CMIP6冰盖模式比较计划(ISMIP)概况与评述

冰盖是大面积(超过50000 km^2)覆盖陆地表面的极厚冰体,在重力作用下的形变宏观上表现为由内陆向沿海流动[1],当前世界上仅存格陵兰和南极两大冰盖。广大的内陆区域冰雪终年不化,以极低的速率积累表面降雪继而密实化为冰川。受基岩性质和地热通量的影响,冰盖底部融化润滑在冰盖内部形成快速冰流通道。如果融水在下游积累到一定程度,则会进一步发育成为相互连通的冰下水文系统,并最终汇入海洋[2]。当固体冰川流向海洋时,受地形约束可能形成冰架,由冰水密度比值可知只有约1/10漂浮在海面以上,绝大部分冰架与海水直接接触。     

国际大气环流模式比较计划（AMIP）进展

介绍了国际大气环流模式比较计划（AMIP）的概况，它的分析子计划及执行情况、科学进展、相关计划及未来发展等情况，以便国内学者了解并积极参与该研究计划。     

第六次国际耦合模式比较计划（CMIP6）评述

世界气候研究计划（WCRP）发起了新一轮的国际耦合模式比较计划（CMIP6),目的是回答当前气候变化领域面临的新的科学问题,为实现WCRP“大挑战”计划所确立的科学目标提供数据支撑。文中回顾了CMIP的发展历程,介绍了CMIP6的组织思路,阐述了CMIP6核心试验及23个模式比较子计划（MIPs）的科学关注点,总结了参与CMIP6的全球模式概况以及中国的贡献。最后,从继承性和创新性等角度对CMIP6进行了评述,指出了CMIP6组织和实施中存在的问题,并对CMIP未来的发展进行了展望。     

大气模式比较计划（AMIP）

文章介绍了ＡＭＩＰ及参加ＡＭＩＰ的模式的模拟概况，指出几乎所有模式都能够模拟出大尺度大气环流的平均季节结构，但没有任何一个模式在各方面都好，而且模式一般高估了季节循环的方法，低估了年际变率，并且各个模式在模拟不同气候要素的时空变化时彼此差别也较大，文章还重点讨论了云辐射及陆面水文过程，指出观测与模拟高低云量存在较大差异，而云量可能并不是影响辐射平衡唯一因子，云的季节变化与气温的年循环存在着正相关，     

亚洲区域气候模式比较计划的进展

区域气候变化的信息是气候变化影响评估的基础。在发展全球气候模式的同时 ,发展高分辨的区域气候模式是获取区域气候变化信息的重要途径之一。作者介绍了由中国科学院大气物理研究所START全球变化东亚区域研究中心发起和主持 ,有中、美、韩、日和澳大利亚 1 0个研究组参加的亚洲区域气候模式比较计划的目的、意义、工作任务和试验设计等主要内容 ,给出了该国际比较计划第 1阶段 (连续 1 8个月积分 )和第 2阶段( 1 988～ 1 998年连续 1 0年积分 )的初步结果 ,讨论了区域气候模式在亚洲应用中的一些共性问题以及进一步研究的方向。     

基于国际大气化学-气候模式比较计划模式数据评估中国沙尘气溶胶直接辐射强迫

目前气候模式对沙尘气溶胶直接辐射强迫模拟仍有很大不确定性,多模式对比有助于定量评估不确定范围。国际大气化学—气候模式比较计划（Atmospheric Chemistry and Climate Model Intercomparison Project,ACCMIP）旨在评估当前模式对短寿命大气成分辐射强迫和气候效应的模拟能力。基于7个ACCMIP模式模拟的中国地区沙尘气溶胶浓度,我们评估了中国区域沙尘气溶胶直接辐射强迫和不确定性范围。结果显示,中国区域沙尘气溶胶年排放总量为215±163 Tg a-1,区域年均地表浓度为41±27 μg m-3,柱浓度为9±4 kg m-2,光学厚度为0.09±0.05。中国区域年均沙尘气溶胶产生的大气顶短波、长波和总辐射强迫分别为-1.3±0.8 W m-2、0.7±0.4 W m-2和-0.5±0.7 W m-2;地表短波、长波和总的辐射强迫值为-1.5±1.0 W m-2、1.8±0.9 W m-2和0.2±0.2 W m-2。沙尘气溶胶长波辐射强迫对沙尘浓度的垂直分布敏感。高层沙尘气溶胶浓度越大,其在大气顶产生更强的正值长波辐射强迫。然而,沙尘气溶胶短波辐射强迫主要受整层沙尘柱浓度控制,对沙尘浓度的垂直分布较不敏感。本文结果可为中国沙尘气溶胶的气候模拟提供参考。     

土地利用模式比较计划(LUMIP)简评

为进一步促进土地利用和土地覆盖变化（Land-Use and Land-Cover Change,LULCC）以及土地管理对气候影响的理解,第六次国际耦合模式比较计划（CMIP6）设立了土地利用模式比较计划（LUMIP）。该计划主要包括两个阶段的试验设计：第一阶段涉及理想的毁林情景耦合试验和陆面模式模拟试验,旨在促进LULCC对气候影响过程的理解,并量化模式对LULCC的敏感性。第二阶段的试验重点关注土地利用变化的历史影响,以及未来土地管理决策在减缓气候变化方面的潜力。本文概述了其科学背景、试验设计和方案、参与模式情况等,并简评了该计划的研究意义和特色,以期读者迅速了解其相关的研究要点和发展方向。     

地圈、生物圈计划特别委员会及近期活动

国际科联执委会于1987年1月任命了国际地圈、生物圈计划(IGBP,下同)特别委员会(SCGB,下同)负责制定IGBP实施计划。为此,SCGB于1987年7月16—19日在法国巴黎召开了第一次会议,再次重申     

全球季风模式比较计划（GMMIP）概述

全球季风模式比较计划（GMMIP）是第六次国际耦合模式比较计划（CMIP6）的重要组成部分。文中首先介绍了GMMIP发起的科学背景,指出发起GMMIP的必要性和历史机遇。进一步扼要描述了GMMIP试验设计的总体思路和方案、试验的用途以及与CMIP6其他模式比较子计划的相关性。最后对GMMIP的科学意义进行了评述,指出其在提升和扩大中国季风模拟和研究领域国际影响力方面的重要作用。     

Snowpack model estimates of the mass balance of the Greenland ice sheet and its changes over the twentyfirst century

The performance of a snow cover model in capturing the ablation on the Greenland ice sheet is evaluated. This model allows an explicit calculation of the formation of melt water, of the fraction of melt water which re-freezes, and of runoff in the ablation region. The input climate variables to the snowpack model come from two climate models. While the higher resolution general circulation model (ECHAM 4), is closest to observations in its estimate of accumulation, it fails to give accurate results in its predictions of runoff, primarily in the southern half of the ice sheet. The two-dimensional low-resolution climate model (MIT 2D LO) produces estimates of runoff from the Greenland ice sheet within the range of uncertainty of the Inter governmental Panel on Climate Change (IPCC1) 1995 estimates. Both models reproduce some of the characteristics of the extent of the wet snow zone observed with satellite remote sensing; the MIT model is closer to observations in terms of areal extent and intensity of the melting in the southern half of the ice-sheet in July and August while the ECHAM model reproduces melting in the northern half of the ice sheet well. Changes in runoff from Greenland and Antarctica are often cited as one of the major concerns linked to anthropogenic changes in climate. Because it is based on physical principles and relies on the surface energy balance as input, the snow cover model can respond to the current climatic forcing as well as to future changes in climate on the century time scale without the limitations inherent in empirical parametrizations. For a reference climate scenario similar to the IPCC's IS92a, the model projects that the Greenland ice sheet does not contribute significantly to changes in the level of the ocean over the twenty-first century. Increases in accumulation over the central portion of the ice sheet offset most of the increase in melting and runoff, which takes place along the margins of the ice sheet. The range of uncertainty in the predictions of sea-level rise is estimated by repeating the calculation with the MIT model for seven climate change scenarios. The range is –0.5 to 1.7 cm.     

A climate model intercomparison at the dynamics level

Until now, climate model intercomparison has focused primarily on annual and global averages of various quantities or on specific components, not on how well the general dynamics in the models compare to each other. In order to address how well models agree when it comes to the dynamics they generate, we have adopted a new approach based on climate networks. We have considered 28 pre-industrial control runs as well as 70 20th-century forced runs from 23 climate models and have constructed networks for the 500 hPa, surface air temperature (SAT), sea level pressure (SLP), and precipitation fields for each run. We then employed a widely used algorithm to derive the community structure in these networks. Communities separate “nodes” in the network sharing similar dynamics. It has been shown that these communities, or sub-systems, in the climate system are associated with major climate modes and physics of the atmosphere (Tsonis AA, Swanson KL, Wang G, J Clim 21: 2990–3001 in 2008; Tsonis AA, Wang G, Swanson KL, Rodrigues F, da Fontura Costa L, Clim Dyn, 37: 933–940 in 2011; Steinhaeuser K, Ganguly AR, Chawla NV, Clim Dyn 39: 889–895 in 2012). Once the community structure for all runs is derived, we use a pattern matching statistic to obtain a measure of how well any two models agree with each other. We find that, with the possible exception of the 500 hPa field, consistency for the SAT, SLP, and precipitation fields is questionable. More importantly, none of the models comes close to the community structure of the actual observations (reality). This is a significant finding especially for the temperature and precipitation fields, as these are the fields widely used to produce future projections in time and in space.     

Initial findings of recent investigations of air-snow relationships in the summit region of the Greenland ice sheet

The concentrations of⁷Be,²¹⁰Pb and major ions have been measured in acrosol and snow samples collected near Summit, Greenland (72°20N, 38°45W) in the summers of 1989 and 1990. Comparison to previous results from free tropospheric sampling of the North American Arctic indicates that some acrosol-associated species are as much as 50% depleted in near surface air over the Greenland Ice Sheet. It is shown that local atmospheric processes, particularly isolation of air masses beneath a near surface inversion, can exert dominant influence on the chemistry of surface-level air. These findings illustrate the extreme caution that must be taken if the results of surface-based atmospheric sampling are to be used to examine the relationship between the chemistry of the atmosphere and snow falling from it.Depth profiles of⁷Be in the surface layers of the snowpack near Summit suggest that up to half of the annual accumulation of snow may occur in the two to three month late spring-early summer period. If this is generally true for the Summit region, previous regional studies of snow chemistry that assumed linear dependence of age on depth to convert depth profiles to time series will have to be reassesed. However, spatial heterogeneity of near surface snow chemistry, that is currently not well understood, makes interpretation of the⁷Be profiles tentative at present.     

A model of late Pleistocene ice sheet growth with realistic geography and simplified cryodynamics and geodynamics

A global two-dimensional one-level seasonal energy-balance model is asynchronously coupled to vertically integrated ice-flow models (which depend both on latitude and longitude) to study the response of the atmosphere-ocean-cryosphere-lithosphere system to solar forcing for the last ice age cycle of the late Pleistocene. The model simulates the position of the North American and European ice sheet complexes at the last glacial maximum satisfactorily. Both the geographic distributions of the ice volumes delivered by the model and their masses are a reasonable approximation to those inferred on the basis of relative sea level data (Tushingham and Peltier 1990). The sensitivity of the coupled model over the last glacial-interglacial cycle to solar forcing is nevertheless low, which suggests that further physical mechanisms will have to be added to the model (such as explicit basal sliding and ice shelves which would respond to sea-level variations and therefore permit marine incursions), if it is to adequately simulate the terminations that control the 10⁵ year ice age cycle. One should also incorporate long-term variations of the greenhouse gases (Manabe et al. 1985b).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. Dümenil     

Global dynamics of the Antarctic ice sheet

The total mass budget of the Antarctic ice sheet is studied with a simple axi-symmetrical model. The ice-sheet has a parabolic profile resting on a bed that slopes linearly downwards from the centre of the ice sheet into the ocean. The mean ice velocity at the grounding line is assumed to be proportional to the water depth. The accumulation rate is a linear function of the distance to the centre. Setting the total mass budget to zero yields a quadratic equation for the steady-state ice-sheet radius R. Analysis of the equilibrium states sheds light on the sensitivity of the ice-sheet radius to changes in sea level (S) and precipitation with respect to the present state (P_rel). For model parameters obtained by matching the analytical model to the present state of the Antarctic ice sheet, the sensitivity values are dR/dS = -2400 and dR/dP_rel = 4000 m/%. The model can also be used to study transient behaviour of the ice sheet. The characteristic relaxation time (e-folding time scale) is about 3500 years. Forcing the model with a sea-level and accumulation history over the past few hundred thousands of years yields Antarctic ice-volume curves that are similar to those obtained by comprehensive numerical modelling. The current imbalance predicted by the model corresponds to a sea-level rise of 0.25 mm yr^-1.     

A 3-D model for the Antarctic ice sheet: a sensitivity study on the glacial-interglacial contrast

On the longer climatic time scales, changes in the elevation and extent of the Antarctic ice sheet have an important role in modulating global atmospheric and oceanographic processes, and contribute significantly to world-wide sea levels. In this paper, a 3-D time-dependent thermomechanical model for the entire ice sheet is presented, that is subsequently used to examine the effects of glacial-interglacial shifts in environmental boundary conditions on its geometry. The model takes into account a coupled ice shelf, grounding-line dynamics, basal sliding and isostatic bed adjustment and considers the fully coupled velocity and temperature fields. Ice flow is calculated on a fine mesh (40 km horizontal grid size and 10 layers in the vertical) for grounded and floating ice and a stress transition zone in between at the grounding line, where all stress components contribute in the effective stress in the flow law. There is free interaction between ice sheet and ice shelf, so that the entire geometry is internally generated. A simulation of the present ice sheet reveals that the model is able to yield realistic results. A series of sensitivity experiments are then performed, in which lower temperatures, reduced accumulation rates and lower global sea level stands are imposed, either singly or in combination. By comparing results of pairs of experiments, the effects of each of these environmental changes can be determined. In agreement with glacial-geological evidence, we found that the most pronounced changes show up in the West Antarctic ice sheet configuration. They appear to be essentially controlled by variations in eustatic sea level, whereas typical glacial-interglacial changes in temperature and ice deposition rates tend to balance one another. These findings support the hypothesis that the Antarctic ice sheet basically follows glacial episodes in the northern hemisphere by means of sea-level teleconnections. Grounding occurs more readily in the Weddell sea than in the Ross sea and long time scales appear to be involved: it may take up to 30–40000 years for these continental shelf areas to become completely grounded after an initial stepwise perturbation in boundary conditions. According to these reconstructions, a steady state Antarctic ice sheet may contribute some 16 m to global sea level lowering at maximum glaciation.     

大气河对南极冰盖及海冰的影响

南极冰盖与海冰对全球气候具有重要影响。大气河作为高纬度地区经向水汽输送的重要途径,其对南极冰盖与海冰的影响在近年来愈发受到重视。南极大气河通常形成于高压脊(阻塞高压)与温带气旋之间的强向极经向输送带内。低频的大气河活动为南极带来强降雪,有利于冰盖质量增加。然而,强暖湿水汽侵入同时会导致表面融化、冰架崩解和极端高温,对冰盖质量存在潜在负贡献。大气河携带极端暖湿水汽与强风通过热力与动力过程导致海冰密集度下降。目前,大气河的识别算法仍不完善,其对液态降水的直接影响、与南大洋的相互作用等仍不清楚,需要进一步明晰大气河对南极冰盖与海冰的影响机制,以准确预估未来大气河对南极冰盖物质平衡与海冰变化的作用。     

Sensitivity of a Greenland ice sheet model to ice flow and ablation parameters: consequences for the evolution through the last climatic cycle

Sensitivity experiments are conducted to test the influence of poorly known model parameters on the simulation of the Greenland ice sheet by means of a three dimensional numerical model including the mechanical and thermal processes within the ice. Two types of experiments are performed: steady-state climatic conditions and simulations over the last climatic cycle with a climatic forcing derived from the GRIP record. The experiments show that the maximum altitude of the ice sheet depends on the ice flow parameters (deformation and sliding law coefficients, geothermal flux) and that it is low when the ice flow is fast. On the other hand, the maximum altitude is not sensitive to the ablation strength and consequently during the climatic cycle it is driven by changes in accumulation rate. The ice sheet extension shows the opposite sensitivity: it is barely affected by ice flow velocity and the ice covered area is smaller for large ablation coefficients. For colder climates, when there is no ablation, the ice sheet extension depends on the sea level. An interesting result is that the variations with time of the altitude at the ice divide (Summit) do not depend on the parameters we tested. The present modelled ice sheets resulting from the climatic cycle experiments are compared with the present measured ice sheet in order to find the set of parameters that gives the best fit between modelled and measured geometry. It seems that, compared to the parameter set most commonly used, higher ablation rate coefficents must be used. Received: 19 September 1995 / Accepted: 30 May 1996