Energy and Water Balance at Soil-Air Interface in a Sahelian Region

l. IntroductionModel simulation of soll physical properties is very 1mportant for climate studies becauseof the role they play in different interaction processes with the atmosphere. One of the mostwidespread studies is the implementation of soil models 1n General Circulation Models(GCMs); previous studies showed, in fact, that climate simulat1ons are sensitive to theparameterization of the energy and mass fluxes at the land surface (V1terbo, l995; Beljiaars etal., l996; Dolman et al., l997…     

NUMERICAL SIMULATION ON THE RESPONSE OF LAND SURFACE TO SEVERE WEATHER*

A coupled model of RAMS3b(Regional Atmospheric Modeling System,Version 3b) and LSPM(a land surface process model),in which some basic hydrological processes such as precipitation,evapotranspiration.surface runoff,infiltration and bottom drainage are included,has been established.With the coupled model,we have simulated the response of soil to the sever eweather process which caused the disastrous flood in north italy during 4-7.November,1994,simultaneously compared with the observation and the original RAMS3b,which has a soil and vegetation parameterization scheme(hereafter,SVP) emphasizing on the surface energy fluxes,while some hydrological processes in the soil are not described clearly.The results show that the differences between coupling LSPM and SVP exist mainly in the response of soil to the precipitation.The soil in the SVP never saturates under the strong input of precipitation,while the newly coupled model seems better,the soil has been saturated for one day or more and causes strong surface runoff,which constitutes the flood.Further sensitivity experiments show that the surface hydrological processes are very sensitive to the initial soil moisture and soil type when we compared the results with a relatively dry case and sandy soil.The coupled model has potentiality for simulation on the interaction between regional climate and land surface hydrological processes,and the regional water resources research concerning desertification,drought and flood.     

NUMERICAL SIMULATION ON THE RESPONSE OF LAND SURFACE TO SEVERE WEATHER

A coupled model of RAMS3b(Regional Atmospheric Modeling System,Version 3b)andLSPM(a land surface process model),in which some basic hydrological processes such asprecipitation,evapotranspiration.surface runoff,infiltration and bottom drainage are included,has been established.With the coupled model,we have simulated the response of soil to the severeweather process which caused the disastrous flood in north italy during 4-7.November,1994,simultaneously compared with the observation and the original RAMS3b,which has a soil andvegetation parameterization scheme(hereafter,SVP)emphasizing on the surface energy fluxes,while some hydrological processes in the soil are not described clearly.The results show that the differences between coupling LSPM and SVP exist mainly in theresponse of soil to the precipitation.The soil in the SVP never saturates under the strong input ofprecipitation,while the newly coupled model seems better,the soil has been saturated for one dayor more and causes strong surface runoff,which constitutes the flood.Further sensitivityexperiments show that the surface hydrological processes are very sensitive to the initial soilmoisture and soil type when we compared the results with a relatively dry case and sandy soil.The coupled model has potentiality for simulation on the interaction between regional climateand land surface hydrological processes,and the regional water resources research concerningdesertification,drought and flood.     

计算非均匀地表通量的一种简化PDF及其应用

提出描述地表非均匀特性的简化概率密度函数（PDF），它可代替各种具体的PDF用于求解次网格尺度平均通量而不影响其精度，这种简化PDF可直接加入陆面过程模式方程组中进行陆－气通量交换的数值试验。它对非均匀地表陆面过程参数化具有一定的普适性。本文仅讨论了对称分布的简化计算（非对称分布另文讨论），列举了非均匀分布的观测事实，并以地表净红外辐射通量计算为例，详细验证了应用这种简化PDF的可行性和可靠性。     

江汉平原不同稻作模式下温室气体排放特征

采用静态箱-气相色谱法在江汉平原开展早稻、晚稻、中稻、虾稻和再生稻5种稻作类型温室气体排放监测试验,研究不同稻作模式下稻田CH₄和N₂O排放特征、总增温潜势及温室气体排放强度,为准确评估稻田生态系统温室气体排放提供参考依据。结果表明:CH₄排放集中在水稻前期淹水阶段,排放峰值最高为虾稻(85.7 mg·m^-2·h^-1),较其他稻作模式高71.7%～191.5%。N₂O排放峰值主要出现于中期晒田和施肥阶段,排放峰值最高为再生稻(1100.7μg·m^-2·h^-1),较其他稻作模式高16.8%～654.9%。CH₄累积排放量从大到小依次为虾稻、再生稻、早稻、晚稻、中稻;N₂O累积排放量从大到小依次为再生稻、早稻、晚稻、中稻、虾稻;总增温潜势从大到小依次为虾稻、再生稻、早稻、晚稻、中稻;温室气体排放强度从大到小依次为虾稻、早稻、再生稻、晚稻、中稻。CH₄排...     

大气PM2.5源解析“源清单化学质量平衡法(I-CMB)”模型的建立与应用

针对受体模型对大气PM2.5中二次无机、有机气溶胶不能给出有效源贡献的问题,建立了一种基于污染源清单的化学质量平衡(Inventory-Chemical Mass Balance,I-CMB)颗粒物源解析受体模型,代入北京市近年的污染物排放数据进行了解析应用。结果表明,燃煤是北京大气PM2.5的最大来源(占比约28.06%),其余依次为机动车(19.73%)、扬尘(17.88%)、工业(16.50%)、餐饮(3.43%)、植物(3.40%)。相比于传统的化学质量平衡法(Chemical Mass Balance,CMB),I-CMB的源解析过程对源成分谱的要求较低、抗干扰性更强,计算结果均衡、详尽,比较适合我国当前大气PM2.5控制的需求。     

中国长序列资料测站月降水、月均温相关联系的稳定性分析

选取我国长序列资料测站点中月降水与月均温资料较全的6个站点：西安、广州、汉口、沈阳、重庆、上海,以10a为一次成组实验,时域分辨率定为季,计算出各季月降水与月均温的相关系数,然后用相关分析和贝努里概型分析月均温与月降水之间的相关联系,初步得出我国长序列资料测站点春、夏、秋、冬月降水与月均温的相关稳定性联系。结果表明：①我国月降水与月均温在春、夏、秋、冬季均存在相关关系,以夏、秋季节最显著且为负相关,故我国常见干热或湿凉型夏、秋季;②我国华南地区春季月降水与月均温负相关关系显著,故常呈现干热或湿冷型春季;西北地区冬季月降水与月均温负相关关系较为明显,常呈现干热或湿冷型冬季。     

利用卫星资料研究云对地面净辐射的影响

采用2002年1月、2月、7月、8月每日8～16时(北京时间)的GMS-5卫星云图资料以及相同时次的漠河和郑州两个辐射站的地面净辐射资料,通过读取红外1、红外2、水汽和可见光云图上的卫星计数值,并将卫星计数值按照GMS-5定标表转换成亮度温度和反射率,最终形成一套利用卫星资料研究云对地面净辐射影响的数据集。采用统计的方法将地面净辐射与影响地面净辐射的各因子：太阳天顶角、地面及云面反射率等有关因子进行拟合,发现地面净辐射与这些因子之间有很好的相关性,特别在引入卫星红外通道亮温值减水汽通道亮温值这一因子后,在有云状况下,拟合的相关系数有较明显的提高,原因可能是这一因子包含了云分类的信息,这一方法的提出为利用卫星资料研究云对地面净辐射的影响提出了一个新的思路。     

基于UTCI指数的1980—2019年中国夏季人体舒适度变化特征分析

基于ERA5-HEAT再分析资料中的通用热气候指数（UTCI）数据,利用旋转经验正交函数（REOF）方法将我国划分为8个区,分别为长江、华南、华北、西北、东北、北疆、南疆和西部地区。分析了1980—2019年我国夏季不同地区人体舒适度的变化特征,并初步解释了UTCI变化的原因。主要结论如下：我国夏季UTCI呈不断增加趋势,其中西北地区增速最快（平均增率为0.053℃/a),且西部、西北和南疆地区夜间UTCI相较白天增加更明显,主要表现为这些地区的UTCI最小值增率分别较其最大值增率偏高了112%、34%和33%。随着UTCI的上升,我国大部分地区（西部除外）的热不舒适天数及发生热不舒适持续事件的频次都呈增加趋势,其中增率最大的区域是华北地区,分别为1.7 d/(10 a)和2.4次/(10 a)。从气候影响因子的分析发现,我国夏季UTCI增加的原因是气温、露点温度和平均辐射温度的增加以及风速的减少。其中,气温是UTCI增加的主要气候因子,平均贡献率为49%;辐射是大部分地区（西部和华南除外）的第二大因子,而其他因子对UTCI的贡献率主要与各地区的变率大小有关。     

An overview of MODIS radiometric calibration and characterization

The Moderate Resolution Imaging Spectroradiometer (MODIS) is one of the key instruments for NASA’s Earth Observing System (EOS), currently operating on both the Terra and Aqua satellites. The MODIS is a major advance over the previous generation of sensors in terms of its spectral, spatial, and temporal resolutions. It has 36 spectral bands: 20 reflective solar bands (RSB) with center wavelengths from 0.41 to 2.1 μm and 16 thermal emissive bands (TEB) with center wavelengths from 3.7 to 14.4 μm, making observations at three spatial resolutions: 250 m (bands 1–2), 500 m (bands 3–7), and 1km (bands 8-36). MODIS is a cross-track scanning radiometer with a wide field-of-view, providing a complete global coverage of the Earth in less than 2 days. Both Terra and Aqua MODIS went through extensive pre-launch calibration and characterization at various levels. In orbit, the calibration and characterization tasks are performed using its on-board calibrators (OBCs) that include a solar diffuser (SD) and a solar diffuser stability monitor (SDSM), a v-grooved flat panel blackbody (BB), and a spectro-radiometric calibration assembly (SRCA). In this paper, we present an overview of MODIS calibration and characterization activities, methodologies, and lessons learned from pre-launch characterization and in-orbit operation. Key issues discussed in this paper include in-orbit efforts of monitoring the noise characteristics of the detectors, tracking the solar diffuser and optics degradations, and updating the sensor’s response versus scan angle. The experiences and lessons learned through MODIS have played and will continue to play major roles in the design and characterization of future sensors.     

Modes of Mesoscale Convective System Organization During Meiyu Season over the Yangtze River Basin

Mesoscale convective systems （MCSs） are classified and investigated through a statistical analysis of composite radar reflectivity data and station observations during June and July 2010-2012. The number of linear-mode MCSs is slightly larger than the number of nonlinear-mode MCSs. Eight types of linear-mode MCSs are identified： trailing stratiform MCSs （TS）, leading stratiform MCSs （LS）, training line/adjoining stratiform MCSs （TL/AS）, back-building/quasi-stationary MCSs （BB）, parallel stratiform MCSs （PS）, bro- ken line MCSs （BL）, embedded line MCSs （EL）, and long line MCSs （LL）. Six of these types have been identified in previous studies, but EL and LL MCSs are described for the first time by this study. TS, LS, PS, and BL MCSs are all moving systems, while TL/AS, BB, EL, and LL MCSs are quasi-stationary. The average duration of linear-mode MCSs is more than 7 h. TL/AS and TS MCSs typically have the longest durations. Linear-mode MCSs often develop close to the Yangtze River, especially over low-lying areas and river valleys. The diurnal cycle of MCS initiation over the Yangtze River valley contains multiple peaks. The vertical distribution of environmental wind is decomposed into storm-relative perpendicular and parallel wind components. The environmental wind field is a key factor in determining the organizational mode of a linear-mode MCS.     

东北地区冬季气温与北极涛动年代际关系研究

利用中国160站气温资料、北极涛动指数资料及关国NCEP／NCAR再分析资料中月平均海平面气压场、高度场、风场资料，分析了东北地区冬季气温、冬季北极涛动的年代际特征及其关系。结果表明：在年代际时间尺度上，两者之间存在显著正相关。冬季北极涛动处于低（高）指数期，东北冬季气温为持续冷冬（暖冬）期。可能影响机制是：在地面，冬季北极涛动处于低（高）指数期时，西伯利亚高压增强（减弱），亚洲大陆偏北冬季风增强（减弱），东北为持续冷冬（暖冬）期；在对流层中层，冬季北极涛动处于低（高）指数期时，东亚大槽加深（减弱），贝加尔湖以西以北脊增强（减弱），环流呈经向（纬向）型发展，东北对流层中层偏北风增强（减弱），东北为持续冷冬（暖冬）期。     

A comprehensive study on the surface chemistry of particulate matter collected from Jeddah,Saudi Arabia

In this work, the X-ray Photoelectron Spectroscopy (XPS) technique is utilized to analyze the surface chemical composition of particulate matter (PM) which was collected from various locations at Jeddah, Saudi Arabia. The main elements found on the surface of PM are carbon (C), oxygen (O) and silicon (Si) with combined percentage of 89.4–94.9 while traces of nitrogen (N), calcium (Ca), aluminum (Al), sodium (Na), chlorine (Cl), manganese (Mg), and sulfur (S) were also present. The analyzed XPS chemical state of C, O and Si was further used to determine their bonding with other elements occurring over the surface of PM. Carbon was found in the form of carbides (18.86%), fluorides (2.39%) and carbonates (78.75%); oxygen was observed as oxides (21.05%) and hydroxides (73.42%) of other metals; and silicon was detected as silicones (12.16%), nitrides (82.53%) and silicates (5.25%). The particle size of a PM is also of great concern for health issues, and thus has been investigated by the Field Emission Scanning Electron Microscope (FESEM). The Energy Dispersive X-ray Spectroscopy (EDS) was employed for cross verification of detected elements by XPS.     

重庆山地区域气象要素空间插值方法对比

利用重庆地区1999年和2018年气象数据,分别采用薄盘光滑样条、协同克里金、普通克里金、反距离加权4种方法,从年和月两种尺度对气温、降水、太阳总辐射三个要素进行空间插值;采取交叉验证方法,用MAE、MRE、RMSE评估插值精度,确定各要素最优插值方法。结果表明：气温和太阳总辐射最优插值方法为薄盘光滑样条,降水为反距离加权;插值精度上气温、太阳总辐射高值月份优于低值月份,降水则相反,但三个要素均表现出年尺度优于月尺度。MRE检验表明,插值精度为气温>太阳总辐射>降水,1999年年尺度插值精度分别为1.86%、4.60%、6.87%,月尺度插值精度分别为2.79%、5.82%、17.42%;2018年太阳总辐射年、月尺度插值精度分别为3.03%、4.88%,区域站加密后气温、降水年尺度插值精度分别为2.03%、11.20%,月尺度对应插值精度分别为3.20%、23.14%。     

华西秋雨准4年周期特征及其与赤道太平洋海表温度的关系

利用1959～2011年华西地区气象台站资料、NCEP/NCAR再分析资料、NOAA海表温度资料, 采用多锥度—奇异值分解(MTM-SVD)方法, 研究了华西秋雨的准4年周期特征及其与赤道太平洋海表温度的协同变化关系。研究结果表明:华西秋雨具有显著的准4年周期, 其典型循环表现为"偏强, 略偏强, 偏弱, 略偏弱"的特点。在准4年周期上赤道中太平洋海表温度对华西秋雨的协同变化表现为"偏低, 略偏低, 偏高, 略偏高", 这种协同变化从初夏就体现出来, 并一直持续到秋末。同时在准4年周期上, 华西秋雨对ENSO事件也存在一定的响应, 但是主要体现在发生强ENSO事件时。准4年周期的环流分析表明, 夏季到秋季赤道中太平洋海表温度偏低(高)时, 秋季500 hPa高度场出现东亚/太平洋(EAP)遥相关波列正(负)异常, 西太平洋副热带高压偏西(东), 华西地区来自南海西太平洋和孟加拉的水汽输送偏多(少), 华西秋雨偏强(弱)。     

浙江省近34年年平均风速序列均一性检验研究

采用标准正态检验(SNHT:Standard Normal Homogeneity Test)方法.对浙江省36个代表站1971～2004年的年平均风速资料序列进行均一性检验.结果表明:36站中有23个测站出现间断,其中因迁站原因造成非均一性的测站有13个,占非均一性总数的57%,环境变化原因有5个,占非均一性总数的22%;原因不明有3个,占非均一性总数的13%;测风仪高度变化、规定变更各为1个,占非均一性总数的4%.迁站是导致风速序列非均一性的主要原因.     

Laboratory Studies of the Hydrogen Kinetic Isotope Effects (KIES) of the Reaction of Non-Methane Hydrocarbons with the OH Radical in the Gas Phase

The hydrogen kinetic isotope effects (KIEs) of the reactions of 15 non-methane hydrocarbons (NMHCs) with the OH radical were measured at 298 ± 2 K. The measurements were made using NMHCs without artificial isotopic labeling or enrichment. The following average hydrogen KIE values, in per mil (), were obtained: 29.8 ± 2.1 (toluene),51.6 ± 2.1 (n-butane), 97.3± 12.5 (i-butane), 63.2 ± 5.9 (cyclopentane), 10.5 (p-xylene), 26.8 ± 3.5 (ethylbenzene), 65.9± 7.0 (n-pentane), 79.5 ± 9.6 (cyclohexane), 52.8 ± 5.0(n-hexane), 38.9 ± 7.8 (n-heptane), 33.4 ± 3.1 (n-octane), 29.6 ± 1.6(n-nonane), and 29.0 ± 5.3 (n-decane). The KIEs for reactions of two alkenes (cyclohexene and 1-heptene) could not be determined accurately due to interference from reaction with ozone, but nevertheless the results clearly show that the KIEs for reaction of alkenes with OH are significantly lower than those for saturated hydrocarbons. The KIEs for reaction of alkanes are smaller than isotope effects reported in literature for the reactions of NMHCs artificially labeled with deuterium. The main reason for this difference is the reduced probability for reaction at a labeled site for compounds with close to natural deuterium abundance, although some impact of secondary isotope effects cannot be ruled out. Still, the KIEs for NMHCs with natural or close to natural abundance of deuterium are of sufficient magnitude to allow determination of the extent of chemical processing of hydrocarbons in the atmosphere using methods analogous to stable carbon KIE studies. Furthermore, it is shown that combining stable hydrogen and stable carbon isotope ratio data has the potential to also provide valuable information regarding the stable isotope ratios of emissions, and specifically to test one of the key assumptions of the stable isotope hydrocarbon clock, the absence of significant variations of the stable isotope ratio for the emitted NMHCs.     

Large-Eddy Simulation of Wind-Turbine Wakes: Evaluation of Turbine Parametrisations

Large-eddy simulation (LES), coupled with a wind-turbine model, is used to investigate the characteristics of a wind-turbine wake in a neutral turbulent boundary-layer flow. The tuning-free Lagrangian scale-dependent dynamic subgrid-scale (SGS) model is used for the parametrisation of the SGS stresses. The turbine-induced forces (e.g., thrust, lift and drag) are parametrised using two models: (a) the ‘standard’ actuator-disk model (ADM-NR), which calculates only the thrust force and distributes it uniformly over the rotor area; and (b) the actuator-disk model with rotation (ADM-R), which uses the blade-element theory to calculate the lift and drag forces (that produce both thrust and rotation), and distribute them over the rotor disk based on the local blade and flow characteristics. Simulation results are compared to high-resolution measurements collected with hot-wire anemometry in the wake of a miniature wind turbine at the St. Anthony Falls Laboratory atmospheric boundary-layer wind tunnel. In general, the characteristics of the wakes simulated with the proposed LES framework are in good agreement with the measurements in the far-wake region. The ADM-R yields improved predictions compared with the ADM-NR in the near-wake region, where including turbine-induced flow rotation and accounting for the non-uniformity of the turbine-induced forces appear to be important. Our results also show that the Lagrangian scale-dependent dynamic SGS model is able to account, without any tuning, for the effects of local shear and flow anisotropy on the distribution of the SGS model coefficient.     

Representativeness of Four Precipitation Observational Networks of China

Four precipitation observational networks with varied station densities are maintained in China. They are: the Global Climate Observation System (GCOS) Surface Network (GSN), the national Reference Climate Network (RCN), the national Basic Meteorological Network (BMN), and the national Ordinary Meteorological Network (OMN). The GSN, RCN, BMN, and the merged network of RCN and BMN (R&B) have been widely used in climatology and climate change studies. In this paper, the impact of the usage of different networks on the precipitation climatology of China is evaluated by using the merged dataset of All Station Network (ASN) as a benchmark. The results show that all networks can capture the main features of the country average precipitation and its changing trends. The differences of average annual precipitation of the various networks from that of the ASN are less than 50 mm ( 10%). All networks can successfully detect the rising trend of the average annual precipitation during 1961-2009, with the R&B exhibiting the best representativeness (only 2.90% relative difference) and the GSN the poorest (39.77%). As to the change trends of country average monthly precipitation, the networks can be ranked in descending order as R&B (1.27%), RCN (2.35%), BMN (4.17%), and GSN (7.46%), and larger relative differences appear from August to November. The networks produce quite consistent spatial patterns of annual precipitation change trends, and all show an increasing trend of precipitation in Northwest and Southeast China, and a decreasing trend in North China, Northeast China, and parts of central China. However, the representativeness of the BMN and R&B are better in annual and seasonal precipitation trends, in spite of the fact that they are still far from satisfactory. The relative differences of trends in some months and regions even reach more than 50%. The results also show that the representativeness of the RCN for country average precipitation is higher than that of the BMN because the RCN has a more homogeneous distribution of stations.     

LPJ模型对1981～1998年中国区域潜在植被分布和碳通量的模拟

利用一个基于过程的动态植被模型LPJ DGVM（Lund Potsdam Jena Dynamic Global Vegetation Model）,模拟了中国区域潜在植被分布,考察了1981～1998年中国区域净初级生产〖JP〗力（NPP）、异养呼吸（Rh）和净生态系统生产力（NEP）的年际变化。模拟结果表明,在LPJ模型提供的植被功能类型（PFT）划分的条件下,中国区域除了分布裸土外,主要分布了6种潜在植被功能类型,即热带常绿阔叶林带、温带常绿阔叶林带、温带夏绿阔叶林带、北方常绿针叶林带、北方夏绿针叶林带和温带草本植物。在所考察的时间段内,中国区域总NPP从2.91 Gt · a-1（C）（1982年）变化到3.37 Gt · a-1（C）（1990年）,平均每年增加0.025 Gt（C）,其平均增长率为096%。中国区域总Rh从2.59 Gt · a-1（C）（1986年）变化到3.19 Gt · a-1（C）（1998年）,具有105% 的平均年增长率,即平均每年增加0.025 Gt（C）,并且中国区域温带草本植物相比其他植被功能类型,其NPP和Rh线性增加的趋势最为显著。研究结果还表明,LPJ模型在引入火灾机制后,中国区域总NEP的变化范围更加合理,即每年总NEP在-0.06 Gt · a-1（C）（1998年）和0.34 Gt · a-1（C）（1992年）之间变化,其平均值为0.12 Gt · a-1（C）。该结果表明,在所考察的时间段内,中国区域的陆地生态系统是碳汇。上述结果与其他研究结果基本一致,因而此模型模拟中国区域潜在植被分布和碳循环是有效的。