Relative performance of CMIP5 and CMIP6 models in simulating rainfall in Peninsular Malaysia

Theoretical and Applied Climatology - This study evaluated the skills of global climate models (GCMs) of the fifth and sixth Coupled Model Intercomparison Project (CMIP5 and CMIP6) in simulating...     

Evaluation of the performance of CMIP5 and CMIP6 models in simulating the South Pacific Quadrupole-ENSO relationship

先前的观测研究表明,南太平洋四极子海温模态(SPQ)可以有效地作为ENSO的前兆信号.本文利用20个CMIP6模式及其对应的20个先前的CMIP5模式的工业化前气候模拟试验数据,评估和比较了CMIP6以及CMIP5模式对SPQ与ENSO的关系的模拟能力.结果表明,大多数CMIP5和CMIP6模式可以合理地模拟SPQ的基...     

CMIP6与CMIP5对历史大气层顶和地表辐射收支模拟的时空对比

基于云和地球辐射能量系统观测数据集（CERES),对比分析了耦合模式比较计划第五（CMIP5）和第六阶段（CMIP6）模拟的历史大气层顶和地表辐射收支的年际变化和空间分布,明确了多模式间不确定性大的关键区域。结果表明：在年际尺度上,除地表向上长波辐射外,CMIP6的辐射分量的集合均值较CMIP5更接近于CERES观测值,全球地表向下短波辐射的高估和大气逆辐射的低估在CMIP6中分别降低了1.9 W/m²和3.3 W/m²。除大气逆辐射外,CMIP6的辐射分量在多模式间的一致性较CMIP5提高。在北极,CMIP6对大气层顶反射短波、大气层顶出射长波和地表向下短波辐射的模拟偏差较CMIP5大。在南北纬60°,CMIP6对大气逆辐射的模拟偏差较CMIP5大。其他区域CMIP6的辐射分量更接近CERES观测值。CMIP6模拟的地表向下短波辐射和大气逆辐射的不确定性较大区域面积较CMIP5减小,但不确定性极大区域面积无变化。地表净辐射的不确定性空间分布在两代CMIP间变化甚小。青藏高原、赤道太平洋、热带雨林、阿拉伯半岛和南极洲沿海依然是地球系统模式模拟辐射收支不确定性极大的关键区域。     

Uncertainty of ENSO-amplitude projections in CMIP5 and CMIP6 models

There is a long-standing debate on how the El Niño/Southern Oscillation (ENSO) amplitude may change during the twenty-first century in response to global warming. Here we identify the sources of uncertainty in the ENSO amplitude projections in models participating in the Coupled Model Intercomparison Phase 5 (CMIP5) and Phase 6 (CMIP6), and quantify scenario uncertainty, model uncertainty and uncertainty due to internal variability. The model projections exhibit a large spread, ranging from increasing standard deviation of up to 0.6 °C to diminishing standard deviation of up to − 0.4 °C by the end of the twenty-first century. The ensemble-mean ENSO amplitude change is close to zero. Internal variability is the main contributor to the uncertainty during the first three decades; model uncertainty dominates thereafter, while scenario uncertainty is relatively small throughout the twenty-first century. The total uncertainty increases from CMIP5 to CMIP6: while model uncertainty is reduced, scenario uncertainty is considerably increased. The models with “realistic” ENSO dynamics have been analyzed separately and categorized into models with too small, moderate and too large ENSO amplitude in comparison to instrumental observations. The smallest uncertainties are observed in the sub-ensemble exhibiting realistic ENSO dynamics and moderate ENSO amplitude. However, the global warming signal in ENSO-amplitude change is undetectable in all sub-ensembles. The zonal wind-SST feedback is identified as an important factor determining ENSO amplitude change: global warming signal in ENSO amplitude and zonal wind-SST feedback strength are highly correlated across the CMIP5 and CMIP6 models.

     

On the interannual variability of arctic sea‐level pressure and sea ice

Abstract

Monthly mean sea‐level pressure (SLP) data from the Northern Hemisphere for the period January 1952‐December 1987 are analysed. Fluctuations in this field over the Arctic on interannual time‐scales and their statistical association with fluctuations farther south are determined. The standard deviation of the interannual variability is largest compared with that of the annual cycle along the seaboards of the major land masses. The SLP anomalies are generally in phase over the entire Arctic Basin and extend south over the northern Russia and Canada, but tend to be out of phase with fluctuations at mid‐latitudes. The anomalies are most closely associated with fluctuations over the North Atlantic and Europe except near the Chukchi Sea to the north of Bering Strait. The associations with the North Pacific fluctuations become increasingly more prominent at most Arctic sites (e.g. the Canadian Arctic Archipelago) as the time‐scale increases.

Associations between the SLP fluctuations and atmospheric indices that represent processes affecting sea‐ice drift (wind stress and wind stress curl) are determined. In every case local associations dominate, but some remote ones are also evident. For example, changes in the magnitude of the wind stress curl over the Beaufort Sea are increased if the atmospheric circulation over the North Pacific is intensified; wind stress over the region where sea ice is exchanged between the Beaufort Gyre and the Transpolar Drift Stream is modulated by both the Southern and North Atlantic Oscillations.

Severe sea‐ice conditions in the Greenland Sea (as measured by the Koch Ice Index) coincide with a weakened atmospheric circulation over the North Atlantic.     

Projection of subtropical gyre circulation and associated sea level changes in the Pacific based on CMIP3 climate models

For all of the IPCC Special Report on Emission Scenarios (SRESs), sea level is projected to rise globally. However, sea level changes are not expected to be geographically uniform, with many regions departing significantly from the global average. Some of regional distributions of sea level changes can be explained by projected changes of ocean density and dynamics. In this study, with 11 available Coupled Model Intercomparison Project Phase 3 climate models under the SRES A1B, we identify an asymmetric feature (not recognised in previous studies) of projected subtropical gyre circulation changes and associated sea level changes between the North and South Pacific, through analysing projected changes of ocean dynamic height (with reference to 2,000 db), depth integrated steric height, Sverdrup stream function, surface wind stress and its curl. Poleward expansion of the subtropical gyres is projected in the upper ocean for both North and South Pacific. Contrastingly, the subtropical gyre circulation is projected to spin down by about 20 % in the subsurface North Pacific from the main thermocline around 400 m to at least 2,000 m, while the South Pacific subtropical gyre is projected to strengthen by about 25 % and expand poleward in the subsurface to at least 2,000 m. This asymmetrical distribution of the projected subtropical gyre circulation changes is directly related to differences in projected changes of temperature and salinity between the North and South Pacific, forced by surface heat and freshwater fluxes, and surface wind stress changes.     

Modes of interannual variability of Southern Hemisphere atmospheric circulation in CMIP3 models: assessment and projections

An assessment is made of the modes of interannual variability in the seasonal mean summer and winter Southern Hemisphere 500 hPa geopotential height in the twentieth century in models from the Coupled Model Intercomparison Project phase 3 (CMIP3) dataset. The analysis is done for both the intraseasonal and slow components of the geopotential height. When the CMIP3 models are assessed against reanalysis data, the spatial structure and variance of the leading modes in the intraseasonal component are generally well reproduced. There are systematic differences between the models in their reproduction of the leading modes in the slow component. An overall score using the leading modes in the slow component allows a categorisation of CMIP3 model performance. Using an ensemble from four models that suitably reproduce the twentieth century modes, modes of variability in the slow-internal and slow-external components are estimated. The leading mode of the slow-external component is shown to be related to observed changes in greenhouse gas concentrations. In this ensemble, there is little change in the leading modes in the intraseasonal component in the twenty-first century. Larger changes in variance, and subtle changes in regional-scale structure, are found for the leading modes in the slow-internal component. These are related to changes in the slowly varying dynamics of the Southern Annular Mode and the El Niño-Southern Oscillation. By far the biggest change is in the leading mode of the slow-external component. The spatial structure becomes uniform in the twenty-first century, and the variance increases with increasing greenhouse gas concentrations.     

Greenland Ice Sheet Contribution to Future Global Sea Level Rise based on CMIP5 Models简

Sea level rise （SLR） is one of the major socioeconomic risks associated with global warming. Mass losses from the Greenland ice sheet （GrIS） will be partially responsible for future SLR, although there are large uncertainties in modeled climate and ice sheet behavior. We used the ice sheet model SICOPOLIS （Simulation COde for POLythermal Ice Sheets） driven by climate projections from 20 models in the fifth phase of the Coupled Model Intercomparison Project （CMIP5） to estimate the GrlS contribution to global SLR. Based on the outputs of the 20 models, it is estimated that the GrIS will contribute 0-16 （0-27） cm to global SLR by 2100 under the Representative Concentration Pathways （RCP） 4.5 （RCP 8.5） scenarios. The projected SLR increases further to 7-22 （7-33） cm with 2~basal sliding included. In response to the results of the multimodel ensemble mean, the ice sheet model projects a global SLR of 3 cm and 7 cm （10 cm and 13 cm with 2~basal sliding） under the RCP 4.5 and RCP 8.5 scenarios, respectively. In addition, our results suggest that the uncertainty in future sea level projection caused by the large spread in climate projections could be reduced with model-evaluation and the selective use of model outputs.     

CMIP6全球气候模式对中亚极端降水模拟能力的评估

本文基于NOAA再分析逐日降水数据和22个CMIP6模式的降水模拟数据,选取了6个极端降水指数,从气候态和相对变率两个角度对CMIP6模式在中亚地区极端降水方面的模拟能力开展了评估。结果表明,在气候态方面,中亚地区降水的空间分布表现为由西南向东北递增,其东南部山地迎风侧降水偏多;多模式集合对SDII(简单降水强度)和CDD(最大无雨期)模拟的平均误差分别为-5.43%和0.45%,对PRCPTOT(年总降水量)、R1mm(有雨日数)、Rx5day(最大连续五日降水)和CWD(最大雨期)的模拟结果存在明显高估,且在中亚东南部高海拔地区误差偏高。在相对变率方面,多模式集合模拟的中亚极端降水的相对变率偏小,其中对CWD的模拟效果相对较好,平均误差为-4.78%;对R1mm的模拟效果最差,平均误差为-36.16%。模式间进行比较,TaiESM1、EC-Earth3-Veg-LR和GFDL-ESM为22个CMIP6模式中模拟能力最好的前3个模式。     

CMIP6不同分辨率全球气候模式对中国降水模拟能力评估

基于参与CMIP6高分辨率模式比较计划(HighResMIP)9个模式组的18个全球气候模式模拟数据,通过与CN05.1观测资料的对比,评估了不同分辨率气候模式对中国区域1961—2014年降水特征的模拟能力.结果表明:低、高分辨率模式均能模拟出中国区域多年平均降水的总体空间分布特征,以及降水冬弱夏强的季节变化特征,但...     

Comparing the Arctic climate in Chinese and other CMIP6 models

本研究采用来自耦合模式相互比较项目第六阶段(CMIP6)模式,评估和对比了10个中国模式和27个其他国际模式对北极冬季气候的历史模拟性能.本文的主要目的是展现中国模式对北极气候的模拟能力,并了解其在国际上的模拟水平.结果表明,对于气候态的模拟,中国模式在模拟北极温度场和大气场这些气候学方面与其他国际模式相当.而在趋势方面,中国模式同样和其他国际模式都能很好地模拟出北极变暖的特征.此外,与观测到的环流相比,CMIP6多模式集合平均值(MME)并没有显著的正趋势,这可能是因为外部强迫的作用.     

BCC模式及其开展的CMIP6试验介绍

世界气候研究计划（WCRP）正在组织实施第六次国际耦合模式比较计划（CMIP6),国家气候中心作为参与单位之一,通过近几年的模式研发,推出3个最新模式版本参与该计划,包括含有气溶胶化学模块的地球系统模式BCC-ESM1.0、中等分辨率气候模式BCC-CSM2-MR和高分辨率气候模式BCC-CSM2-HR。除了CMIP6中的气候诊断、评估和描述试验（DECK）和历史气候模拟试验（Historical),这3个模式共将参与CMIP6中的10个模式比较子计划。文中主要介绍这3个模式的基本情况以及所开展的CMIP试验,并对BCC-CSM2-MR模式的Historical试验结果进行简要评估,为试验数据使用者提供参考。     

Interannual variability of the sea surface salinity and its related freshwater flux in the tropical Pacific: A comparison of CMIP5 and CMIP6

This paper assesses the interannual variabilities of simulated sea surface salinity (SSS) and freshwater flux (FWF) in the tropical Pacific from phases 5 and 6 of the Coupled Model Intercomparison Project (CMIP5 and CMIP6). The authors focus on comparing the simulated SSS and FWF responses to El Niño–Southern Oscillation (ENSO) from two generations of models developed by the same group. The results show that CMIP5 and CMIP6 models can perform well in simulating the spatial distributions of the SSS and FWF responses associated with ENSO, as well as their relationship. It is found that most CMIP6 models have improved in simulating the geographical distribution of the SSS and FWF interannual variability in the tropical Pacific compared to CMIP5 models. In particular, CMIP6 models have corrected the underestimation of the spatial relationship of the FWF and SSS variability with ENSO in the central-western Pacific. In addition, CMIP6 models outperform CMIP5 models in simulating the FWF interannual variability (spatial distribution and intensity) in the tropical Pacific. However, as a whole, CMIP6 models do not show improved skill scores for SSS interannual variability, which is due to their overestimation of the intensity in some models. Large uncertainties exist in simulating the interannual variability of SSS among CMIP5 and CMIP6 models and some improvements with respect to physical processes are needed.摘要通过比较CMIP5和CMIP6来自同一个单位两代模式模拟, 表明CMIP5和CMIP6均能较好地模拟出热带太平洋的海表盐度 (SSS) 和淡水通量 (FWF) 对ENSO响应的分布及其响应间的关系. 与CMIP5模式相比, 大部份CMIP6模式模拟的SSS和FWF年际变化分布均呈现改进, 特别是纠正了较低的中西太平洋SSS和FWF变化的空间关系. 但是, 整体上, CMIP6模式模拟的SSS年际变化技巧没有提高, 与SSS年际变率的强度被高估有关. CMIP5和CMIP6模式模拟SSS的年际变化还存在较大的不确定性, 在物理方面需要改进.     

CMIP6模式大气中南北半球际涛动的季节循环

利用1958—2014年47个CMIP6模式输出资料和NCEP/NCAR再分析资料,研究了模式大气中南北涛动(InterHemispheric Oscillation,IHO)的季节变化特征,且评估了CMIP6对IHO季节特征的模拟能力。结果表明:47个CMIP6模式都能模拟出IHO的季节演变特征,但模式间存在一定差异。通过比较,筛选出模拟IHO季节循环较好的16个模式,它们能成功模拟出半球大气质量的时间演变和空间结构。进一步分析表明,水汽对IHO季节变化有抵消作用且半球内部水汽质量变化可驱动越赤道质量流的产生;地表净短波辐射夏高冬低,其加热造成的水汽蒸发在水汽质量变化中起到重要作用;地表净长波辐射在春秋变化幅度较大,与大气质量逐月变化吻合。对比再分析资料表明,CMIP6模式模拟的半球大气质量的峰谷值变化有明显的月份偏差,且CMIP6模式模拟的地表气压异常值的偏差主要出现在北太平洋、欧亚大陆、南半球中纬度地区和两极极区,模拟的南北半球的蒸发和降水量、赤道风场、地表净长波和短波辐射通量等均存在明显的偏差。     

从检验CMIP5气候模式看CMIP6地球系统模式的发展

世界气候研究项目（WCRP）正在组织第六次气候模式对比计划（CMIP6）,全球各个气候模式组正在抓紧发展新模式和做多种相关的数值试验。此时,有必要回顾大量CMIP5气候模式模拟气候变化的效果,以便展望CMIP6的地球系统模式的可能发展前景。目前IPCC第六次评估报告正在启动和进行中,其中所用的主要工具是CMIP6的地球系统模式。     

Comparison of precipitation projections of CMIP5 and CMIP6 global climate models over Yulin,China

Theoretical and Applied Climatology - This study compared precipitation projections of CMIP5 and CMIP6 GCMs over Yulin City, China. The performance of CMIP5 and CMIP6 GCMs in replicating Global...     

CMIP6HighResMIP对青藏高原气候模拟的评估和预估

高分辨率模式模拟被认为是研究资料相对欠缺的青藏高原地区气候变化的重要方法之一。第六次国际耦合模式比较计划(CMIP6)新增了高分辨率模式比较计划(HighResMIP),但其对青藏高原气候的模拟性能尚未系统评估。本研究分析了6对(更高、较低分辨率)CMIP6 HighResMIP模式对青藏高原当前气候的模拟能力,并集合预估了近期青藏高原气候的变化趋势。相对较粗分辨率模拟,所有(2/3)模式的更高分辨率模拟减少了平均降水(气温)的区域平均偏差。泰勒图涉及指标的综合评估显示,约1/3模式的更高分辨率对平均气温和降水模拟效果优于较低分辨率,其余模式的更高分辨率则接近或者劣于较低分辨率。集合平均结果优于单个模式,且其更高分辨率模拟效果总体优于较低分辨率。更高分辨率模式集合预估显示,相对于1995—2014年,在SSP5-8.5情景下到2021—2040年青藏高原整体呈增温趋势,东南部增温相对较弱;降水从北到南呈增加-减少-增加的变化模态;青藏高原气温将平均增加(0.81±0.91)℃,降水将平均增加(0.05±0.25) mm/d。     

Underestimated relationship between westerly wind bursts and ENSO in CMIP6 models

观测表明,热带太平洋的西风爆发(WWBs)在厄尔尼诺南方涛动(ENSO)的发生,发展和多样性中起着关键作用.因此,在耦合模式中真实地再现WWBs对于改进ENSO的模拟和预测有重要意义.在本研究中,作者发现CMIP6的耦合模式的集合平均能很好地再现了热带太平洋WWB发生频率的纬向分布及其年际变动.然而,大多数CMIP6模型极大低估了WWB和ENSO的线性关系.这可能是因为大多数CMIP6模式里海气耦合强度低于观测:海气耦合强度与WWB-ENSO关系的模式间相关系数高达0.91.     

Stochastic models and spectra of interannual variability of mean annual sea surface temperature in the North Atlantic

Estimates of one- and two-variate autoregressive models of mean annual sea surface temperature (SST) in five Smed squares in the North Atlantic are obtained by analysing time series of SST, 1881–1970. Year-to-year variations of SST are shown to follow the AR model of order one with a regression parameter of 0.5 so that their generalized spectrum decreases monotonically and relatively fast with frequency while the limits of statistical predictability amount up to two years. Two-variate models of SST reveal frequency-dependent time lags up to three years and possess slightly better statistical predictability. A feedback in the system of warm and cold currents is found with a characteristic time scale of about six years, which plays an important role in the system's energy budget.     

Evaluation of CMIP5 dynamic sea surface height multi-model simulations against satellite observations

We evaluate the representation of dynamic sea surface height (SSH) fields of 33 global coupled models (GCMs) contributed to the fifth phase of the Coupled Model Intercomparison Project (CMIP5). We use observations from satellite altimetry and basic performance metrics to quantify the ability of the GCMs to replicate observed SSH of the time-mean, seasonal cycle, and inter-annual variability patterns. The time-mean SSH representation has markedly improved from CMIP3 to CMIP5, both in terms of overall reduction in root-mean square differences, and in terms of reduced GCM ensemble spread. Biases of the time-mean SSH field in the Indian and Pacific Ocean equatorial regions are consistent with biases in the zonal surface wind stress fields identified with independent measurements. In the Southern Ocean, the latitude of the maximum meridional gradient of the zonal mean SSH CMIP5 models is shifted equatorward, consistent with the GCMs’ spatial biases in the maximum of the zonal mean westerly surface wind stress fields. However, while the Southern Ocean SSH gradients correlate well with the maximum Antarctic circumpolar current transports, there is no significant correlation with the maximum zonal mean wind stress amplitudes, consistent with recent findings that the eddy parameterisations in GCMs dominate over wind stress amplitudes in this region. There is considerable spread across the CMIP5 ensemble for the seasonal and interannual SSH variability patterns. Because of the short observational period, the interannual variability patterns depend on the time-period over which they are derived, while no such dependency is found for the time-mean patterns. The model performance metrics for SSH presented here provide insight into GCM shortcoming due to inadequate model physics or processes. While the diagnostics of CMIP5 GCM performance relative to observations reveal that some models are clearly better than others, model performance is sensitive to the spatio-temporal scales chosen.