GAMIL模式海气湍流通量参数化方案的改进及其对大气环流年际变率模拟效果的影响

通过引人中尺度对流运动对海表湍流通量的贡献,改进了大气环流模式GAMIL1.0的海气湍流通量参数化方案.利用1979年1月至2000年12月的观测海温资料驱动GAMIL1.0模式,研究了海气湍流通量参数化改进对大气环流年际变化模拟效果的影响.结果表明:采用改进的海气湍流通量参数化方案,模拟的热带海表湍流热通量得到增强,...     

CAM3模式模拟厄尔尼诺事件对大气环流异常的影响

采用CAM3（Community Atmosphere Model Version3）模式中海气湍流通量参数化原方案和改进方案,利用观测海温驱动CAM3模式进行气候模拟,以分析模式对厄尔尼诺事件影响气候变化的模拟能力。结果表明,采用CAM3模式海气湍流通量参数化改进方案,模式能够更好地模拟出由厄尔尼诺事件引起的北太平洋和北美地区大气环流的变化,尤其是对厄尔尼诺年冬季阿留申低压强度和与PNA遥相关型有关的500hPa位势高度异常的模拟。     

大气环流模式CAM中土壤冻融过程改进对东亚气候模拟的影响

本文在改进了大气环流模式NCAR CAM3.1中的土壤冻融过程参数化的基础上,模拟研究了改进的冻土过程对东亚气候模拟的影响.模拟结果分析表明,改进冻融过程参数化后,冬季欧亚大陆上大部分地区大气对地表的加热偏强,而夏季地表对大气的加热偏强,尤其是青藏高原对大气的加热作用显著增强.东亚气候对冻土过程参数化方案非常敏感,冬、...     

基于WRF模式的海面湍流通量参数化方案的研究

中尺度数值模拟结果特别是高影响天气的精细预报对近地层动量和热量通量极为敏感,因此近地层湍流通量参数化方案一直是大气科学研究中一个十分重要的课题.以TOGA-COARE观测试验资料为基础,本文将湍流通量参数化方案模块从天气研究预报(WRF)模式中提取出来,与最新研发的湍流通量参数化方案(即LGLC方案)进行对比测试分析....     

SAMIL大气环流模式海面湍流通量参数化方案研究

将中国科学院大气物理研究所大气科学和地球流体力学数值模拟国家重点实验室发展的大气环流谱模式SAMIL_R42L26 2.08中的海气通量参数化方案——Louis方案, 与新发展的一种新型近海层湍流通量参数化方案——LGLC方案进行比较和分析。离线测试结果表明, LGLC方案计算的通量结果与观测数据具有更好的一致性, 且由于其区分热力粗糙度和动力粗糙度, 使得对热量通量的计算更加准确。在线测试则证明, 引入LGLC方案的SAMIL模式对洋面风应力、 感热通量、 潜热通量和降水率的模拟能力有了进一步的提高, 尤其对北半球夏季印度季风和南海季风区的降水改善明显。     

区域气候模式对中国东部夏季气候的模拟试验

在美国国家大气研究中心第二代区域气候模式(NCAR/RegCM2)的基础上,通过改进其中的陆面过程、积云对流、辐射传输和边界层等物理过程的参数化方案,发展了一个有多种方案选择的改进的区域气候模式.分别利用原区域气候模式和改进的区域气候模式,对1994年和1998年夏季的异常季风降水过程进行了数值模拟试验,并与观测结果进行了比较.结果表明,新方案模拟的1994年夏季的雨带位置与实际位置非常一致,而原区域气候模式模拟的雨带都位于中国北方地区,与观测的差别较大.从环流场的模拟比较也可以看出,新方案模拟的1994年和1998年夏季环流形势都比原方案的结果更为合理.     

积云参数化方案对夏季东亚季风区海气系统位相关系模拟的影响

本文利用区域海气耦合模式RegCM-POM,分别选取Grell积云参数化方案和Emanuel积云参数化方案对北半球夏季(5—10月)的东亚气候进行模拟,研究不同积云对流参数化方案(CPS)对东亚夏季季风区海气系统位相关系模拟的影响。结果表明:不同CPS模拟的陆地降水具有一定的不确定性,而海洋降水和海温的模拟受CPS选择的影响更大。其中,Emanuel方案对海洋降水和海温的分布形势模拟总体上要好于Grell方案,且可以更好的模拟中国近海各海区的海气系统位相关系,特别是大气对海温的负反馈过程。原因在于Emanuel方案模拟的对流降水与海温的位相关系更接近观测总降水与海温的位相关系;而Grell方案对南海和孟加拉湾的对流降水模拟偏少,对黑潮对流降水的模拟偏多,错误地模拟了这几个海区积云对流过程发挥的作用,故其模拟的海气系统位相关系不如Emanuel方案。     

关于海面湍流通量参数化的两种方案试验

本文对海气间湍流通量计算的参数化进行了两个方案的试验。第一个是对气候模式ＣＣＭ３中的计算方案作了改进,用半解析的计算方法代替纯迭代的方法,减少了计算量而达到相同精度。第二个是用Ｂｒｕｔｓａｅｒｔ提出的廓线函数计算海面通量,达到了当前最精确模式相同的精度。这二种方案均可用于大气模式或用于由实测气象资料求通量。     

混合海气耦合模式中与ENSO相关的大气年际变化性

利用混合海气耦合模式45年模拟积分的结果,对模式大气的年际变化性进行了分析。结果表明,在这样的海气耦合系统中,大气分量表现出显著的年际变化,冬、夏季异常环流型的分布与观测资料的分析结果基本相符。因此,该模式不仅能较好地再现热带太平洋的ENSO变化性,而且能较好地再现ENSO引起的全球大气环流的年际变化性。     

积云参数化方案对热带降水年循环模态模拟的影响

本文利用中国科学院大气物理研究所大气科学和地球流体力学数值模拟国家重点实验室( LASG)发展的大气环流模式(SAMIL),采用Zhang-McFarlane (ZM)和Tiedtke (TDK)两种积云对流参数化方案,讨论了积云对流参数化方案对热带降水年循环模态模拟的影响.结果表明,两种积云对流参数化方案均能合理再现...     

东北冷涡持续活动时期的北半球500 hPa环流特征分析

分别对5月和6～8月东亚东北冷涡活动典型的多寡年份北半球500 hPa高度距平场进行合成、频次累积和相关分析,结果表明:东亚东北冷涡持续性活动不仅与前期、同期和后期北半球的大气环流异常密切相关,而且也是异常区的重要组成部分;500hPa 5月和6～8月东北冷涡活动多寡年的同期500hPa高度距平合成场差异显著;6～8月东北冷涡典型多寡年的同期距平场均与前冬(12～2月)的主要异常区反位相,存在半年尺度的遥相关,与北太平洋涛动(NPO)类同的500 hPa高度距平场,如前冬呈正位相,预报6～8月东北冷涡持续活动弱,反之,冷涡持续活动强;合成场和相关场通过信度检验的关键区主要位于东亚中高纬度至阿留申群岛及其以南的副热带地区、青藏高原接近巴基斯坦一侧和北非乍得盆地与撒哈拉大沙漠等地区;由此可以认为东亚地区中高纬度5月和6～8月东北冷涡持续性活动是北半球大气环流异常持续或调整的重要表征.     

The Relationship between Melt Season Sea Ice over the Bering Sea and Summer Precipitation over Mid-Latitude East Asia

Independent datasets consistently indicate a significant correlation between the sea ice variability in the Bering Sea during melt season and the summer rainfall variability in the Lake Baikal area and Northeastern China. In this study, four sea ice datasets(Had ISST1, Had ISST2.2, ERA-Interim and NOAA/NSIDC) and two global precipitation datasets(CRU V4.01 and GPCP V2.3) are used to investigate co-variations between melt season(March-April-May-June, MAMJ)Bering Sea ice cover(BSIC) and summer(June-July-August, JJA) East Asian precipitation. All datasets demonstrate a significant correlation between the MAMJ BSIC and the JJA rainfall in Lake Baikal-Northeastern China(Baikal-NEC).Based on the reanalysis datasets and the numerical sensitivity experiments performed in this study using Community Atmospheric Model version 5(CAM5), a mechanism to understand how the MAMJ BSIC influences the JJA Baikal-NEC rainfall is suggested. More MAMJ BSIC triggers a wave train and causes a positive sea level pressure(SLP) anomaly over the North Atlantic during MAMJ. The high SLP anomaly, associated with an anti-cyclonic wind stress circulation anomaly,favors the appearance of sea surface temperature(SST) anomalies in a zonal dipole-pattern in the North Atlantic during summer. The dipole SST anomaly drives a zonally orientated wave train, which causes a high anomaly geopotential height at 500 h Pa over the Sea of Japan. As a result, the mean East Asian trough moves westward and a low geopotential height anomaly occurs over Baikal-NEC. This prevailing regional low pressure anomaly together with enhanced moisture transport from the western North Pacific and convergence over Baikal-NEC, positively influences the increased rainfall in summer.     

Decadal climate variability in the Mediterranean region: roles of large-scale forcings and regional processes

We analyze decadal climate variability in the Mediterranean region using observational datasets over the period 1850–2009 and a regional climate model simulation for the period 1960–2000, focusing in particular on the winter (DJF) and summer (JJA) seasons. Our results show that decadal variability associated with the winter and summer manifestations of the North Atlantic Oscillation (NAO and SNAO respectively) and the Atlantic Multidecadal Oscillation (AMO) significantly contribute to decadal climate anomalies over the Mediterranean region during these seasons. Over 30% of decadal variance in DJF and JJA precipitation in parts of the Mediterranean region can be explained by NAO and SNAO variability respectively. During JJA, the AMO explains over 30% of regional surface air temperature anomalies and Mediterranean Sea surface temperature anomalies, with significant influence also in the transition seasons. In DJF, only Mediterranean SST still significantly correlates with the AMO while regional surface air temperature does not. Also, there is no significant NAO influence on decadal Mediterranean surface air temperature anomalies during this season. A simulation with the PROTHEUS regional ocean–atmosphere coupled model is utilized to investigate processes determining regional decadal changes during the 1960–2000 period, specifically the wetter and cooler 1971–1985 conditions versus the drier and warmer 1986–2000 conditions. The simulation successfully captures the essence of observed decadal changes. Model set-up suggests that AMO variability is transmitted to the Mediterranean/European region and the Mediterranean Sea via atmospheric processes. Regional feedbacks involving cloud cover and soil moisture changes also appear to contribute to observed changes. If confirmed, the linkage between Mediterranean temperatures and the AMO may imply a certain degree of regional decadal climate predictability. The AMO and other decadal influences outlined here should be considered along with those from long-term increases in greenhouse gas forcings when making regional climate out-looks for the Mediterranean 10–20?years out.     

The observed teleconnection between the equatorial Amazon and the Intra-Americas Seas

Using observations of rainfall and SST analysis it is shown that there is a robust relationship with two-season lag between the austral summer (December–January–February [DJF]) Equatorial Amazon (EA) rainfall and the following boreal summer season (June–July–August [JJA]) Intra-Americas Seas (IAS) Sea Surface Temperature Anomalies (SSTA). It is observed that in wetter than normal austral summer seasons over EA, the SSTA in the IAS are cooler than normal in the following JJA season. This teleconnection also manifests in the ocean heat content of the IAS region. Our analysis indicates that the net surface heat flux into the ocean (particularly the surface longwave and the shortwave radiative fluxes) dictates the strongest influence on the JJA Caribbean SSTA, the core region of the IAS where the observed teleconnection with EA rainfall is strongest. This study also finds that this teleconnection is in fact a manifestation of the remote ENSO forcing on the Caribbean SSTA through its modulation of the EA rainfall anomalies. In a wet DJF year over EA, the Atlantic Inter-Tropical Convergence Zone (ITCZ) moves further southward than climatology. This causes the dry limb of the associated overturning circulation of the Atlantic ITCZ to reside over the Caribbean Sea region in the subsequent March–April–May and JJA seasons. As a result of this large-scale descent in the wet DJF year over EA, there is a net decrease in the heat flux into the ocean from increased emission of surface longwave radiation in the presence of anomalously dry atmosphere. In a dry DJF year over EA the Atlantic ITCZ is nearly co-located in the core region of the IAS, which is northward than the climatological location, resulting in the descending limb of the overturning location to be located further south of the Caribbean Sea leading to warmer SSTA.     

The Beijing Climate Center atmospheric general circulation model: description and its performance for the present-day climate

The Beijing Climate Center atmospheric general circulation model version 2.0.1 (BCC_AGCM2.0.1) is described and its performance in simulating the present-day climate is assessed. BCC_AGCM2.0.1 originates from the community atmospheric model version 3 (CAM3) developed by the National Center for Atmospheric Research (NCAR). The dynamics in BCC_AGCM2.0.1 is, however, substantially different from the Eulerian spectral formulation of the dynamical equations in CAM3, and several new physical parameterizations have replaced the corresponding original ones. The major modification of the model physics in BCC_AGCM2.0.1 includes a new convection scheme, a dry adiabatic adjustment scheme in which potential temperature is conserved, a modified scheme to calculate the sensible heat and moisture fluxes over the open ocean which takes into account the effect of ocean waves on the latent and sensible heat fluxes, and an empirical equation to compute the snow cover fraction. Specially, the new convection scheme in BCC_AGCM2.0.1, which is generated from the Zhang and McFarlane’s scheme but modified, is tested to have significant improvement in tropical maximum but also the subtropical minimum precipitation, and the modified scheme for turbulent fluxes are validated using EPIC2001 in situ observations and show a large improvement than its original scheme in CAM3. BCC_AGCM2.0.1 is forced by observed monthly varying sea surface temperatures and sea ice concentrations during 1949–2000. The model climatology is compiled for the period 1971–2000 and compared with the ERA-40 reanalysis products. The model performance is evaluated in terms of energy budgets, precipitation, sea level pressure, air temperature, geopotential height, and atmospheric circulation, as well as their seasonal variations. Results show that BCC_AGCM2.0.1 reproduces fairly well the present-day climate. The combined effect of the new dynamical core and the updated physical parameterizations in BCC_AGCM2.0.1 leads to an overall improvement, compared to the original CAM3.     

Atmospheric circulation anomalies due to 115 kyr BP climate forcing dominated by changes in the North Pacific Ocean

Climate at the time of inception of the Laurentide Ice Sheet (LIS) at ~115 kyr BP is simulated with the fully coupled NCAR Community Climate System Model (CCSM3) and compared to a simulated preindustrial climate (circa 1870) in order to better understand land surface and atmospheric responses to orbital and greenhouse cooling at inception. The interaction between obliquity and eccentricity produces maximum decrease in TOA insolation in JJA over the Arctic but increases occur over the tropics in DJF. The land surface response is dominated by widespread summer cooling in the Northern Hemisphere (NH), increases in snowfall, and decreases in melt rates and total precipitation. CCSM3 responds to the climate forcing at 115 kyr BP by producing incipient glaciation in the areas of LIS nucleation. We find that the inception of the LIS could have occurred with atmospheric circulation patterns that differ little from the present. The location of the troughs/ridges, mean flow over the Canadian Arctic and dominant modes of the atmospheric circulation are all very similar to the present. Larger changes in mean sea level pressure occur upstream of the inception region in the North Pacific Ocean and downstream in Western Europe. In the North Pacific region, the 115 kyr BP anomalies weaken both the Pacific high and Aleutian low making NH summers look more like the PREIND winters and vice versa. The occurrence of cold JJA anomalies at 115 kyr BP favors outbreaks of cold air not in the winter as in contemporary climates but during the summer instead and reinforces the cooling from orbital and GHG reductions. Increased poleward eddy transport of heat and moisture characterizes the atmospheric response in addition to reduced total cloud cover in the Arctic.     

有关南半球大气环流与东亚气候的关系研究的若干新进展

南半球大气环流是全球大气环流的重要组成部分,也是影响气候变化和亚洲季风系统的一个重要因素.中国气象学家很早就注意到南半球大气环流对东亚夏季风降水的影响.近年来,有关南半球气候变率的研究目前正受到世界气象学家越来越多的关注.南半球中高纬大气资料的丰富及南极涛动的确定,使得认识南半球高中纬环流的年际变动规律及其与东亚气候关系成为可能.本文主要介绍近年来有关南极涛动的年际变化与沙尘天气发生频次及东亚冬春季气候的关系,古气候资料揭示的南极涛动与华北降水的关系,以及南半球大气环流与长江中下游夏季降水的关系和南极涛动变率的可预测性等方面的研究进展.并对未来研究方向作了初步的展望.