Customization of regional climate model (RegCM4) over Indian region

The regional climate model (RegCM4) is customized for 10-year climate simulation over Indian region through sensitivity studies on cumulus convection and land surface parameterization schemes. The model is configured over 30° E–120° E and 15° S–45° N at 30-km horizontal resolution with 23 vertical levels. Six 10-year (1991–2000) simulations are conducted with the combinations of two land surface schemes (BATS, CLM3.5) and three cumulus convection schemes (Kuo, Grell, MIT). The simulated annual and seasonal climatology of surface temperature and precipitation are compared with CRU observations. The interannual variability of these two parameters is also analyzed. The results indicate that the model simulated climatology is sensitive to the convection as well as land surface parameterization. The analysis of surface temperature (precipitation) climatology indicates that the model with CLM produces warmer (dryer) climatology, particularly over India. The warmer (dryer) climatology is due to the higher sensible heat flux (lower evapotranspiration) in CLM. The model with MIT convection scheme simulated wetter and warmer climatology (higher precipitation and temperature) with smaller Bowen ratio over southern India compared to that with the Grell and Kuo schemes. This indicates that a land surface scheme produces warmer but drier climatology with sensible heating contributing to warming where as a convection scheme warmer but wetter climatology with latent heat contributing to warming. The climatology of surface temperature over India is better simulated by the model with BATS land surface model in combination with MIT convection scheme while the precipitation climatology is better simulated with BATS land surface model in combination with Grell convection scheme. Overall, the modeling system with the combination of Grell convection and BATS land surface scheme provides better climate simulation over the Indian region.     

区域气候模式RegCM砾石参数化方案在青藏高原不同区域土壤水分输送的模拟分析

在耦合CLM4.5的区域气候模式RegCM4.7中分别应用原始土壤水热参数化方案与改进后的砾石参数化方案在青藏高原西部、中部与东南部区域进行模拟,并根据砾石分布特征在每个区域选取单点分析了两种方案模拟结果存在差异的原因.在此基础上利用中国陆面融合再分析数据(CRA-40)检验了砾石参数化方案在高原不同区域对于土壤含水量...     

Land surface coupling in regional climate simulations of the West African monsoon

Coupling of the Community Land Model (CLM3) to the ICTP Regional Climate Model (RegCM3) substantially improves the simulation of mean climate over West Africa relative to an older version of RegCM3 coupled to the Biosphere Atmosphere Transfer Scheme (BATS). Two 10-year simulations (1992–2001) show that the seasonal timing and magnitude of mean monsoon precipitation more closely match observations when the new land surface scheme is implemented. Specifically, RegCM3–CLM3 improves the timing of the monsoon advance and retreat across the Guinean Coast, and reduces a positive precipitation bias in the Sahel and Northern Africa. As a result, simulated temperatures are higher, thereby reducing the negative temperature bias found in the Guinean Coast and Sahel in RegCM3–BATS. In the RegCM3–BATS simulation, warmer temperatures in northern latitudes and wetter soils near the coast create excessively strong temperature and moist static energy gradients, which shifts the African Easterly Jet further north than observed. In the RegCM3–CLM3 simulation, the migration and position of the African Easterly Jet more closely match reanalysis winds. This improvement is triggered by drier soil conditions in the RegCM3–CLM3 simulation and an increase in evapotranspiration per unit precipitation. These results indicate that atmosphere–land surface coupling has the ability to impact regional-scale circulation and precipitation in regions exhibiting strong hydroclimatic gradients.     

陆面过程模型CoLM与区域气候模式RegCM3的耦合及初步评估

陆面过程通过影响陆面和大气之间物质（如,水分）和能量的交换影响气候, 其参数化方案对数值天气预报、全球及区域气候模拟有重要影响。本研究利用对生物物理、生物化学过程考虑更全面的陆面模式Common Land Model(CoLM) 替代区域气候模式RegCM3原有的陆面模式BATS, 发展了耦合区域气候模式C－RegCM3; 将其应用于东亚地区典型洪涝年份夏季气候模拟以进行评估, 结果表明新耦合的模式C－RegCM3能合理模拟大尺度环流场、近地表气温和降水的分布特征, 对西北半干旱地区降水模拟比RegCM3有所改进。通过利用区域气候模式C－RegCM3及RegCM3对地表能量和水文过程模拟结果的比较, 发现在半干旱、半湿润过渡区C－RegCM3模拟的潜热增大、感热减小; 模拟的地表吸收太阳辐射差异较明显的地区位于模式模拟的主要雨区; C-RegCM3在上述过渡区模拟的夏季地表土壤湿度比RegCM3偏干, 这与它在过渡区降水模拟偏少、蒸散发模拟偏大相对应, 体现了该模式在半干旱、半湿润过渡带模拟出比RegCM3更明显的局地土壤湿度－降水－蒸散发之间的正反馈作用。     

陆面过程模式的改进及其检验

文中对陆面过程模式 (BATS)进行了改进 ,改进后的模式能较好地模拟地表物理量的年、季和日变化 ,它有两方面的特点 :采用热扩散方程模拟 7层土壤温度 ,模拟的温度可与实测值进行比较 ;在BATS的地表径流方案中 ,考虑了空间不均匀性的一般地表径流 (GVIC)过程 ,研究结果表明 :⑴模式能很好地模拟各层土壤温度的年、季和日变化。冬季土壤温度下层高于上层 ,而在夏季上层高于下层 ,这种上下层温度的转换时间大约在 4和 10月份 ,这与实测土壤温度的年变化非常一致。较为准确地模拟了各层土壤温度日变化的时滞效应。⑵用南京和武汉站的资料 ,将BATS地表径流方案模拟的地表水分分量与GVIC方案进行比较 ,BATS地表径流方案模拟的地表水分分量 ,与总水量的平衡相差较大 ,而GVIC模拟的效果相对较好 ,地表总水量基本上与降水总量达到了平衡     

Modeling the hydroclimatology of the midwestern United States. Part 1: current climate

An ensemble of six 22-year numerical experiments was conducted to evaluate the ability of Regional Climate Model version 3 (RegCM3) to simulate the energy and water budgets of the midwestern United States. RegCM3 was run using two surface physics schemes: Integrated Biosphere Simulator (IBIS) and Biosphere-Atmosphere Transfer Scheme 1e (BATS1e), and two convective closure assumptions: Fritsch & Chappell (FC80) and Arakawa & Schubert (AS74). Boundary conditions were provided by the National Centers for Environmental Prediction-Department of Energy Reanalysis 2 dataset and the ECHAM5 general circulation model. A companion paper examines the American Midwest under future climate scenarios. Overall, the model that reproduces the observed seasonal cycles of the midwestern United States climate system best is RegCM3 using IBIS and the AS74 convective closure assumption. IBIS simulates shortwave radiation more accurately, while BATS1e simulates longwave radiation more accurately. Summer two-meter air temperature is overestimated by the combination of IBIS and the FC80 convective closure assumption. All models contain a wet bias and overestimate evapotranspiration during the spring. Total runoff, surface runoff, groundwater runoff, and root zone soil moisture are best simulated by RegCM3 using IBIS and the AS74 convective closure assumption. While BATS1e does capture the seasonal cycle of total runoff, gross errors in the partitioning of total runoff between surface runoff and groundwater runoff exist. The seasonal cycle of root zone soil moisture simulated by RegCM3 using IBIS and the AS74 convective closure assumption is dry, but agrees with observations during the summer. The rest of the models underestimate root zone soil moisture.     

Incorporating groundwater dynamics and surface/subsurface runoff mechanisms in regional climate modeling over river basins in China

To improve the capability of numerical modeling of climate-groundwater interactions, a groundwater component and new surface/subsurface runoff schemes were incorporated into the regional climate model RegCM3, renamed RegCM3_Hydro. 20－year simulations from both models were used to investigate the effects of groundwater dynamics and surface/subsurface runoff parameterizations on regional climate over seven river basins in China. A comparison of results shows that RegCM3_Hydro reduced the positive biases of annual and summer (June, July, August) precipitation over six river basins, while it slightly increased the bias over the Huaihe River Basin in eastern China. RegCM3_Hydro also reduced the cold bias of surface air temperature from RegCM3 across years, especially for the Haihe and the Huaihe river basins, with significant bias reductions of 0.80C and 0.88C, respectively. The spatial distribution and seasonal variations of water table depth were also well captured. With the new surface and subsurface runoff schemes, RegCM3_Hydro increased annual surface runoff by 0.11－0.62 mm d－1 over the seven basins. Though previous studies found that incorporating a groundwater component tends to increase soil moisture due to the consideration of upward groundwater recharge, our present work shows that the modified runoff schemes cause less infiltration, which outweigh the recharge from groundwater and result in drier soil, and consequently cause less latent heat and more sensible heat over most of the basins.     

RegCM3.0与RegCM4.0对中国区域多雨年夏季气候模拟的对比分析

采用RegCM3.0和RegCM4.0模式,利用NCEP/DOE Reanalysis II数据、NOAA的周平均海温资料以及BATS、CLM3.5两种陆面过程方案,对我国4个典型多雨年(1998、2003、2007、2010年)的夏季气候进行模拟试验。结果表明,RegCM4-BATS1e模拟的降水量和雨带位置都与观测事实更为接近,尤其是对东南沿海地区强降水带的模拟,模式两个版本对湿润区的降水模拟均偏少,对干旱半干旱、湿润半湿润区的降水模拟则偏多;对于气温的模拟,其模拟结果均存在负偏差,但都能够模拟出位于东南沿海及新疆沙漠地带的温度高值区,RegCM4-CLM3.5模拟温度的量值更准确,而RegCM4-BATS1e模拟的温度空间分布型态与实际最为接近。     

根系吸水过程参数化方案对青藏高原陆面过程模拟的影响研究

根系吸水过程对地表能量平衡和水循环起着重要作用，目前不同的根系吸水过程参数化方案对青藏高原陆面过程模拟的影响尚不明确，探讨相关参数化方案的影响，可以为今后建立陆面过程模式根系参数化方案提供参考。本文利用2010年6月1日至9月30日青藏高原玛曲站的观测资料作为大气强迫资料，驱动BCC_AVIM模式（北京气候中心陆面模式）引入不同的根系吸水过程参数化方案，对玛曲站2010年6月1日至9月30日时段感热通量、潜热通量、土壤温度、土壤含水量等要素进行数值模拟，分析根系吸水过程参数化方案对青藏高原地区陆面过程的影响。模式中有关根系吸水过程的参数化方案主要分为根分布模型和土壤水分对根系有效性函数两类，根分布模型用Jackson方案、Schenk方案替换，土壤水分对根系有效性函数用Li方案、LSM1.0方案、CLM4.5方案替换。对比结果表明:不同的根系吸水过程参数化方案对土壤温度、土壤含水量的模拟影响较小，对感热通量、潜热通量模拟影响较大，尤其对冠层蒸腾量模拟差异显著，相关参数化方案的变动直接影响冠层蒸腾量。两类方案模拟的差异受降水的影响，在多雨期，根分布对比方案与原模式方案模拟的感热、潜热通量间存在较大差异；在少雨期，土壤水分对根系有效性函数对比方案与原模式方案模拟的感热、潜热通量间存在较大差异。     

区域气候模式(RegCM2)与水文模式耦合的数值试验

建立不均匀的地表径流算法，修改RegCM2的径流方案，设计了一个适合与气候模式RegCM2耦合、能模拟水文站流量的汇流模式，模拟了1998年6、7、8月降水的空间分布，分析了该径流方案对降水、地表热量通量、地表径流、土壤湿度产生的影响。结果表明：（1）该方案在模拟1998年长江流域降水空间分布上有一定的合理性，在一定程度上改善了降水量的模拟，其影响大致是总降水量的10％；（2）地表径流方案改变了地面向大气输送的热量通量，这种作用随时间发生变化，这种变化与地表水分的再分配有关；（3）本方案计算的土壤渗透率较强，在暴雨初期，产生径流较少，而在暴雨后期土壤湿度增大，产生的地表径流较大，这一点更符合洪水形成的特点；（4）水文一气候耦合模式模拟了两个长江水文站的流量，模拟值基本反映了实测值的变化趋势，也表明耦合模式基本能反映1998年夏季长江流域大暴雨期间的地表水文过程。     

Modeling the hydroclimatology of the midwestern United States. Part 2: future climate

An ensemble of six 22-year numerical experiments was conducted to quantify the response of soil moisture to multiple climate change scenarios over the American Midwest. Regional Climate Model version 3 (RegCM3) was run using two surface physics schemes: Integrated Biosphere Simulator (IBIS) and Biosphere-Atmosphere Transfer Scheme 1e (BATS1e); and two convective closure assumptions: Fritsch and Chappell and Arakawa and Schubert. Experiments were forced with a surrogate climate change scenario constructed using the National Centers for Environmental Prediction-Department of Energy Reanalysis 2 dataset and the ECHAM5 A1B climate change scenario. RegCM3-IBIS and RegCM3-BATS1e simulate increased two-meter air temperature and downward longwave radiation throughout the year under both climate change scenarios. While differences in shortwave radiation are relatively small; some model configurations and climate change scenarios produce additional precipitation, evapotranspiration, and total runoff during the spring and summer. Soil moisture is unchanged or increased throughout the growing season as enhanced rainfall offsets greater evaporative demand. Negligible drying in root zone soil moisture is found in all climate change experiments conducted, regardless of surface physics scheme, boundary conditions, or convective closure assumption.     

陆面模式中土壤湿度影响蒸散参数化方案的评估

本文将四个常见陆面模式CLM3.5（Community Land Model Version 3.5）、Noah_LSM（The Noah Land Surface Model）、VIC（Variable Infiltration Capacity）以及SSiB（The Simplified Simple Biosphere Model）中土壤湿度影响蒸散的参数化方案进行简化,并利用实验观测资料对不同参数化方案进行评估,探究不同陆面模式对土壤湿度与蒸散关系的模拟差异,从而为提高模式的模拟能力提供依据。结果表明,（1）CLM与SSiB中计算土壤湿度影响裸土蒸发的参数化方案较Noah_LSM和VIC更接近真实的物理过程,同时CLM与SSiB模式中土壤湿度对蒸发的影响程度较Noah_LSM和VIC大;而对于下垫面有植被条件下的蒸散而言,CLM中包含了植被光合作用、呼吸作用等生物物理学过程,与实际情况更为接近,并且CLM与SSiB中土壤湿度对植被蒸散的影响程度大于VIC,Noah_LSM最低;（2）根据干旱区、半干旱区、半湿润区以及湿润区各站点的分析可知,CLM、SSiB与Noah_LSM中土壤湿度影响蒸散的参数化方案的拟合效果较VIC好,同时在部分站点CLM与SSiB的参数化方案稍优于Noah_LSM。区域之间比较说明,四个模式对干旱半干旱区的模拟效果明显较半湿润区和湿润区好。     

Climate change impact on precipitation for the Amazon and La Plata basins

We analyze the local and remote impacts of climate change on the hydroclimate of the Amazon and La Plata basins of South America (SA) in an ensemble of four 21st century projections (1970–2100, RCP8.5 scenario) with the regional climate model RegCM4 driven by the HadGEM, GFDL and MPI global climate models (GCMs) over the SA CORDEX domain. Two RegCM4 configurations are used, one employing the CLM land surface and the Emanuel convective schemes, and one using the BATS land surface and Grell (over land) convection schemes. First, we find considerable sensitivity of the precipitation change signal to both the driving GCM and the RegCM4 physics schemes (with the latter even greater than the first), highlighting the pronounced uncertainty of regional projections over the region. However, some improvements in the simulation of the annual cycle of precipitation over the Amazon and La Plata basins is found when using RegCM4, and some consistent change signals across the experiments are found. One is a tendency towards an extension of the dry season over central SA deriving from a late onset and an early retreat of the SA monsoon. The second is a dipolar response consisting of reduced precipitation over the broad Amazon and Central Brazil region and increased precipitation over the La Plata basin and central Argentina. An analysis of the relative influence on the change signal of local soil-moisture feedbacks and remote effects of Sea Surface Temperature (SST) over the Niño 3.4 region indicates that the former is prevalent over the Amazon basin while the latter dominates over the La Plata Basin. Also, the soil moisture feedback has a larger role in RegCM4 than in the GCMs.     

Sensitivity evaluation of the different physical parameterizations schemes in regional climate model RegCM4.5 for simulation of air temperature and precipitation over North and West of Iran

In this research the dynamic downscaling method by Regional Climate Model (RegCM4.5) was used to assess the performance and sensitivity of seasonal simulated North and West of Iran (NI&WI) climate factors to different convection schemes, and transforms the large-scale simulated climate variables into land surface states over the North of Iran (NI) and West of Iran (WI). A 30-year (1986–2015) numerical integration simulation of climate over NI&WI was conducted using the regional climate model RegCM4.5 nested in one-way ERA-Interim reanalysis data. The Grell, Kuo and MIT-Emanuel cumulus convection with Holtslag and University of Washington (UW) planetary boundary layer (PBL) parameterization schemes were applied in the running of RegCM4.5 to test their capability in simulating precipitation and temperature in winter-spring (January–April) over NI and WI. The results demonstrated that the RegCM4.5 model has a good potential for simulating the variables and trend of surface temperature over the NI and WI region. Magnitude of the model bias for land surface temperature over different regions of Iran varies by convection parameterization schemes. In most cases, the root mean square error between post-processed simulated seasonal average temperature and observation value was less than 1 °C, but there is a systematic “cold bias”. In general, with respect to land surface temperature simulations, a better performance is obtained when using post-processing model’s data with Holtslag PBL-Grell and Holtslag PBL-Kuo configuration schemes, compared to the other simulations, over the NI&WI region. Also, the UW PBL convection schemes show a relatively excellent spatial correlations and normalized standard deviations closer to 1 for thirty-year seasonal land surface temperature anomalies over the entire NI&WI region. However, the simulation accuracy of model for precipitation is not as optimal as for temperature. The dominant feature in model simulations is a dry bias with the largest average value (∼1.04 mm/day) over NI region, while the lowest mean bias precipitation (∼−0.47 mm/day), mainly located in WI region. In the comparison of six configuration convection schemes, the Emanuel scheme has been proven to be the most accurate for simulating winter-spring seasonal mean precipitation over NI&WI region. The accuracy of the scheme also showed great difference in simulated station interpolation of precipitation, which urges the improvement for the simulation capability of spatial distribution of precipitation. In general, for seasonal variation of precipitation, the Emanuel convection with two (Holtslag, UW) PBL configuration schemes outperforms with a good correlation score between 0.7−0.8 and normalized standard deviations closer to 1.     

Sensitivity studies of the RegCM3 simulation of summer precipitation, temperature and local wind field in the Caribbean Region

Summary We present a preliminary evaluation of the performance of three different cumulus parameterization schemes in the ICTP Regional Climate Model RegCM3 for two overlapping domains (termed “big” and “small”) and horizontal resolutions (50 and 25 km) in the Caribbean area during the summer (July–August–September). The cumulus parameterizations were the Grell scheme with two closure assumptions (Arakawa–Schubert and Fritsch–Chappell) and the Anthes-Kuo scheme. An additional sensitivity test was performed by comparing two different flux parameterization schemes over the ocean (Zeng and BATS). There is a systematic underestimation of air temperature and precipitation when compared with analyzed data over the big domain area. Greater (∼2 °C) and smaller (∼0.9 °C) negative temperature biases are obtained in Grell–FC and Kuo convective scheme, respectively, and intermediate values are obtained in Grell–AS. The small domain simulation produces results substantially different, both for air temperature and precipitation. Temperature estimations are better for the small domain, while the precipitation estimations are better for the big domain. An additional experiment showed that by using BATS to calculate the ocean fluxes in the big domain instead of the Zeng scheme, precipitation increases by 25% and the share of convective precipitation rose from 18% to 45% of the total, which implies a better simulation of precipitation. These changes were attributed to an increase of near surface latent heating when using BATS over the ocean. The use of BATS also reduces the cold bias by about 0.3–0.4 °C, associated with an increase of minimum temperature. The behavior of the precipitation diurnal cycle and its relation with sea breeze was investigated in the small domain experiments. Results showed that the Grell–Arakawa–Schubert closure describes better this circulation as compared with Grell–Fritsch–Chappell closure.     

RegCM4区域气候模式对新疆地区冬季地表状态的模拟分析

利用区域气候模式Reg CM4.3(Regional Climate Mode version 4.3)对新疆地区冬季的地表状态进行了模拟分析,通过与ERA40再分析资料的对比分析发现,温度分布形势模拟较好,地面热力状态受地形影响显著,陡峭地形附近由于热性质差异大和非均匀性强会导致较大模拟误差;模式较好模拟出降水和潜热通量北疆多南疆少,山区多盆地少的分布特征,模拟出通过反照率影响,地表吸收的短波辐射呈现出沙漠腹地吸收多而天山地区吸收少的分布,对北疆呈感热通量汇而南疆呈感热通量源的感热分布形势也模拟较好;模拟的雪水当量与降水分布有较好的一致性,春季融雪径流与冬季雪水当量分布及降水均有较好的对应关系。通过模拟分析也发现,现有方案实际感热通量计算中以地面温度代替地面位温,造成感热通量偏小,因此会低估南疆感热源效应和高估北疆感热汇效应。此外,积雪量和地面温度模拟偏高可能是春季北疆主要积雪区径流偏强的原因。     

Regional model simulation of summer rainfall over the Philippines: Effect of choice of driving fields and ocean flux schemes

Summary The latest version of the Abdus Salam International Centre for Theoretical Physics (ICTP) regional model RegCM is used to investigate summer monsoon precipitation over the Philippine archipelago and surrounding ocean waters, a region where regional climate models have not been applied before. The sensitivity of simulated precipitation to driving lateral boundary conditions (NCEP and ERA40 reanalyses) and ocean surface flux scheme (BATS and Zeng) is assessed for 5 monsoon seasons. The ability of the RegCM to simulate the spatial patterns and magnitude of monsoon precipitation is demonstrated, both in response to the prominent large scale circulations over the region and to the local forcing by the physiographical features of the Philippine islands. This provides encouraging indications concerning the development of a regional climate modeling system for the Philippine region. On the other hand, the model shows a substantial sensitivity to the analysis fields used for lateral boundary conditions as well as the ocean surface flux schemes. The use of ERA40 lateral boundary fields consistently yields greater precipitation amounts compared to the use of NCEP fields. Similarly, the BATS scheme consistently produces more precipitation compared to the Zeng scheme. As a result, different combinations of lateral boundary fields and surface ocean flux schemes provide a good simulation of precipitation amounts and spatial structure over the region. The response of simulated precipitation to using different forcing analysis fields is of the same order of magnitude as the response to using different surface flux parameterizations in the model. As a result it is difficult to unambiguously establish which of the model configurations is best performing.     

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。     

陆面模型Noah-MP的不同参数化方案在沙漠区域的适用性研究

为研究陆面模型Noah-MP在沙漠下垫面的最优参数化方案组合,本文利用中国气象局塔克拉玛干沙漠气象野外科学试验基地观测数据,根据沙漠环境特征进行不同参数化方案组合的三组模拟实验,利用观测数据对10 cm土壤温湿度、感热、潜热通量模拟值对比分析得出最优组合。研究表明:第三组对10 cm的土壤温度模拟效果最好,主要原因是Chen97感热交换系数和全网格二流近似(gap=0)辐射传输方案比较符合沙漠的环境特征。三组试验对土壤湿度模拟效果差,其主要原因是沙漠的土壤信息未能体现在模式中,第二组选择CLM方案对土壤类型影响蒸发方面有一定考虑,其模拟结果相对较好。对于感热通量,第一、二组模拟值在波峰存在高估,尤其是第二组模拟值在降水后出现了明显低估情况,第三组模拟效果最好,主要得益于选择了感热交换系数Chen97方案,能够较为真实的刻画Ch变化特征。潜热通量在四个特征量中模拟效果最差,主要原因是沙漠土壤水分极低,观测降水和实际进入土壤的水量有差异,另外没有植被和植物根系,模式无法准确计算土壤蒸发和植被蒸散。根据统计分析和泰勒图可知,第三组能够更好地还原沙漠区域的陆面过程。