Surface energy and water vapor fluxes observed on a megadune in the Badain Jaran Desert, China

The Badain Jaran Desert is the second-largest area of shifting sands in China. Our first measurements of the energy components and water vapor fluxes on a megadune using eddy covariance technology were taken from April 2012 to April 2013. The results indicate that the Iongwave and shortwave radiative fluxes exhibited large fluctuations and seasonal dynamics. The total radiative energy loss by Iongwave and shortwave radiation was greater on the megadune than from other underlying surfaces. The radiation partitioning was different in different seasons. The land-atmosphere interaction was primarily represented by the sensible heat flux. The average sensi- ble heat flux （40.1 W/m2） was much larger than the average latent heat flux （14.5 W/m2）. Soil heat flux played an important role in the energy balance. The mean actual evaporation was 0.41 mm/d, and the cumulative actual evaporation was approximately 150 mm/a. The water vapor would transport downwardly and appear as dew con- densation water. The amount of precipitation determined the actual evaporation. The actual evaporation was sup- posed to be equal to the precipitation on the megadune and the precipitation was difficult to recharge the ground- water. Our study can provide a foundation for further research on land-atmosphere interactions in this area.

Application of least squares vector machines in modelling water vapor and carbon dioxide fluxes over a cropland

Least squares support vector machines (LS-SVMs), a nonlinear kemel based machine was introduced to investigate the prospects of application of this approach in modelling water vapor and carbon dioxide fluxes above a summer maize field using the dataset obtained in the North China Plain with eddy covariance technique. The performances of the LS-SVMs were compared to the corresponding models obtained with radial basis function (RBF) neural networks. The results indicated the trained LS-SVMs with a radial basis function kernel had satisfactory performance in modelling surface fluxes; its excellent approximation and generalization property shed new light on the study on complex processes in ecosystem.

Monitoring and simulation of water,heat,and CO_2 fluxes in terrestrial ecosystems based on the APEIS-FLUX system

The Integrated Environmental Monitoring (IEM) project, part of the Asia-Pacific Environmental Innovation Strategy (APEIS) project, developed an integrated environmental monitoring system that can be used to detect, monitor, and assess environmental disasters, degradation, and their impacts in the Asia-Pacific region. The system primarily employs data from the moderate resolution imaging spectrometer (MODIS) sensor on the Earth Observation System-(EOS-) Terra/Aqua satellite, as well as those from ground observations at five sites in different ecological systems in China. From the preliminary data analysis on both annual and daily variations of water, heat and CO2 fluxes, we can confirm that this system basically has been working well. The results show that both latent flux and CO2 flux are much greater in the crop field than those in the grassland and the saline desert, whereas the sensible heat flux shows the opposite trend. Different data products from MODIS have very different correspondence, e.g. MODIS-derived land surface temperature has a close correlation with measured ones, but LAI and NPP are quite different from ground measurements, which suggests that the algorithms used to process MODIS data need to be revised by using the local dataset. We are now using the APEIS-FLUX data to develop an integrated model, which can simulate the regional water, heat, and carbon fluxes. Finally, we are expected to use this model to develop more precise high-order MODIS products in Asia-Pacific region.

Modeling water and carbon fluxes above summer maize field in North China Plain with back-propagation neural networks

In this work, datasets of water and carbon fluxes measured with eddy covariance technique above a summer maize field in the North China Plain were simulated with artificial neural networks (ANNs) to explore the fluxes responses to local environmental variables. The results showed that photosynthetically active radiation (PAR), vapor pressure deficit (VPD), air temperature (T) and leaf area index (LAI) were primary factors regulating both water vapor and carbon dioxide fluxes. Three-layer back-propagation neural networks (BP) could be applied to model fluxes exchange between cropland surface and atmosphere without using detailed physiological information or specific parameters of the plant.

Diagnosing anomalous characteristics of atmospheric water cycle structure during seasonal-scale drought events:A case study in middle and lower reaches of Yangtze River

Anomalous characteristics of the atmospheric water cycle structure are highly significant to the mechanisms of seasonal-scale meteorological droughts.They also play an important role in the identification of indicative predictors of droughts.To better understand the causes of seasonal meteorological droughts in the middle and lower reaches of the Yangtze River(MLRYR),characteristics of the atmospheric water cycle structure at different drought stages were determined using standardized anomalies.The results showed that the total column water vapor(TCWV)was anomalously low during drought occurrence periods.In contrast,there were no anomalous signals at the drought persistence and recovery stages in the MLRYR.Moreover,there was no significant temporal correlation between the TCWV anomaly and seasonal-scale drought index(the 3-month standardized precipitation index(SPI_(3))).During drought events,water vapor that mainly originated from the Bay of Bengal was transported southwest of the MLRYR.Meanwhile,the anomalous signal of water vapor transport was negative at the drought appearance stage.At the drought persistence stage,the negative anomalous signal was the most significant.Water vapor flux divergence in the MLRYR showed significant positive anomalous signals during drought events,and the signal intensity shifted from an increasing to a decreasing trend at different drought stages.In addition,a significant positive correlation existed between the anomaly of water vapor flux divergence and regional SPI_(3).Overall,water vapor flux divergence is more predictive of droughts in the MLRYR.

The Influence of Airflow Transport Pathways on Precipitation during the Rainy Season in the Liupan Mountains of Northwest China

This study investigates the influence of airflow transport pathways on seasonal rainfall in the mountainous region of the Liupan Mountains(LM) during the rainy seasons from 2020 to 2022, utilizing observational data from seven ground gradient stations located on the eastern slopes, western slopes, and mountaintops combined with backward trajectory cluster analysis. The results indicate 1) that the LM's rainy season, characterized by overcast and rainy days, is mainly influenced by cold and moist airflows(CMAs) from the westerly direction and warm and moist airflows(WMAs) from a slightly southern direction. The precipitation amounts under four airflow transport paths are ranked from largest to smallest as follows: WMAs, CMAs, warm dry airflows(WDAs), and cold dry airflows(CDAs). 2) WMAs contribute significantly more to the intensity of regional precipitation than the other three types of airflows. During localized precipitation events,warm airflows have higher precipitation intensities at night than cold airflows, while the opposite is true during the afternoon. 3) During regional precipitation events, water vapor content is the primary influencing factor. Precipitation characteristics under humid airflows are mainly affected by high water vapor content, whereas during dry airflow precipitation, dynamic and thermodynamic factors have a more pronounced impact. 4) During localized precipitation events, the influence of dynamic and thermodynamic factors is more complex than during regional precipitation, with the precipitation characteristics of the four airflows closely related to their water vapor content, air temperature and humidity attributes, and orographic lifting. 5) Compared to regional precipitation, the influence of topography is more prominent in localized precipitation processes.

基于EOF的1951-2020年东亚季风区降水特征及其对夏季风不同配置的响应研究

东亚季风区夏季降水受季风影响显著,不同季风配置通过影响区域水汽输送,在东亚季风区形成不同的降水格局,降水格局的变化容易引起旱涝灾害的发生。本文基于经验正交函数(EOF)分析,利用全球降水气候中心(GPCC)降水资料、美国国家环境预测中心/大气研究中心(NCEP/NCAR)再分析资料和不同夏季风指数,分析了1951-2020年东亚季风区夏季降水格局,进一步结合相关分析、水汽通量分析等,研究了4种夏季风强弱不同配置对东亚季风区夏季降水的影响。结果表明:(1)1951-2020年东亚季风区降水经历了先减少后增加的变化。EOF分析较好地展现了东亚季风区夏季降水的时空分布,东亚季风区夏季降水主要表现为南北向“-、+、-”的三极型分布与南北方降水反相变化的偶极型特征;东亚季风区夏季降水异常主要发生在三极型降水结构的相位转换上,其次是偶极型的相位转换;(2)东亚季风区夏季降水异常是东亚季风、南亚季风、西风环流以及西太平洋季风等系统共同作用的结果。导致东亚季风区降水异常增加(减少)的季风配置主要为配置1:西太平洋季风强,东亚季风和西风弱(配置2:西风强,东亚季风和南亚季风弱);(3)配置1时,西太副高偏南偏西,中高纬形成西风槽,季风区南方季风较强,容易通过切变线以及抬升作用在季风区中部形成降水,导致异常降水增加,配置2时,西风强劲,南方水汽动力不足,无法深入大陆,造成异常降水减少。本文研究结果为气候变化背景下,探究东亚季风区异常降水机理提供理论基础,也为应对区域极端降水事件以及旱涝灾害防治工作提供重要的科学参考依据。

初始场水汽通量在一次登陆台风降水模拟中的作用

用三维变分同化方法,通过同化加密地面观测资料和X波段雷达观测资料,研究初始场陆地侧水汽通量对台风“狮子山”登陆期间降水模拟效果的影响.结果表明,同化加密地面资料能够明显改进初始场陆地侧大气边界层的热动力场,通过减弱海-陆热力对比及陆地向登陆台风的大气边界层东北的水汽通量,改善登陆台风外围雨带影响下的沿岸陆地-海洋两侧地区降水的模拟效果. X波段雷达资料通过增强初始场中雷达探测范围内的低层大气水汽通量改善登陆台风外围雨带降水的模拟效果.

全球变暖背景下南海夏季风变化特征

南海夏季风的爆发和推进影响着中国夏季雨带的进程。采用美国国家环境预报中心(National Centers for Environmental Prediction,NCEP)和美国国家大气研究中心(National Center for Atmospheric Research,NCAR)再分析资料分析全球变暖前、后南海夏季风的演变特征。研究结果表明,全球变暖导致南海夏季风减弱,主要出现以下特征:(1)南海夏季风的平均建立时间提早,平均撤退时间推迟,历时长度更长,持续时间有上升趋势。(2)南海夏季风爆发后(6—9月),南海西北部对流层低层(700 hPa以下)由海陆热力差异导致的局地环流在全球变暖后有减弱趋势,进入中国华南和西南地区的西南夏季风有所减弱。(3)夏季风盛行期间,西南风携孟加拉湾水汽经过中南半岛进入中国南海的水汽呈减少趋势,且从南海输入华南的水汽减少,导致中国东部降水变化趋势存在空间差异。(4)南海夏季风指数表明,南海夏季风对南海中南部以及华南东部的影响加强,而对南海北部和西南地区的影响强度明显减弱。

Analysis on the Formation Reason of Regional Rainstorm in Shandong Province during July 8-9,2009

By using the data which included the conventional weather chart,the satellite cloud image,the regional automatic meteorological station and the new generation of weather radar,the regional strong precipitation process which happened in Shandong Province during July 8-9 in 2009 was analyzed comprehensively.The results showed that Shandong Province was in the strong convergence zone of atmospheric vorticity in the low layer and the ascent zone of vertical velocity.The shear line was generated in the eastward process of northwest vortex,and the ground inverted trough extended to Shandong,which provided the dynamic condition for the formation of rainstorm.The coupling of jet stream in the high-low altitude enhanced the development of convection.The low-altitude jet stream was the main water vapor transportation channel,which provided the water vapor condition for the generation of rainstorm.The water vapor was mainly from the South China Sea and the Bay of Bengal.

西北地区大气水汽的区域分布特征及其变化

对西北地区大气水汽的区域分布及变化特征进行了分析.结果表明:受不同气候系统影响的西北地区可划分为西风带、高原区与东亚季风等3个气候影响区,水汽沿西北、西方与西南3条路径输送到西北地区;东亚季风区是西北大气可降水量和水汽通量的最丰富区,西风带区是次之,高原区最少.平均状况下,高原区的边坡、东亚季风区、天山及祁连山等西北地区降水最大和次大中心维持水汽的辐合状态.西风带区在1978年以前净水汽通量呈“亏损”状态,之后维持“盈余”;高原区净水汽通量一直为“亏损”状态;东亚季风区90年代以前净水汽通呈“盈余”状况,其后基本维持平衡,且数值远大于其它区.西风带区降水和大气水汽在变化过程中均有突变发生,时间分别为1990年和1985年,其它两区没有突变现象发生.

半干旱地区地气界面水汽和二氧化碳通量的日变化及季节变化

采用涡动相关方法连续观测2002年10月到2003年12月半干旱地区地气界面水汽和二氧化碳通量变化，分析水汽和二氧化碳通量的季节和日变化规律，同时比较农田和退化草地两种不同下垫面物质和能量通量交换过程的差异，得到如下一些主要结果：（1）半干旱地区湿季，相距5km的两种不同下垫面，即使在同一天气过程控制下，不同植被下垫面的降雨分布仍不尽相同，甚至相差很大。这表明降雨空间的分布是很不均匀的，具有很强的局地特征。（2）在干季近地面层能量收支中，两种不同下垫面上的有效能量（净辐射与地表热流量之差）主要分配为感热通量，潜热通量在非生长季（干季）通常很小。在湿季（生长季），潜热通量与感热通量相当，但农田下垫面的潜热通量大于退化草原下垫面。（3）土壤的温度和湿度日变化主要集中在0～20cm土壤层内，在湿季农田下垫面土壤的湿度有明显的跳跃，这与降雨过程有很好的相关。（4）在非生长季，两种不同下垫面地气间二氧化碳通量差别不大，都很小。白天由于光合作用，在生长季农田下垫面吸收CO2通量较退化草原大，但比湿润地区稻田下垫面小一个量级，远小于森林生态系统。

夏季东亚季风区水汽输送特征及其与南亚季风区水汽输送的差别

利用ＥＣＭＷＦ所分析的１９８０～１９８９年每日各层的水汽和风场资料分析了东亚季风区夏季风的水汽输送特征，并与印度季风区夏季水汽输送进行比较。分析结果表明了东亚季风区夏季水汽输送特征明显不同于印度季风区夏季水汽输送，东亚季风区夏季水汽输送经向输送要大于纬向输送，而印度季风区夏季水汽输送则以纬向输送为主。分析结果还表明东亚季风区由于夏季水汽分布是南边大、北边小，偏南季风气流所引起的水汽平流是湿平流。因此，水汽的辐合主要由季风气流所引起的水汽平流所造成，而印度季风区季风气流所引起的水汽平流是干平流，它利于水汽输送的辐散，水汽的辐合主要是由于风场的辐合所造成。

大型浅水湖泊与大气之间的动量和水热交换系数——以太湖为例

湖泊水面与大气之间垂直方向的动量、水汽和热量通量与风速、湿度和温度梯度之间存在比例关系,因此在湖泊水-气相互作用研究中,这比例系数(交换系数)是关键因子.在以往的研究中,交换系数通常直接采用水面梯度观测法或海洋大气近地层的参数化方案进行计算.本文采用涡度相关系统和小气候系统仪器在太湖平台上直接观测的通量和气象要素,对上述交换系数(最小均方差原则)进行优化,结果为:动量交换系数CD10N=1.52×10-3、水汽交换系数CE10N=0.82×10-3、热量交换系数CH10N=1.02×10-3,与其他内陆湖泊涡度相关观测数据的推导结果一致.本文的研究结果表明:与海洋参数化方案相比,在相同的风速条件下,湖面的空气动力学粗糙度比海洋高,这可能是由于受到水深的影响;如果采用海洋参数化方案,会导致湖泊年蒸发量的估算值偏大40%.太湖的动量、水汽和热量交换系数可以视为常数,可以不考虑稳定度和风速的影响.这是因为本文中83%的数据为近中性条件.敏感性分析表明:如果考虑稳定度的影响,LE模拟值的平均误差降低了0.5 W/m2,H的平均误差降低了0.4 W/m2,u*的计算值没有变化;如果考虑风速的影响,u*模拟值的平均误差降低了0.004 m/s,LE的平均误差升高了1.3 W/m2,H的模拟结果几乎不受影响.这一结果能为湖气相互作用研究提供参考.

2003年稻纵卷叶螟大发生的水汽条件分析

为了弄清大气水汽环境对稻纵卷叶螟大发生的影响,在ArcGIS支持下,对2003年6月16日、7月21日和9月1日全国每667m2稻纵卷叶螟平均蛾量的地理分布进行空间分析,并选取对害虫迁入影响最大的850、925和1000hPa等压面上的大气相对湿度场和水汽通量场进行模拟和客观分析.结果表明,高空的水汽输送状况和相对湿度分布对稻纵卷叶螟的迁入具有很强的指示意义.在稻纵卷叶螟发生区域,从地面到850hPa,各层次空气相对湿度均达到50%以上.在稻纵卷叶螟迁飞过程中,迁入地空气相对湿度不断增大,源地的空气相对湿度不断减小.850hPa等压面是水汽输送的主要层次,也是稻纵卷叶螟迁飞的主要通道,该层的水汽输送方向与稻纵卷叶螟迁飞方向基本一致.

祁连山-黑河流域水循环中的大气过程

利用气象台站探空资料、地面观测资料和NCEP/NCAR再分析气候资料,分析了祁连山 黑河流域水循环中的大气过程,结果表明:受西风带波动影响的水汽来源贫乏是此区大气水汽含量少的原因之一;水汽输送通量辐散是此区大气水汽含量少的原因之二;就年平均而言,祁连山 黑河流域大气水汽含量仅为高湿的江南地区的20%,为半干旱区的华北中部的约40%;高海拔的祁连山区因降水效率高,地面蒸发量小,地表水物质易于聚积形成径流;黑河流域因降水效率低,降水量值与地面蒸发量值相当,对地表水的贡献很小。在祁连山 黑河流域2 5°×2 5°区域上空,大气年输入水量为6678亿m3,输出为6502亿m3,净输入水量为176亿m3;输入水汽呈逐年减少的趋势。20世纪70～80年代有明显的下降,近40年来祁连山 黑河流域的气温在升高,大气中的水汽含量在减少,降水量的减少将难以避免。

安吉毛竹林水汽通量变化特征及其与环境因子的关系

以浙江省安吉县毛竹(Phyllostachys edulis)林生态系统为研究对象,利用涡度相关技术进行观测,获取2011年毛竹林的水汽通量数据,同时结合常规气象观测数据,分析了水汽通量全年变化。结果表明:毛竹林全年水汽通量基本为正值,月尺度上,水汽通量呈单峰型变化趋势,且各月的最大值均在12:00—14:00出现,呈现一定规律性,7月(0.1116 g m-2s-1)最高,12月(0.0209 g m-2s-1)最低;季节尺度上,夏季最高(0.0873 g m-2s-1),呈现典型单峰型变化趋势,春秋季(均为0.0541 g m-2s-1)次之,变化特征与夏季相似,冬季最低(0.0221 g m-2s-1),曲线变化复杂,波动较大。毛竹林全年蒸散量占全年降水量48.26%。2、4、5、11、12月蒸散量略大于降水量,其余月份蒸散量均小于降水量,6月份降水量与蒸散量差别最大。季节尺度上,对毛竹林水汽通量与净辐射进行回归关系分析,夏季最大,R2为0.6111,秋季为0.5295,春季为0.2605,冬季最小0.0455。通过F检验,水汽通量与净辐射有极显著线性关系。在植物生长期,毛竹林水汽通量随饱和水汽压差的增大而增大,植物发育成熟后,当饱和水汽压差增大到一定程度时,其增大反而抑制了水分的蒸散。

用GPS可降水量资料对一次大—暴雨过程的分析

利用2 0 0 2年9月1 0～2 0日GPS的可降水量资料与实况降水场做了分析比较,结果表明,每30分钟的可降水量连续观测资料对实际降水预报有着一定的指导意义。首先,可降水量第一次达到及最后一次出现50mm的时间与实际降水的开始、结束时间有着较好的对应关系,而可降水量≥50mm的持续时间越长,实际降水量也就越大,反之则相反;其次,可降水量的3小时及2 4小时变化对预报未来降水区域和雨量分布有着一定的指示作用;最后,可降水量在降水过程中不同阶段的趋势变化反映了50 0hPa流场、70 0hPa水汽通量场的变化,这为实际降水预报中水汽的来源及输送提供了更有利的依据。

东亚地区秋季水汽输送特征及水汽源地分析

用1980～1997年垂直积分的水汽输送通量资料,分析了秋季东亚地区大尺度水汽输送演变的气候特征以及主要水汽源地,结果表明:秋季各个月东亚大陆的主要水汽来源地并不相同,9月主要来源于孟加拉湾、南海和西太平洋地区;10～11月主要来源于南海、西太平洋地区。从夏季型到冬季型水汽输送的转换特征表现为:来自南半球的越赤道输送的显著减弱、消失直至转向,东亚南支偏西风水汽输送的逐渐建立,赤道太平洋地区的偏东风水汽输送的加强西进。秋季亚洲季风区范围最大的强水汽源地位于南海、西太平洋地区(115～120°E,15～25°N)。

夏季东亚地区水汽输送的气候特征

使用 1980—1997年垂直积分的水汽输送通量资料,分析了夏季大尺度水汽输送演变的气候特征及偏南风水汽输送在中国区域内的推进特征。结果表明:夏季各支大尺度水汽输送汇合成一条行星尺度水汽输送大值带,它从南半球出发,经过亚洲季风区,进入北太平洋;东亚夏季偏南风水汽输送所能到达的北界为东北北部50°N附近;西太平洋副高南侧的东南风水汽输送所能到达的西界为甘肃东南部100°E附近。垂直积分的水汽输送通量强辐合区大多位于行星尺度水汽输送大值带中,与降水大值区之间有很好的对应关系。