一个水文模型与区域气候模式耦合的数值模拟研究(英)

在陆面过程方案中考虑精细的水文模型有助于改善对区域水文及气候的模拟。建立了一个考虑降水及入渗空间非均匀性的水文模型,并将其并入陆面过程方案BATS中。通过区域气候模式耦合模拟试验,得到如下主要结论:陆面水文的模拟对降水及入渗空间非均匀性的考虑非常敏感:考虑入渗非均匀性后,提高了径流系数,这与湿润地区水分平衡的观测结果更一致;入渗非均匀参数化方案的引入对区域水文及气候模拟的影响比降水非均匀参数化方案的引入要大:不透水面积在区域中的考虑所揭示的特征与我国北方干旱化趋势是一致的。     

一个水文模型与区域气候模式耦合的数值模拟研究

在陆面过程方案中考虑精细的水模型有助于改善对区域水及气候的模拟。建立了一个考虑降水及入诊空间非均匀性的水模型，并将其并入陆面过程方案BATS中。通过区域气候模式耦合模拟试验，得到如下主要结论：陆面水的模拟对降水及入渗空间非均匀性的考虑非常敏感；考虑入渗非均匀性后，提高了径流系数，这与湿润地区水分平衡的观测结果更一致；入渗非均匀参数化方案的引入对区域水及气候模拟的影响比降水非均匀参数化方案的引入要大；不透水面积在区域中的考虑所揭示的特征与我国北方干旱化趋势是一致的。     

一个区域气候模式水文过程的改进及年尺度模拟研究

本文将更符合物理过程实际的考虑入渗非均匀和降水非均匀的水文模型VXM并入区域气候模式RegCM3模式,利用此区域水文气候模式分别对1988、1990、1991年3个不同气候年的水文气候进行了模拟.模拟结果表明,模式对入渗非均匀和降水非均匀的响应在年尺度上是敏感的:模式能成功模拟年平均降水及降水的年内变化,较好地再现了降水分布和大小;并入VXM模型后模式对南方径流的模拟能力得到较大的提高,模拟的年平均及年内变化与实际较为一致.结果还表明,径流机制的改进有助于改善降水模拟能力,并引起蒸发、温度等气候要素相应的变化;并入VXM模型后对模拟结果的影响更主要体现在夏季.     

AREM模式中陆面过程的改进与试验

为了提高AREM模式业务预报能力,对AREM业务模式陆面过程参数化方案作了修改,将陆面过程模式BATS耦合其中;同时,应用耦合BATS的AREM模式与原模式分别对2006年6～7月我国南方汛期降水过程进行了典型个例模拟分析和批量后报试验;另外,对降水预报进行了分区统计检验。结果表明,引入BATS方案使模式对降水区和降水中心预报有较好的改进,漏报率减小,Ts评分明显提高,这说明恰当描述陆面过程对改进AREM模式降水预报具有重要作用。     

BATS1e陆面模式对p-σ九层区域气候模式性能的影响

将BATS1e (Biosphere-Atmosphere Transfer Scheme version 1e) 陆面模式与p-σ九层区域气候模式(PσRCM9) 进行耦合，发展了一个包含有更复杂陆－气相互作用的区域气候模式(BATS1e-PσRCM9)。通过对东亚地区1月和7月气候平均场和1991年江淮流域梅雨期间三次强降水过程的数值模拟，考察了BATS1e陆面模式对PσRCM9模式模拟性能的影响。数值试验结果表明，BATS1e-PσRCM9模式对东亚区域冬、 夏季气候平均场的模拟能力有明显提高，且对近地层和对流层低层各气象要素场模拟效果的改善比对流层中高层更加明显。与PσRCM9模式的模拟结果相比，BATS1e-PσRCM9模式对中国东南部地区降水的模拟与观测更为一致，并且对江淮流域梅雨期间的强降水过程也有较好的模拟能力。由于BATS1e-PσRCM9模式改进了地气之间动量、热量和水汽通量交换的计算，更好地描述了陆地下垫面与大气之间的相互作用，从而改善了模式对近地层各气象要素场的模拟。因此，通过耦合BATS1e陆面模式能较明显地提高PσRCM9模式模拟东亚区域短期气候变化的能力，这为区域气候模式的进一步发展奠定了基础。     

GRAPES NOAH-LSM陆面模式水文过程的改进及试验研究

土壤含水量的计算影响着陆面过程的能量平衡和水量平衡,是陆面模式的核心计算要素之一。目前,GRAPES_Meso模式采用的NOAH-LSM(Noah-Land Surface Model)陆面模式既不能有效地表达径流产源面积的变动情况,也不能完整描述水文循环过程。本次试验针对以上问题对其进行了改进:(1)加入蓄水容量曲线,考虑网格内产流面积的变化及土壤含水量的不均匀性;(2)加入汇流模式,以考虑水平二维水分再分配,提高模式对径流和流量模拟能力。选取2008年8月至9月降水进行模拟试验,研究陆面水循环过程对近地面气象要素的影响。结果表明:改进后的模式模拟土壤湿度、2 m温度等近地面气象要素更接近观测值,并最终对降水量以及降水落区也产生了一定的影响。     

“结合法”表示的下垫温非均匀对夏季风气候影响的数值试验

用能较好表示陆面非均匀性且计算高效省时的"结合法"(马赛克法及统计-动力法解析表达型两者的结合),在区域气候模式RegCM2中BATSle方案内考虑下垫面附近各种温度、各种湿度的非均匀性,选用1991年夏季梅雨期实测资料,进行了模拟试验.与Giorgi针对暖季温度非均匀的单点独立试验结论不同,应用较线性概率密度函数(PDF)计算效率更高的余弦函数型PDF,发现总体上大气对陆面温度非均匀的响应是敏感的;与Giorgi结论类似,气候场对陆面湿度非均匀更为敏感,且其变化较有规律.可见,对夏季风气候的模拟能力可通过适当的温湿非均匀表示来提高.此外,其他结果也显示出单点独立试验的局限性,要反映陆气相互作用,耦合模式试验非常必要.     

对RIEMS模式中陆面过程的一个改进

中尺度区域气候模式RIEMS中陆面过程使用BATS模式,其缺点是土壤内部过程较为简单,本文把10层土壤模式引入BATS,代替原来的二层土壤模式,并采用了TOPMODEL水文模式中的一些处理方法,使土壤温度、水文的计算更为合理,模拟二个个例,每个例均为夏季一个月的模拟,表明在降水、气压场、流场上均较原RIEMS模式为优,因而是对原RIEMS模式一个改进。     

干旱区陆面过程参数改进对气候模拟结果的影响

利用改进的我国西北地区陆面过程参数的大气环流模式CCM3与原CCM3模式分别做了数值模拟并加以对比分析。结果表明,改进后的模式较原模式对东亚季风和西北干旱区降水的模拟能力有一定提高,对西北部分地区感热、潜热通量的模拟有所改进。这说明通过观测改进陆面过程模式的参数是提高CCM3气候模式模拟能力的一种重要途径。     

非均匀下垫面陆面过程参数化问题研究进展

非均匀下垫面对陆面过程模式应用有着重要影响。若将下垫面一概视为均一,在很多情况下会影响模式模拟的准确性。本文详细介绍了目前非均匀地表陆面过程参数化的方法(Mosaic法、统计—动力法和其它方法),初步分析了这些参数化方法的缺陷,并简单探讨了陆面参数尺度转换问题,最后对今后研究的问题给出了建议,其中特别提出要寻找适当方法实现陆面物理量不同尺度间的转换。     

A Numerical Study on Effects of Land-Surface Heterogeneity from ‘Combined Approach’ on Atmospheric Process Part II: Coupling-Model Simulations

1.IntroductionInthecompanionPaper(hereafterreferredtoas299),wecombinedthemosaicapproachandtheanalyticaltypeofstatistical--dynamicalapproach,andproPOsedaacombinedapProach",whichcouldrepresentbothinterpatchvariabilityandintrapatchvariabilityaswellascomputationallycostless.Aftertheheterogeneityoftheroughnesslengthic(or/andzeroplanedisplacementheightd,)isconsideredbythecombinedapproachinBiosphere/AtmosphereTransferSchemeVersionie(BATSie)(Dickinsonetal.,1993),expressions,suchasdragcoefficienta…     

A Numerical Study on Effects of Land-Surface Heterogeneity from ‘Combined Approach’ on Atmospheric Process Part II: Coupling-Model Simulations

Two land surface schemes, one the standard Biosphere / Atmosphere Transfer Scheme Version le (B0Z) and the other B1Z based on B0Z and heterogeneously-treated by ‘combined approach’ , were coupled to the meso-scale model MM4, respectively. Through the calculations of equations from the companion paper, parameters representing land surface heterogeneity and suitable for the coupling models were found out. Three cases were simulated for heavy rainfalls during 36 hours, and the sensitivity of short-term weath-er modeling to the land surface heterogeneity was tested. Through the analysis of the simulations of the three heavy rainfalls, it was demonstrated that B1Z, compared with B0Z, could more realistically reflect the features of the land surface heterogeneity, therefore could more realistically reproduce the circulation and precipitation amount in the heavy rainfall processes of the three cases. This shows that even short-term weather is sensitive to the land surface heterogeneity, which is more obvious with time passing, and whose influence is more pronounced in the lower layer and gradually extends to the middle and upper layer. Through the analysis of these simulations with B1Z, it is suggested that the bulk effect of smaller-scale fluxes (i.e., the momentum, water vapor and sensible heat fluxes) near the significantly-heterogeneous Land surface is to change the larger-scale (i.e., meso-scale) circulation, and then to influence the development of the low-level jets and precipitation. And also, the complexity of the land-atmosphere interaction was shown in these simulations.     

具有Horton及Dunne机制的径流模型在VIC模型中的应用(英)

地表径流主要由蓄满(Dunne)和超渗产流(Horton)机制产生;土壤性质的空间变异性、前期土壤水、地形及降水的空间变异性导致不同的径流机制。在研究区域或模型网格内,蓄满产流及超渗产流可能同时出现,缺乏考虑任何一种机制以及土壤性质的次网格空间变率可能导致地表径流的过高或过低估计,从而影响土壤水的计算。利用Philip入渗公式用于时间压缩逼近(TCA)给出了一种径流参数化方法,该方法可以动态实现模型网格中的Horton及Dunne产流机理,它考虑了土壤空间变异性对Horton和Dunne径流的影响。该径流模型应用到基于水文原理的陆面过程模型VIC,在淮河流域及美国宾西法尼亚州的一个流域进行了测试,结果表明:新的参数化方法对地表径流和土壤水分含量的分配起着重要作用,对于改进径流和土壤水的模拟有重要意义。     

Effects of subgrid heterogeneities in soil infiltration capacity and precipitation on regional climate: a sensitivity study

Summary ?One of the most pronounced features of the land surface is its heterogeneity. In order to further understand land-atmosphere interactions and improve climate modeling it is very important to investigate effects of subgrid scale heterogeneities, especially hydrological-process heterogeneities. In this paper, after the construction and sensitivity tests of a hydrological model (VXM), which accounts for precipitation heterogeneity (PH) and infiltration heterogeneity (IH), we incorporated VXM into the NCAR (National Center for Atmospheric Research) regional climate model RegCM2 and thus obtained the augmented regional climate model (hereafter, ARCM). By using 3-month (May–July) observational data of 1991 Meiyu season, we conducted numerical experiments with ARCM, analyzed the sensitivities, and found that: (1) The regional climate and surface hydrology are very sensitive to IH as well as PH, i.e., the simulations for the surface fluxes, soil temperature, soil moisture, precipitation and surface runoff can be greatly affected by those heterogeneities. (2) ARCM can effectively improve the simulation of hydrological processes, i.e., it can greatly enhance the surface runoff ratio (i.e., the ratio of surface runoff to precipitation), which is consistent with observations over humid areas in China. (3) It seems that the IH influence on the surface climate is larger than the PH influence. (4) The modeled climate is sensitive to the VXM parameters. For example, it is significantly modified after the surface impermeable fraction has been accounted for, suggesting some features of aridification. Received June 18, 2001; revised February 14, 2002; accepted March 3, 2002     

Evaluation of Atmosphere–Land Interactions in an LES from the Perspective of Heterogeneity Propagation

Atmosphere–land interactions simulated by an LES model are evaluated from the perspective of heterogeneity propagation by comparison with airborne measurements. It is found that the footprints of surface heterogeneity, though as 2D patterns can be dissipated quickly due to turbulent mixing, as 1D projections can persist and propagate to the top of the atmospheric boundary layer. Direct comparison and length scale analysis show that the simulated heterogeneity patterns are comparable to the observation. The results highlight the model's capability in simulating the complex effects of surface heterogeneity on atmosphere–land interactions.     

The Impact of Vegetation Cover on Sahelian Drought Persistence

The sensitivity of the potential for convective precipitation to land surface characteristics in the West African Sudano-Sahelian zone is studied. Simulations are performed with a one-dimensional version of a mesoscale atmospheric model coupled to a detailed land surface model to investigate the influence of the land surface on rain infiltration, surface evapotranspiration, and their impact on the convective available potential energy. The simulations show that the presence of a densely vegetated surface acts as a catalyst in the hydrological cycle, creating a positive feedback and enhancing precipitation recycling. It is argued that this is due to the relation between the characteristic drying-out time of the soil and the return frequency of the rain-triggering African easterly waves.     

Implementation of a Surface Runoff Model with Horton and Dunne Mechanisms into the Regional Climate Model RegCM_NCC

A surface runoff parameterization scheme that dynamically represents both Horton and Dunne runoff generation mechanisms within a model grid cell together with a consideration of the subgrid-scaie soil heterogeneity, is implemented into the National Climate Center regional climate model （RegCM_NCC）. The effects of the modified surface runoff scheme on RegCMANCC performance are tested with an abnormal heavy rainfall process which occurred in summer 1998. Simulated results show that the model with the original surface runoff scheme （noted as CTL） basically captures the spatial pattern of precipitation, circulation and land surface variables, but generally overestimates rainfall compared to observations. The model with the new surface runoff scheme （noted as NRM） reasonably reproduces the distribution pattern of various variables and effectively diminishes the excessive precipitation in the CTL. The processes involved in the improvement of NRM-simulated rainfall may be as follows： with the new surface runoff scheme, simulated surface runoff is larger, soil moisture and evaporation （latent heat flux） are decreased, the available water into the atmosphere is decreased; correspondingly, the atmosphere is drier and rainfall is decreased through various processes. Therefore, the implementation of the new runoff scheme into the RegCMANCC has a significant effect on results at not only the land surface, but also the overlying atmosphere.     

不同边界层和陆面过程参数化方案对比分析

利用WRF模式选用不同的边界层参数化方案 (YSU、MRF) 结合三种陆面过程方案 (RUC、SLAB、Noah) , 模拟了2011年5月1~3日的四川东部暴雨过程, 对不同参数化方案结合不同陆面过程结果进行对比试验基础上发现, 模式对24h降水落区及强度有较强预报能力, 但对单站小时降水分布的预报能力还需改进;不同边界层方案与陆面过程的对比试验说明降水对于边界层物理过程有一定敏感性, 各试验的差异主要体现在对暴雨中心雨强以及降水峰值强度和峰值出现时段的预报上;WRF模式基本上能够模拟出边界层要素日变化特征。