a coarse spatial resolution, nevertheless capturing the major features of the Earth's geography. The model describes temporal
variability of the system on seasonal and longer time scales. Due to the fact that the model does not employ flux adjustments
and has a fast turnaround time, it can be used to study climates significantly different from the present one and to perform
long-term (multimillennia) simulations. The comparison of the model results with present climate data show that the model
successfully describes the seasonal variability of a large set of characteristics of the climate system, including radiative
balance, temperature, precipitation, ocean circulation and cryosphere.
Received: 12 January 1998 / Accepted: 2 July 1999 相似文献
10.
A large nuclear war could produce massive quantities of smoke from burning cities and industries. A portion of this smoke would fall out on Arctic sea ice, thus lowering its albedo and potentially increasing the solar energy absorbed by the ice and the snow that covers it. We use a one-dimensional thermodynamic sea ice model to examine the effect of smokefall on the seasonal variation of sea ice. In particular, we test the sensitivity of the model results to the time of year, duration, and latitude of smokefall.Sea ice thickness variations and the period of summer ice-free conditions are sensitive to the season of smokefall. The largest sea ice perturbations are generated by smokefall in spring. In this case the period of ice-free conditions during the summer can increase by 2 – 3.5 months between 67.5° N and 82.5° N. In any given season, the annual cycle of sea ice is not very sensitive to the duration of smokefall. The equilibrium annual cycle of sea ice variation is restored within a few years of smokefall when the smoke is flushed out of the ice/snow system.Since the sea ice model used here is not a comprehensive global climate model, it is difficult to predict the mid-latitude climate effects of the massive, but temporary, Arctic sea ice changes. However, our results suggest that future global climate model simulations of the effects of nuclear war smoke include interactive sea ice calculations.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
11.
Two experiments are performed with the NCAR Community Climate Model (CCM) coupled to a swamp ocean with annually averaged solar forcing. A swamp ocean model is one in which the ocean temperature is computed from a surface energy balance. Both experiments are run with present (1 × CO2) and doubled (2 × CO2) amounts of atmospheric carbon dioxide (CO2). The first tests the sensitivity of the model to a snow and sea-ice-albedo formulation which facilitates relatively greater ice melt. The second assesses the model response when the basic state of the model in the control run is colder due to a 2% decrease in solar constant. Both are compared to a previous experiment with the same model using a different snow and sea-ice-albedo formulation and the present value of the solar constant. It is found that the globally averaged surface air temperature increase due to a doubling of CO2 is highly dependent on (1) the type of snow-sea-ice-albedo formulation used such that the parameterization which better facilitates relatively greater ice melt exhibits a greater sensitivity to increased CO2, and (2) the basic state of the control run such that the colder the basic state, the greater the warming due to increased CO2.A portion of this study is supported by the U.S. Department of Energy as part of its Carbon Dioxide Research Program.The National Center for Atmospheric Research is sponsored by the National Science Foundation 相似文献
12.
A. L. Steiner J. S. Pal F. Giorgi R. E. Dickinson W. L. Chameides 《Theoretical and Applied Climatology》2005,82(3-4):225-243
Summary We replace the existing land surface parameterization scheme, the Biosphere-Atmosphere Transfer Scheme (BATS), in a regional climate model (RegCM) with the newly developed Common Land Model (CLM0). The main improvements of CLM0 include a detailed 10-layer soil model, the distinction between soil ice and water phases, a linked photosynthesis-stomatal conductance model, a multilayer snow model, and an improved runoff parameterization. We compare the performance of CLM0 and BATS as coupled to the RegCM in a one year simulation over East Asia. We find that the RegCM/CLM0 improves the winter cold bias present in the RegCM/BATS simulation. With respect to the surface energy balance, lower CLM0 albedos allow the absorption of more solar radiation at the surface. CLM0 tends to simulate higher sensible heat and lower latent heat fluxes than its BATS counterpart. The surface water balance also changes considerably between the two land surface schemes. Compared to BATS, CLM0 precipitation is reduced overall and surface runoff is increased, thereby allowing less water to enter the soil column. Evapotranspiration is lower in CLM0 due to lower ground evaporation, which leads to a wetter surface soil in CLM0 in spite of less precipitation input. However, transpiration is greater in CLM0 than BATS, which has an overall effect of less surface storage during the summertime. Comparison with station observations indicates that CLM0 tends to improve the simulation of root zone soil water content compared to BATS. Another pronounced difference between the two schemes is that CLM0 produces lower snow amounts than BATS because of different snow models and warmer CLM0 temperatures. In this case, BATS snow cover amounts are more in line with observations. Overall, except for the snow amounts, CLM0 appears to improve the RegCM simulation of the surface energy and water budgets compared to BATS. 相似文献
13.
本文利用简单的一维能量平衡模拟全球冰雪面积增减,太阳常数增减,地面反照率增减,大气中二氧化碳浓度增减以及气溶胶浓度增减等对全球温度的影响。同时还模拟多个因子综合对冰河期的影响。敏感试验给出各种自然变化和人类活动对全球温度影响的可能的数值结果,从而为保护大气与环境提供一定参考数据。 相似文献
14.
Benjamin I. Cook Gordon B. Bonan Samuel Levis Howard E. Epstein 《Climate Dynamics》2008,31(1):107-124
We use a state of the art climate model (CAM3–CLM3) to investigate the sensitivity of surface climate and land surface processes
to treatments of snow thermal conductivity. In the first set of experiments, the thermal conductivity of snow at each grid
cell is set to that of the underlying soil (SC-SOIL), effectively eliminating any insulation effect. This scenario is compared
against a control run (CTRL), where snow thermal conductivity is determined as a prognostic function of snow density. In the
second set of experiments, high (SC-HI) and low (SC-LO) thermal conductivity values for snow are prescribed, based on upper
and lower observed limits. These two scenarios are used to envelop model sensitivity to the range of realistic observed thermal
conductivities. In both sets of experiments, the high conductivity/low insulation cases show increased heat exchange, with
anomalous heat fluxes from the soil to the atmosphere during the winter and from the atmosphere to the soil during the summer. The increase in surface heat exchange leads to soil cooling of up to 20 K in the winter, anomalies that
persist (though damped) into the summer season. The heat exchange also drives an asymmetric seasonal response in near-surface
air temperatures, with boreal winter anomalies of +6 K and boreal summer anomalies of −2 K. On an annual basis there is a
net loss of heat from the soil and increases in ground ice, leading to reductions in infiltration, evapotranspiration, and
photosynthesis. Our results show land surface processes and the surface climate within CAM3–CLM3 are sensitive to the treatment
of snow thermal conductivity. 相似文献
15.
A frequently made assumption in simple models of long-term climatic behavior (e.g. ‘energy balance’ models) is that, owing to instability engendered by the ice-albedo feedback, the climatic system (surface temperature, in particular) can exhibit multiple steady states within the paleoclimatologically observed range of temperature. Here we show that, for a more comprehensive model than an energy balance model, the CCM1 general circulation model, such a bimodality does not exist for present values of the solar constant and atmospheric CO2 even if one excludes the existence of a seasonal cycle of radiative forcing. Thus, no evidence is found to support the whole class of ice-age theories tuned to present CO2 levels that depend on this bimodality. As a corollary, support is found for the idea that surficial temperature and snow-sea-ice cover are essentially ‘slaved’, fast-response, climatic variables that equilibrate uniquely with the prescribed external forcing and the slow-response climatic variables (e.g. the ice sheets and deep ocean state). It is also implied that, although care should be exercised in the choice of initial conditions to minimize computer time, the selection of initial conditions is not likely to affect the final outcome of general circulation model studies of climate for fixed (near-present) values of the solar constant and CO2 forcing. 相似文献
16.
Results from a two-dimensional energy balance model with a realistic land-ocean distribution show that the small ice cap instability exists in the Southern Hemisphere, but not in the Northern Hemisphere. A series of experiments with a one-dimensional energy balance model with idealized geography are used to study the roles of the seasonal cycle and the land-ocean distribution. The results indicate that the seasonal cycle and land-ocean distribution can influence the strength of the albedo feedback, which is responsible for the small ice cap instability, through two factors: the temperature gradient and the amplitude of the seasonal cycle. The land-ocean distribution in the Southern Hemisphere favors the small ice cap instability, while the land-ocean distribution in the Northern Hemisphere does not. Because of the longitudinal variations of land-ocean distribution in the Northern Hemisphere, the behavior of ice lines in the Northern Hemisphere cannot be simulated and explained by the model with zonally symmetric land-ocean distribution. Model results suggest that the small ice cap instability may be a possible mechanism for the formation of the Antarctic icesheet. The model results cast doubt, however, on the role of the small ice cap instability in Northern Hemisphere glaciations.
Offprint requests to: J Huang 相似文献
17.
Recent observational and numerical studies of the maritime snow cover in the Antarctic suggest that snow on top of sea ice
plays a major role in shaping the seasonal growth and decay of the ice pack in the Southern Ocean. Here, we make a quantitative
assessment of the importance of snow accumulation in controlling the seasonal cycle of the ice cover with a coupled snow–sea-ice–upper-ocean
model. The model takes into account snow and ice sublimation and snow deposition by condensation. A parametrisation of the
formation of snow ice (ice resulting from the freezing of a mixture of snow and seawater produced by flooding of the ice floes)
is also included. Experiments on the sensitivity of the snow–sea-ice system to variations in the sublimation/condensation
rate, the precipitation rate, and the amount of snowfall transported by the wind into leads are discussed. Although we focus
on the model response in the Southern Hemisphere, results for the Arctic are also discussed in some cases to highlight the
relative importance of the processes under study in both hemispheres. It is found that the snow loss by sublimation can account
for the removal of 0.45 m of snow per year in the Antarctic and that this loss significantly affects the total volume of snow
ice. A precipitation decrease of 50% is conducive to large reductions in the Antarctic snow and snow-ice volumes, but it leads
only to an 8% decrease in the annual mean ice volume. The Southern Ocean ice pack is more sensitive to increases in precipitation.
For precipitation rates 1.5 times larger than the control ones, the annual mean snow, ice, and snow-ice volumes augment by
30, 20, and 180%, respectively. It is also found that the transfer to the ocean of as much as 50% of the precipitating snow
as a result of wind transport has almost negligible effects on the total ice volume. All the experiments exhibit a marked
geographical contrast in the ice-cover response, with a much larger sensitivity in the western sector of the Southern Ocean
than in the eastern sector. Our results suggest that snow-related processes are of secondary importance for determining the
sensitivity of the Arctic sea ice to environmental changes but that these processes could have an important part to play in
the response of the Antarctic sea-ice cover to future, or current, climatic changes.
Received: 30 June 1997/Accepted: 2 October 1998 相似文献
18.
Based on dynamical energy transport and thermodynamic energy balance in the earth’s atmosphere-ocean system a steady two-dimensional climate model with residual circulation is proposed. In the model, we include some important physical processes with feedbacks such as ice caps-albedo, water vapor-tempera-ture, etc. The simulated steady temperature field is very close to that of the real atmosphere. The numerical experiments show that doubling of the atmospheric carbon dioxide results in temperature increase of 1~2oC at the low latitude surface and 6~8oC at the high latitude surface. It is shown that a 6% decrease in the solar constant is required for the -10oC ice edge to move from its present latitude ~70o to~50o. 相似文献
19.
20.
Relative contribution of soil moisture and snow mass to seasonal climate predictability: a pilot study 总被引:1,自引:1,他引:0
Hervé Douville 《Climate Dynamics》2010,34(6):797-818
Land surface hydrology (LSH) is a potential source of long-range atmospheric predictability that has received less attention
than sea surface temperature (SST). In this study, we carry out ensemble atmospheric simulations driven by observed or climatological
SST in which the LSH is either interactive or nudged towards a global monthly re-analysis. The main objective is to evaluate
the impact of soil moisture or snow mass anomalies on seasonal climate variability and predictability over the 1986–1995 period.
We first analyse the annual cycle of zonal mean potential (perfect model approach) and effective (simulated vs. observed climate)
predictability in order to identify the seasons and latitudes where land surface initialization is potentially relevant. Results
highlight the influence of soil moisture boundary conditions in the summer mid-latitudes and the role of snow boundary conditions
in the northern high latitudes. Then, we focus on the Eurasian continent and we contrast seasons with opposite land surface
anomalies. In addition to the nudged experiments, we conduct ensembles of seasonal hindcasts in which the relaxation is switched
off at the end of spring or winter in order to evaluate the impact of soil moisture or snow mass initialization. LSH appears
as an effective source of surface air temperature and precipitation predictability over Eurasia (as well as North America),
at least as important as SST in spring and summer. Cloud feedbacks and large-scale dynamics contribute to amplify the regional
temperature response, which is however, mainly found at the lowest model levels and only represents a small fraction of the
observed variability in the upper troposphere. 相似文献