不同水平分辨率区域气候模式对青藏高原气候特征模拟

青藏高原地区气候特殊、地形复杂,气象观测站点稀少,对其区域气候和水循环过程的观测和模拟存在很大的困难。本文基于RegCM模式和WRF模式,探究不同水平分辨率10km、25km、50km下区域气候模式对该地区1989—2008年气候时空分布规律的模拟能力。研究结果表明:在10 km水平分辨率下,RegCM模式模拟多年平均气温绝对误差为0.33℃,WRF模式模拟绝对误差为1.77℃,比25 km和50 km水平分辨率下绝对误差减少1.60~2.12℃,且四季气温模拟值与实测值的相关性有所提高;随着水平分辨率的提高,WRF模式对青藏高原东南部和南部的降水量高估有所改善,RegCM模式模拟值逐渐接近实测值(模拟年降水量相对误差由169%降至75%)且对高原北部降水量的模拟有所改善,但整体上模式对降雨的高估依然存在;两个模式随水平分辨率的提高对地形起伏最大的雅鲁藏布江源区降水量的误差减少最为明显。本研究可为揭示气候变化下青藏高原水文响应机理奠定基础。

RegCM4.1对中国区域气候模拟能力评估

利用中国气象局提供的1985—2004年756个台站的逐日降水和气温观测数据评估了区域气候模式(Reg CM4.1)对中国地区不同季节的降水和气温的模拟性能,并结合中国的区域气候特征和气候带分布进行分区讨论。结果表明Reg CM4.1能够较好地再现中国地区四季降水占全年百分比、降水率的空间分布特点以及降水带南北摆动的季节变化特征。Reg CM4.1对平均气温分布模拟较好,强度和高低中心与观测事实接近,但对青藏高原地区的气温分布模拟值一致偏低。同时发现Reg CM4.1能够合理再现内陆地区气温日较差明显大于沿海地区的总体分布特征,不过模拟值在新疆和沿海地区比观测结果均偏低。

次网格坡地辐射参数化对RegCM4.1模式模拟东亚夏季气候的影响

本研究将次网格坡地辐射参数化方案引入到区域气候模式(RegCM4. 1)中,并研究次网格坡地辐射参数化对RegCM4. 1模拟东亚夏季气候性能的影响。结果表明:RegCM4. 1高估了夏季青藏高原的热源作用,模拟低层偏强的西南季风导致了模拟的中国夏季降水量总体偏大。引入次网格坡地辐射参数化方案后,模式模拟的青藏高原夏季地表太阳辐射通量和长波辐射通量减小分别可达5%和12%以上,夏季减弱的青藏高原热源作用使得低层西南季风减弱,从而改善了模式对中国夏季降水的模拟;而且改善程度自东南向西北递减,在东南地区模拟夏季降水的相对均方根误差减小9%,空间相关系数和Taylor评分分别提高0. 14和0. 08。

Comparison of convective parameterizations in RegCM4 experiments over China with CLM as the land surface model

in the latest version of the international Centre for Theoretical Physics＇ regional climate model, RegCM4, CLM was introduced as a new land surface scheme. The performance over China of RegCM4-CLM with different convection schemes is analyzed in this study, based on a series of short- term experiments.The model is driven by ERA-Interim data at a grid spacing of 25 km.The convection schemes employed are： Emanuel; Grell; Emanuel over land and Grell over ocean; Grell over land and Emanuel over ocean; and Tiedtke. The simulated mean surface air temperature and precipitation in December-February-January and June-July-August are compared against observation. In general, better performance of Emanuel is found both for temperature and precipitation, and in both seasons. Thus, the model physics of CLM and Emanuel for the land surface processes and convection, respectively, are recommended for further application of RegCM4 over the China region. The de^ciencies that remain in the model arealso outlined and discussed.

Simulation of a Persistent Snow Storm over Southern China with a Regional Atmosphere-Ocean Coupled Model

A regional atmosphere-ocean coupled model, RegCM3-POM, was developed by coupling the regional climate model （RegCM3） with the Princeton Ocean Model （POM）. The performance of RegCM3-POM in simulating a persistent snow storm over southern China and the impact of the Madden Julian oscillation （MJO） on this persistent snow storm were investigated. Compared with the stand-alone RegCM3, the coupled model performed better at reproducing the spatial-temporal evolution and intensity of the precipitation episodes. The power spectral analysis indicated that the coupled model successfully captured the dominant period between 30 and 60 days in the precipitation field, leading to a notable improvement in simulating the magnitude of intraseasonal precipitation variation, and further in enhancing the intensity of the simulated precipitation. These improvements were mainly due to the well-simulated low-frequency oscillation center and its eastward propagation characteristics in each MJO phase by RegCM3-POM, which improved the simulations of MJO-related low-frequency vertical motions, water vapor transport, and the deep inversion layer that can directly influence the precipitation event and that further improved the simulated MJOprecipitation relationship. Analysis of the phase relationship between convection and SST indicated that RegCM3-POM exhibits a near-quadrature relation between the simulated convection and SST anomalies, which was consistent with the observations. However, such a near-quadrature relation was not as significant when the stand-alone RegCM3 was used. This difference indicated that the inherent coupled feedback process between the ocean and atmosphere in RegCM3-POM played an important part in reproducing the features of the MJO that accompanied the snow storm.

FUTURE CHANGE OF PRECIPITATION EXTREMES OVER THE PEARL RIVER BASIN FROM REGIONAL CLIMATE MODELS

Based on RegCM4,a climate model system,we simulated the distribution of the present climate(1961-1990)and the future climate(2010-2099),under emission scenarios of RCPs over the whole Pearl River Basin.From the climate parameters,a set of mean precipitation,wet day frequency,and mean wet day intensity and several precipitation percentiles are used to assess the expected changes in daily precipitation characteristics for the 21 st century.Meanwhile the return values of precipitation intensity with an average return of 5,10,20,and 50 years are also used to assess the expected changes in precipitation extremes events in this study.The structure of the change across the precipitation distribution is very coherent between RCP4.5 and RCP8.5.The annual,spring and winter average precipitation decreases while the summer and autumn average precipitation increases.The basic diagnostics of precipitation show that the frequency of precipitation is projected to decrease but the intensity is projected to increase.The wet day percentiles(q90 and q95) also increase,indicating that precipitation extremes intensity will increase in the future.Meanwhile,the5-year return value tends to increase by 30%-45%in the basins of Liujiang River,Red Water River,Guihe River and Pearl River Delta region,where the 5-year return value of future climate corresponds to the 8-to 10-year return value of the present climate,and the 50-year return value corresponds to the 100-year return value of the present climate over the Pearl River Delta region in the 2080 s under RCP8.5,which indicates that the warming environment will give rise to changes in the intensity and frequency of extreme precipitation events.

Development of a Single-Column Model in RegCM4 and Its Preliminary Application for Evaluating PBL Schemes in Simulating the Dry Convection Boundary Layer

A single-column model(SCM)is developed in the regional climate model RegCM4.The evolution of a dry convection boundary layer(DCBL)is used to evaluate this SCM.Moreover,four planetary boundary layer(PBL)schemes,namely the Holtslag-Boville scheme(HB),Yonsei University scheme(YSU),and two University of Washington schemes(UW01,Grenier-Bretherton-Mc Caa scheme and UW09,Bretherton-Park scheme),are compared by using the SCM approach.A large-eddy simulation(LES)of the DCBL is performed as a benchmark to examine how well a PBL parameterization scheme reproduces the LES results,and several diagnostic outputs are compared to evaluate the schemes.The results show that the SCM is properly constructed.In general,with the DCBL case,the YSU scheme performs best for reproducing the LES results,which include well-mixed features and vertical sensible heat fluxes;the simulated wind speed,turbulent kinetic energy,entrainment flux,and height of the entrainment zone are all underestimated in the UW09;the UW01 has all those biases of the UW09 but larger,and the simulated potential temperature is not well mixed;the HB is the least skillful scheme,by which the PBL height,entrainment flux,height of the entrainment zone,and the vertical gradients within the mixed layer are all overestimated,and a inversion layer near the top of the surface layer is wrongly simulated.Although more cases and further testing are required,these simulations show encouraging results towards the use of this SCM framework for evaluating the simulated physical processes by the RegCM4.

两种温室气体排放情景下中国汛期江淮暴雨低涡特征研究

本文基于一个水平分辨率为50 km的区域气候模式Reg CM4(Regional Climate Model,version 4.0)的模拟与预估结果,对我国汛期江淮暴雨低涡在气候变化背景下的统计特征与合成结构进行分析,进一步对两种温室排放情景下未来中国汛期的江淮暴雨低涡特征进行预估。结果表明:Reg CM4模式对环境要素及低涡都具有一定的模拟能力,低涡的伸展高度、生命期及暴雨位置模拟结果与观测较为接近,但模拟的低涡个数、最大暖区高度以及温、湿要素分布均比实际略偏低,而风速和低涡的强度模拟则偏强;在未来两种温室排放情景预估方面,RCP4.5(Representative Concentration Pathways,简称RCP)典型浓度排放情景下,暴雨低涡数量比例减少,强度减弱,但低涡发展高度仍以850 h Pa为主,生命期多为2 d以内,低涡雨区分布及最大暖区高度均与历史时段相近;RCP8.5情景下,暴雨低涡比例明显大于RCP4.5情景,低涡发展高度以700 h Pa为主,生命期达3 d的增多,强度增强,最大暖区厚度范围显著伸展。两种情景下均有低涡中温度锋区减弱,而湿度锋区增强,但RCP8.5情景减弱与增强更显著,显示更高的温室气体排放将导致未来出现更强的暴雨低涡,造成伴随暴雨的低涡灾害性天气的增加,因此应进一步深化对低涡暴雨灾害性天气发展趋势的研究。

印度夏季风与中国华北降水的遥相关分析及数值模拟

20世纪80年代中国学者揭示了印度夏季风与中国华北降水的正相关关系,以后国内外又有一些研究证实了这种正相关关系的存在。文中利用1951—2005年多种气象资料和数值模拟方法,详细讨论了印度夏季风和中国华北地区夏季降水的关系,并针对由印度西北部经青藏高原到中国华北地区形成的正、负、正的遥相关型,从动力因子和热力因子两方面探讨了其中的内在联系,所得结果不但确证了以往的结论,而且进一步揭示了印度夏季风对华北地区降水的影响机制。结果表明:(1)印度夏季风强(弱)时,华北地区容易出现降水偏多(少)的天气;华北地区降水偏多(少)时,印度夏季风偏强(弱)的机率却低一些,这说明印度夏季风的异常变化对华北地区夏季降水有更大的影响。(2)印度夏季风强度主要受印度季风槽的影响,在印度季风槽加深的同时,中高纬的低压槽也加深发展,而这时西太平洋高压脊西伸,来自低纬的西南风水汽输送和源于西太平洋的副热带高压南侧的东南风水汽输送共同作用,有利于华北地区的降水偏多;反之则不利于华北地区的降水。(3)区域气候模式模拟结果也很好地模拟出印度夏季风和华北夏季降水的遥相关关系,其相应的环流异常系统与诊断分析结果非常一致,这从另一方面证实了这种遥相关关系的存在和可靠性。

IAP AGCM 4.1对淮河流域夏季降水的预报技巧评估

基于中国科学院大气物理研究所新一代大气环流模式IAP AGCM 4.1共30 a(1981—2010年)的集合回报试验结果,评估了模式对淮河流域夏季降水的预报技巧。分析结果表明,模式总体上可以较好地再现出淮河流域夏季平均降水南多北少的空间分布特征,其中模式模拟的6月降水量与观测值的空间相关可达0.93。但降水强度与观测相比具有系统性的偏差,且模式模拟的降水年际变率显著偏弱。基于降水距平相关系数的确定性预报技巧分析表明,模式对流域西南部夏季降水的预测技巧较高,达到0.2以上,且模式对6月降水异常的预测能力相对最好,7月次之。针对淮河不同子流域的预报技巧分析表明,IAP AGCM 4. 1对蚌埠、鲁台子、王家坝水文控制站以上集水面积的夏季面雨量异常具有一定的预报技巧,30 a集合回报的时间相关系数分别为0. 11、0. 13、0. 16。基于降水等级的概率预报技巧评估表明,模式对7月淮河流域南部少雨事件具有很好的预报能力,同时对6月流域中部多雨事件的预报技巧也较高。

Projection of the Future Changes in Tropical Cyclone Activity Affecting East Asia over the Western North Pacific Based on Multi-RegCM4 Simulations

Future changes in tropical cyclone(TC)activity over the western North Pacific(WNP)under the representative concentration pathway RCP4.5 are investigated based on a set of 21 st century climate change simulations over East Asia with the regional climate model RegCM4 driven by five global models.The RegCM4 reproduces the major features of the observed TC activity over the region in the present-day period of 1986-2005,although with the underestimation of the number of TC genesis and intensity.A low number of TCs making landfall over China is also simulated.By the end of the 21st century(2079-98),the annual mean frequency of TC genesis and occurrence is projected to increase over the WNP by16%and 10%,respectively.The increase in frequency of TC occurrence is in good agreement among the simulations,with the largest increase over the ocean surrounding Taiwan Island and to the south of Japan.The TCs tend to be stronger in the future compared to the present-day period of 1986-2005,with a large increase in the frequency of strong TCs.In addition,more TCs landings are projected over most of the China coast,with an increase of~18%over the whole Chinese territory.

Performance of RegCM4 over Major River Basins in China

A long-term simulation for the period 1990–2010 is conducted with the latest version of the International Centre for Theoretical Physics＇ Regional Climate Model（RegCM4）, driven by ERA-Interim boundary conditions at a grid spacing of 25 km. The Community Land Model（CLM） is used to describe land surface processes, with updates in the surface parameters,including the land cover and surface emissivity. The simulation is compared against observations to evaluate the model performance in reproducing the present day climatology and interannual variability over the 10 main river basins in China,with focus on surface air temperature and precipitation. Temperature and precipitation from the ERA-Interim reanalysis are also considered in the model assessment. Results show that the model reproduces the present day climatology over China and its main river basins, with better performances in June–July–August compared to December–January–February（DJF）.In DJF, we find a warm bias at high latitudes, underestimated precipitation in the south, and overestimated precipitation in the north. The model in general captures the observed interannual variability, with greater skill for temperature. We also find an underestimation of heavy precipitation events in eastern China, and an underestimation of consecutive dry days in northern China and the Tibetan Plateau. Similar biases for both mean climatology and extremes are found in the ERA-Interim reanalysis, indicating the difficulties for climate models in simulating extreme monsoon climate events over East Asia.

SIMULATION OF SPATIO-TEMPORAL DISTRIBUTION CHARACTERISTICS AND RADIATIVE FORCING OF ORGANIC CARBON AEROSOLS IN CHINA

The International Centre for Theoretical Physics(ICTP,Italy) Regional Climate Model version 3.0(RegCM3) is used to simulate spatio-temporal distribution characteristics and radiative forcing(RF) of organic carbon(OC) aerosols in and around China.The preliminary simulation results show that OC aerosols are mostly concentrated in the area to the south of Yellow River and east of Tibetan Plateau.There is a decreasing trend of column burden of OC aerosols from south to north in China.The maximum value of column burden of OC aerosols is above 3 mg/m2 and located in the central and southern China,southeastern Tibet,and southwestern China's Yunnan,Guizhou,Sichuan provinces.The simulation on the seasonal variation shows that the maximum value of column burden of OC aerosols appears in winter and the secondary value is in spring and the minimum in summer.The RF of OC aerosols which varies seasonally is negative at the top of the atmosphere(TOA) and surface.The spatio-temporal characteristics of the RF of OC aerosols are basically consistent with that of IPCC,implying the high accuracy of the parameterization scheme for OC aerosols in RegCM3.

积云对流参数化方案模拟我国东南沿海及台湾海峡地区降水的适用性

我国东南沿海及台湾海峡地区地形和下垫面情况复杂,积云对流活动强烈,这给该地区降水的模拟和预测带来很大困难。为探讨不同积云对流参数化方案在我国东南沿海及台湾海峡地区的适用性,选择了4种参数化方案(Anthes-Kuo方案、Arakawa-Schubert方案、Fritsch-Chappell方案和MIT-Emanuel方案),基于区域气候模式RegCM 4.0分别模拟了该地区的降水情况,并选用了与模式分辨率相当的TRMM(Tropical Rainfall Measuring Mission,0.25°×0.25°)月平均降水资料进行验证。模拟结果表明,4种方案均能大致模拟出我国东南沿海及台湾海峡地区降水的空间结构和季节变化特征。其中,Fritsch-Chappell方案和MIT-Emanuel方案均能较好地模拟出降水空间分布,包括台湾岛南部和广东沿海的降水极值中心,而MIT-Emanuel方案降水的季节和年际变化特征模拟最好,如能够基本再现夏季降水在6月和8月份的双峰结构。此外,基于各高度层假相当位温的计算结果表明,MIT-Emanuel方案模拟的对流活动强烈,产生的对流性降水较多,使得其模拟的降水量值更接近实测资料。因此,MIT-Emanuel方案可能是最适用于模拟我国东南沿海和台湾海峡地区降水的积云对流参数化方案。

Dynamical Donwscaling for Railroad Areas in Eastern Amazon and Southeastern Brazil:Current Climate and Near-Future Projections

We performed a dynamic downscaling using REGCM4 regional model driven by MPI global model for current (1990/2012) and near-future (2015/2039) climate in order to characterize the seasonal rainfall regimes throughout the railroad areas in eastern Amazon and southeastern Brazil. The analysis of observational data for the current climate indicated the existence of pronounced spatial variations in rainfall regime across railroad regions during both the rainy and dry seasons. Although models have presented generalized underestimation, the regional model showed improvements on spatial representation and intensity of the rainfall in comparison with global model results. We reported the future projections taking into account the correction of simulated rainfall by the values of the biases found in each respective seasonal regime, so that the results are expressed by percentage changes of the future (2015/2037) relative to the current climate patterns. For the railroad in eastern Amazon, projections indicate a weak decrease of rainfall of about -15% in the rainy season (January to May), however during the dry season (June to October) are expected drastic reductions between -70% and -90% in south (Carajás in Pará state) and north (Sao Luis in Maranhao state) portions. Conversely, for the railroad in southeast Brazil, model projections point out for an increased rainfall regime during the rainy season (October to February) around +30% to +40% in the east part of the region over the Espírito Santo state.

Sensitivity Study of the RegCM4’s Surface Schemes in the Simulations of West Africa Climate

Two simulations of five years (2003-2007) were conducted with the Regional Climate models RegCM4, one coupled with Land surface models BATS and the other with CLM4.5 over West Africa, where simulated air temperature and precipitation were analyzed. The purpose of this study is to assess the performance of RegCM4 coupled with the new CLM4.5 Land surface scheme and the standard one named BATS in order to find the best configuration of RegCM4 over West African. This study could improve our understanding of the sensitivity of land surface model in West Africa climate simulation, and provide relevant information to RegCM4 users. The results show fairly realistic restitution of West Africa’s climatology and indicate correlations of 0.60 to 0.82 between the simulated fields (BATS and CLM4.5) for precipitation. The substitution of BATS surface scheme by CLM4.5 in the model configuration, leads mainly to an improvement of precipitation over the Atlantic Ocean, however, the impact is not sufficiently noticeable over the continent. While the CLM4.5 experiment restores the seasonal cycles and spatial distribution, the biases increase for precipitation and temperature. Positive biases already existing with BATS are amplified over some sub-regions. This study concludes that temporal localization (seasonal effect), spatial distribution (grid points) and magnitude of precipitation and temperature (bias) are not simultaneously improved by CLM4.5. The introduction of the new land surface scheme CLM4.5, therefore, leads to a performance of the same order as that of BATS, albeit with a more detailed formulation.

Hindcast Experiment of Extraseasonal Short-Term Summer Climate Prediction over China with RegCM3_IAP9L-AGCM

The regional climate model RegCM3 has been one-way nested into IAP9L-AGCM, the nine-level atmospheric general circulation model of the Institute of Atmospheric Physics, Chinese Academy of Sciences, to perform a 20-yr （1982-2001） hindcast experiment on extraseaonal short-term prediction of China summer climate. The nested prediction system is referred to as RegCM3_IAP9L-AGCM in this paper. The results show that hindeasted climate fields such as 500-hPa geopotential height, 200- and 850-hPa zonal winds from RegCM3_IAP9L-AGCM have positive anomaly correlation coefficients （ACCs） with the observations, and are better than those from the stand-alone IAP9L-AGCM. Except for the 850-hPa wind field, the positive ACCs of the other two fields with observations both pass the 90% confidence level and display a zonal distribution. The results indicate that the positive correlation of summer precipitation anomaly percentage between the nested prediction system and observations covers most parts of China except for downstream of the Yangtze River and north of Northeast and Northwest China. The nested prediction system and the IAP9L-AGCM exhibit different hindcast skills over different regions of China, and the former demonstrates a higher skill over South China than the latter in predicting the summer precipitation.

Simulation of Effects of Grassland Degradation on Regional Climate over Sanjiangyuan Region in Qinghai-Tibet Plateau

Regional climate model （RegCM3） was applied to explore the possible effects of land use changes （e.g., grassland degradation in this study） on local and regional climate over the Sanjiangyuan region in the Qinghai-Tibet Plateau. Two multiyear （1991-1999） numerical simulation experiments were conducted： one was a control experiment with current land use and the other was a desertification experiment with potential grassland degradation. Preliminary analysis indicated that RegCM3 is appropriate for simulating land- climate interactions, as the patterns of the simulated surface air temperature, the summer precipitation, and the geopotential height fields are consistent with the observed values. The desertification over the Sanjiangyuan region will cause different climate effects in different regions depending on the surrounding environment and climate characteristics. The area with obvious change in surface air temperature inducing by grassland degradation over the Sanjiangyuan region is located in the Qinghai-Tibet Plateau. A winter surface air temperature drop and the other seasons＇ surface air temperature increase will be observed over the Qinghai-Tibet Plateau based on two numerical simulation experiments. Surface air temperature changes in spring are the largest （0.46℃）, and in winter are the smallest （smaller than 0.03℃）, indicating an increasing mean annual surface air temperature over the Qinghai-Tibet Plateau. Surface air temperature changes will be smaller and more complex over the surrounding region, with minor winter changes for the regions just outside the plateau and notable summer changes over the north of the Yangtze River. The reinforced summer heat source in the plateau will lead to an intensification of heat low, causing the West Pacific subtropical high to retreat eastward. This will be followed by a decrease of precipitation in summer. The plateau＇s climate tends to become warm and dry due to the grassland degradation over the Sanjiangyuan region.

Effects of Updated RegCM4 Land Use Data on Near-Surface Temperature Simulation in China

Biogeophysical effects of land use and land cover （LULC） changes play a significant role in modulating climate on various spatial scales. In this study, a set of recent LULC products with a spatial resolution of 500 m was developed in China for update in RegCM4 （regional climate model version 4）. Two sets of comparative numerical experiments were conducted to study the effects of LULC changes on near-surface temperature simulation. The results show that after LULC changes, areas of crops and mixed woodlands as well as urban areas increase over entire China, accom- panied with greatly expanded mixed farming and forests/field mosaics in southern China, and reduced areas of 1） ir- rigated crops and short grasses in northern China and the Tibetan Plateau, and 2） semi-desert and desert in northwest-em China. Improvements in the LULC data clearly result in more accurate simulations of the near-surface temperat-ure. Specifically, increasing latent heat and longwave albedo due to enhanced LULC in certain areas lead to reduc-tion in land surface temperature （LST）, while changes in shortwave albedo and sensible heat also exert a great influ- ence on the LST. Overall, these parameter adjustments reduce the biases in near-surface temperature simulation.