青藏高原地区不同下垫面陆面过程的数值模拟研究

利用陆面过程模式Common Land Model(CoLM),选取青藏高原上3个不同下垫面观测站(藏东南站、纳木错站和珠峰站)的观测资料,对这3个野外观测站进行了单点数值模拟试验。根据3个测站的试验数据,对模式中土壤孔隙度和饱和导水率进行了优化,针对青藏高原地区土壤层薄的特点,对模式中土壤分层方案进行了调整。结果表明,调整分层方案后的CoLM模式对3个测站土壤湿度的模拟性能较原分层方案有明显提高,平均偏差均减小0.014以上。但是与观测值相比,藏东南站土壤湿度的模拟整体偏低,纳木错站和珠峰站则整体偏高。对土壤温度而言,3个测站模拟与观测的相关系数都达到了0.9以上,珠峰站偏差较大,调整分层方案后模拟的偏差有一定的改进。模式较好地模拟了3个测站的净辐射、感热通量和潜热通量的日变化和季节变化情况,调整分层方案后潜热通量的改进最为明显。     

三个陆面模式对新疆地区陆面过程模拟的对比研究

利用实测的大气观测数据建立陆面模式驱动场, 分别驱动Biosphere-Atmosphere Transfer Scheme（BATS）, Land Surface Model（LSM）, Common Land Model（CoLM）三个陆面模式, 对新疆地区99个测站的陆面热力过程进行了off-line模拟研究, 对比分析了三个模式模拟结果的异同, 并利用观测的土壤温度检验了各个模式的模拟性能。结果表明： 三个模式对所吸收的太阳辐射、 地表感热通量、 地表潜热通量和Bowen比的模拟结果有明显差别, 其中CoLM模拟的太阳辐射、 感热通量和土壤温度比BATS和LSM大。用观测的土壤温度对三个模式模拟性能的检验表明 BATS模拟的土壤温度最接近观测值, 大约偏低1℃, 而LSM和CoLM的模拟结果偏高, CoLM模拟的年际变化趋势与观测值相关性达到0.877, 高于另外两个模式的模拟; BATS在天山以北模拟值偏低, CoLM在天山以南模拟结果偏高, LSM模拟的区域分布状况与实际观测最一致。这些结果为研究陆面模式在新疆地区的应用提供了一些参考, 对于深入了解新疆地区的陆面过程具有重要意义。     

陆面模式中土壤和植被经验参数随机误差的传播研究

数据质量问题和模式参数化方案的非完备性是陆面模拟中不确定性的主要来源。本文将高斯误差传播原理 (Gaussian Error Propagation, GEP) 应用于通用陆面模式 (the Common Land Model, CoLM), 研究关键的植被和土壤属性参数随机误差在模式中的传播, 确定由此类误差导致的CoLM模拟的不确定性。结果表明: (1) 基于本研究给定的土壤和植被参数的不确定性, CoLM模拟的表层土壤温度、 土壤湿度和植被蒸散通量 (植冠蒸腾+地表蒸发) 的相对误差分别为0.11%、 34.07%和5.58%; 砂土和稀疏森林上模拟效果最差。土壤参数随机误差对CoLM模拟的影响高于植被参数, 而土壤水文参数 (孔隙率、 饱和基质势、 气孔尺寸分布指数和饱和导水率) 对各模拟量不确定性的贡献率均远大于热力参数 (饱和反照率和热容)。对于本研究涉及的所有模拟变量而言, 最关键的参数均是气孔尺寸分布指数b, 这可能与描述基质势与体积水含量关系的函数有关, 其次重要的是砂土的孔隙度和粘土的饱和导水率。混交森林上的根深分布和苔原上的动力学粗糙度对蒸散通量贡献显著。本身相对误差大的经验参数对CoLM模拟不确定性的贡献不一定多。 (2) 干燥条件下 (表层液态水饱和度小于0.1) 土壤温度的不确定性大; 相变发生时刻附近 (表层土壤温度在0℃附近且表层液态水含量大于0) 土壤湿度不确定性显著; 蒸散通量的不确定性随本身绝对值的增大而增大, 在相对温暖干燥环境中 (表层土壤温度高于280 K且表层液态水饱和度小于0.3) 其不确定性最高。研究证实, GEP能够辨识CoLM中需优先提高观测精度的关键参数和关键参数化过程, 对陆面模拟的参数选定、 不确定性评估和模式完善具有重要意义。     

土壤数据集对全球陆面过程模拟的影响

基于通用陆面模式（Common Land Model, CoLM）,首次评估了两套最新的全球土壤数据集GSDE（Global Soil Dataset for Earth System Model）和SG（SoilGrids）对全球陆面过程模拟的影响。比较分析了两套数据中砂粒、粘粒、砾石、有机碳的含量和容重这五个土壤属性在全球分布上的差异以及这种差异造成的对模式估计的土壤特性参数、水力热力变量的影响。结果表明,土壤特性参数在全球的空间分布主要受土壤粒径分布（砂粒、粉粒和粘粒）影响,同时也受砾石、有机碳和容重的影响。土壤资料对全球模拟结果影响主要体现在区域差异,对水文学变量的影响（R_e最大达到±100%）大于对土壤热力学变量的影响（R_e<±10%）,对地表辐射变量的影响较小（R_e<±5%）。其中,土壤体积含水量在加拿大中部及西北部、俄罗斯东南部及中西部和澳大利亚中部地区模拟结果相差较大,总径流在低纬地区模拟结果出现较大的差异,热力学变量在非洲北部、加拿大西北部以及俄罗斯中北部的差异稍大。将模拟的土壤体积含水量与站点观测相比,两套数据的表现接近,与站点观测相比都存在一定的偏差,但SG更接近观测,其中在Molly Caren站点（39°57′N,83°27′W）上SG相比GSDE整体提高约0.01～0.02。本研究表明,模式模拟结果受不同土壤数据集的影响显著,可优先考虑诸如SG较准确的土壤数据。土壤属性对陆面模拟的影响需进一步研究。     

三类陆面模式模拟土壤湿度廓线的对比研究

针对不同陆面模式对土壤湿度方程求解方法以及对土壤分层结构的差异, 本文选取了三类陆面模式（CLM, CABLE和ECMWF陆面模式）作比较研究。为了避免不同模式参数化方案引起的上边界误差, 上边界采用固定蒸发率、 入渗率和固定表层土壤湿度三类边界条件。土壤分层采用101层（细网格）和11层（粗网格）两种, 并考虑土壤性质沿深度变化。结果表明： 当土壤性质均匀时, 求解的差别主要在第三类边界条件下CLM 求出的水分入渗速度比其它两种快; 改用粗网格后由于土壤深层厚度加大无法与细网格得出的土壤湿度廓线相重合。当土壤性质非均匀时, 模拟结果间差别加大, 只有ECMWF模式模拟的土壤湿度廓线是严格连续的。对于模式和上边界的不同组合, 粗、 细网格模拟结果间均方根偏差不一致。一般而言, CABLE模拟的偏差除第一类条件较小外, 其它都是最大的。第二三类边界条件引起的偏差较大, 第一类最小。上述结果提示我们, 在比较不同陆面模式以及用观测资料来检验模拟结果时应充分考虑土壤分层及土壤性质非均匀性的可能影响。     

Coupling a Terrestrial Biogeochemical Model to the Common Land Model

A terrestrial biogeochemical model (CASACNP) was coupled to a land surface model (the Common Land Model,CoLM) to simulate the dynamics of carbon substrate in soil and its limitation on soil respiration.The combined model,CoLM CASACNP,was able to predict long-term carbon sources and sinks that CoLM alone could not.The coupled model was tested using measurements of belowground respiration and surface fluxes from two forest ecosystems.The combined model simulated reasonably well the diurnal and seasonal variations of net ecosystem carbon exchange,as well as seasonal variation in the soil respiration rate of both the forest sites chosen for this study.However,the agreement between model simulations and actual measurements was poorer under dry conditions.The model should be tested against more measurements before being applied globally to investigate the feedbacks between the carbon cycle and climate change.     

基于陆面模式基准平台ILAMB对陆面模式CoLM的评估

模式评估是模式发展中不可或缺的重要一环。本文利用最新版陆面模式评估软件—ILAMB（International Land Model Benchmarking）对通用陆面模式 (The Common Land Model, CoLM)进行客观评估,并与NCAR陆面模式CLM5(Community Land Model version 5)结果进行比较。作为一个陆面模式评估软件,ILAMB能对参与评估的模式变量自动生成诊断图形并对模式性能进行评分。评估结果表明,CoLM总体性能良好,模拟结果与基准数据较为接近。与CLM5相比,CoLM在总初级生产力及水文方面的表现略微逊色,在辐射方面则表现相当,对部分变量如地表向上长波辐射、地表净辐射等的模拟甚至优于CLM5。通过对比CRUNCEPv7和GSWP3v1两种强迫资料发现,它们在气候平均态上具有一定的差异,模式在GSWP3v1强迫下的表现相对较好。CoLM和CLM5在CRUCNEPv7强迫下模拟的潜热通量在亚马逊平原、亚洲东部和南部地区以及北美东部一带正偏差显著,而在GSWP3v1强迫下的模拟则有明显改善。这两个模式对感热通量的模拟在非洲北部、亚洲中部一带均明显偏高。在辐射方面,CoLM模拟的地表向上短波辐射在全球以偏高为主,这在一定程度上造成了地表净辐射的模拟偏低。各组试验模拟的地表向上长波辐射得分相差不大,但在具体的空间分布上有一定的差别。     

基于FDTD的不同土壤类型及湿度对雷电电磁场传播影响的研究

为深入研究土壤类型和土壤湿度对雷电电磁场传播效应的影响, 首次将工程勘察领域研究得出的土壤湿度和电导率计算关系应用到雷电电磁场模拟计算中。基于Heidler雷电通道基电流函数模型和MTLL回击模型, 在Mur一阶边界条件下, 利用2D-FDTD计算粘土、粉土和砂土这三种具有代表性土壤在不同土壤湿度和观测距离下的雷电电磁场。研究结果表明: 相比于粉土和砂土, 雷电电磁场沿粘土地表传播过程中产生的水平电场更容易受土壤湿度的影响, 特别是土壤湿度较低时, 即土壤湿度从5%到6%变化过程中, 水平电场峰值的波动幅度达39.86%;当土壤类型为粘土时, 水平电场E_r、垂直电场E_z和磁场H_φ受土壤湿度影响等级为E_z > H_φ; 随着闪电电磁辐射传播距离和土壤湿度的增大, 场幅值减小, 波形的波头上升沿时间变慢。研究结果为准确评估和量化不同土壤类型和土壤湿度对雷电电磁场传播的影响以及优化闪电站网定位提供了重要的科学依据。      

CoLM模式对青藏高原中部BJ站陆面过程的数值模拟

利用公共陆面模式Common Land Model(CoLM)及"全球协调加强观测计划之亚澳季风青藏高原试验"(CAMP/Tibet)中那曲地区Bujiao(BJ)站2002—2004年的观测资料对该地区进行了单点数值模拟试验。通过比较模拟与观测的地表能量通量,表明CoLM较成功地模拟了该地区的能量分配。模式对向上的短波辐射、向上的长波辐射、净辐射及土壤热通量模拟得较好,但冬季存在偏差。进一步比较了模拟和观测的土壤温度及土壤湿度,发现浅层60 cm土壤温度模拟较好,深层存在偏差,表现为土壤温度变化滞后于实际变化。土壤湿度总体偏小,尤其是冬季冻结期,土壤冻融过程中忽略了土壤液态水在温度0℃以下仍能存在,含冰量模拟偏高。     

Sensitivity of the simulated African monsoon of summers 1993 and 1999 to convective parameterization schemes in RegCM3

In this study, the International Center for Theoretical Physics Regional Climate Model version 3 (RegCM3) was used to investigate the sensitivity of the simulation of the West African monsoon using four different cumulus and closures parameterization schemes of Anthes Kuo (AK), Grell and Fristish Chappell (GFC), Grell and Arakawa Schubert (GAS), and MIT-Emmanuel (EM) while maintaining other physical packages unchanged. The contrasting monsoon years of 1993 and 1999, which were dry and wet years, respectively, were simulated. The model was integrated from a period of 5 months, starting from May 1 to September 30 of each year using the European Centre for Medium-Range-Weather Forecast (ECMWF) Reanalysis data (ERA40) as input boundary conditions. The 6-hourly reanalysis data were used to provide the lateral boundary conditions, and the observed weekly Reynolds Sea Surface Temperature interpolated to 6 h was used as the lower boundary forcing. The results show that in West Africa, monsoon precipitations are sensitive to the choice of cumulus parameterization and closure schemes. None of the schemes is able to simulate the monsoon rainfall accurately, and furthermore, there is little difference in behavior among schemes between dry and wet years. The spatial features of precipitation are not identical among schemes, although they all show a northward shift of the rain bands, giving a very wet Sahel and dry Guinean Coast. The GFC and EM schemes are able to capture the diurnal cycle of precipitation and the zonal averages of stratiform rain fractions as observed in the Tropical Rainfall Measuring Mission (TRMM), although they overestimated rainfall amounts. The most important deficiencies, however, cannot be attributed to the schemes. In particular, the northward shift of both the rain band and the AEJ in RegCM3 is the result of unrealistic soil moisture resulting from the way albedo is parameterized, leading to an excessive northward penetration of monsoon flow. A sensitivity study showed that an adjustment of initial albedo values over the Sahel improved the simulation, and in particular the position of rain bands and of the AEJ.     

下垫面非均匀性的模拟

用美国大气科学中心ＧＥＮＥＳＩＳ模式中的陆面过程方案,我们在一个全球大气模式网格尺度范围内,研究了来自非均匀下垫面的水汽,能量等通量。基于３种不同的模拟下垫面非均匀性的方法,即马赛克法、混合法以及显式次网格法,我们设计了４种不同的试验。模拟结果表明,３种方法计算出的结果有很大的不同：地面吸收的太阳辐射差异达４％;感热通量达１２％;潜热通量达６６％;土壤水分可达３０％。这一结果说明有必要用实测数据来检验不同的模拟下垫面非均匀性的方法以及用区域气候模式来模拟下垫面的非均匀性。     

中国地区土壤湿度记忆性及其与降水特征变化的关系

本文首先利用中国气象局国家气象信息中心提供的中国732个站点观测的土壤体积含水量,评估了CLM4.5（Community Land Model version 4.5）在CFSR（Climate Forecast System Reanalysis）近地面大气数据驱动下模拟的逐月土壤湿度（记为CLM4.5-CFSR）,然后基于CLM4.5-CFSR比较了皮尔逊相关法和自相关法计算得到的1980～2009年中国地区土壤湿度记忆性的区域及季节分布特征,量化了土壤湿度的记忆能力,研究了降水频率、降水强度和近地表气温分别对土壤湿度记忆性的影响。结果表明:CLM4.5-CFSR能较好地反映出大部分地区月时间尺度上土壤湿度的变化特征。两种方法描述的土壤湿度记忆性的空间分布特征相似,但季节特征不同。不同深度土壤湿度的记忆时长相差不大,在0.85～2.2个月不等,其中内蒙古东北部较大,新疆西南部较小。春季,较湿的土壤记忆性也较强。当降水频率较低时,其对蒸发速率较大的地区土壤湿度的记忆性影响很小,当降水强度较大时,它会迅速补充土壤散失的水分,破坏初始时刻土壤的干湿状态,引起其记忆性减弱。近地表气温变化主要通过影响土壤的蒸发过程减弱土壤湿度的记忆性。未来可利用气候模式开展数值敏感性试验对本文得到的结论进行机理研究,为进一步提高季节和季节内尺度的降水预报提供依据。     

The Construction of SCM in GRAPES and Its Applications in Two Field Experiment Simulations

A Single Column Model(SCM) for Global and Regional Atmospheric Prediction Enhanced System (GRAPES) is constructed for the purpose of evaluating physical process parameterizations.Two observational datasets including Wangara and the third Global Energy and Water Cycle Experiment Atmospheric Boundary Layer Study(GABLS-3) SCM field observations have been applied to evaluate this SCM.By these two numerical experiments,the GRAPES_SCM is verified to be correctly constructed.Furthermore, the interaction between the land surface process and atmospheric boundary layer(ABL) is discussed through the second experiment.It is found that CASE3(CoLM land surface scheme coupled with ABL scheme) simulates less sensible heat fluxes and smaller surface temperature which corresponds with its lower potential temperature at the bottom of the ABL.Moreover,CASE3 simulates turbulence that is weaker during the daytime and stronger during nighttime,corresponding with its wind speed at 200 m which is bigger during daytime and smaller during nighttime.However,they are generally opposite in CASE2(SLAB coupled with ABL).The initial profile of the water vapor mixing ratio is artificially increased by the experiment setup which results in the simulated water vapor mixing becoming wetter than actually observed.CASE1 (observed surface temperature taken as lower thermal forcing) and CASE2 have no soil moisture prediction and simulate a similar water vapor mixing ratio,while CASE3 has a soil moisture prediction and simulates wetter.It is also shown that the time step may affect the stabilization of the ABL when the vertical levels of the SCM are fixed.     

An Assessment of CAMS-CSM in Simulating Land–Atmosphere Heat and Water Exchanges

The Chinese Academy of Meteorological Sciences (CAMS) has been devoted to developing a climate system model (CSM) to meet demand for climate simulation and prediction for the East Asian region. In this study, we evaluated the performance of CAMS-CSM in regard to sensible heat flux (H), latent heat flux (LE), surface temperature, soil moisture, and snow depth, focusing on the Atmospheric Model Intercomparison Project experiment, with the aim of participating in the Coupled Model Intercomparison Project phase 6. We systematically assessed the simulation results achieved by CAMS-CSM for these variables against various reference products and ground observations, including the FLUXNET model tree ensembles H and LE data, Climate Prediction Center soil moisture data, snow depth climatology data, and Chinese ground observations of snow depth and winter surface temperature. We compared these results with data from the ECMWF Interim reanalysis (ERA-Interim) and Global Land Data Assimilation System (GLDAS). Our results indicated that CAMS-CSM simulations were better than or comparable to ERAInterim reanalysis for snow depth and winter surface temperature at regional scales, but slightly worse when simulating total column soil moisture. The root-mean-square differences of H in CAMS-CSM were all greater than those from the ERA-Interim reanalysis, but less than or comparable to those from GLDAS. The spatial correlations for H in CAMS-CSM were the lowest in nearly all regions, except for North America. CAMS-CSM LE produced the lowest bias in Siberia, North America, and South America, but with the lowest spatial correlation coefficients. Therefore, there are still scopes for improving H and LE simulations in CAMS-CSM, particularly for LE.     

基于集合卡尔曼滤波的土壤温湿度同化试验

以通用陆面模式CLM 3.0(Community Land Model 3.0)为模型算子,基于集合卡尔曼滤波(Ensemble Kalman Filter,En KF)发展了一个土壤温湿度同化系统,主要用于改进模式对土壤温湿度和地表水热通量的模拟精度,并考察集合样本数、同化频率及不同观测量的组合对同化效果的影响。该系统同化了FLUXNET两个站点(阿柔和Bondville)不同土壤深度、不同时间频率的土壤温度和湿度数据。通过对阿柔站不同集合样本数的设计,综合考虑计算成本和计算精度,最终将集合样本数设置为40。通过分析三种同化方案对同化频率的敏感性得出,同化土壤温度最为敏感,同时同化土壤温湿度次之,同化土壤湿度最不敏感。对于阿柔站点,同化系统对不同土壤深度温度和湿度的模拟精度均能提高90%,潜热通量的均方根误差由94.0 W·m~(-2)降为46.3 W·m~(-2),感热通量均方根误差由55.9 W·m~(-2)降为24.6 W·m~(-2)。Bondville站点浅层土壤温度的改进在30%左右,深层土壤温度改进达到60%,对土壤湿度的改进均在70%以上,潜热通量和感热通量的均方根误差分别从57.4 W·m~(-2)和54.4 W·m~(-2)降为51.0 W·m~(-2)和42.5 W·m~(-2)。试验结果表明,同化站点土壤温湿度数据对土壤水热状况及通量的模拟改进非常有效,同时也验证了同化土壤水分遥感产品的可行性和必要性。     

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.     

土壤干旱化对短期气候影响的数值模拟

用加进了奥勒冈州立大学陆面模式(OSULSM)的美国PSU／NCAR第五代中尺度模式(MM5)进行了减少土壤含水量对短期气候影响的模拟试验,目的在于探讨我国北方干旱化对短期气候的影响。试验结果表明,对整个模拟区域月降水总量没有明显的影响,但对不同地区有明显的影响。对月降水量较大地区的影响表现为使月降水量有一定程度的减少,而对月降水量中等以下地区的影响则相反,使月降水量略有增加。分析结果表明,其原因是土壤含水量减少会造成地面潜热通量减少、感热通量增加和陆面温度增高,最后生成一个浅薄的偏差热低压。这个偏差热低压在对流层低层有偏差辐合上升气流与之相配合,在对流层中层以上则与偏差辐散下沉气流相伴。这对于浅薄的降水系统的发展是有利的,但对于强大而深厚的降水系统的发展则不利。     

Coupling the Common Land Model to ECHAM5 Atmospheric General Circulation Model

The ECHAM5 model is coupled with the widely used Common Land Model(CoLM). ECHAM5 is a state-of-theart atmospheric general circulation model incorporated into the integrated weather and climate model of the Chinese Academy of Meteorological Sciences(CAMS-CSM). Land surface schemes in ECHAM5 are simple and do not provide an adequate representation of the vegetation canopy and snow/frozen soil processes. Two AMIP(Atmospheric Model Intercomparison Project)-type experiments using ECHAM5 and ECHAM5-CoLM are run over 30 yr and the results are compared with reanalysis and observational data. It is found that the pattern of land surface temperature simulated by ECHAM5-CoLM is significantly improved relative to ECHAM5. Specifically, the cold bias over Eurasia is removed and the root-mean-square error is reduced in most regions. The seasonal variation in the zonal mean land surface temperature and the in situ soil temperature at 20-and 80-cm depths are both better simulated by ECHAM5-CoLM. ECHAM5-CoLM produces a more reasonable spatial pattern in the soil moisture content, whereas ECHAM5 predicts much drier soils. The seasonal cycle of soil moisture content from ECHAM5-CoLM is a better match to the observational data in six specific regions. ECHAM5-CoLM reproduces the observed spatial patterns of both sensible and latent heat fluxes. The strong positive bias in precipitation over land is reduced in ECHAM5-CoLM, especially over the southern Tibetan Plateau and middle–lower reaches of the Yangtze River during the summer monsoon rainy season.     

Antarctic Radiosonde Observations Reduce Uncertainties and Errors in Reanalyses and Forecasts over the Southern Ocean:An Extreme Cyclone Case

Cyclones with strong winds can make the Southern Ocean and the Antarctic a dangerous environment.Accurate weather forecasts are essential for safe shipping in the Southern Ocean and observational and logistical operations at Antarctic research stations.This study investigated the impact of additional radiosonde observations from Research Vessel"Shirase"over the Southern Ocean and Dome Fuji Station in Antarctica on reanalysis data and forecast experiments using an ensemble data assimilation system comprising the Atmospheric General Circulation Model for the Earth Simulator and the Local Ensemble Transform Kalman Filter Experimental Ensemble Reanalysis,version 2.A 63-member ensemble forecast experiment was conducted focusing on an unusually strong Antarctic cyclonic event.Reanalysis data with(observing system experiment)and without(control)additional radiosonde data were used as initial values.The observing system experiment correctly captured the central pressure of the cyclone,which led to the reliable prediction of the strong winds and moisture transport near the coast.Conversely,the control experiment predicted lower wind speeds because it failed to forecast the central pressure of the cyclone adequately.Differences were found in cyclone predictions of operational forecast systems with and without assimilation of radiosonde observations from Dome Fuji Station.     

Improving CLM4.5 simulations of land–atmosphere exchange during freeze–thaw processes on the Tibetan Plateau

Soil is heterogeneous and has different thermal and hydraulic properties, causing varied behavior in heat and moisture transport. Therefore, soil has an important effect on land–atmosphere interactions. In this study, an improved soil parameterization scheme that considers gravel and organic matter in the soil was introduced into CLM4.5 (Community Land Model). By using data from the Zoige and Madoi sites on the Tibetan Plateau, the ability of the model to simultaneously simulate the duration of freeze–thaw periods, soil temperature, soil moisture, and surface energy during freeze–thaw processes, was validated. The results indicated that: (1) the new parameterization performed better in simulating the duration of the frozen, thawing, unfrozen, and freezing periods; (2) with the new scheme, the soil thermal conductivity values were decreased; (3) the new parameterization improved soil temperature simulation and effectively decreased cold biases; (4) the new parameterization scheme effectively decreased the dry biases of soil liquid water content during the freezing, completely frozen, and thawing periods, but increased the wet biases during the completely thawed period; and (5) the net radiation, latent heat flux, and soil surface heat flux of the Zoige and Madoi sites were much improved by the new organic matter and thermal conductivity parameterization.