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.

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.

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.

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。

2021年盛夏黄河三花区间暴雨过程的水汽输送特征

2021年盛夏黄河中游三花区间降水量553.3 mm,位列1961年以来第一位。持续的强降水过程造成了流域罕见特大洪水。本文针对2021年7月—8月三花间4次持续强降水天气过程,利用水汽通量、湿位涡分析了暴雨过程的水汽输送和强降水期间的对流结构变化。结果表明:2021年三花区间盛夏暴雨过程的主要水汽通道有四条,分别是中国南海的东南水汽流输送、源于孟加拉湾的西南季风水汽流输送、来自副热带太平洋的偏东风水汽流输送以及来自西风带的水汽输送;过程强降水时段暖湿水汽在河南西部山区及华北地区汇聚后进入三花区间。四次暴雨过程均对应经向(纬向)水汽通量辐合和纬向(经向)水汽通量辐散,东风波内部纬向水汽通量辐合造成的强降水具有明显极端性(局地小时降水量连续5 h超过40 mm/h)。2021年盛夏三花区间暴雨期间对流层低层对流不稳定和斜压不稳定同时存在,降水过程强降水时段发生在对流不稳定和斜压不稳定交汇附近,低层湿位涡大值中心与过程强降水时段具有较好对应关系。

银川平原夏半年不同等级降雨水汽输送机制

全球气候变暖加速了区域水循环,改变了水汽的传输路径,了解不同等级降雨稳定同位素特征及水汽来源为水资源的利用及旱涝灾害的防治提供依据。基于2018—2020年夏半年(5—10月)采集的银川平原降雨样品,研究不同等级降雨中氢氧稳定同位素的变化特征及其二次蒸发效应,并利用后向轨迹模型及水汽通量等方法分析降雨的水汽来源及潜在蒸发源区。结果表明:银川平原夏半年不同等级降雨稳定同位素随着降雨等级的增加而偏负,小雨氘盈余(d-excess)值偏负而中雨和大雨偏正,大气降水线斜率和截距随着雨量级的增加呈现出递减的规律。二次蒸发作用的强弱随气温升高而增大,随降雨量、相对湿度和雨滴直径增大而减弱。西风水汽为银川平原夏半年降雨的主控水汽,同时小雨、中雨、大雨还分别受到陆地蒸发水汽、大西洋水汽及太平洋水汽的影响。潜在蒸发源区对小雨影响较大,主要位于研究区周边及北部、南部和东南部地区;中雨潜在蒸发源区主要分布在研究区周边地区及其西北部和东南部;大雨主要分布在研究区周边及东南部地区。

黄土区苹果园土壤剖面水、汽通量模拟研究

黄土疏松多孔且黄土区干旱少雨,汽态水可能在剖面水分运移中扮演重要角色。因此,了解非饱和带土壤水汽通量的循环运移规律,对实现干旱区水资源的可持续发展具有重要意义。基于黄土高原旱地苹果园剖面(0~200 cm)高频定位监测试验,采用水-汽-热-气耦合的STEMMUS(Simultaneous Transfer of Energy,Mass and Momentum in Unsaturated Soil)模型,探讨黄土剖面液态水和汽态水通量运移规律。结果表明:STEMMUS模型准确地再现了旱地苹果园剖面土壤水分(d介于0.81~0.98,NRMSE介于5.5%~15%)和土壤温度(d介于0.98~0.99,NRMSE介于1.4%~4.6%)的动态变化,对苹果树蒸发蒸腾量的模拟表现出良好的一致性(d介于0.92~0.96)。降雨对基质势梯度、温度梯度、液态水与汽态水通量均有显著影响,液态水与汽态水运移分别主要由基质势梯度与温度梯度驱动,且二者对土壤水分的最大补给深度在研究期内分别为100 cm和160 cm,表明土壤水通过向下的汽态水能够运移至更深层土壤。研究结果可增进对黄土剖面水分运移规律的认识。

2020—2021年沈阳地区4次短时强降水过程的大气可降水量变化对比分析

选取2020—2021年夏季沈阳地区出现的4次短时强降水过程,利用欧洲中心(ECMWF,European Center for Medium-Range Weather Forecasts)ERA5再分析资料、地基GPS(Global Position System)大气可降水量资料和常规观测资料,分析不同天气系统影响下,沈阳地区短时强降水过程中GPS水汽与水汽通量的变化特征。结果表明:短时强降水过程前,水汽累积时间的长短与相应的天气系统关系密切。副热带高压系统外围导致的强降水过程,大气可降水量(Precipitable Water Vapor,PWV)可以一直维持在较高水平,水汽增长速度可达1.1 mm·h^(-1)。此外,强降水出现时段与PWV峰值阶段相对应,但二者峰值并不完全重合;短时强降水出现时,沈阳站的大气可降水量超过38 mm;强降水结束后,PWV明显减弱。

SR型与EAP型遥相关“结合模态”对2020年江淮入梅初期强降水的影响

利用ERA5逐日再分析资料和中国气象局提供的逐日站点降水资料,分析了丝绸之路型(Silk-Road,SR)与东亚—太平洋型(East Asia–Pacific,EAP)遥相关的“结合模态”对2020年江淮梅雨入梅的影响,结果表明“结合模态”可以触发江淮流域的持续性降水。2020年6月初,负SR型(Silk-Road)和正EAP型(East Asia–Pacific)同时出现,并且位相差达到6月份最大值,二者协同作用下导致2020年入梅时间异常偏早。主要表现为:(1)负SR型引起西风急流加速,促使急流入口区南侧的江淮流域上空出现强的高层辐散。(2)负SR型有利于南亚高压东移,正EAP型有利于西太平洋副热带高压西移,二者相向而行。负SR型和正EAP型于6月9日位相差达最大,此时南亚高压和西太平洋副热带高压重叠于120°E左右,有利于江淮流域持续性降水。(3)低层东亚中、低纬度有一对与正EAP型相关的异常“气旋—反气旋”环流,使低空(20°~35°N,100°~125°E)盛行强西南气流,中纬度的偏北气流有利于干冷空气向南输送,与西南暖湿气流汇合于江淮流域上空,带来强烈的水汽辐合,也使得大气的局地上升运动更为强烈。

大气扰动分解技术在副高边缘大暴雨落区精细化分析中的应用

利用欧洲中期天气预报中心(European Centre for Medium-Range Weather Forecasts,ECMWF)再分析资料,基于大气扰动分解技术,对2012年7月华北东部两次副高边缘大暴雨事件进行扰动分析。结果表明:边界层及对流层低层扰动辐合中心与副高边缘大暴雨中心有较好地对应关系;扰动锋区和扰动比湿大值区(4 g·kg^(-1))叠加的区域与大暴雨落区相对应,与切变线类暴雨不同,副高边缘暴雨中心并不是出现在冷暖空气対峙扰动(0℃线)的位置,而是发生在扰动锋区内的暖区一侧(扰动温度0℃以南);两次过程均存在自南向北的水汽通道,且水汽在输送过程中不断得到抬升,大暴雨落区对应的扰动水汽通量散度中心分别达到-6.8×10^(-8) g·cm^(-2)·hPa^(-1)·s^(-1)和^(-1)1.9×10^(-8) g·cm^(-2)·hPa^(-1)·s^(-1),为大暴雨的形成提供了较好地水汽条件。

四川地区一次特大暴雨天气过程分析

利用四川省加密气象站逐时降水资料、FY-2G卫星TBB产品及NCEP/NCAR的1°×1°逐6 h再分析资料,对2020年8月15-18日四川地区的一次特大暴雨天气过程进行诊断分析。结果表明:此次过程具有降水强度大、范围广、持续时间长、夜雨特征明显等特征。高空影响槽东移叠加在低空低涡之上,为强降水过程发生发展提供了有利的环流背景和天气尺度动力抬升条件;西太平洋副热带高压(以下简称“副高”)稳定少动是强降水过程长时间维持的主要原因。孟加拉湾低涡槽前西南暖湿气流与副高外围偏南暖湿气流共同为此次强降水过程提供了充足的水汽。中尺度对流系统强烈发展是造成强降水的主要原因,云图TBB≤-52℃的冷云区和TBB等值线梯度极大值区与强降水落区对应关系较好,可为强降水监测预警工作提供参考。

水汽通量散度分解在一次台风暴雨中的应用

作为表征异常降水的一个重要参数,水汽通量散度(Q v)根据亥姆霍兹定理被分解为三个分量,即旋转风引起的水汽平流(Q r)、辐散风引起的水汽平流(Q d)和气流辐合辐散造成的水汽通量散度(Q div)。以2018年18号台风温比亚造成的河南商丘和江苏徐州的强降水为例,分析了水汽通量散度分解后的三个分量的时空演变。结果表明:Q v仅能得到水汽聚集的情况,分解之后的分量可以更清楚地了解不同的降水时段内具体是哪些项起到了主导因素。总的Q v贡献主要来自于Q div,而降水的增强一般与Q r的正贡献对应较好,降水的减小往往是由于Q d的抑制作用引起的,未来将应用这种水汽通量散度分解方法有效改进台风降水落区的诊断和分析。

衢州一次局地暴雨天气物理量诊断及极端性预报指标分析

利用国家一般气象站和区域自动站数据,NCEP/NCAR1°×13个再分析资料,ECMWF数值预报产品和ECMWF集合预报极端预报指数EFI产品,多普勒雷达PUP产品和衢州地形资料分析了2019年6月6日局地极端强降水形成的天气形势和物理量场。结果表明:降水前后的螺旋度和水汽通量散度对衢州西部、南部暴雨发生有较好的预测,但对极端性和降水尺度的预报不足。衢州暴雨概念模型的指标矩形中700 hPa U、V分量,850 hPa U、V分量均满足衢州局地暴雨指标,较好地预报了极端强降水的尺度。结合前2种暴雨极端性指标与物理量指标,可以提前判断此次强降水的落区和强度。

东北冷涡引发的一次区域持续性暴雨天气过程诊断分析

利用常规气象观测资料、NCEP 1°×1°逐6 h再分析资料、探空和卫星云图资料,对鞍山地区2019年7月29—30日一次区域持续性暴雨天气过程进行了降水成因分析与物理量场的诊断分析。结果表明:低空冷涡切变东移与副热带高压西伸北抬为此次强降水天气提供了大尺度环流背景,700 hPa低空急流建立了水汽输送通道,将西南暖湿空气向辽宁地区输送,为此次鞍山地区暴雨天气过程提供了较好的水汽条件;由于副高西伸北抬,暖湿气流不断与低涡后部冷空气在辽宁交汇,形成列车效应。此外,K指数较大,大气层结不稳定,具有对流降水特征。

不同水汽源地对夏季青藏高原降水过程影响的模拟研究

基于对青藏高原夏季水汽来源主要为阿拉伯海、孟加拉湾和南海三地的认知,开展了不同水汽源地对青藏高原夏季东部型和西部型降水影响的模拟研究。利用常规观测资料、NCEP/NCAR全球再分析资料以及中尺度数值模式WRF对2016年6月28日至7月2日(东部型)和2018年7月19-23日(西部型)青藏高原上两次强降水过程进行了不同水汽源地水汽含量减少的数值模拟试验,通过将阿拉伯海、孟加拉湾和南海三地的相对湿度分别由地面至100 hPa依次减少70%、60%、50%、40%、30%三组敏感性试验和控制性试验的对比,从环流场、水汽输送及降水变化等角度深入探讨不同水汽源地水汽含量的减少对高原夏季降水的影响,得到以下主要结论:(1)三个水汽源地水汽含量的减少对青藏高原夏季降水有影响且影响程度不同,其中减少孟加拉湾上空水汽,使2016年(东部型)和2018年(西部型)青藏高原夏季降水量相较于控制性试验显著下降约10%,而减少南海上空水汽对两次高原夏季降水过程影响极小。减少阿拉伯海上空水汽对高原西部型降水起促进作用,降水量相对于控制性试验增加约10%;对高原东部型降水抑制作用,使得降水量相较于控制性试验减少约5%。(2)改变孟加拉湾水汽源地的水汽条件对高原降水影响最明显,可能的原因是减少孟加拉湾上空水汽条件,使得高原南侧的低值系统有所减弱,高原上偏南风减弱,水汽输送较弱,致使高原上的降水减少。(3)在模拟初期控制性试验和三个敏感性试验的高原地区水汽收支差异不明显,但随着模拟时间的增加(约48 h后),青藏高原地区水汽收支存在明显差异,且水汽收支情况与日降水量存在明显的相关关系。