区域和全球模式的嵌套技术 及其长期积分试验

将区域模式嵌入澳大利亚CSIRO (Commonwealth Scientific and Industrial Research Organization）的全球模式中,并将其应用于区域模式的长期气候积分试验。模拟结果表明,当区域与全球模式嵌套时,边界吸收问题十分重要,由区域模式得到的高分辨率大尺度环流形式在边界上必须与全球模式提供的强迫一致,同时区域模式必须给出基于模式内部物理过程产生的高分辨信息。因此,在嵌套过程中,必须仔细考虑缓冲区的设置,使大尺度强迫与中尺度特征充分混合,既保持区域模式内外的一致性,又使区域内部中尺度强迫物理过程得到充分发展。将区域模式与澳大利亚CSIRO的9层21波三角形截断谱模式嵌套后,完成了连续3年的区域气候模式积分。模拟结果表明,由于区域模式较好地刻划了区域尺度的地形、下垫面和海岸线分布等的细节特征,模拟的区域气候特征比全球模式有较大的改进,尤其是对季风降水的模拟,区域模式明显改进了全球模式的模拟结果。     

区域气候模式中侧边界地形缓冲区作用的数值试验

利用区域环境系统集成模式以1998年夏季为例,通过数值试验研究了侧边界地形缓冲区对区域气候模拟结果的影响。结果表明,设置侧边界地形缓冲区使模拟场和观测的均方根误差都有所减小,区域平均中尺度动能也减小,从而有利于维持区域模式长期积分的稳定性。设置地形缓冲区并不改变模拟降水分布格局,但对主要降水区各降水时段降水强度的模拟有不同程度的改进。     

区域气候模式在东亚地区的应用研究——垂直分辨率与侧边界对夏季季风降水影响研究

将美国国家大气研究中心（NCAR）的区域气候模式（RegCM2-1996）设置在东亚-西太平洋区域（简称东亚区域气候模式RegCM2/EA）。利用该模式研究东亚区域气候模式的几个重要问题，即：垂直分辨率的影响，侧边界条件（如嵌套技术、缓冲区宽度、不同资料）的重要性等。数值试验结果表明：细垂直分辨率模拟的降水分布优于粗分辨率模式，但容易引起“数值点暴雨”；RegCM2/EA与不同来源的大尺度侧边界嵌套，模拟的降水会有明显的不同；当用RegCM2/EA模拟较大区域时，应该取较宽的缓冲区；在各种嵌套方案中，指数松弛嵌套方法最好。这些结果为进一步探讨东亚区域气候模式的特点以及发展与改造区域气候模式提供一定的依据。研究结果还需要用更多的数值试验来验证。     

区域气候模式侧边界的处理对东亚夏季风降水模拟的影响

在区域气候模式模拟中,侧边界的作用是引入大尺度强迫场。如何处理好侧边界,即大尺度强迫场和区域气候模式本身之间的关系问题,对于区域气候模式模拟和预报东亚夏季风降水具有重要意义。本文利用美国纽约州立大学Albany分校的区域气候模式（SUNYA-ReCM）,设计了两种不同的侧边界处理方法,来探讨侧边界对东亚夏季风降水模拟的影响。驱动区域模式的大尺度强迫场来自欧洲中期天气预报中心（ECMWF）及热带海洋大气研究计划（TOGA）的分析资料场。试验结果表明:（1）当模式的区域较大时,采用较小的侧边界缓冲区会在缓冲区与模式内部的交界处产生不连续;扩大缓冲区并且考虑不同尺度强迫在垂直方向上的不同作用,可以避免这一缺陷。（2）更重要的是采用后一种方案,即减少了区域气候模式在模拟大尺度环流场方面所起的作用,使得模式更多地依赖侧边界来得到更真实的、对东亚夏季风降水起重大影响的一些气流,如副高、西南季风和南海季风,对东亚夏季风降水无论是在大小上还是在雨带位置的演变上都能进行更好的模拟。     

初、边值条件对区域气候模拟的影响

利用区域气候模式(RegCM2)对1998年夏季风气候进行了模拟,并就初、边值条件对模拟结果的影响情况进行了讨论,结果表明:该模式可以较好地模拟出月际尺度的气候变化,但对降水异常的模拟还需作进一步完善.通过在几个季节采用不同初始场进行的数值模拟发现,从春季开始的积分其结果对初始场的敏感性较高,初始场的差别会对后期模拟产生明显影响.相对来说,从冬季开始的积分,其对初始场的依赖性较小,初始场的差别会在积分过程中逐渐减小,因而在利用RegCM2进行区域气候模拟时宜从冬季开始.另外,通过对采用不同侧边界嵌套方案的模拟效果进行简单讨论,发现当采用较少的缓冲区(5圈)时,海绵边界对温度、比湿及位势高度的模拟要比指数松弛及流入流出边界好,降水的模拟也要比其他方案好一些,但对风场的模拟则不如指数松弛方案.     

论区域气候模式与全球模式嵌套时边界区的选择

做了3个试验,第一个试验只用大气环流模式(GCM),主要考察GCM的性能并确定其误差的区域分布.后两个为对比试验,一个试验中,将区域气候模式(RCM)(NjU-RCM)的侧边界放在全球模式(L9R15)中我们感兴趣的区域,未考虑侧边界区GCM的误差大小,另一个试验中,RCM的侧边界位置根据GCM预报误差的空间分布选取,使其落在GCM预报误差较小的区域.3个试验都对1998年5、6、7月份中国区域的降水过程进行了模拟和比较.结果表明:单独使用GCM的效果最差;当用GCM-RCM嵌套模式对区域气候进行预测时,GCM侧边界值的误差对RCM的模拟结果有显著的影响,嵌套侧边界若选择在GCM系统性误差较小的地区,模拟或预测效果会有明显的改进.     

区域气候模式在东亚地区的应用研究：垂直分辨率与边界对夏季季风降水影响

将美国国家大气研究中心（ＮＣＡＲ）的区域气候模式（ＲｅｇＣＭ２－１９９６）设置在东亚－西太平洋区域。利用该模式研究东亚区域气候模式的几个重要问题,即：垂直分辨率的影响,侧边界条件的重要性等。数值试验结果表明：细垂直分辨率模拟的降水分布优于粗分辨率模式,但容易引起“数值点暴雨”;ＥｅｇＣＭ２／ＥＡ与不崃源的大尺度侧边界嵌套,模拟的降水会有明显的不同,当用ＲｅｇＣＭ２／ＥＡ与不同来源的大尺度侧边界嵌套     

一粗细网格模式“三维嵌套”方案的设计及试验结果分析

该文简要地分析了水平侧边界嵌套技术中存在的问题，提出了“三维嵌套”的设想，并就不同范围对水平侧边界嵌套及三维嵌套方案进行了对比试验。试验结果表明：（１）三维嵌套方案对区域模式的降水及中、下层形势场的预报均有所改进；（２）嵌套区域越小，三维嵌套方案对预报的改进效果越明显；（３）三维嵌套方案对预报的改进随积分时间的增长而愈加显著     

区域气候模拟中侧边界嵌套误差的研究

在复杂地形条件下嵌套细网格模式的基础上，建立了与球圈模式相嵌套的区域模式系统，对几种不同条件下的嵌套误差进行了比较分析，研究了区域模式嵌套误差的特征分布及时空演变特征。初步分析表明:区域模式嵌套造成的误差在不同区域的分布不同，且不同的物理量在时空的分布也不同；动能场的误差主要在边界区上层的流入区，感热场的误差在边界区上层，水汽的误差在边界区上层的流入区；侧边界输入时间间隔对模式嵌套误差有一定的影响。有限区细网格模式在上层长波误差大于粗网格环圈模式上层误差，在下层短波模拟的误差比粗网格环圈模式的下层误差要小。相速误差对侧边界嵌套误差的影响在下层很严重，嵌套误差的大小与大小模式的网格距之比有关；在大小模式物理参数化过程一致的条件下，无日变化的区域模式其嵌套误差远大于有日变化的区域模式嵌套误差。     

一有限区域模式对1979年7月气候平均场的模拟

使用一个有限区域数值模式，以１９７９年７月１日００：００为初值，用７月份每天的实况资料进行侧边界嵌套，对模式连续发３１ｄ。模拟的７月气候平均状态与实况比较表明：模拟结果与实况场较为一致，该模式可用于研究区域气候变化问题。     

Sources of systematic errors in the climatology of a regional climate model over Europe

 Two ten-year simulations made with a European regional climate model (RCM) are compared. They are driven by the same observed sea surface temperatures but use different lateral boundary forcing. For one simulation, RCM AMIP, this forcing is obtained from a standard integration of a global general circulation model (GCM AMIP), whereas for the other simulation, RCM ASSIM, it is derived from a time series of operational analyses. The archive of analysis fields (surface pressure plus winds and temperatures on various pressure levels) is not sufficiently comprehensive to provide directly the full set of driving fields required for the RCM (in particular, no moisture fields are present), so these are obtained via a GCM integration, GCM ASSIM, in which the model is continuously relaxed towards the analysis fields using a data assimilation technique. Errors in RCM AMIP can arise either from the internal RCM physics or from errors in the lateral boundary forcing inherited from GCM AMIP. Errors in RCM ASSIM can arise from the internal RCM physics or the boundary moisture forcing but not from the driving circulation. Although previous studies have considered RCM integrations driven either by output from standard GCM integrations or operational analyses, our study is the first to compare parallel integrations of each type. This allows the total systematic error in an RCM integration driven by standard GCM output to be partitioned into components arising from the driving circulation and the internal RCM physics. These components indicate the scope for reducing regional simulation biases by improving either the driving GCM or the RCM itself. The results relate mainly to elements of surface climate likely to be influenced by both the driving circulation and regional physical processes operating in the RCM. For cloud cover, errors are found to arise largely from the internal RCM physics. Values are too low despite a positive relative humidity bias, indicating shortcomings in the parametrisation scheme used to calculate cloud cover. In summer, surface temperature and precipitation errors are also explained principally by regional processes. For example excessive solar heating leads to anomalously high surface temperatures over southern Europe and excessive drying of the soil reduces precipitation in the south eastern sector of the domain. The lateral boundary forcing reduces precipitation in the south eastern sector of the domain. The lateral boundary forcing also exerts some influence, mainly via a tropospheric cold bias which partially offsets the warming over southern Europe and also increases precipitation. In other seasons the lateral boundary forcing and the regional physics both contribute significantly to the errors in surface temperature and precipitation. In winter the boundary forcing (apart from moisture) is responsible for about 60% of the total error variance for temperature and about 40% for precipitation, due to the cold bias and circulation errors such as a southward shift in the storm track. The remaining errors arise from the regional physics, although for precipitation an excessive supply of moisture from the lateral boundaries also contributes. The skill of the mesoscale component of the surface temperature and precipitation distributions exceeds previous estimates, due to more realistic observed climatology. The mesoscale patterns are very similar in the two RCM simulations indicating that errors in the simulation of fine scale detail arise mainly from inadequate representations of local forcings rather than errors in the large-scale circulation. Circulation errors in RCM AMIP (e.g. cold bias, southward shift of storm track) are also present in GCM AMIP, but are largely absent in RCM ASSIM except in summer. This confirms evidence from previous work that the key to reducing most circulation errors in the RCM lies in improving the driving GCM. Regional processes only make a major contribution to circulation errors in summer, when reduced advection from the boundaries allows errors in surface temperature to be transmitted more effectively into the troposphere. Finally, we find evidence of error balances in the GCM which act to minimise biases in important climatological variables. This reflects tuning of the model physics at GCM resolution. In order to achieve simultaneous optimisation of the RCM and GCM at widely differing resolutions it may be necessary to introduce explicit scale dependences into some aspects of the physics. Received: 17 September 1997/Accepted: 10 March 1998     

Regional model simulation of summer rainfall over the Philippines: Effect of choice of driving fields and ocean flux schemes

Summary The latest version of the Abdus Salam International Centre for Theoretical Physics (ICTP) regional model RegCM is used to investigate summer monsoon precipitation over the Philippine archipelago and surrounding ocean waters, a region where regional climate models have not been applied before. The sensitivity of simulated precipitation to driving lateral boundary conditions (NCEP and ERA40 reanalyses) and ocean surface flux scheme (BATS and Zeng) is assessed for 5 monsoon seasons. The ability of the RegCM to simulate the spatial patterns and magnitude of monsoon precipitation is demonstrated, both in response to the prominent large scale circulations over the region and to the local forcing by the physiographical features of the Philippine islands. This provides encouraging indications concerning the development of a regional climate modeling system for the Philippine region. On the other hand, the model shows a substantial sensitivity to the analysis fields used for lateral boundary conditions as well as the ocean surface flux schemes. The use of ERA40 lateral boundary fields consistently yields greater precipitation amounts compared to the use of NCEP fields. Similarly, the BATS scheme consistently produces more precipitation compared to the Zeng scheme. As a result, different combinations of lateral boundary fields and surface ocean flux schemes provide a good simulation of precipitation amounts and spatial structure over the region. The response of simulated precipitation to using different forcing analysis fields is of the same order of magnitude as the response to using different surface flux parameterizations in the model. As a result it is difficult to unambiguously establish which of the model configurations is best performing.     

Sub-Saharan Northern African climate at the end of the twenty-first century: forcing factors and climate change processes

A regional climate model, the Weather Research and Forecasting (WRF) Model, is forced with increased atmospheric CO₂ and anomalous SSTs and lateral boundary conditions derived from nine coupled atmosphere–ocean general circulation models to produce an ensemble set of nine future climate simulations for northern Africa at the end of the twenty-first century. A well validated control simulation, agreement among ensemble members, and a physical understanding of the future climate change enhance confidence in the predictions. The regional model ensembles produce consistent precipitation projections over much of northern tropical Africa. A moisture budget analysis is used to identify the circulation changes that support future precipitation anomalies. The projected midsummer drought over the Guinean Coast region is related partly to weakened monsoon flow. Since the rainfall maximum demonstrates a southward bias in the control simulation in July–August, this may be indicative of future summer drying over the Sahel. Wetter conditions in late summer over the Sahel are associated with enhanced moisture transport by the West African westerly jet, a strengthening of the jet itself, and moisture transport from the Mediterranean. Severe drought in East Africa during August and September is accompanied by a weakened Indian monsoon and Somali jet. Simulations with projected and idealized SST forcing suggest that overall SST warming in part supports this regional model ensemble agreement, although changes in SST gradients are important over West Africa in spring and fall. Simulations which isolate the role of individual climate forcings suggest that the spatial distribution of the rainfall predictions is controlled by the anomalous SST and lateral boundary conditions, while CO₂ forcing within the regional model domain plays an important secondary role and generally produces wetter conditions.     

我国对流层臭氧增加对气温的影响

利用耦台的区域气候模式和大气化学模式模拟对流层臭氧的产生、分布和对辐射传输、地表温度、气温等的影响。通过对比模拟发现：对流层中臭氧的增加基本使大气顶晴空辐射强迫为正；对流层中的臭氧含量变化能影响云量且进一步影响温度。由于对流层臭氧增加导致的晴空辐射强迫在4月份最大、1月份最小。     

RegCM3模式对新疆1996年降水和气温的数值模拟分析

通过数值模拟方法,研究了降水和气温对模式分辨率、初始和边界条件的敏感性。结果表明：区域模式RegCM3对新疆1996年冬季和夏季的降水和气温具有一定的模拟能力,气温的模拟要优于降水。分辨率、初始和边界条件对区域模式的模拟结果有较大的影响。模式分辨率的提高,可以增强对气温的模拟能力,尤其是气温沿地形变化的特点。分辨率的提高,同样可以改进降水的量级和落区。相同分辨率下,不同初始和边界条件,对降水的模拟结果影响不大。无论分辨率和初始,边界条件如何变化,塔克拉玛干沙漠南麓均有虚假降水出现,说明该模式在刻画复杂地形方面,还存在不足。     

Numerical Simulation of Regional Climate Change under IPCC A2 Scenario in China

Regional climate change in China under the IPCC A2 Scenario, was simulated for continuous 10-yr period by the MM5V3, using the output of an IPCC A2 run from CISRO Mark 3 climate system model as lateral and surface boundary conditions. The regional climate change of surface air temperature, precipitation, and circulation were analyzed. The results showed that （1） the distribution of mean circulation, surface air temperature, and precipitation was reproduced by the MM5V3. The regional climate model was capable to improve the regional climate simulation driven by GCM. （2） The climate change simulation under the IPCC A2 Scenario indicated that the surface air temperature in China would increase in the future, with a stronger trend in winter and the increasing magnitude from the south to the north. The precipitation distribution would appear a distinct change as well. Annual mean precipitation would remarkably increase in Northeast China, Yangtze and Huaihe River Valley, and the south area of the valley. Meanwhile, rainfall would show a decreasing trend in partial areas of North China, and many regions of Southwest and Northwest China.     

Regional climate change experiments over southern South America. I: present climate

We present an analysis of a regional simulation of present-day climate (1981–1990) over southern South America. The regional model MM5 was nested within time-slice global atmospheric model experiments conducted by the HadAM3H model. We evaluate the capability of the model in simulating the observed climate with emphasis on low-level circulation patterns and surface variables, such as precipitation and surface air mean, maximum and minimum temperatures. The regional model performance was evaluated in terms of seasonal means, seasonal cycles, interannual variability and extreme events. Overall, the regional model is able to capture the main features of the observed mean surface climate over South America, its seasonal evolution and the regional detail due to topographic forcing. The observed regional patterns of surface air temperatures (mean, maxima and minima) are well reproduced. Biases are mostly within 3°C, temperature being overestimated over central Argentina and underestimated in mountainous regions during all seasons. Biases in northeastern Argentina and southeastern Brazil are positive during austral spring season and negative in other seasons. In general, maximum temperatures are better represented than minimum temperatures. Warm bias is larger during austral summer for maximum temperature and during austral winter for minimum temperature, mainly over central Argentina. The broad spatial pattern of precipitation and its seasonal evolution are well captured; however, the regional model overestimates the precipitation over the Andes region in all seasons and in southern Brazil during summer. Precipitation amounts are underestimated over the La Plata basin from fall to spring. Extremes of precipitation are better reproduced by the regional model compared with the driving model. Interannual variability is well reproduced too, but strongly regulated by boundary conditions, particularly during summer months. Overall, taking into account the quality of the simulation, we can conclude that the regional model is capable in reproducing the main regional patterns and seasonal cycle of surface variables. The present reference simulation constitutes the basis to examine the climate change simulations resulting from the A2 and B2 forcing scenarios which are being reported in a separate study.     

区域气候模拟研究

区域气候模拟是近几年发展起来的研究有限区域气候及气候变化的方法。由于区域气候模式较好地表示了地形和地表状况，同时包含较详细的陆地过程方案，因而能捕获许多大气环流模式难以分辨的区域尺度温度、降水分布和土壤水分变化特征。此外，区域气候模拟对于了解温室气体强迫可能导致的全球增暖在区域尺度上的特征及生态、环境效应也具有重要的意义。该文总结区域气候模式和模拟试验结果，并指出存在问题及今后研究的重点。