东亚区域极端气候事件变化的数值模拟试验

使用ResCM2区域气候模式,嵌套澳大利亚CSIRO R21L9全球海气耦合模式,进行了温室效应（二氧化碳加倍）对东亚（主要是中国区域）极端气候事件影响的数值试验。控制试验的结果表明,区域模式能够较好地模拟中国区域的极端气候事件。对温室效应引起的它们的变化进行了信度检验,分析结果表明,温室效应将引起日最高和最低气温增加,日较差减小;使得高温天气增多,低温日数减少。降水日数和大雨日数在一些地区将增加。同时还会引起影响中国的台风活动的变化。     

Limitations of time-slice experiments for predicting regional climate change over South Asia

While time-slice simulations with atmospheric general circulation models (GCMs) have been used for many years to regionalize climate projections and/or assess their uncertainties, there is still no consensus about the method used to prescribe sea surface temperature (SST) in such experiments. In the present study, the response of the Indian summer monsoon to increasing amounts of greenhouse gases and sulfate aerosols is compared between a reference climate scenario and three sets of time-slice experiments, consisting of parallel integrations for present-day and future climates. Different monthly mean SST boundary conditions have been tested in the present-day integrations: raw climatological SST derived from the reference scenario, observed climatological SST, and observed SST with interannual variability. For future climate, the SST forcing has been obtained by superimposing climatological monthly mean SST anomalies derived from the reference scenario onto the present-day SST boundary conditions. None of these sets of time-slice experiments is able to capture accurately the response of the Indian summer monsoon simulated in the transient scenario. This finding suggests that the ocean–atmosphere coupling is a fundamental feature of the climate system. Neglecting the SST feedback and variability at the intraseasonal to interannual time scales has a significant impact on the projected monsoon response to global warming. Adding interannual variability in the prescribed SST boundary conditions does not mitigate the problem, but can on the contrary reinforce the discrepancies between the forced and coupled experiments. The monsoon response is also shown to depend on the simulated control climate, and can therefore be sensitive to the use of observed rather than model-derived SSTs to drive the present-day atmospheric simulation, as well as to any approximation in the prescribed radiative forcing. While such results do not challenge the use of time-slice experiments for assessing uncertainties and understanding mechanisms in transient scenarios, they emphasize the need for high-resolution coupled atmosphere-ocean GCMs for dynamical downscaling, or at least for high-resolution atmospheric GCMs coupled with a slab or a regional ocean model.     

Intercomparison of precipitation simulated by regional climate models over East Asia in 1997 and 1998

Regional climate simulations in Asia from May 1997 to August 1998 were performed using the Seoul National University regional climate model （SNURCM） and Iowa State University regional climate model （ALT.MM5/LSM）, which were developed by coupling the NCAR/Land Surface Model （LSM） and the Mesoscale Model （MM5）. However, for physical processes of precipitation, the SNURCM used the Grell scheme for the convective parameterization scheme （CPS） and the simple ice scheme for the explicit moisture scheme （EMS）, while the ALT.MM5/LSM used the Betts-Miller scheme for CPS and the mixed phase scheme for EMS.
The simulated precipitation patterns and amounts over East Asia for the extreme climatic summer in 1997 （relative drought conditions） and 1998 （relative flood conditions） were especially focused upon. The ALT.MM5/LSM simulated more precipitation than was observed in 1997 due to more moisture and cloud water in the lower levels, despite weak upward motion. In the SNURCM, strong upward motion resulted in more precipitation than that was observed in 1998, with more moisture and cloud water in the middle levels. In the ALT.MM5/LSM, weak upward motion, unchanged moisture in the lower troposphere, and the decrease in latent heat flux at the surface increased convective precipitation only by 3% for the 1998 summer event. In the SNURCM, strong upward motion, the increase in moisture in the lower troposphere, and the increase in latent heat flux at the surface increased convective precipitation by 48% for the summer of 1998. The main differences between both simulations were moisture availability and horizontal momentum transport in the lower troposphere, which were also strongly influenced by large-scale forcing.     

Regional variability of climate change hot-spots in East Asia

The regional climate change index (RCCI) is employed to investigate hot-spots under 21st century global warming over East Asia. The RCCI is calculated on a 1-degree resolution grid from the ensemble of CMIP3 simulations for the B1, A1B, and A2 IPCC emission scenarios. The RCCI over East Asia exhibits marked sub-regional variability. Five sub-regional hot-spots are identified over the area of investigation: three in the northern regions (Northeast China, Mongolia, and Northwest China), one in eastern China, and one over the Tibetan Plateau. Contributions from different factors to the RCCI are discussed for the sub-regions. Analysis of the temporal evolution of the hot-spots throughout the 21st century shows different speeds of response time to global warming for the different sub-regions. Hot-spots firstly emerge in Northwest China and Mongolia. The Northeast China hot-spot becomes evident by the mid of the 21st century and it is the most prominent by the end of the century. While hot-spots are generally evident in all the 5 sub-regions for the A1B and A2 scenarios, only the Tibetan Plateau and Northwest China hot-spots emerge in the B1 scenario, which has the lowest greenhouse gas (GHG) concentrations. Our analysis indicates that sub-regional hot-spots show a rather complex spatial and temporal dependency on the GHG concentration and on the different factors contributing to the RCCI.     

Contrasting regional and global climate simulations over South Asia

Climate Dynamics - Two ensembles of climate simulations, one global and one regional, are used to investigate model errors and projected climate change in seasonal mean temperature and...     

大尺度土地利用变化对东亚地表能量、水分循环及气候影响的敏感性试验

利用NCAR大气环流模式CAM4.0,针对潜在植被和当代植被的分布情形进行了两组25 a的积分试验,探讨了土地利用变化对东亚地区地表能量平衡、水分循环和气候的可能影响.结果表明:以森林退化、农田迅速增加为主的当代土地利用变化,显著改变地表属性,使得东亚地区不同季节的地表反照率均明显增加,并显著改变东亚地区的冬、春季节的地表能量和水分循环.此外,当代大尺度土地利用变化对东亚地区大气环流也有一定影响,可引起东亚冬季风环流显著加强和东亚夏季较弱的偏南风异常.当代土地利用变化未能引起东亚地区近地面气温的显著变化,但可引起东亚北(南)部地区春季降水的显著增加(减小).     

Assessment of future climate change over East Asia due to the RCP scenarios downscaled by GRIMs-RMP

This study assesses future climate change over East Asia using the Global/Regional Integrated Model system—Regional Model Program (RMP). The RMP is forced by two types of future climate scenarios produced by the Hadley Center Global Environmental Model version 2 (HG2); the representative concentration pathways (RCP) 4.5 and 8.5 scenarios for the intergovernmental panel on climate change fifth assessment report (AR5). Analyses for the current (1980–2005) climate are performed to evaluate the RMP’s ability to reproduce precipitation and temperature. Two different future (2006–2050) simulations are compared with the current climatology to investigate the climatic change over East Asia centered in Korea. The RMP satisfactorily reproduces the observed seasonal mean and variation of precipitation and temperature. The spatial distribution of the simulated large-scale features and precipitation by the RMP is generally less reflective of current climatic conditions than that is given by the HG2, but their inter-annual variations in East Asia are better captured by the RMP. Furthermore, the RMP shows higher reproducibility of climate extremes including excessive heat wave and precipitation events over South Korea. In the future, strong warming is distinctly coupled with intensified monsoonal precipitation over East Asia. In particular, extreme weather conditions are increased and intensified over South Korea as follows: (1) The frequency of heat wave events with temperature greater than 30 °C is projected to increase by 131 and 111 % in the RCP 8.5 and 4.5 downscaling, relative to the current climate. (2) The RCP 8.5 downscaling shows the frequency and variability of heavy rainfall to increase by 24 and 31.5 %, respectively, while the statistics given by the RCP 4.5 downscaling are similar to those of the current climate.     

21个气候模式对东亚夏季环流模拟的评估II:年际变化

利用欧洲中期天气预报中心的ERA40再分析资料, 评估了参与政府间气候变化专门委员会第四次评估报告的21个全球海气耦合模式对东亚地区夏季大气环流年际变率的模拟能力,结果表明：（1）模式对东亚地区不同要素的年际变率模拟能力整体偏弱, 500 hPa高度场的模拟能力总体优于海平面气压场及850 hPa风场;（2）两大环流系统年际变率的模拟结果评估表明：就相关系数而言,副高强度、面积的模拟能力优于印度低压,多数模式能正确模拟出副高1970s后期增强的趋势;就标准差来看,模式对印度低压、印度低压东伸槽模拟效果相对较好;（3）评估三种季风指数的模拟能力结果显示,环流异常指数模拟效果略好,但多数模式都不能模拟出海陆气压差、经向风、环流异常季风指数的年际变化。     

The simulation of aerosol transport over East Asia region

This study was carried out to understand the contribution of PM10 from China emission to Seoul Metropolitan Area (SMA) during high concentration period in January, 2007. The hourly PM10 concentration in Seoul Metropolitan Area had reached up to over 150 μg/m³ on 17th and 23rd of January in 2007. The aerosol transports from China along the Northwestern wind becomes the background concentrations in Korea and the assessment of the amount of contribution from China is very important in managing the air quality improvement plan in SMA.The U.S. EPA's Models-3/CMAQ (Community Multiscale Air Quality) was used to simulate PM10 concentration. The CMAQ performance was evaluated by comparing with the measurements in SMA for the episode period. The predictions were relatively in a good agreement with the measurements.The results show that the PM10 transport from China to Korea is significant and its contribution reaches up to 80% in the episode period. In order to assess more extensively the aerosol transport in East Asia region, the study to run the model in full year with speciated PM component measurements in super site is underway.     

The simulation of aerosol transport over East Asia region

This study was carried out to understand the contribution of PM10 from China emission to Seoul Metropolitan Area (SMA) during high concentration period in January, 2007. The hourly PM10 concentration in Seoul Metropolitan Area had reached up to over 150 μg/m³ on 17th and 23rd of January in 2007. The aerosol transports from China along the Northwestern wind becomes the background concentrations in Korea and the assessment of the amount of contribution from China is very important in managing the air quality improvement plan in SMA.The U.S. EPA's Models-3/CMAQ (Community Multiscale Air Quality) was used to simulate PM10 concentration. The CMAQ performance was evaluated by comparing with the measurements in SMA for the episode period. The predictions were relatively in a good agreement with the measurements.The results show that the PM10 transport from China to Korea is significant and its contribution reaches up to 80% in the episode period. In order to assess more extensively the aerosol transport in East Asia region, the study to run the model in full year with speciated PM component measurements in super site is underway.     

Future change of extreme temperature climate indices over East Asia with uncertainties estimation in the CMIP5

How well the climate models simulate extreme temperature over East Asia and how the extreme indices would change under anthropogenic global warming are investigated. The indices studied include hot days (HD), tropical nights (TN), growing degree days (GDD), and cooling degree days (CDD) in summer and heating degree days (HDD) and frost days (FD) in winter. The representative concentration pathway 4.5 (RCP 4.5) experiments for the period of 2075–2099 are compared with historical simulations for the period of 1979–2005 from 15 coupled models that are participated in phase 5 of the Coupled Model Intercomparison Project (CMIP5). To optimally estimate future change and its uncertainty, groups of best models are selected based on Taylor diagrams, relative entropy, and probability density function (PDF) methods previously suggested. Overall, the best models’ multi-model ensemble based on Taylor diagrams has the lowest errors in reproducing temperature extremes in the present climate among three methods. Selected best models in three methods tend to project considerably different changes in the extreme indices from each other, indicating that the selection of reliable models are of critical importance to reduce uncertainties. Three groups of best models show significant increase of summerbased indices but decrease of the winter-based indices. Over East Asia, the most significant increase is seen in the HD (336 ± 23.4% of current climate) and the most significant decrease is appeared in the HDD (82 ± 4.2%). It is suggested that the larger future change in the HD is found over in the Southeastern China region, probably due to a higher local maximum temperature in the present climate. All of the indices show the largest uncertainty over Southeastern China, particularly in the TN (~3.9 times as large as uncertainty over East Asia) and in the HD (~2.4). It is further noted that the TN reveals the largest uncertainty over three East Asian countries (~1.7 and 1.4 over Korea and Japan, respectively). These future changes in extreme temperature events have an important implication for energy-saving applications and human molarity in the future.     

A multi-physics ensemble of regional climate change projections over the Iberian Peninsula

This study illustrates the sensitivity of regional climate change projections to the model physics. A single-model (MM5) multi-physics ensemble of regional climate simulations over the Iberian Peninsula for present (1970–1999) and future (2070–2099 under the A2 scenario) periods is assessed. The ensemble comprises eight members resulting from the combination of two options of parameterization schemes for the planetary boundary layer, cumulus and microphysics. All the considered combinations were previously evaluated by comparing hindcasted simulations to observations, none of them providing clearly outlying climates. Thus, the differences among the various ensemble members (spread) in the future projections could be considered as a matter of uncertainty in the change signals (as similarly assumed in multi-model studies). The results highlight the great dependence of the spread on the synoptic conditions driving the regional model. In particular, the spread generally amplifies under the future scenario leading to a large spread accompanying the mean change signals, as large as the magnitude of the mean projected changes and analogous to the spread obtained in multi-model ensembles. Moreover, the sign of the projected change varies depending on the choice of the model physics in many cases. This, together with the fact that the key mechanisms identified for the simulation of the climatology of a given period (either present or future) and those introducing the largest spread in the projected changes differ significantly, make further claims for efforts to better understand and model the parameterized subgrid processes.     

Evaluation of a high-resolution regional climate simulation over Greenland

A simulation of the 1991 summer has been performed over south Greenland with a coupled atmosphere–snow regional climate model (RCM) forced by the ECMWF re-analysis. The simulation is evaluated with in-situ coastal and ice-sheet atmospheric and glaciological observations. Modelled air temperature, specific humidity, wind speed and radiative fluxes are in good agreement with the available observations, although uncertainties in the radiative transfer scheme need further investigation to improve the model’s performance. In the sub-surface snow-ice model, surface albedo is calculated from the simulated snow grain shape and size, snow depth, meltwater accumulation, cloudiness and ice albedo. The use of snow metamorphism processes allows a realistic modelling of the temporal variations in the surface albedo during both melting periods and accumulation events. Concerning the surface albedo, the main finding is that an accurate albedo simulation during the melting season strongly depends on a proper initialization of the surface conditions which mainly result from winter accumulation processes. Furthermore, in a sensitivity experiment with a constant 0.8 albedo over the whole ice sheet, the average amount of melt decreased by more than 60%, which highlights the importance of a correctly simulated surface albedo. The use of this coupled atmosphere–snow RCM offers new perspectives in the study of the Greenland surface mass balance due to the represented feedback between the surface climate and the surface albedo, which is the most sensitive parameter in energy-balance-based ablation calculations.     

土壤湿度对东亚夏季气候潜在可预报性影响的数值模拟

利用全球大气环流模式NCARCAM3进行了在给定的观测海温条件下的22a（1979—2000年）5—8月的2组集合试验。运用方差分析方法,分析了在气候态和年际变化的表层土壤湿度情况下,CAM3模式模拟的东亚夏季气候潜在可预报性及其差异。结果表明：在给定的观测海温条件下,采用气候态的土壤湿度时,CAM3模式模拟的东亚夏季气候的潜在可预报性偏低;而采用年际变化的土壤湿度时,模拟的夏季气候潜在可预报性有所提高,尤其是在中国西北地区;后者模拟的中国西北地区夏季降水和气温的潜在可预报性比前者的模拟结果提高0．1以上。其原因可能是：采用年际变化的土壤湿度时,模式可以更好地模拟出中国西北地区的地表蒸发量和湍流热通量的年际变化,进而使得模式对该地区夏季气候的预报技巧得到提高。     

21个气候模式对东亚夏季环流模拟的评估Ｉ：气候态.

利用欧洲中期天气预报中心的40 a再分析资料(ERA40),评估了参与政府间气候变化专门委员会第四次评估报告(IPCC AR4)的21个全球海气耦合模式对东亚地区夏季大气环流气候态的模拟能力.结果表明:(1)尽管各模式模拟性能差异较大,但模式对东亚地区海平面气压场(SLP)、850 hPa风场及500 hPa位势高度场的气候态均有较好模拟;整体来说,500 hPa位势高度场模拟效果最好,SLP场模拟相对较差;(2)SLP在高原上模拟存在明显不足;多数模式能较好模拟850 hPa纬向、经向风场的基本特征;500 hPa位势高度场各模式模拟偏差一致性的区域性差异不明显;(3)模式对东亚地区夏季两大环流系统模拟整体偏弱,西太平洋副热带高压模拟明显偏弱.     

Comparison of four ensemble methods combining regional climate simulations over Asia

A number of uncertainties exist in climate simulation because the results of climate models are influenced by factors such as their dynamic framework, physical processes, initial and driving fields, and horizontal and vertical resolution. The uncertainties of the model results may be reduced, and the credibility can be improved by employing multi-model ensembles. In this paper, multi-model ensemble results using 10-year simulations of five regional climate models (RCMs) from December 1988 to November 1998 over Asia are presented and compared. The simulation results are derived from phase II of the Regional Climate Model Inter-comparison Project (RMIP) for Asia. Using the methods of the arithmetic mean, the weighted mean, multivariate linear regression, and singular value decomposition, the ensembles for temperature, precipitation, and sea level pressure are carried out. The results show that the multi-RCM ensembles outperform the single RCMs in many aspects. Among the four ensemble methods used, the multivariate linear regression, based on the minimization of the root mean square errors, significantly improved the ensemble results. With regard to the spatial distribution of the mean climate, the ensemble result for temperature was better than that for precipitation. With an increasing number of models used in the ensembles, the ensemble results were more accurate. Therefore, a multi-model ensemble is an efficient approach to improve the results of regional climate simulations.     

Interannual variability and expected regional climate change over North America

This study aims to analyse the interannual variability simulated by several regional climate models (RCMs), and its potential for disguising the effect of seasonal temperature increases due to greenhouse gases. In order to accomplish this, we used an ensemble of regional climate change projections over North America belonging to the North American Regional Climate Change Program, with an additional pair of 140-year continuous runs from the Canadian RCM. We find that RCM-simulated interannual variability shows important departures from observed one in some cases, and also from the driving models’ variability, while the expected climate change signal coincides with estimations presented in previous studies. The continuous runs from the Canadian RCM were used to illustrate the effect of interannual variability in trend estimation for horizons of a decade or more. As expected, it can contribute to the existence of transitory cooling trends over a few decades, embedded within the expected long-term warming trends. A new index related to signal-to-noise ratio was developed to evaluate the expected number of years it takes for the warming trend to emerge from interannual variability. Our results suggest that detection of the climate change signal is expected to occur earlier in summer than in winter almost everywhere, despite the fact that winter temperature generally has a much stronger climate change signal. In particular, we find that the province of Quebec and northwestern Mexico may possibly feel climate change in winter earlier than elsewhere in North America. Finally, we show that the spatial and temporal scales of interest are fundamental for our capacity of discriminating climate change from interannual variability.     

IPCC A2情景下中国区域气候变化的数值模拟

在政府间气候变化委员会(IPCC)排放情景特别报告 (SRES)的A2情景下,利用CSIRO Mark3海气耦合模式模拟现代和未来2个10年的模拟结果,驱动MM5区域气候模式进行中国未来区域气候变化的数值模拟试验,研究了IPCC A2情景下未来中国温度、降水和环流等的变化趋势.结果表明,(1)区域气候模式MM5V3能够再现气候平均环流、降水和温度分布的主要特征,具有较好的区域气候变化模拟能力;(2)IPCC A2情景下,未来中国平均地面气温将有明显的升高,特别是中国的东北、西北和西南地区增幅超过了1 ℃.冬季,地面平均气温的增幅由南至北逐渐增加;夏季,在内蒙和中国西南地区有明显的增温.伴随温度的升高,降水也有明显的变化,年平均降水在中国的东北地区、江淮流域及以南大部分地区都有明显的增强,而中国华北部分地区及西南、西北大部分地区降水将呈减少趋势.不同季节不同地区的降水变化也不同,秋季华北、华南和江淮地区降水都增加,而冬季减少.降水的年内变化也有所增强.     

Convection-permitting regional climate simulation of warm-season precipitation over Eastern China

Climate Dynamics - Convection-permitting regional climate models have been shown to improve precipitation simulation in many aspects, such as the diurnal cycle, precipitation frequency, intensity...