The impact of ecosystem functional type changes on the La Plata Basin climate

In this paper, the effects of land cover changes on the climate of the La Plata Basin in southern South America are investigated using the Weather and Research Forecasting (WRF) Model configured on a 30/10km two-way interactive nested grid. To assess the regional climate changes resulting from land surface changes, the standard land cover types are replaced by time-varying Ecosystem Functional Types (EFTs), which is a newly devised land-cover classification that characterizes the spatial and interannual variability of surface vegetation dynamics. These variations indicate that natural and anthropogenic activities have caused changes in the surface physical parameters of the basin, such as albedo and roughness length, that contributed to regional climate changes. EFTs are obtained from functional attributes of vegetation computed from properties of the Normalized Difference Vegetation Index (NDVI) to represent patches of the land surface with homogeneous energy and gas exchanges with the atmosphere. Four simulations are conducted, each experimental period ranging from September to November in two contrasting years, 1988 and 1998. The influence of an identical EFT change on the surface heat fluxes, 2-m temperature and humidity, 10-m winds, convective instabilities and large-scale moisture fluxes and precipitation are explored for 1988 (a dry year) and 1998 (a wet year). Results show that the surface and atmospheric climate has a larger response to the same EFT changes in a dry year for 2-m temperature and 10-m wind; the response is larger in a wet year for 2-m water vapor mixing ratio, convective available potential energy, vertically integrated moisture fluxes and surface precipitation. For EFTs with high productivity and a weak seasonal cycle, the nearsurface temperature during the spring of 1988 and 1998 increased by as much as 1℃ in the central and western portions of La Plata Basin. Additionally, for higher productivity EFTs, precipitation differences were generally positive in both dry and wet years, although the patterns are not uniform and exhibit certain patchiness with drier conditions.     

南京地区下垫面变化对城市热岛效应影响的数值模拟

利用新一代中尺度研究和预报模式(Weather Research and Forecasting Model,简称WRF)分别耦合多冠层、单冠层和平板模式三种情况进行南京地区2007年8月1日的天气过程模拟,分析不同城市冠层方案对南京气象场的模拟效果。在此基础上,结合模拟效果最好的城市冠层方案,研究南京城市下垫面的变化对其热岛的影响。结果表明:多冠层方案对近地面气温、10 m风场的模拟效果最好;城区的扩张使南京地区近地面气温升高,主要表现为城市区域夜间升温显著,并且导致热岛强度明显增强;城市扩张后,城区白天风速大范围地减小,同时热岛环流更加显著,且具有明显的城市热岛的"下游效应"。     

变网格模式LMDZ对东亚夏季气候平均态的模拟能力评估

将可变网格大气环流模式LMDZ的模拟中心移动至中国地理中心附近(37°N,112.5°E),在东亚地区进行加密,使用其对应全球模式同步输出资料进行环流强迫,以观测海表温度SST和海冰SIC资料对下边界强迫,对1979-2008年各年5-9月对500 hPa高度场,850 hPa温度场和地面要素等进行了模拟,并利用同期的NCEP/NCAR再分析资料和由中国气象台站资料生成的格点资料,评估该模式对东亚地区高空环流场、西太平洋副热带高压及地面温度、降水等的夏季气候平均态的模拟能力.结果表明:LMDZ可以较好的模拟平均环流场,其模拟结果能够反映实际的500 hPa高度场和850 hPa温度场的分布特征和趋势,但总体模拟值较观测值偏低;对副高强度的模拟能力偏弱、模拟的副高位置偏东,但准确的表现了副高随时间变化的移动特性;模式较好的再现了中国区域夏季地面气温和降水的空间分布特征;但从数值吻合度看,温度模拟主要呈区域性偏冷距平,在东南沿海地区偏低1～3℃,在西部青藏高原地区偏低3～4℃及以上,中部和东北大部基本无偏差;降水的模拟在中国西北地区与实际观测较为一致,其误差主要表现为在中国东南部沿海模拟的降水偏多;对7个子区域,模式对850 hPa温度场和地面日均气温的再现能力优于对500 hPa高度场的模拟,且子区域间模拟偏差结果相差大,其中华北区地面气温模拟偏差最小,西北区降水值模拟偏差最小.     

近20年中国土地利用变化影响区域气候的数值模拟

区域尺度土地利用/土地覆盖变化(LUCC)的气候效应以及土地覆盖数据的不确定性, 一直是LUCC研究不可忽视的关键问题。本研究基于最新的遥感资料, 采用新的区域气候模式RegCM4.0, 探讨了1990年至2010年中国LUCC对区域气候的影响。结果表明, 中国区域LUCC使得局地气温和日较差发生了显著改变, 而降水及低层环流场变化不显著;LUCC的影响存在季节性差异, 其中, 夏秋季响应程度较大且主要体现在边界层内。就LUCC对气候影响的机理各地区有所不同, 华北地区LUCC的气候效应主要受蒸散发作用主导, 而长江流域则由反照率与蒸散发共同作用。这些结果均说明, 较短时间尺度的LUCC气候效应主要体现在其局地范围, 且在不同的季节有所差异。     

陆面过程参数化对太湖地区雷暴过程模拟的影响

以2010年8月发生在太湖地区的一次雷暴过程为例,利用WRF模式进行48 h的短期天气模拟,分析两个陆面参数化方案(Noah方案和RUC方案)对雷暴过程模拟的影响。对比模式结果与实况降水以及太湖地区两个站点的近地面要素表明:雷暴过程对陆面参数化方案的选取较为敏感,不同陆面参数化方案可影响雷暴发生的时间、地点及强度,两种方案的降水中心值差达40 mm以上,其中Noah方案所模拟的降水与实况更为接近。通过对两个方案模拟的物理量场的对比分析发现,RUC方案中对流发展滞后于Noah方案2 h;这表明陆面过程对雷暴等中尺度对流过程有显著的反馈作用,不同陆面参数化方案的使用影响雷暴发生的动力和热力作用,并改变雷暴的时空分布特征。陆面过程通过改变地面热通量输送影响边界层结构,使得水平和垂直方向上的风和温度等发生变化并产生辐合辐散,进而影响对流的启动时间和对流发展强度。由于对不同植被的参数化处理的差异,Noah方案对下垫面特征的描述能力优于RUC方案,尤其是对城市下垫面的处理,这也使得之后该方案模拟的雷暴发生时间更加接近于实况且雷暴过程更加强烈。     

中国气候变化预估数据在河北地区的检验分析

应用观测资料对中国地区预估数据集进行检验分析。结果表明:1)7月降水量,区域模式在张家口南部桑洋河盆地和北部坝上地区的模拟值偏大,而在北京东边兴隆高山区和东南沿海地区的模拟值明显偏小。2)7月最高气温,在北京东边兴隆高山区和东部平原的模拟值明显偏高,而在张家口南部桑洋河盆地和太行山东侧的模拟值偏低。3)1月最低气温,在北京东边兴隆高山区、太行山北段高山区和东部平原地区的模拟值偏高,而在张家口南部桑洋河盆地和太行山东侧的模拟值偏低。4)无论是对降水还是气温,由于全球模式的空间分辨率偏低、很难描述河北地区的地形特征,所以模拟结果很差。由于区域气候模式的分辨率提高、对河北地区地形特征的描述有了改进,所以模拟效果有明显改善;但受分辨率所限,它对局部地形如兴隆高山、桑洋河盆地、太行山北部高山等地形特征的描述不是很好,造成模拟结果在这些地区出现系统性偏差,因此应用这些数据时需加以订正。     

The Interannual Variability of Climate in a Coupled Ocean-Atmosphere Model

In this paper, the interannual variability simulated by the coupled ocean-atmosphere general circulation model of the Institute of Atmospheric Physics (IAP CGCM) in 40 year integrations is analyzed, and compared with that by the corresponding IAP AGCM which uses the climatic sea surface temperature as the boundary condition in 25 year integrations.The mean climatic states of January and July simulated by IAP CGCM are in good agreement with that by IAP AGCM, i.e., no serious ‘climate drift’ occurs in the CGCM simulation. A comparison of the results from AGCM and CGCM indicates that the standard deviation of the monthly averaged sea level pressure simulated by IAP CGCM is much greater than that by IAP AGCM in tropical region. In addition, both Southern Oscillation (SO) and North Atlantic Oscillation (NAO) can be found in the CGCM simulation for January, but these two oscillations do not exist in the AGCM simulation.The interannual variability of climate may be classified into two types: one is the variation of the annual mean, another is the variation of the annual amplitude. The ocean-atmosphere interaction mainly increases the first type of variability. By means of the rotated EOF, the most important patterns corresponding to the two types of interannual variability are found to have different spatial and temporal characteristics.     

基于WRF模式对华北一次飑线过程中雷电活动的间接和直接模拟研究

将非感应起电机制和放电参数化方案耦合到WRF模式的Morrison双参数微物理方案中,并在模式中引入了闪电潜势指数LPI,在此基础上模拟了2009年6月16日华北一次飑线过程,讨论模式对闪电活动再现能力。模拟结果显示,模式能够较好地再现雷达回波和降水分布特征,说明模式对此次飑线过程的宏观和微观特征具有一定的模拟能力。利用计算闪电潜势指数LPI的间接模拟,能够指示出大致的闪电分布特征,但闪电潜势指数LPI分布范围明显大于实际闪电落区;而通过耦合电过程的WRF模式直接输出闪电密度的直接模拟,模拟结果与实际闪电密度分布的对应关系较好,但由于模式中输出的闪电密度为总闪电密度,与观测地闪密度资料相比,模拟的闪电密度偏大。     

华北地区夏季降水模拟研究:区域气候模式性能评估

利用高分辨率区域气候模式Reg CM3对华北地区1991—2002年夏季气候进行了数值模拟,对照中国台站的实测资料,对模拟的华北地区夏季降水、温度进行了较为全面的比较,以检验模式的模拟性能。对平均场的模拟结果检验认为,该区域气候模式对华北地区夏季降水的空间分布模拟存在一定的误差,河套地区及黄河以南地区降水量接近实况,沿着太行山脉及东部沿海地区降水量明显偏多。模式对温度的模拟误差较小,较好地再现了气温的空间分布特征,但山西及以北地区模拟的温度略偏低。模式能够较好地模拟出华北地区夏季降水和气温的年际变化,成功再现了该区域降水和气温的异常变化。模式能够成功模拟出该区域降水和气温日变化特征,特别是对于逐年夏季的降水日变化过程的峰值和谷值均有成功表现,对于典型年份华北地区较强降水过程中降水发生的时间、落区、强度等也有再现能力,不足的是模拟的降水量比观测偏大。对于模式误差是否与地形或模式积云对流参数化方案等有关,需要进一步探讨。     

一例苏皖中尺度对流复合体模拟结果的诊断分析

利用2010年7月22日苏皖中尺度对流复合体（MCC）数值模拟输出结果,考察了模式对MCC的模拟能力,并对模拟结果做了动力和热力诊断分析,以揭示盛夏江淮下游MCC的特征。结果表明：1） 三重嵌套网格距为3.3 km的区域WRF模式的模拟效果较佳,结果与实况一致,并可利用模拟降水的范围及强度来确定MCC的位置及演变。2） 此MCC维持约10 h,其南北不对称,并随西太平洋副热带高压西伸北抬而随之北抬。MCC核心区对流层低层有水汽丰沛的入流,并有强辐合区,呈对流不稳定层结;中层有深厚的强上升运动,并因凝结潜热大量释放呈中性层结;高层则有出流;MCC核心区对流降水非常强。3） 在垂直剖面上,该核心区散度存在中低层辐合、高层辐散的柱状结构,此配置有利于强对流维持和加强,中低层以上有深厚的强上升气流柱,这些都是MCC核心区存在强对流的标志。该MCC的螺旋结构表明其中的强对流高度有组织。     

Modeling impacts of vegetation in western China on the summer climate of northwestern China

Using the monthly NCEP-NCAR reanalysis dataset, the monthly temperature and precipitation at surface stations of China, and the MM5 model, we examine impacts of vegetation cover changes in western China on the interdecadal variability of the summer climate over northwestern China during the past 30 years. It is found that the summer atmospheric circulation, surface air temperature, and rainfall in the 1990s were different from those in the 1970s over northwestern China, with generally more rainfall and higher temperatures in the 1990s. Associated with these changes, an anomalous wave train appears in the lower troposphere at the midlatitudes of East Asia and the low-pressure system to the north of the Tibetan Plateau is weaker. Meanwhile, the South Asian high in the upper troposphere is also located more eastward. Numerical experiments show that change of vegetation cover in western China generally forces anomalous circulations and temperatures and rainfall over these regions. This consistency between the observations and simulations implies that the interdecadal variability of the summer climate over northwestern China between the 1990s and 1970s may result from a change of vegetation cover over western China.     

Results of a CLM4 Land Surface Simulation over China Using a Multisource Integrated Land Cover Dataset

In this study, the high-accuracy multisource integrated Chinese land cover （MICLCover） dataset was used in version 4 of the Community Land Model （CLM4） to assess how the new land cover information affected land surface simulation over China. Compared to the default land cover dataset in CLM4, the MICL data indicated lower values for bare soil （14.6% reduction）, nee- dleleaf tree （3.6%）, and broadleaf tree （1.9%）; higher values for shrub cover （1.8% increase）, grassland （9.9%）, cropland （5.0%）, glaciers （0.5%）, lakes （1.6%）, and wetland （1.1%）; and unchanged for urban areas. Two comparative CLM4 simulations were conducted for the 33-yr period from 1972 to 2004, one using the MICL dataset and the other using the default dataset. The results revealed that the MICL data produced a 0.3% lower mean annual surface albedo over China than the original data. The largest contributor to the reduced value was semiarid regions （2.1% reduction）. The MICL-data albedo value agreed more closely with observations （MODIS broad- band black-sky albedo products） over arid and semiarid regions than for the original data to some extent. The simulated average sensible heat flux over China increased by only 0.1 W m 2 owing to the reduced values in arid and semiarid regions, as opposed to increases in humid and semihumid regions, while an increased latent heat flux of I W m-2 was reflected in almost identical changes over the whole region. In addition, the mean annual runoff simulated by CLM4 using MICL data decreased by 6.8 mm yr-1, primarily due to large simulated decreases in humid regions.     

Simulating Crop Net Primary Production in China from 2000 to 2050 by Linking the Crop-C model with a FGOALS＇s Model Climate Change Scenario

Net primary production （NPP） of crop represents the capacity of sequestrating atmospheric CO2 in agro-ecosystem, and it plays an important role in terrestrial carbon cycling. By linking the Crop-C model with climate change scenario projected by a coupled GCM FGOALS via geographical information system （GIS） techniques, crop NPP in China was simulated from 2000 to 2050. The national averaged surface air temperature from FGOALS is projected to increase by 1.0℃ over this period and the corresponding atmospheric CO2 concentration is 535 ppm by 2050 under the IPCC A1B scenario. With a spatial resolution of 10 ×10 km^2, model simulation indicated that an annual average increase of 0.6 Tg C yr^-1 （Tg=10^12 g） would be possible under the A1B scenario. The NPP in the late 2040s would increase by 5% （30 Tg C） within the 98×10^6 hm^2 cropland area in contrast with that in the early 2000s. A further investigation suggested that changes in the NPP would not be evenly distributed in China. A higher increase would occur in a majority of regions located in eastern and northwestern China, while a slight reduction would appear in Hebei and Tianjin in northern China. The spatial characteristics of the crop NPP change are attributed primarily to the uneven distribution of temperature change.     

BCC气候模式对中国近50a极端气候事件的模拟评估

利用中国区域437站1958—2005年逐日气温和降水资料,评估了国家气候中心（BeijingCli-mateCenter,BCC）气候模式对中国近50a极端气候事件空间分布、时间演变等方面的模拟能力。结果表明：1）模式对极端温度和降水多年平均的空间分布具有一定的模拟能力,但尚存在系统性的偏差。暖昼日数的模拟优于冷夜日数,全年冷夜日数的模拟优于冬季和夏季的模拟,而全年和夏季暖昼日数的模拟优于冬季的模拟。极端降水频次的模拟优于极端降水量的模拟;夏季和全年的模拟优于冬季的模拟。夏季极端降水频次的模拟较好,但冬季的模拟在长江中下游和华南偏小、北方偏大,而全年的模拟在长江下游及南部沿海地区系统性偏大;夏季和全年极端降水量的模拟系统性偏低,而冬季在北方偏高、南方偏低。2）模式较好地模拟出了夏季和全年冷夜日数的全国较为一致的减少趋势,再现东北和东南沿海地区冬季冷夜日数的减少趋势,但模拟的趋势较实测偏弱。模式对暖昼日数长期趋势的模拟效果较理想,较好地反映出了大部分地区暖昼事件发生频率显著增加的特征,但冬季的模拟尚有待改进。模式较好地模拟出了夏季和全年极端降水频次的长期趋势,较好地刻画了极端降水频次＂南增北减＂的特征;模式对冬季极端降水频次的变化趋势几乎无模拟能力。同样,模式也较好地模拟出了极端降水量夏季南增北减的分布形势和冬季的总体增加趋势,但对全年的模拟不理想。3）模式能较好地模拟出冷夜日数和暖昼日数异常变化的主要空间型,对EOF第一模态的时间演变特征具有一定模拟能力;但模式对第二模态时间演变特征的刻画能力较差。模式对极端降水指标的年际变化具有一定的模拟能力,对部分区域极端降水事件的年际变化具有较好的模拟能力;但模拟能力表现出了明显的区域性差异,部分区域极端降水年际变化的模拟结果与实况甚至相反,模式对极端降水年际变化的模拟能力还有待提高。所得结果可为BCC气候模式的改进及极端气候模拟、预估提供一定的参考。     

Comparison of a very-fine-resolution GCM with RCM dynamical downscaling in simulating climate in China

Regional climate simulation can generally be improved by using an RCM nested within a coarser-resolution GCM. However, whether or not it can also be improved by the direct use of a state-of-the-art GCM with very fine resolution, close to that of an RCM, and, if so, which is the better approach, are open questions. These questions are important for understanding and using these two kinds of simulation approaches, but have not yet been investigated. Accordingly, the present reported work compared simulation results over China from a very-fine-resolution GCM (VFRGCM) and from RCM dynamical downscaling. The results showed that: (1) The VFRGCM reproduces the climatologies and trends of both air temperature and precipitation, as well as inter-monthly variations of air temperature in terms of spatial pattern and amount, closer to observations than the coarse-resolution version of the GCM. This is not the case, however, for the inter-monthly variations of precipitation. (2) The VFRGCM captures the climatology, trend, and inter-monthly variation of air temperature, as well as the trend in precipitation, more reasonably than the RCM dynamical downscaling method. (3) The RCM dynamical downscaling method performs better than the VFRGCM in terms of the climatology and inter-monthly variation of precipitation. Overall, the results suggest that VFRGCMs possess great potential with regard to their application in climate simulation in the future, and the RCM dynamical downscaling method is still dominant in terms of regional precipitation simulation.     

区域气候模式RegCM_NCC在东北地区的应用研究

引进国家气候中心业务化的区域气候模式RegCM_NCC,通过操作系统调试、模拟区域确定、模式分辨率调整等本地化工作,初步建立了针对东北地区的区域气候模式系统,并应用该模式以夏季为例,对东北地区的气候进行了15 a（1991—2005年）时间长度的数值积分试验。结果表明：模式对环流的特征和东北地区地面气温具有一定的模拟能力,对气温模拟存在系统性的暖偏差,对降水模拟能力较差。     

Seasonal evolution of subtropical anticyclones in the climate system model FGOALS-s2

The simulation characteristics of the seasonal evolution of subtropical anticyclones in the Northern Hemisphere are documented for the Flexible Global Ocean-Atmosphere-Land Systemmodel, Spectral Version 2 (FGOALS-s2), developed at the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, the Institute of Atmospheric Physics. An understanding of the seasonal evolution of the subtropical anticyclones is also addressed. Compared with the global analysis established by the European Centre for Medium-Range Forecasts, the ERA-40 global reanalysis data, the general features of subtropical anticyclones and their evolution are simulated well in both winter and summer, while in spring a pronounced bias in the generation of the South Asia Anticyclone(SAA) exists. Its main deviation in geopotential height from the reanalysis is consistent with the bias of temperature in the troposphere. It is found that condensation heating (CO) plays a dominant role in the seasonal development of the SAA and the subtropical anticyclone over the western Pacific (SAWP) in the middle troposphere. The CO biases in the model account for the biases in the establishment of the SAA in spring and the weaker strength of the SAA and the SAWP from spring to summer. CO is persistently overestimated in the central-east tropical Pacific from winter to summer, while it is underestimated over the area from the South China Sea to the western Pacific from spring to summer. Such biases generate an illusive anticyclonic gyre in the upper troposphere above the middle Pacific and delay the generation of the SAA over South Asia in April. In midsummer, the simulated SAA is located farther north than in the ERA-40 data owing to excessively strong surface sensible heating (SE) to the north of the Tibetan Plateau. Whereas, the two surface subtropical anticyclones in the eastern oceans during spring to summer are controlled mainly by the surface SE over the two continents in the Northern Hemisphere, which are simulated reasonably well, albeit with their centers shifted westwards owing to the weaker longwave radiation cooling in the simulation associated with much weaker local stratiform cloud. Further improvements in the related parameterization of physical processes are therefore identified.     

天津城市环境对一次局地降水过程影响的模拟研究

采用中尺度气象模式WRF结合自动站观测资料,对天津城区及附近发生的一次局地降水过程进行数值模拟和敏感性试验,研究了城市环境(城市地表、城市大气污染)对降水发生发展的影响。结果表明:城市地表引起的热岛环流,叠加海风环流后,改变了辐合线的位置和强度,直接影响了对流降水的发生及落区。城市大气污染状况可影响对流发展后的强度及降水量,敏感性试验结果显示气溶胶浓度增大后区域平均降水量增加约25%;气溶胶的增雨效应主要表现在可增进对流云中液态水和冰相物质含量,增多的液态水物质被强的上升气流抬升到较高处冻结形成冰晶,这一过程中增多的凝结潜热又可促进对流发展,最终导致地面总降水量增多,研究个例中气溶胶浓度增加可使潜热加热率最大增加110 K·h~(-1)。     

The thermoinsulation effect of snow cover within a climate model

We use a state of the art climate model (CAM3–CLM3) to investigate the sensitivity of surface climate and land surface processes to treatments of snow thermal conductivity. In the first set of experiments, the thermal conductivity of snow at each grid cell is set to that of the underlying soil (SC-SOIL), effectively eliminating any insulation effect. This scenario is compared against a control run (CTRL), where snow thermal conductivity is determined as a prognostic function of snow density. In the second set of experiments, high (SC-HI) and low (SC-LO) thermal conductivity values for snow are prescribed, based on upper and lower observed limits. These two scenarios are used to envelop model sensitivity to the range of realistic observed thermal conductivities. In both sets of experiments, the high conductivity/low insulation cases show increased heat exchange, with anomalous heat fluxes from the soil to the atmosphere during the winter and from the atmosphere to the soil during the summer. The increase in surface heat exchange leads to soil cooling of up to 20 K in the winter, anomalies that persist (though damped) into the summer season. The heat exchange also drives an asymmetric seasonal response in near-surface air temperatures, with boreal winter anomalies of +6 K and boreal summer anomalies of −2 K. On an annual basis there is a net loss of heat from the soil and increases in ground ice, leading to reductions in infiltration, evapotranspiration, and photosynthesis. Our results show land surface processes and the surface climate within CAM3–CLM3 are sensitive to the treatment of snow thermal conductivity.     

用 IAP／LASG GOALS模式模拟CO2增加引起的东亚地区气候变化

Two simulations, one for the control run and another for the perturbation run, with a global coupled ocean-atmosphere-land system model (IAP / LASG GOALS version 4) have been carried out to study the global warming, with much detailed emphasis on East Asia. Results indicate that there is no climate drift in the control run and at the time of CO2 doubling the global temperature increases about 1.65℃. The GOALS model is able to simulate the observed spatial distribution and annual cycles of temperature and precipitation for East Asia quite well. But, in general, the model underestimates temperature and overestimates rainfall amount for regional annual average. For the climate change in East Asia, the temperature and precipitation in East Asia increase 2. l℃ and 5% respectively, and the maximum warming occurs at middle-latitude continent and the maximum precipitation increase occurs around 25°N with reduced precipitation in the tropical western Pacific.