Given the crucial role of land surface processes in global and regional climates, there is a pressing need to test and verify the performance of land surface models via comparisons to observations. In this study, the ...Given the crucial role of land surface processes in global and regional climates, there is a pressing need to test and verify the performance of land surface models via comparisons to observations. In this study, the eddy covariance measurements from 20 FLUXNET sites spanning more than 100 site-years were utilized to evaluate the performance of the Common Land Model （CoLM） over different vegetation types in various climate zones. A decomposition method was employed to separate both the observed and simulated energy fluxes, i.e., the sensible heat flux, latent heat flux, net radiation, and ground heat flux, at three timescales ranging from stepwise （30 rain） to monthly. A comparison between the simulations and observations indicated that CoLM produced satisfactory simulations of all four energy fluxes, although the different indexes did not exhibit consistent results among the different fluxes, A strong agreement between the simulations and observations was found for the seasonal cycles at the 20 sites, whereas CoLM underestimated the latent heat flux at the sites with distinct dry and wet seasons, which might be associated with its weakness in simulating soil water during the dry season. CoLM cannot explicitly simulate the midday depression of leaf gas exchange, which may explain why CoLM also has a maximum diurnal bias at noon in the summer. Of the eight selected vegetation types analyzed, CoLM performs best for evergreen broadleaf forests and worst for croplands and wetlands.展开更多
Towards a better understanding of hydrological interactions between the land surface and atmosphere, land surface mod- els are routinely used to simulate hydro-meteorological fluxes. However, there is a lack of observ...Towards a better understanding of hydrological interactions between the land surface and atmosphere, land surface mod- els are routinely used to simulate hydro-meteorological fluxes. However, there is a lack of observations available for model forcing, to estimate the hydro-meteorological fluxes in East Asia. In this study, Common Land Model （CLM） was used in offline-mode during the summer monsoon period of 2006 in East Asia, with different forcings from Asiaflux, Korea Land Data Assimilation System （KLDAS）, and Global Land Data Assimilation System （GLDAS）, at point and regional scales, separately. The CLM results were compared with observations from Asiaflux sites. The estimated net radiation showed good agreement, with r = 0.99 for the point scale and 0.85 for the regional scale. The estimated sensible and latent heat fluxes using Asiaflux and KLDAS data indicated reasonable agreement, with r = 0.70. The estimated soil moisture and soil temperature showed similar patterns to observations, although the estimated water fluxes using KLDAS showed larger discrepancies than those of Asiaflux because of scale mismatch. The spatial distribution of hydro-meteorological fluxes according to KLDAS for East Asia were compared to the CLM results with GLDAS, and the GLDAS provided online. The spatial distributions of CLM with KLDAS were analogous to CLM with GLDAS, and the standalone GLDAS data. The results indicate that KLDAS is a good potential source of high spatial resolution forcing data. Therefore, the KLDAS is a promising alternative product, capable of compensating for the lack of observations and low resolution grid data for East Asia.展开更多
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 Aca...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.展开更多
Improving and validating land surface models based on integrated observations in deserts is one of the challenges in land modeling. Particularly, key parameters and parameterization schemes in desert regions need to b...Improving and validating land surface models based on integrated observations in deserts is one of the challenges in land modeling. Particularly, key parameters and parameterization schemes in desert regions need to be evaluated in-situ to improve the models. In this study, we calibrated the land-surface key parameters and evaluated several formulations or schemes for thermal roughness length （z 0h ） in the common land model （CoLM）. Our parameter calibration and scheme evaluation were based on the observed data during a torrid summer （29 July to 11 September 2009） over the Taklimakan Desert hinterland. First, the importance of the key parameters in the experiment was evaluated based on their physics principles and the significance of these key parameters were further validated using sensitivity test. Second, difference schemes （or physics-based formulas） of z 0h were adopted to simulate the variations of energy-related variables （e.g., sensible heat flux and surface skin temperature） and the simulated variations were then compared with the observed data. Third, the z 0h scheme that performed best （i.e., Y07） was then selected to replace the defaulted one （i.e., Z98）; the revised scheme and the superiority of Y07 over Z98 was further demonstrated by comparing the simulated results with the observed data. Admittedly, the revised model did a relatively poor job of simulating the diurnal variations of surface soil heat flux, and nighttime soil temperature was also underestimated, calling for further improvement of the model for desert regions.展开更多
The method to estimate NSSR （net surface shortwave radiation） from LST （land surface temperature） in regional scale is discussed. First, an elliptical model between the time series of normalized LST and NSSR was d...The method to estimate NSSR （net surface shortwave radiation） from LST （land surface temperature） in regional scale is discussed. First, an elliptical model between the time series of normalized LST and NSSR was developed using the daily evolution of LST and NSSR. Second, time series of LST and NSSR were simulated by common land model （CoLM） and were proved to be of high accuracy. On the basis of these, a non-linear least square ellipse fitting using the genetic algorithm method was used to fit the normalized LST and NSSR. Finally, LST was inverted using MODIS （moderate resolution imaging spectroradiometer） data with the split-window algorithm, and the regional NSSR was then estimated with LST and an elliptical model. The validation result shows that the derived average NSSR of 50×50 pixels of MODIS data was quite close to the observed data, and the distribution was reasonable, which indicates that the proposed method was capable of estimating NSSR on a regional scale.展开更多
Precise high-temperature weather forecasts are essential, as heatwaves are increasing in frequency under the ongoing climate change. Land-surface schemes have been demonstrated to be crucial to numerical weather predi...Precise high-temperature weather forecasts are essential, as heatwaves are increasing in frequency under the ongoing climate change. Land-surface schemes have been demonstrated to be crucial to numerical weather predictions.However, few studies have explored the impact of land surface schemes on short-range high-temperature weather forecasts via operational numerical weather prediction models. To evaluate the impact of the soil thermal process on high-temperature weather forecasts, we coupled the soil thermal process of the state-of-the-art Common Land Model(CoLM) with the South China operational numerical weather prediction model(CMA-TRAMS) and compared the coupled model with the original CMA-TRAMS, which incorporated the Simplified Model for land Surface(SMS). Contrast experiments based on two versions of CMA-TRAMS were conducted for the year 2022 when persistent extreme heatwaves were observed in Central-East China. The results are as follows:(1) Short-range high-temperature weather forecasts were sensitive to soil thermal process schemes. The original CMA-TRAMS clearly underestimated the summertime near-surface air temperature(T2m) over almost all areas of China, whereas the CoLM led to a reduction of the negative biases by approximately 0.5°C.(2) The more accurate initial soil temperatures and the deeper soil structure used in the CoLM test contributed to actual predictions of soil heat flux, soil temperature, and T2m. Nevertheless, the SMS test failed to capture upward heat transport from deeper to shallower soil layers at night due to the shallow soil structure and lower accuracy of the bottom and initial soil temperatures.(3) Higher soil temperatures resulted in increased near-surface moisture and cloud cover in the CoLM test, which led to the warmer soil and further mitigated the cold biases of T2m through reduced longwave and shortwave radiation losses at the land surface.展开更多
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,...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。展开更多
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,...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。展开更多
利用1998年5月1日至9月18日狮泉河自动气象站(AWS)的观测资料作为强迫场,运用改进的陆面过程模式CoLM(Common Land Model),对青藏高原西部的陆面特征进行了模拟研究.结果表明,该模式能够较好地模拟出高原地区的陆面特征.在高原西部地表...利用1998年5月1日至9月18日狮泉河自动气象站(AWS)的观测资料作为强迫场,运用改进的陆面过程模式CoLM(Common Land Model),对青藏高原西部的陆面特征进行了模拟研究.结果表明,该模式能够较好地模拟出高原地区的陆面特征.在高原西部地表能量平衡过程中,感热通量占主要地位,潜热通量较小,但在高原西部的湿季,潜热通量也是不可忽略的.在5月及6月初表层土壤频繁的发生水分相变,使土壤在相变过程中不断地吸收和释放潜热.降水及土壤表层频繁的冻结-消融使地表有效通量(感热+潜热)发生变化.有效辐射中的感热、潜热的分配,即Bowen会发生变化,进一步影响到对大气的加热及大气水汽输送情况,大气状况的改变又反过来影响地表蒸散及土壤持水能力,使土壤水分状态和含量发生变化.展开更多
本文针对青藏高原部分地区土壤有机质和砾石含量较高的特点,在前人工作的基础上,发展了一个新的参数化方案以描述土壤有机质和砾石对土壤导热率、导水率的影响。通过对通用陆面模式CoLM中的土壤水、热参数化方案以及地表蒸发阻抗三方面...本文针对青藏高原部分地区土壤有机质和砾石含量较高的特点,在前人工作的基础上,发展了一个新的参数化方案以描述土壤有机质和砾石对土壤导热率、导水率的影响。通过对通用陆面模式CoLM中的土壤水、热参数化方案以及地表蒸发阻抗三方面的逐步改进,对青藏高原藏东南站和纳木错站两种不同下垫面进行单点数值模拟分析。对比原方案与最终优化方案的模拟结果表明:采用新方案的CoLM模式对藏东南站土壤湿度模拟性能明显提高,平均偏差减小到0.04,而对纳木错站浅层20 cm以上土壤湿度的模拟偏差略微增大。新方案在藏东南站对土壤内部温度的模拟改善较为显著,平均偏差减小了0.2°C;而在纳木错站40 cm以上有所改进。新参数化方案较好地模拟了两个观测站表面能量通量的时间变化,纳木错站7、8月份的潜热通量改进尤为明显,比原方案减少大约20 W m^(-2),与观测结果较为接近。展开更多
基于集合卡尔曼滤波和通用陆面模型(CLM1.0)发展了一个地表温度的同化系统。这个系统同化了MODIS温度产品,并将MODIS的叶面积指数引入CLM模型中,主要用于改进地表水热通量的估算精度。将CLM输出的地表温度与MODIS地表温度建立关系,并作...基于集合卡尔曼滤波和通用陆面模型(CLM1.0)发展了一个地表温度的同化系统。这个系统同化了MODIS温度产品,并将MODIS的叶面积指数引入CLM模型中,主要用于改进地表水热通量的估算精度。将CLM输出的地表温度与MODIS地表温度建立关系,并作为同化系统的观测算子。将MODIS地表温度与实测地表温度进行了比较,将其均方差(Root Mean Square Error,RMSE)作为观测误差。选取3个美国通量网站点(Blackhill、Bondville、Brookings)作为实验数据,结果表明:同化结果中地表温度、显热通量的估算精度均有提高。其中Blackhill站的估算精度改进最大,均方差由81.5W·m-2减小到58.4W·m-2,Bondville站均方差由47.0W·m-2减小到31.8W·m-2,Brookings站均方差由46.5W·m-2减小到45.1W·m-2。潜热通量估算精度在Bondville站均方差由88.6W·m-2减小到57.7W·m-2,Blackhill站均方差由53.4W·m-2减小到47.2W·m-2。总之,结合陆面过程模型同化MODIS温度产品估算地表水热通量是可行的。展开更多
使用前苏联Valdai 1966～1971年的气象观测资料，研究了通用陆面模式（Common Land Model，CoLM）模拟的水分循环和地表通量在12种土壤质地和8种土壤亮度条件下的差异。结果表明，在相同的气象条件下，模拟的热通量对土壤质地和亮度都...使用前苏联Valdai 1966～1971年的气象观测资料，研究了通用陆面模式（Common Land Model，CoLM）模拟的水分循环和地表通量在12种土壤质地和8种土壤亮度条件下的差异。结果表明，在相同的气象条件下，模拟的热通量对土壤质地和亮度都比较敏感，而地表水文过程只对土壤质地敏感。土壤亮度相同时，相对砂性土壤，粘土含量高的土壤保水性强，土壤湿度、地表蒸发和径流量都比较大（月均最大差值：土壤湿度约为5kg·m^-2，地表蒸发和径流量约为年降水量的7％和1．2％），相应地在热通量分配上存在明显差异（月均最大差值为8W·m^-2）；土壤质地相同，亮度由亮变暗时，潜热通量变化很小，地表温度略有升高，而感热通量和净辐射增加显著（月均摄大差值为7W·m^-2）。土壤质地和亮度对模拟的影响主要存在于降水少、植被覆盖度低的3～5月。展开更多
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...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280K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。展开更多
构建了基于通用陆面模型(CoLM,Common Land Model)、微波辐射传输模型L-MEB(Lband Microwave Emission of the Biosphere)和集合平滑算法(EnKS,Ensemble Kalman Smoother)的土壤水分数据同化框架,用于联合同化MODIS地表温度和机载L波段...构建了基于通用陆面模型(CoLM,Common Land Model)、微波辐射传输模型L-MEB(Lband Microwave Emission of the Biosphere)和集合平滑算法(EnKS,Ensemble Kalman Smoother)的土壤水分数据同化框架,用于联合同化MODIS地表温度和机载L波段被动微波亮温数据。以2012年HiWATER试验期间中游大满超级站为实验站点,分析了3种LAI数据产品对土壤温度模拟结果的影响,进而分析了联合同化地表温度和微波亮度温度对土壤水分估计结果的影响。研究结果表明:3种LAI数据对土壤温度模拟结果的影响显著,MODIS LAI产品在该研究区显著低估,导致土壤温度模拟结果高估4~6K;同化亮度温度、同化地表温度以及联合同化两者均可以改进土壤水分的估计精度,联合同化地表温度和亮度温度对于土壤水分的改进最为显著,土壤水分同化结果的RMSE减少31%~53%。展开更多
基金supported by the R&D Special Fund for Nonprofit Industry (Meteorology) (Grant Nos. GYHY200706025, GYHY201206013 and GYHY201306066)
文摘Given the crucial role of land surface processes in global and regional climates, there is a pressing need to test and verify the performance of land surface models via comparisons to observations. In this study, the eddy covariance measurements from 20 FLUXNET sites spanning more than 100 site-years were utilized to evaluate the performance of the Common Land Model （CoLM） over different vegetation types in various climate zones. A decomposition method was employed to separate both the observed and simulated energy fluxes, i.e., the sensible heat flux, latent heat flux, net radiation, and ground heat flux, at three timescales ranging from stepwise （30 rain） to monthly. A comparison between the simulations and observations indicated that CoLM produced satisfactory simulations of all four energy fluxes, although the different indexes did not exhibit consistent results among the different fluxes, A strong agreement between the simulations and observations was found for the seasonal cycles at the 20 sites, whereas CoLM underestimated the latent heat flux at the sites with distinct dry and wet seasons, which might be associated with its weakness in simulating soil water during the dry season. CoLM cannot explicitly simulate the midday depression of leaf gas exchange, which may explain why CoLM also has a maximum diurnal bias at noon in the summer. Of the eight selected vegetation types analyzed, CoLM performs best for evergreen broadleaf forests and worst for croplands and wetlands.
基金supported by Space Core Technology Development Program through the National Research Foundation of Korea(NRF)funded by the Ministry of Science,ICTFuture Planning(NRF-2014M1A3A3A02034789)+1 种基金Basic Science Research Program through the National Research Foundation of Korea(NRF)funded by the Ministry of Education(NRF-2013R1A1A2A10004743)the Korea Meteorological Administration Research and Development Program under Grant Weather Information Service Engine(WISE)project,KMA-2012-0001-A
文摘Towards a better understanding of hydrological interactions between the land surface and atmosphere, land surface mod- els are routinely used to simulate hydro-meteorological fluxes. However, there is a lack of observations available for model forcing, to estimate the hydro-meteorological fluxes in East Asia. In this study, Common Land Model （CLM） was used in offline-mode during the summer monsoon period of 2006 in East Asia, with different forcings from Asiaflux, Korea Land Data Assimilation System （KLDAS）, and Global Land Data Assimilation System （GLDAS）, at point and regional scales, separately. The CLM results were compared with observations from Asiaflux sites. The estimated net radiation showed good agreement, with r = 0.99 for the point scale and 0.85 for the regional scale. The estimated sensible and latent heat fluxes using Asiaflux and KLDAS data indicated reasonable agreement, with r = 0.70. The estimated soil moisture and soil temperature showed similar patterns to observations, although the estimated water fluxes using KLDAS showed larger discrepancies than those of Asiaflux because of scale mismatch. The spatial distribution of hydro-meteorological fluxes according to KLDAS for East Asia were compared to the CLM results with GLDAS, and the GLDAS provided online. The spatial distributions of CLM with KLDAS were analogous to CLM with GLDAS, and the standalone GLDAS data. The results indicate that KLDAS is a good potential source of high spatial resolution forcing data. Therefore, the KLDAS is a promising alternative product, capable of compensating for the lack of observations and low resolution grid data for East Asia.
基金Supported by the National Key Research and Development Program of China(2016YFB0200801,2017YFA0604300,and 2018YFC1507003)Strategic Priority Research Program of the Chinese Academy of Sciences(XDA20100300)Basic Research Fund of the Chinese Academy of Meteorological Sciences(2017Y004)
文摘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.
基金jointly funded by the National Natural Science Foundation of China(GrantNo40775019)Desert Meteorology Science Foundation of China(Grant NoSqj2009012)Project of Key Laboratory of Oasis Ecology(Xinjiang University)Ministry of Education(Grant NoXJDX0206-2009-08)
文摘Improving and validating land surface models based on integrated observations in deserts is one of the challenges in land modeling. Particularly, key parameters and parameterization schemes in desert regions need to be evaluated in-situ to improve the models. In this study, we calibrated the land-surface key parameters and evaluated several formulations or schemes for thermal roughness length （z 0h ） in the common land model （CoLM）. Our parameter calibration and scheme evaluation were based on the observed data during a torrid summer （29 July to 11 September 2009） over the Taklimakan Desert hinterland. First, the importance of the key parameters in the experiment was evaluated based on their physics principles and the significance of these key parameters were further validated using sensitivity test. Second, difference schemes （or physics-based formulas） of z 0h were adopted to simulate the variations of energy-related variables （e.g., sensible heat flux and surface skin temperature） and the simulated variations were then compared with the observed data. Third, the z 0h scheme that performed best （i.e., Y07） was then selected to replace the defaulted one （i.e., Z98）; the revised scheme and the superiority of Y07 over Z98 was further demonstrated by comparing the simulated results with the observed data. Admittedly, the revised model did a relatively poor job of simulating the diurnal variations of surface soil heat flux, and nighttime soil temperature was also underestimated, calling for further improvement of the model for desert regions.
基金Supported by the Knowledge Innovation Programs of Chinese Academy of Sciences (XMXX280722)China International Science and Technology Cooperation Project (0819)+1 种基金National Program on Key Basic Research Project (2010CB428800)Wong K C Education Foundation, Hong Kong
文摘The method to estimate NSSR （net surface shortwave radiation） from LST （land surface temperature） in regional scale is discussed. First, an elliptical model between the time series of normalized LST and NSSR was developed using the daily evolution of LST and NSSR. Second, time series of LST and NSSR were simulated by common land model （CoLM） and were proved to be of high accuracy. On the basis of these, a non-linear least square ellipse fitting using the genetic algorithm method was used to fit the normalized LST and NSSR. Finally, LST was inverted using MODIS （moderate resolution imaging spectroradiometer） data with the split-window algorithm, and the regional NSSR was then estimated with LST and an elliptical model. The validation result shows that the derived average NSSR of 50×50 pixels of MODIS data was quite close to the observed data, and the distribution was reasonable, which indicates that the proposed method was capable of estimating NSSR on a regional scale.
基金National Natural Science Foundation of China(U2242203, 42305164, 42175105)Key Innovation Team of China Meteorological Administration (CMA2023ZD08)Science and Technology Research Project of Guangdong Meteorological Service (GRMC2023M31)。
文摘Precise high-temperature weather forecasts are essential, as heatwaves are increasing in frequency under the ongoing climate change. Land-surface schemes have been demonstrated to be crucial to numerical weather predictions.However, few studies have explored the impact of land surface schemes on short-range high-temperature weather forecasts via operational numerical weather prediction models. To evaluate the impact of the soil thermal process on high-temperature weather forecasts, we coupled the soil thermal process of the state-of-the-art Common Land Model(CoLM) with the South China operational numerical weather prediction model(CMA-TRAMS) and compared the coupled model with the original CMA-TRAMS, which incorporated the Simplified Model for land Surface(SMS). Contrast experiments based on two versions of CMA-TRAMS were conducted for the year 2022 when persistent extreme heatwaves were observed in Central-East China. The results are as follows:(1) Short-range high-temperature weather forecasts were sensitive to soil thermal process schemes. The original CMA-TRAMS clearly underestimated the summertime near-surface air temperature(T2m) over almost all areas of China, whereas the CoLM led to a reduction of the negative biases by approximately 0.5°C.(2) The more accurate initial soil temperatures and the deeper soil structure used in the CoLM test contributed to actual predictions of soil heat flux, soil temperature, and T2m. Nevertheless, the SMS test failed to capture upward heat transport from deeper to shallower soil layers at night due to the shallow soil structure and lower accuracy of the bottom and initial soil temperatures.(3) Higher soil temperatures resulted in increased near-surface moisture and cloud cover in the CoLM test, which led to the warmer soil and further mitigated the cold biases of T2m through reduced longwave and shortwave radiation losses at the land surface.
文摘利用公共陆面模式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。
文摘利用陆面过程模式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。
文摘利用1998年5月1日至9月18日狮泉河自动气象站(AWS)的观测资料作为强迫场,运用改进的陆面过程模式CoLM(Common Land Model),对青藏高原西部的陆面特征进行了模拟研究.结果表明,该模式能够较好地模拟出高原地区的陆面特征.在高原西部地表能量平衡过程中,感热通量占主要地位,潜热通量较小,但在高原西部的湿季,潜热通量也是不可忽略的.在5月及6月初表层土壤频繁的发生水分相变,使土壤在相变过程中不断地吸收和释放潜热.降水及土壤表层频繁的冻结-消融使地表有效通量(感热+潜热)发生变化.有效辐射中的感热、潜热的分配,即Bowen会发生变化,进一步影响到对大气的加热及大气水汽输送情况,大气状况的改变又反过来影响地表蒸散及土壤持水能力,使土壤水分状态和含量发生变化.
文摘本文针对青藏高原部分地区土壤有机质和砾石含量较高的特点,在前人工作的基础上,发展了一个新的参数化方案以描述土壤有机质和砾石对土壤导热率、导水率的影响。通过对通用陆面模式CoLM中的土壤水、热参数化方案以及地表蒸发阻抗三方面的逐步改进,对青藏高原藏东南站和纳木错站两种不同下垫面进行单点数值模拟分析。对比原方案与最终优化方案的模拟结果表明:采用新方案的CoLM模式对藏东南站土壤湿度模拟性能明显提高,平均偏差减小到0.04,而对纳木错站浅层20 cm以上土壤湿度的模拟偏差略微增大。新方案在藏东南站对土壤内部温度的模拟改善较为显著,平均偏差减小了0.2°C;而在纳木错站40 cm以上有所改进。新参数化方案较好地模拟了两个观测站表面能量通量的时间变化,纳木错站7、8月份的潜热通量改进尤为明显,比原方案减少大约20 W m^(-2),与观测结果较为接近。
文摘基于集合卡尔曼滤波和通用陆面模型(CLM1.0)发展了一个地表温度的同化系统。这个系统同化了MODIS温度产品,并将MODIS的叶面积指数引入CLM模型中,主要用于改进地表水热通量的估算精度。将CLM输出的地表温度与MODIS地表温度建立关系,并作为同化系统的观测算子。将MODIS地表温度与实测地表温度进行了比较,将其均方差(Root Mean Square Error,RMSE)作为观测误差。选取3个美国通量网站点(Blackhill、Bondville、Brookings)作为实验数据,结果表明:同化结果中地表温度、显热通量的估算精度均有提高。其中Blackhill站的估算精度改进最大,均方差由81.5W·m-2减小到58.4W·m-2,Bondville站均方差由47.0W·m-2减小到31.8W·m-2,Brookings站均方差由46.5W·m-2减小到45.1W·m-2。潜热通量估算精度在Bondville站均方差由88.6W·m-2减小到57.7W·m-2,Blackhill站均方差由53.4W·m-2减小到47.2W·m-2。总之,结合陆面过程模型同化MODIS温度产品估算地表水热通量是可行的。
文摘使用前苏联Valdai 1966～1971年的气象观测资料，研究了通用陆面模式（Common Land Model，CoLM）模拟的水分循环和地表通量在12种土壤质地和8种土壤亮度条件下的差异。结果表明，在相同的气象条件下，模拟的热通量对土壤质地和亮度都比较敏感，而地表水文过程只对土壤质地敏感。土壤亮度相同时，相对砂性土壤，粘土含量高的土壤保水性强，土壤湿度、地表蒸发和径流量都比较大（月均最大差值：土壤湿度约为5kg·m^-2，地表蒸发和径流量约为年降水量的7％和1．2％），相应地在热通量分配上存在明显差异（月均最大差值为8W·m^-2）；土壤质地相同，亮度由亮变暗时，潜热通量变化很小，地表温度略有升高，而感热通量和净辐射增加显著（月均摄大差值为7W·m^-2）。土壤质地和亮度对模拟的影响主要存在于降水少、植被覆盖度低的3～5月。
文摘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280K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。
文摘构建了基于通用陆面模型(CoLM,Common Land Model)、微波辐射传输模型L-MEB(Lband Microwave Emission of the Biosphere)和集合平滑算法(EnKS,Ensemble Kalman Smoother)的土壤水分数据同化框架,用于联合同化MODIS地表温度和机载L波段被动微波亮温数据。以2012年HiWATER试验期间中游大满超级站为实验站点,分析了3种LAI数据产品对土壤温度模拟结果的影响,进而分析了联合同化地表温度和微波亮度温度对土壤水分估计结果的影响。研究结果表明:3种LAI数据对土壤温度模拟结果的影响显著,MODIS LAI产品在该研究区显著低估,导致土壤温度模拟结果高估4~6K;同化亮度温度、同化地表温度以及联合同化两者均可以改进土壤水分的估计精度,联合同化地表温度和亮度温度对于土壤水分的改进最为显著,土壤水分同化结果的RMSE减少31%~53%。
