一个引入近地层的区域气候模式

把近地层引入到NCAR的区域气候模式RegCM2中(简称为RCMC1)，用该模式及1991年梅雨期间的观测资料作了3组模拟试验，并同实况进行了比较。结果表明，在区域气候模式中引入近地层后，能够更合理的模拟出地表及植被同大气之间的感热和潜热通量输送，从而改善模式模拟的月降水及月平均地面温度的分布。l0层的RCMC1比18层RCM具有更优的模拟气候的能力，且一个模式天的计算量节省227s。     

基于投影寻踪原理的动态聚类模型及其在气候区划中的应用

以投影寻踪原理为基础, 结合动态聚类方法, 建立了基于投影寻踪原理的动态聚类模型, 并首次将其应用于气候区划分析中。首先, 利用线性投影技术将多因素聚类问题转换为投影特征值的线性聚类问题; 其次, 利用动态聚类方法完成投影特征值序列的聚类分析; 最后, 通过气候区划实例验证了基于投影寻踪原理的动态聚类模型的可行性与有效性。     

一个包含土壤和植被的区域气候模式及其性能检验

本文研制了一个三维地气耦合的区域气候模式，该模式由大气、土壤和植被三个子模式组成，各子模式间通过动量、能量和水份交换过程进行相互作用。在大气子模式中提出用z-z*混合坐标系处理地形的新方法，并把诊断分析中的散度修订方案引入数值模式，使其在物理依据上更加合理。此外，模式中较为详细地考虑了影响区域气候形成和变化的物理过程。简单的数值试验表明，区域气候模式比较真实地模拟了土壤和植被冠层的温度日变化，对区域气候平均态也有一定的模拟能力，可较好地处理大地形，具有良好的稳定性能，并对下垫面热力非均匀性的响应也是敏感的。     

Low-Level Wind Forecast over the La Plata River Region with a Mesoscale Boundary-Layer Model Forced by Regional Operational Forecasts

A mesoscale boundary-layer model (BLM) is used for running 12-h low-level wind forecasts for the La Plata River region. Several experiments are performed with different boundary conditions that include operational forecasts of the Eta/CPTEC model, local observations, as well as a combination of both. The BLM wind forecasts are compared to the surface wind observations of five weather stations during the period November 2003–April 2004. Two accuracy measures are used: the hit rate or percentage of cases with agreement in the wind direction sector, and the root-mean-squared error (RMSE) of the horizontal wind components. The BLM surface wind forecasts are always more accurate, since its averaged hit rate is three times greater and its averaged RMSE is one half smaller than the Eta forecasts. Despite the large errors in the surface winds displayed by the Eta forecasts, its 850 hPa winds and surface temperature forecasts are able to drive the BLM model to obtain surface winds forecasts with smaller errors than the Eta model. An additional experiment demonstrates that the advantage of using the BLM model for forecasting low-level winds over the La Plata River region is the result of a more appropriate definition of the land–river surface temperature contrast. The particular formulation that the BLM model has for the geometry of the river coasts is fundamental for resolving the smaller scale details of the low-level local circulation. The main conclusion of the study is that operational low-level wind forecasts for the La Plata River region can be improved by running the BLM model forced by the Eta operational forecasts. L. Sraibman and G. J. Berri—Members of Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) of Argentina. An erratum to this article can be found at     

An Overview of BCC Climate System Model Development and Application for Climate Change Studies

This paper reviews recent progress in the development of the Beijing Climate Center Climate System Model(BCC-CSM) and its four component models(atmosphere,land surface,ocean,and sea ice).Two recent versions are described:BCC-CSM1.1 with coarse resolution(approximately 2.8125°×2.8125°) and BCC-CSM1.1(m) with moderate resolution(approximately 1.125°×1.125°).Both versions are fully coupled climate-carbon cycle models that simulate the global terrestrial and oceanic carbon cycles and include dynamic vegetation.Both models well simulate the concentration and temporal evolution of atmospheric CO_2 during the 20th century with anthropogenic CO2 emissions prescribed.Simulations using these two versions of the BCC-CSM model have been contributed to the Coupled Model Intercomparison Project phase five(CMIP5) in support of the Intergovernmental Panel on Climate Change(IPCC) Fifth Assessment Report(AR5).These simulations are available for use by both national and international communities for investigating global climate change and for future climate projections.Simulations of the 20th century climate using BCC-CSMl.l and BCC-CSMl.l(m) are presented and validated,with particular focus on the spatial pattern and seasonal evolution of precipitation and surface air temperature on global and continental scales.Simulations of climate during the last millennium and projections of climate change during the next century are also presented and discussed.Both BCC-CSMl.l and BCC-CSMl.l(m) perform well when compared with other CMIP5 models.Preliminary analyses indicate that the higher resolution in BCC-CSM1.1(m) improves the simulation of mean climate relative to BCC-CSMl.l,particularly on regional scales.     

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。     

相空间EOF方法及其在气候诊断中的应用

提出了相空间EOF新方法，由此研究了四川测站降水和温度和气候变化。结果表明：突变性是气候变化最重要的特征，周期性是第二位的；突变在气候变化的高层次上有显著反映，低层次对突变具有反馈作用，正（负）反馈作用突出（掩盖）气候变化的突变性；并且在气候诊断分析中，这是一种有特色的方法。     

Searching for Added Value in Simulating Climate Extremes with a High-Resolution Regional Climate Model over Western Canada

We evaluate the capacity of a regional climate model to represent observed extreme temperature and precipitation events and also examine the impact of increased resolution, in an effort to identify added value in this respect. Two climate simulations of western Canada (WCan) were conducted with the Canadian Regional Climate Model (version 4) at 15 (CRCM15) and 45?km (CRCM45) horizontal resolution driven at the lateral boundaries by data from the European Centre for Medium-range Weather Forecasts (ECMWF) 40-year Reanalysis (ERA-40) for the period 1973–1995. The simulations were evaluated using the spline-interpolated dataset ANUSPLIN, a daily observational gridded surface temperature and precipitation product with a nominal resolution of approximately 10?km. We examine a range of climate extremes, comprising the 10th and 90th percentiles of daily maximum (TX) and minimum (TN) temperatures, the 90th percentile of daily precipitation (PR90), and the 27 core Climate Daily Extremes (CLIMDEX) indices.

Both simulations exhibit cold biases compared with observations over WCan, with the bias exacerbated at higher resolution, suggesting little added value for temperature overall. There are instances, however, of regional improvement in the spatial pattern of temperature extremes at the higher resolution of CRCM15 (e.g., the CLIMDEX index for the annual number of days when TX?>?25°C). The high-resolution simulations also reveal similarly localized features in precipitation (e.g., rain shadows) that are not resolved at the 45?km resolution. With regard to precipitation extremes, although both simulations generally display wet biases, CRCM15 features a reduced bias in PR90 in all seasons except winter. This improvement occurs despite the fact that spatial and interannual variability of PR90 in CRCM15 is significantly overestimated relative to both CRCM45 and ANUSPLIN. We posit that these characteristics are the result of demonstrable differences between corresponding topographical datasets used in the gridded observations and CRCM, the resulting errors propagated to physical variables tied to elevation and the beneficial effect of subsequent spatial averaging. Because topographical input is often discordant between simulations and gridded observations, it is argued that a limited form of spatial averaging may contribute added value beyond that which has already been noted in previous studies with respect to small-scale climate variability.     

Numerical Studies with a Regional Atmospheric Climate Model Based on Changes in the Roughness Length for Momentum and Heat Over Antarctica

A regional atmospheric climate model is used toexamine the effect of changes in the roughnesslengths of momentum (_z0m) and heat (_z0h)on the structure of the lower atmosphere and on thesurface energy fluxes over Antarctica. Fourexperiments were carried out in which _z0mand/or _z0h were altered with respect to acontrol experiment. The changes consisted of (1) alowering of _z0m from a field aggregated froma vegetation map with an orographic correction basedon the European Centre for Medium-Range WeatherForecasts _z0m field, to a constant value of10^-3 m; and (2) a lowering of _z0h from a valueequal to _z0m to a constant value of 10^-3 mor a value dependent on the wind speed via a surfacerenewal model. A reduction of _z0m results in theexpected increase in near-surface wind speed. It alsoresults in an increase in the depth of the layer in whichsouth-easterly near-surface winds prevail, and in adecrease in the strength of the large-scale flow overthe continent, in particular in summer. In theescarpment region a decrease of _z0m is foundto result in too high wind speeds. Surface temperatureson average decrease while atmospheric temperaturesincrease, resulting in an increase of near-surfacestatic stability. Changes in roughness lengths donot significantly change the temperature profiles.The surface fluxes, on average found reduced, aremodelled best by using the _z0h based on thesurface renewal method.     

Coupling of a Regional Climate Model with a Crop Development Model and Evaluation of the Coupled Model across China

In this study, the CERES(Crop Estimation through Resource and Environment Synthesis) crop model was coupled with CLM3.5, the land module of the regional climate model RegCM4. The new coupled model was named RegCM4_CERES; and in this model, crop type was further divided into winter wheat, spring wheat, spring maize, summer maize, early rice, late rice,single rice, and other crop types based on each distribution fraction. The development of each crop sub-type was simulated by the corresponding crop model separately, with each planting and harvesting date. A simulation test using RegCM4_CERES was conducted across China from 1999 to 2008; a control test was also performed using the original RegCM4. Data on crop LAI(leaf area index), soil moisture at 10 cm depth, precipitation, and 2 m air temperature were collected to evaluate the performance of RegCM4_CERES. The evaluation provided comparison of single-station time series, regional distributions,seasonal variations, and statistical indices for RegCM4_CERES. The results revealed that the coupled model had an excellent ability to simulate the phonological changes and spatial variations in crops. The consideration of dynamic crop development in RegCM4_CERES corrected the wet bias of the original RegCM4 over North China and the cold bias over South China.However, the degree of improvement was minimal and the statistical indices for RegCM4_CERES were roughly the same as the original RegCM4.     

主分量分析在区域性气候分型中应用的统计试验研究

主分量分析在大气科学研究中的应用日益广泛,但对其应用的可行性和可靠性的研究则比较欠缺.本文对主分量分析的三种方法,即非旋转主分量、正交旋转的方差极大法和斜交旋转的Harris-Kaiser Case ⅡB~TB法,在区域气候分型研究中的应用进行了计算分析和精度拟合,同时进行了区域分割和Monte-Carlo模拟的统计试验.结果表明,非旋转主分量的分型拟合精度不佳,两种旋转主分量方法的效果很好,其中正交旋转又优于斜交旋转.区域范围的变化对旋转主分量方法的分型结果影响不大,对非旋转主分量分析的影响较大.样本大小的变化对主分量分析的各种方法无明显影响.     

A Two-Moment Bulk Microphysics Coupled with a Mesoscale Model WRF: Model Description and First Results

The Chinese Academy of Meteorological Sciences (CAMS) two-moment bulk microphysics scheme was adopted in this study to investigate the representation of cloud and precipitation processes under different environmental conditions.The scheme predicts the mixing ratio of water vapor as well as the mixing ratios and number concentrations of cloud droplets,rain,ice,snow,and graupel.A new parameterization approach to simulate heterogeneous droplet activation was developed in this scheme.Furthermore,the improved CAMS scheme was coupled with the Weather Research and Forecasting model (WRF v3.1),which made it possible to simulate the microphysics of clouds and precipitation as well as the cloud-aerosol interactions in selected atmospheric condition.The rain event occurring on 27-28 December 2008 in eastern China was simulated using the CAMS scheme and three sophisticated microphysics schemes in the WRF model.Results showed that the simulated 36-h accumulated precipitations were generally agreed with observation data,and the CAMS scheme performed well in the southern area of the nested domain.The radar reflectivity,the averaged precipitation intensity,and the hydrometeor mixing ratios simulated by the CAMS scheme were generally consistent with those from other microphysics schemes.The hydrometeor number concentrations simulated by the CAMS scheme were also close to the experiential values in stratus clouds.The model results suggest that the CAMS scheme performs reasonably well in describing the microphysics of clouds and precipitation in the mesoscale WRF model.     

A Water Balance Model for a Subarctic Sedge Fen and its Application to Climatic Change

A model to calculate the water balance of a hummocky sedge fen in the northern Hudson Bay Lowland is presented. The model develops the potential latent heat flux (evaporation) as a function of net radiation and atmospheric temperature. It is about equally sensitive to a 2% change in net radiation and a 1°C change in temperature. The modelled potential evaporation agrees well with the Priestley–Taylor formulation of evaporation under conditions of a non-limiting water supply. The actual evaporative heat flux is modelled by expressing actual/potential evaporation as a function of potential accumulated water deficit. Model evaporation agrees well with energy balance calculations using 7 years of measured data including wet and dry extremes. Water deficit is defined as the depth of water below reservoir capacity. Modelled water table changes concur with measurements taken over a 4 year period. When net radiation, temperature and precipitation measurements are available the water balance can be projected to longer time periods. Over a 30 year interval (1965–1994) the water balance of the sedge fen showed the following. During the growing season, there was an increase in precipitation, no change in temperature and a decrease in net radiation, evapotranspiration and water deficit. There was also a decrease in winter snow depths. The fen was brought back to reservoir capacity during final snowmelt every year but one. Summer rainfall was the most important single factor affecting the water balance and the ratio actual/potential evaporation emerged as a linear function of rainfall amount. A 2 × CO₂ climate warming scenario with an annual temperature increase of 4°C and no precipitation change indicates lesser snow amounts and a shorter snow cover period. A greater summer water deficit, triggered mainly by greater evaporation during the month of May, is partially alleviated by lesser evaporation magnitudes in July. The greater water deficit would be counterbalanced by a 23% increase in summer rainfall. On average, the fen's water reservoir would still be recharged after winter snowmelt but the ground would remain at reservoir capacity for a shorter time. The warming scenario with a 10% decline in summer rainfall would create a large increase in the longevity and severity of the water deficit and this would be particularly evident during drier years. The carbon budget and peat accumulation and breakdown rates are strongly affected by changes in the water balance. Some evidence implies that greater water deficits lead to an increase in net carbon emissions. This implies that the sedge peatland could lose biomass under such conditions. An example is given where increased water deficit results in large decreases in local wetland streamflow.     

一种求解区域平均值的权重面积设计及其应用

针对求解物理量在一定区域内的平均值问题,设计了一种权重面积方法。并以求解西北区域年平均降水量、1月份和7月份的平均空中水汽含量为例,将该方法与算术平均法、泰森多边形法、网格插值法进行了对比试验。结果发现该方法在站点较多、但不均匀的大范围区域内计算气象场的平均分布是可行的,其优点是计算量小、受缺测站点影响较小。     

Searching for Added Value in Simulating Climate Extremes with a High-Resolution Regional Climate Model over Western Canada. II: Basin-Scale Results

We evaluate the capacity of a regional climate model to simulate the statistics of extreme events, and also examine the effect of differing horizontal resolution, at the scale of individual hydrological basins in the topographically complex province of British Columbia, Canada. Two climate simulations of western Canada (WCan) were conducted with the Canadian Regional Climate Model (version 4) at 15 (CRCM15) and 45?km (CRCM45) horizontal resolution driven at the lateral boundaries by global reanalysis over the period 1973–1995. The simulations were evaluated with ANUSPLIN, a daily observational gridded surface temperature and precipitation product and with meteorological data recorded at 28 stations within the upper Peace, Nechako, and upper Columbia River basins. In this work, we focus largely on a comparison of the skill of each model configuration in simulating the 90th percentile of daily precipitation (PR90). The companion paper describes the results for a wider range of temperature and precipitation extremes over the entire WCan domain.

Over all three watersheds, both simulations exhibit cold biases compared with observations, with the bias exacerbated at higher resolution. Although both simulations generally display wet biases in median precipitation, CRCM15 features a reduced bias in PR90 in all three basins in summer and throughout the year in the upper Columbia River basin. However, the higher resolution model is inferior to CRCM45 with respect to rarer heavy precipitation events and also displays high spatial variability and lower spatial correlations with ANUSPLIN compared with the coarser resolution model. A reduction in the range of PR90 biases over the upper Columbia basin is noted when the 15?km results are averaged to the 45?km grid. This improvement is partly attributable to the averaging of errors between different elevation data used in the gridded observations and CRCM, but the sensitivity of CRCM15 to resolved topography is also clear from spatial maps of seasonal extremes. At the station scale, modest but systematic reductions in the bias of PR90 relative to ANUSPLIN are again found when the CRCM15 results are averaged to the 45?km grid. Furthermore, the annual cycle of inter-station spatial variance in the upper Columbia River basin is well reproduced by CRCM15 but not by ANUSPLIN or CRCM45. The former result highlights the beneficial effect of spatial averaging of small-scale climate variability, whereas the latter is evidently a demonstration of the added value at high resolution vis-à-vis the improved simulation of precipitation at the resolution limit of the model.     

A Statistically-Based Low-Level Cloud Scheme and Its Tentative Application in a General Circulation Model

1. Introduction Clouds are active factors in the climate system, and have significant influences on the global hydrolog- ical and thermal budgets. More and more the climate model developers and researchers have realized the im- portance to appropriately describe the interactions be- tween cloud and radiation in the atmospheric general circulation model (AGCM). It is well known that cloud is one of the contributing factors to the uncertainties in the simulation of climate by AGCM. Especiall…     

A Method of Phase Space Modeling of a Climatological Series and its Application

Summary  In this paper, a method of phase space in modeling the climatological series is put forward on the correlation dimension, the theory of phase space and the direct retrieval technique. Then time series of monthly mean temperature are used to build dynamic models of regional climate in phase space in which some dynamic characteristics can be discovered. The results illustrate that the methodology holds promise for a wide variety of applications. Furthermore, the evolution characteristic and the interior interaction mechanism of the regional climate of southern China are also discussed. Received March 29, 1999/Revised November 2, 1999     

低温雨雪冰冻极端气候事件的多指标综合评估技术

评估极端气候事件,往往用某一项极端气候要素进行分析评估,如暴雨量、极端最高(最低)气温等.2008年初出现的持续低温雨雪冰冻过程,具有雨雪量大、持续雨雪时间长、积雪深、积雪时间长、低温持续时间长、但极端最低气温不低的特点,用其中任一因子评估定位该过程,都不能全面反映该过程的综合影响特征.提出低温雨雪过程综合指数的概念,用最长连续雨雪日数及期间雨雪总量作为评估雨雪部分的两项指标,日平均气温≤0.5℃的连续日数、过程平均气温和过程极端最低气温三个要素作为评估低温部分的三项指标,将五个指标分别无量纲化后,采用等权重技术方案建立综合指数计算模型.计算湖北10个代表站建站以来逐年最长低温雨雪冰冻过程综合指数,分析2008年低温雨雪冰冻过程综合指数历史排位、历史重现期,从而对该过程进行评估定位,结果比较客观,方法简单可行,便于推广.     

包含详细水分循环和海冰物理过程的一维气候模式与气候系统内反馈机制的研究

鉴于水分循环和海冰物理过程是气候变化研究中两个比较薄弱的环节，而在以往的一些气候模式中往往简化甚至忽略了其中之一，给气候变化的研究带来了一定的不确定性。因此，我们设计了包含详细水分循环和海冰物理过程的一维气候模式，着重研究了存在气候系统内部的反馈机制，得到以下几点结论:（1）无论在地表还是在大气中，水汽反馈和冰雪反照率反馈均为很强的正反馈，前者比后者要强一些，冰雪反照率反馈在极区比其它地区强一些。（2）降水过程无论在地表还是在大气中均表现为负反馈。（3）在大气中，蒸发过程表现为很强的正反馈；在地表，蒸发过程在中低纬度表现为很强的负反馈，而在高纬度却表现为正反馈。（4）大气中的潜热输送无论在大气中还是在地表均表现为正反馈，其正反馈效应通过放大水汽的温室效应体现出来。(5)大气中的感热输送无论在大气中还是在地表均表现为较弱的负反馈，其负反馈作用通过抑制冰雪反照率反馈而表现出来。（6）不同反馈之间的合成不是两者简单地线性相加，而是以一种非线性方式相互作用。