Madden–Julian Oscillation simulated in BCC climate models

This study evaluates the ability of four versions BCC (Beijing Climate Center or National Climate Center) models (BCC_AGCM2.1, BCC_AGCM2.2, BCC_CSM1.1 and BCC_CSM1.1m) in simulating the MJO phenomenon using the outputs of the AMIP (Atmospheric Model Intercomparison Project) and historical runs. In general, the models can simulate some major characteristics of the MJO, such as the intensity, the periodicity, the propagation, and the temporal/spatial evolution of the MJO signals in the tropics. There are still some biases between the models and the observation/reanalysis data, such as the overestimated total intraseasonal variability, but underestimated MJO intensity, shorter significant periodicity, and excessive westward propagation. The differences in the ability of simulating the MJO between AMIP and historical experiments are also significant. Compared to the AMIP runs, the total intraseasonal variability is reduced and more realistic, however the ratio between the MJO and its westward counterpart decreases in the historical runs. This unrealistic simulation of the zonal propagation might have been associated with the greater mean precipitation over the Pacific and corresponded to the exaggeration of the South Pacific Convergence Zone structure in precipitation mean state. In contrast to the T42 versions, the improvement of model resolution demonstrate more elaborate topography, but the enhanced westward propagation signals over the Arabia Sea followed. The underestimated (overestimated) MJO variability over eastern Indian Ocean (Pacific) was assumed to be associated with the mean state. Three sets of sensitive experiments using BCC_CSM1.1m turn out to support this argument.     

不同分辨率BCC_AGCM模式对东亚区域垂直云量的模拟

基于ISCCP(International Satellite Cloud Climatology Project)和NCEP(National Centers for Environmental Prediction)资料分析了BCC_AGCM2.1(Beijing Climate Center_Atmospheric General Circulation Model 2.1)和BCC_AGCM2.2模拟的云在东亚的垂直分布特点,并探讨了误差来源。两个模式大体上模拟出了总云量的分布形势,较好地模拟出了垂直方向上云量大值带随地形的变化特点,但模拟的总云量偏少。AGCM2.2模拟的云量整体上小于AGCM2.1,除复杂地形外AGCM2.2没有体现出高分辨率的优势。模式对中国东部环流场的模拟效果差导致模拟的云量偏少,尤其是AGCM2.2。模拟的对流层高层相对湿度明显偏大导致高层云量偏大。模式在近海面模拟的相对湿度偏小,四川盆地及周围地区冷季模拟的水汽含量偏少,因而模拟的云量偏少。模式云量对相对湿度的响应能力较好,模拟出了云量对垂直速度和稳定度的响应,但地区差异不明显。模式的云参数化方案中云与相对湿度的关系系数需要调整,应更利于云的生成。     

西南地区云量变化特征

利用西南地区(云南、贵州、四川、重庆)记录较为完整的73个测站1956~2005年月平均云量资料,采用经验正交函数分析和Mann-Kendall突变检验方法,研究分析了西南地区云量的时空分布特征。结果表明:就全年而言,整个西南地区总云量的变化趋势一致,且存在着明显的年际变化特征,1990年代以后全年总云量表现出减少趋势;此外,总云量的分布在一定程度上受地形和区域气候的影响。从季节来看,夏、秋、冬季的总云量在西南地区为空间一致的变化趋势,而春季四川盆地北部总云量的变化趋势与其余地区相反;四季总云量也有明显的年际变化特征。低云量,全年和四季的时空变化特征相似,由于受地形起伏及区域气候差异的影响,川西高原东部和重庆地区的变化趋势与四川盆地的相反,且同样存在着明显的年际变化特征。另外,突变分析结果显示,西南地区的低云量近50a来呈持续减少趋势,而总云量在1990年发生突变,突变前在0线附近震荡,突变后总云量持续减少。     

Decomposition of Fast and Slow Cloud Responses to Quadrupled CO2 Forcing in BCC–AGCM2.0 over East Asia

In this study, the decomposed fast and slow responses of clouds to an abruptly quadrupled CO₂ concentration (approximately 1139 ppmv) in East Asia (EA) are obtained quantitatively by using a general circulation model, BCC–AGCM2.0. Our results show that in the total response, the total cloud cover (TCC), low cloud cover (LCC), and high cloud cover (HCC) all increased north of 40°N and decreased south of 40°N except in the Tibetan Plateau (TP). The mean changes of the TCC, LCC, and HCC in EA were –0.74%, 0.38%, and –0.38% in the total response, respectively; 1.05%, –0.03%, and 1.63% in the fast response, respectively; and –1.79%, 0.41%, and –2.01% in the slow response, respectively. By comparison, we found that changes in cloud cover were dominated by the slow response in most areas in EA due to the changes in atmospheric temperature, circulation, and water vapor supply together. Overall, the changes in the cloud forcing over EA related to the fast and slow responses were opposite to each other, and the final cloud forcing was dominated by the slow response. The mean net cloud forcing (NCF) in the total response over EA was –1.80 W m^–2, indicating a cooling effect which partially offset the warming effect caused by the quadrupled CO₂. The total responses of NCF in the TP, south China (SC), and northeast China (NE) were –6.74 W m^–2, 6.11 W m^–2, and –7.49 W m^–2, respectively. Thus, the local effects of offsetting or amplifying warming were particularly obvious.     

ENERGY BUDGET BIAS IN GLOBAL COUPLED OCEAN-ATMOSPHERE-LAND MODEL*

The energy budget of the two versions of the GOALS model (GOALS-1.1 and GOALS-2) is described and compared to observational estimates.The results illustrate that the simulated surface net shortwave radiation flux is underestimated in the high-latitude regions while the surface net longwave radiation flux is substantially overestimated in that region,which results in the lower surface air temperature (SAT) of the polar region and the stronger negative sensible heat flux in high latitudes.The overestimated sensible heat flux from surface to atmosphere in the continents causes the much warmer SAT centers,which may be the reason for the bias of the model SAT. The bias that the simulated precipitation is less than observation in most regions is closely related to the underestimated latent heat flux over most of the Eurasian Continent and the oceans, especially over the subtropical oceans.It can be seen that the bias in the OLR of the two models lies in low and middle latitudes,where the absorbed solar shortwave radiation flux at the top of the atmosphere is comparable to the NCEP reanalysis,but much less than ERBE data.This indicates that the improvement of cloud-radiation parameterization scheme in low and middle latitudes is of critical importance to the simulation of global energy budget.The simulated cloud cover from the GOALS-2 model with diagnosed cloud scheme is generally less except at equatorial areas, especially in the mid-latitude areas,which causes the large bias of energy budget there.It is suggested that the refinement of cloud parameterization is one of the most important tasks in the model's future development.     

NCEP 全球预报系统在ARM SGP站点预报大气温度、湿度和云量的检验

利用美国大气辐射测量项目(ARM)制作的“气候模拟最佳估计”(CMBE)观测数据集,检验美国环境预报中心(NCEP)全球预报系统(GFS)2001～2008年在ARM Southern Great Plains(SGP)站点预报的大气温度、相对湿度和云量的垂直分布,主要结论如下:(1)NCEP GFS较好地预报出了温度...     

四川盆地秋季气溶胶与云的相关分析

通过对再分析资料总气溶胶光学厚度(total aerosol optical depth,AOD)和低云云量(low cloud cover,LCC)的分析,结果表明:四川盆地秋季气溶胶与云的分布和变化主要是以全区域的一致变化,和以成都、重庆为中心的双支结构为主。气溶胶分布为双支结构时的变化更容易引起云量变化,持续时间不超过两天;气溶胶对云的影响还与二者的分布时间有关,二者高值出现的时间相近(10月),气溶胶会使高云量增加,反之使低云量增加高云量减少(9月)。      

新旧两个版本GAMIL模式对1997/98强E1 Ni(n)o年西太平洋暖池区独特云辐射强迫特征的数值模拟

1997/98年强E1 Ni(n)o背景下西太平洋暖池区云辐射强迫的变化,表现出诸多不同于以往的特征,已经成为检验气候模式性能的一个重要标准.本文基于卫星资料,分析了大气环流模式GAMIL1.0和2.0版对上述现象的模拟能力.结果表明,GAMIL1.0模式对热带地区云辐射特征分布,尤其对西太平洋暖池区的长(短)波云辐射...     

海-陆-气全球耦合模式能量收支的误差

通过分析GOALS模式两个版本GOALS 1.1和GOALS 2的能量收支 ,并与观测对比 ,结果表明 :模式模拟的地表净短波辐射通量在高纬地区偏低 ,而净长波辐射通量又偏高 ,导致极地表面温度偏低 ,感热通量在高纬地区为很高的负值。而在陆地上感热加热作用显著偏强 ,使地表有较大的向上净能量给大气 ,引起陆地上有些暖中心也偏强 ,这也解释了模式模拟地表面空气温度场的误差原因。海洋上潜热通量偏低 ,特别是在副热带洋面上偏少更明显。陆地上的欧亚和北美大陆大部分地区潜热通量仍偏低。这也是模式降水在大部分地区偏少的重要原因。两模式大气顶OLR偏低的模拟主要是在中低纬度 ,大气顶净短波辐射通量的模拟在中低纬度虽然与NCEP结果接近 ,但与地球辐射收支试验ERBE资料比较仍偏小较多 ,说明改进中低纬度云 辐射参数化方案对改进全球能量收支的模拟有重要意义。GOALS 2模式中诊断云方案模拟的云量除赤道地区外普遍偏小 ,尤以中纬度为甚 ,造成那里能量收支出现大的误差 ,这表明了更好的云参数化方案的引入是今后模式发展的重要任务之一     

Evaluating the Impacts of Cloud Microphysical and Overlap Parameters on Simulated Clouds in Global Climate Models

The improvement of the accuracy of simulated cloud-related variables, such as the cloud fraction, in global climate models (GCMs) is still a challenging problem in climate modeling. In this study, the influence of cloud microphysics schemes (one-moment versus two-moment schemes) and cloud overlap methods (observation-based versus a fixed vertical decorrelation length) on the simulated cloud fraction was assessed in the BCC_AGCM2.0_CUACE/Aero. Compared with the fixed decorrelation length method, the observation-based approach produced a significantly improved cloud fraction both globally and for four representative regions. The utilization of a two-moment cloud microphysics scheme, on the other hand, notably improved the simulated cloud fraction compared with the one-moment scheme; specifically, the relative bias in the global mean total cloud fraction decreased by 42.9%–84.8%. Furthermore, the total cloud fraction bias decreased by 6.6% in the boreal winter (DJF) and 1.64% in the boreal summer (JJA). Cloud radiative forcing globally and in the four regions improved by 0.3%?1.2% and 0.2%?2.0%, respectively. Thus, our results showed that the interaction between clouds and climate through microphysical and radiation processes is a key contributor to simulation uncertainty.     

Influence of aerosol on clouds over the Indo-Gangetic Plain, India

Using Total Ozone Mapping Spectrometer Aerosol Index (AI) and NCEP/NCAR reanalysis clouds data for the period 1979–1992, the influence of aerosol on the clouds (low and high cloud cover) over the Indo-Gangetic Plain (IGP) in India has been brought out for the first time in the present study. AI shows increasing tendency over the IGP suggesting that aerosol loading over this region increased significantly during the study period. In our analysis, High Cloud Cover (HCC) shows increasing trend and Low Cloud Cover (LCC) shows decreasing trend over the IGP during the same period. During pre-monsoon season when aerosol loading is more, HCC increases in positive correlation with AI. On the other hand, LCC show decreasing trend and is anti-correlated with AI. During summer monsoon, aerosol shows increasing trend but their effect on HCC and LCC is not seen to be significant. Similarly, the role of humidity on aerosol induced changes in HCC and LCC over the IGP region was also analyzed. In the low to moderate humid areas of IGP region (western and middle IGP), increasing AI leads to increase in HCC and decrease in LCC. On the other hand, in high humid areas (eastern IGP), increase in AI does not show any significant effect on HCC, but LCC shows positive trend. Therefore, we strongly argue that increasing aerosol loading enhances Cloud Condensation Nuclei over the region which in turn, alters the microphysical properties of clouds by reducing the size of cloud droplets, and atmospheric humidity controls the aerosol effect on clouds. During the recent period (2005–2010), similar features have also been observed over the IGP region.     

1960~2012年中国地区总云量时空变化及其与气温和水汽的关系

基于我国地区543个地面气象台站观测的总云量、平均气温和相对湿度日均值资料,采用正交经验函数（EOF）、气候倾向率和线性趋势分析等方法,研究了1960~2012年总云量的时空变化特征及其与气温和水汽的关系。结果表明:（1）我国地区总云量呈南多北少的带状分布特征,最大值在四川盆地（82%）。近53年来总云量气候倾向率为-0.8%（10a）-1,趋势系数为-0.68,通过了99.9%的信度检验。（2）总云量季节变化特点明显,夏季最多,春秋季次之,冬季最少,其中春季、夏季和秋季有显著的下降趋势。（3）EOF分解的前两个模态表明总云量不仅具有一致减少的变化特征,还具有明显的区域差异。以此同时,平均气温和相对湿度不论在总体变化趋势、地区差异、还是时间演变上,均与总云量保持较高的一致性,进一步证明总云量的变化与气温和水汽有密切关系。     

Cloud Radiative Effects and Changes Simulated by the Coupled Model Intercomparison Project Phase 5 Models

Using 32 CMIP5(Coupled Model Intercomparison Project Phase 5) models, this study examines the veracity in the simulation of cloud amount and their radiative effects(CREs) in the historical run driven by observed external radiative forcing for 1850–2005, and their future changes in the RCP(Representative Concentration Pathway) 4.5 scenario runs for2006–2100. Validation metrics for the historical run are designed to examine the accuracy in the representation of spatial patterns for climatological mean, and annual and interannual variations of clouds and CREs. The models show large spread in the simulation of cloud amounts, specifically in the low cloud amount. The observed relationship between cloud amount and the controlling large-scale environment are also reproduced diversely by various models. Based on the validation metrics,four models—ACCESS1.0, ACCESS1.3, Had GEM2-CC, and Had GEM2-ES—are selected as best models, and the average of the four models performs more skillfully than the multimodel ensemble average.All models project global-mean SST warming at the increase of the greenhouse gases, but the magnitude varies across the simulations between 1 and 2 K, which is largely attributable to the difference in the change of cloud amount and distribution. The models that simulate more SST warming show a greater increase in the net CRE due to reduced low cloud and increased incoming shortwave radiation, particularly over the regions of marine boundary layer in the subtropics. Selected best-performing models project a significant reduction in global-mean cloud amount of about-0.99% K~(-1)and net radiative warming of 0.46 W m~(-2)K~(-1), suggesting a role of positive feedback to global warming.     

BCC_AGCM2.1对中国东部地区云辐射特征模拟的偏差分析

通过与观测及再分析资料的对比,评估了中国国家气候中心大气环流模式BCC_AGCM 2.1对中国东部地区云辐射特征的模拟性能,并着重分析了模拟偏差的原因.在云辐射特征的基本气候态模拟方面,模式能大致再现中国东部中纬度层状云大值带,以及层状云冷季多、暖季少的季节特征,模拟的短波云辐射强迫也具有与观测相对应的季节变化特征.在云辐射强迫和地面温度相互影响过程的模拟方面,模式也能模拟出与观测相近的相互作用过程,即地面温度降低伴随着层状云云量增多以及负的净云辐射强迫加强,升温时层状云云量减少和净云辐射强迫减弱.但模式模拟的大陆层状云云量系统性偏少(尤其在冷季),使得模式在该处的短波云辐射强迫明显偏弱.初步分析表明,造成层状云模拟差异的主要原因是在中国西南地区对流层低层模式模拟的偏南气流明显偏弱以及陆-气潜热通量偏小.偏南气流偏弱导致低层散度和垂直运动条件不利于中层云的形成.同时偏南气流偏弱也不利于向西南地区的水汽输送,再加上模式模拟地表向上潜热通量偏小,这二者都使得模式模拟中国西南区域对流层低层的水汽含量严重偏少,相对湿度偏低,同样不利于层状云生成和发展.水汽偏少进一步导致在冷异常情况下青藏高原下游云辐射-地表温度反馈模拟偏弱,即呈现冷异常时,水汽条件偏弱限制了云量增加,弱化了进一步降低温度的反馈过程.     

宁夏三类降水云的时空分布及环流特征分析

利用宁夏24个测站1971—2000年常规地面观测中云状、总云量、低云量、天气现象、降水量等资料,对宁夏30年中层状云、对流云及混合云降水的时空变化特征进行了分析。同时,利用NCEP/NCAR(1971—2000年)全球再分析资料,对宁夏三类降水云的环流特征进行了诊断分析。结果表明:30年中层状云降水次数明显多于对流云和混合云降水次数,是宁夏降水的主要类型,而混合云降水是宁夏大雨以上降水的主要类型;宁夏南部地区以层状云降水为主,北部地区对流云和混合云降水次数相对较多;三类降水云的月、年际和年代际变化特征及所对应的环流背景和影响系统具有明显的差异。     

Spatiotemporal Variations of Cloud Amount over the Yangtze River Delta, China

Based on the NOAA's Advanced Very High Resolution Radiometer(AVHRR) Pathfinder Atmospheres Extended(PATMOS-x) monthly mean cloud amount data, variations of annual and seasonal mean cloud amount over the Yangtze River Delta(YRD), China were examined for the period 1982–2006 by using a linear regression analysis. Both total and high-level cloud amounts peak in June and reach minimum in December, mid-level clouds have a peak during winter months and reach a minimum in summer, and lowlevel clouds vary weakly throughout the year with a weak maximum from August to October. For the annual mean cloud amount, a slightly decreasing tendency(–0.6% sky cover per decade) of total cloud amount is observed during the studying period, which is mainly due to the reduction of annual mean high-level cloud amount(–2.2% sky cover per decade). Mid-level clouds occur least(approximately 15% sky cover) and remain invariant, while the low-level cloud amount shows a significant increase during spring(1.5% sky cover per decade) and summer(3.0% sky cover per decade). Further analysis has revealed that the increased low-level clouds during the summer season are mainly impacted by the local environment. For example,compared to the low-level cloud amounts over the adjacent rural areas(e.g., cropland, large water body, and mountain areas covered by forest), those over and around urban agglomerations rise more dramatically.     

The Extreme Summer Precipitation over East China during 1982–2007 Simulated by the LASG/IAP Regional Climate Model

The extreme summer precipitation over East China during 1982-2007 was simulated using the LASG/IAP regional climate model CREM(the Climate version of a Regional Eta-coordinate Model).The results show that the probability density functions(PDFs) of precipitation intensities are reasonably simulated,except that the PDFs of light and moderate rain are underestimated and that the PDFs of heavy rain are overestimated.The extreme precipitation amount(R95p) and the percent contribution of extreme precipitation to the total precipitation(R95pt) are also reasonably reproduced by the CREM.However,the R95p and R95pt over most of East China are generally overestimated,while the R95p along the coastal area of South China(SC) is underestimated.The bias of R95pt is consistent with the bias of precipitation intensity on wet days(SDII).The interannual variation for R95p anomalies(PC1) is well simulated,but that of R95pt anomalies(PC2) is poorly simulated.The skill of the model in simulating PC1(PC2) increases(decreases) from north to south.The bias of water vapor transport associated with the 95th percentile of summer daily precipitation(WVTr95) explains well the bias of the simulated extreme precipitation.     

GRAPES_Meso区域模式积云计算方案引进及预报效果检验

云量在模式中的准确模拟既是一个重点问题,也是一个难点问题。经评估发现,在GRAPES_Meso（Global/Regional Assimilation and PrEdiction System）模式中存在模拟云量偏少的问题,而ECMWF模式中的积云云量计算方案对云量模拟具有一定优势。鉴于此,本文借鉴ECMWF积云云量计算方案对GRAPES中尺度模式中的云量计算方案进行了适当改进,并通过影响试验模拟三维云量和地面温度来验证其改进效果。结果表明:较改进前,改进云量方案模拟的云量增多,单层云量更加准确,垂直方向云层结构改进效果明显;地面温度与观测值对比误差减小。综合分析模拟结果,认为改进云量计算方案在GRAPES模式中对云量和地面温度的模拟有较好的改进。     

中国大陆卫星反演云参数的评估

该文选取１９８３年７月和１９８４年１月份代表夏季和冬季，利用中国地面气象月报的云量资料以及多年平均的地面观测云气修资料，与中国大陆地区ＩＳＣＣＰ卫星反演的去量和云状资料进行了对比分析。参照大气环流和云天气气候特征，从卫星得到的从云状是比较合理的，但干旱沙漠地区的高云量的估计不足，低云估计偏多。     

Cloud and Radiation Processes Simulated by a Coupled Atmosphere-Ocean Model

Using NCC/IAP T63 coupled atmosphere-ocean general circulation model (AOGCM),two 20-yr integra- tions were processed,and their ability to simulate cloud and radiation was analysed in detail.The results show that the model can simulate the basic distribution of cloud cover,and however,obvious differences still exist compared with ISCCP satellite data and ERA reanalysis data.The simulated cloud cover is less in general,especially the abnormal low values in some regions of ocean.By improving the cloud cover scheme, simulated cloud cover in the eastern Pacific and Atlantic,summer hemisphere's oceans from subtropical to mid-latitude is considerably improved.But in the tropical Indian Ocean and West Pacific the cloud cover difference is still evident,mainly due to the deficiency of high cloud simulation in these regions resulting from deep cumulus convection.In terms of the analysis on radiation and cloud radiative forcing,we find that simulation on long wave radiation is better than short wave radiation.The simulation error of short wave radiation is caused mostly by the simulation difference in short wave radiative forcing,sea ice,and snow cover,and also by not involving aerosol's effect.The simulation error of long wave radiation is mainly resulting from deficiency in simulating cloud cover and underlying surface temperature.Corresponding to improvement of cloud cover,the simulated radiation (especially short wave radiation) in eastern oceans, summer hemisphere's oceans from subtropical to mid-latitude is remarkably improved.This also brings obvious improvement to net radiation in these regions.