Intra-seasonal and Inter-annual variability of Bowen Ratio over rain-shadow region of North peninsular India

Intra-seasonal and inter-annual variability of Bowen Ratio (BR) have been studied over the rain-shadow region of north peninsular India during summer monsoon season. Daily grid point data of latent heat flux (LHF), sensible heat flux (SHF) from NCEP/NCAR Reanalysis for the period 1970–2014 have been used to compute daily area-mean BR. Daily grid point rainfall data at a resolution of 0.25° × 0.25° from APHRODITE’s Water Resources for the available period 1970–2007 have been used to study the association between rainfall and BR. The study revealed that BR rapidly decreases from 4.1 to 0.29 in the month of June and then remains nearly constant at the same value (≤0.1) in the rest of the season. High values of BR in the first half of June are indicative of intense thermals and convective clouds with higher bases. Low values of BR from July to September period are indicative of weak thermals and convective clouds with lower bases. Intra-seasonal and inter-annual variability of BR is found to be inversely related to precipitation over the region. BR analysis indicates that the land surface characteristics of the study region during July–September are similar to that over oceanic regions as far as intensity of thermals and associated cloud microphysical properties are concerned. Similar variation of BR is found in El Nino and La Nina years. During June, an increasing trend is observed in SHF and BR and decreasing trend in LHF from 1976 to 2014. Increasing trend in the SHF is statistically significant.

     

SPATIO-TEMPORAL VARIATION OF SENSIBLE HEAT FLUX OVER SOUTHERN CHINA

The spatio-temporal variation of surface sensible heat flux (SHF) in southern China (SC) is studied based on the data evaluated from conventional observational meteorological data. There exist prominent increasing trends in all seasonal surface sensible heat fluxes in the western SC and decreasing trends in the central-eastern part of southern China. The variations of surface sensible heat flux in all seasons are dominant on interannual time-scales. The land-air temperature difference and the near-surface wind speed are two key factors for the interannual variations of SHF, but the former is more important. The first two major anomalous patterns of SHF are presented as the region-wide in-phase anomalies and the east-west dipole anomalies, respectively, based on the EOF analysis results.     

Comparison of NCEP turbulent heat fluxes with in situ observations over the south-eastern Arabian Sea

Turbulent surface heat fluxes (latent and sensible heat) are the two most important parameters through which air–sea interaction takes place at the ocean–atmosphere interface. These fluxes over the global ocean are required to drive ocean models and to validate coupled ocean–atmosphere global models. But because of inadequate in situ observations these are the least understood parameters over the tropical Indian Ocean. Surface heat fluxes also contribute to the oceanic heat budget and control the sea surface temperature in conjunction with upper ocean stratification and ocean currents. The most widely used flux products in diagnostic studies and forcing of ocean general circulation models are the ones provided by the National Centres for Environment Prediction (NCEP) reanalysis. In this study we have compared NCEP reanalysed marine meteorological parameters, which are used for turbulent heat fluxes, with the moored buoy observation in the south-eastern Arabian Sea. The NCEP latent heat flux (LHF) and sensible heat flux (SHF) derived from bulk aerodynamic formula are also compared with that of ship and buoy derived LHF and SHF. The analysis is being carried out during the pre-monsoon and monsoon season of 2005. The analysis shows that NCEP latent as well as sensible heat fluxes are largely underestimated during the monsoon season, however, it is reasonably comparable during the pre-monsoon period. This is largely due to the underestimation of NCEP reanalysis air temperature (AT), wind speed (WS) and relative humidity (RH) compared to buoy observations. The mean differences between buoy and NCEP parameters during the monsoon (pre-monsoon) period are ~21% (~14%) for WS, ~6% (~3%) for RH, and ~0.75% (0.9%) for AT, respectively. The sudden drop in AT during rain events could not be captured by the NCEP data and, hence, large underestimations in SHF. During the pre-monsoon period, major contribution to LHF variations comes from WS, however, both surface winds and relative humidity controls the LHF variations during the monsoon. LHF is mainly determined by WS and RH during the monsoon and, WS is the main contributor during the pre-monsoon.     

Comparative Analysis of the Mechanisms of Intensified Summer Warming over Europe-West Asia and Northeast Asia since the Mid-1990s through a Process-based Decomposition Method

Previous studies have found amplified warming over Europe-West Asia and Northeast Asia in summer since the mid-1990s relative to elsewhere on the Eurasian continent, but the cause of the amplification in these two regions remains unclear. In this study, we compared the individual contributions of influential factors for amplified warming over these two regions through a quantitative diagnostic analysis based on CFRAM (climate feedback-response analysis method). The changes in surface air temperature are decomposed into the partial changes due to radiative processes (including CO2concentration, incident solar radiation at the top of the atmosphere, surface albedo, water vapor content, ozone concentration, and clouds) and non-radiative processes (including surface sensible heat flux, surface latent heat flux, and dynamical processes). Our results suggest that the enhanced warming over these two regions is primarily attributable to changes in the radiative processes, which contributed 0.62 and 0.98 K to the region-averaged warming over Europe-West Asia (1.00 K) and Northeast Asia (1.02 K), respectively. Among the radiative processes, the main drivers were clouds, CO2concentration, and water vapor content. The cloud term alone contributed to the mean amplitude of warming by 0.40 and0.85 K in Europe-West Asia and Northeast Asia, respectively. In comparison, the non-radiative processes made a much weaker contribution due to the combined impact of surface sensible heat flux, surface latent heat flux, and dynamical processes, accounting for only 0.38 K for the warming in Europe-West Asia and 0.05 K for the warming in Northeast Asia.The resemblance between the influential factors for the amplified warming in these two separate regions implies a common dynamical origin. Thus, this validates the possibility that they originate from the Silk Road pattern.     

关于亚洲夏季风爆发及北半球季节突变的物理机理的诊断分析:Ⅰ季风爆发的阶段性特征

该工作将亚洲季风区作为一个复杂的海-陆-气耦合系统,来深入考察季风区海-气、陆-气相互作用的基本事实和物理过程,探讨它们在决定亚洲季风爆发及北半球行星尺度大气环流的季节突变的物理机理。本文是系列文章的第一篇,着重研究亚洲夏季风爆发的区域性和阶段性特征,以及过渡季节热带、副热带地区海-气、陆-气相互作用的基本事实,初步分析了它们之间的联系。研究表明,热带季风对流于4月底到5月初越过赤道进入北半球,首先出现在孟加拉湾东部-中南半岛西南部地区,然后于5月中旬和6月上旬末分别出现在南海和印度半岛地区,呈阶段性爆发的特征。季风对流在孟加拉湾东部-中南半岛西南部地区爆发阶段,在大气环流变化和对流活动中心位置出现区别于南海季风和印度季风爆发的特征。通过对地表感热通量和海表潜热通量的分析,表明热带海洋上海表感热通量甚小于海表潜热通量,南海季风爆发时期印度洋上海表潜热通量显著增大,印度季风爆发后海表潜热通量的高值中心在孟加拉湾和阿拉伯海上建立起来。印度洋上低层增强的过赤道气流引起的强烈的海-气相互作用导致海表水汽的大量蒸发,并通过其输送作用,为季风对流的爆发提供了充足的水汽来源。过渡季节在副热带地区(沿27.5～37.5°N纬带上), 青藏高原和西太平洋上地(海)表感热通量和潜热通量均有迅速的季节变化性, 但趋势相反。当青藏高原上地表感热通量和潜热通量呈阶段性的显著加大, 西太平洋上海表感热通量和潜热通量迅速减小。这种大陆和海洋对大气加热的显著的季节化的差异, 影响着大气环流的季节转变。     

On the Contrasting Decadal Changes of Diurnal Surface Temperature Range between the Tibetan Plateau and Southeastern China during the 1980s–2000s

The diurnal surface temperature range(DTR) has become significantly smaller over the Tibetan Plateau(TP) but larger in southeastern China, despite the daily mean surface temperature having increased steadily in both areas during recent decades.Based on ERA-Interim reanalysis data covering 1979–2012, this study shows that the weakened DTR over TP is caused by stronger warming of daily minimum surface temperature(Tmin) and a weak cooling of the daily maximum surface temperature(Tmax); meanwhile, the enhanced DTR over southeastern China is mainly associated with a relatively stronger/weaker warming of Tmax/Tmin. A further quantitative analysis of DTR changes through a process-based decomposition method—the Coupled Surface–Atmosphere Climate Feedback Response Analysis Method(CFRAM)—indicates that changes in radiative processes are mainly responsible for the decreased DTR over the TP. In particular, the increased low-level cloud cover tends to induce the radiative cooling/warming during daytime/nighttime, and the increased water vapor helps to decrease the DTR through the stronger radiative warming during nighttime than daytime. Contributions from the changes in all radiative processes(over-2?C) are compensated for by those from the stronger decreased surface sensible heat flux during daytime than during nighttime(approximately 2.5?C), but are co-contributed by the changes in atmospheric dynamics(approximately-0.4?C) and the stronger increased latent heat flux during daytime(approximately-0.8?C). In contrast, the increased DTR over southeastern China is mainly contributed by the changes in cloud, water vapor and atmospheric dynamics. The changes in surface heat fluxes have resulted in a decrease in DTR over southeastern China.     

山西陆面过程对A1B排放情景下全球变化趋势的响应

山西地处气候过渡带,气候敏感、生态脆弱,在全球气候变暖背景下其陆面物理过程受气候波动影响十分明显。本文利用NCAR CCSM IPCC AR4陆面分量模式(CLM)20世纪气候模拟(20C3M)和21世纪SRES A1B排放情景下的模拟结果,对山西省21世纪(2001~2099年)与20世纪(1901~1999年)陆面能量和水文变量进行了对比分析。结果显示:(1)模式模拟出山西地区未来地面温度的空间及时间分布特征。未来山西省地面温度呈明显上升趋势,上升速率冬季大于夏季。空间上,增温幅度冬季自北向南递减,夏季自西向东递减;(2)未来山西省陆面各分量空间上,净辐射通量西北增幅大于东南,降水率和径流率则与其相反,潜热通量与蒸发率一致,西南部增加幅度大,土壤含水率冬夏分布相反,感热通量呈下降趋势,西南下降幅度大;时间上,净辐射通量、潜热通量均表现出不同程度的上升趋势,土壤热通量冬季上升,夏季下降;地表水循环的各分量均呈增加趋势。     

东亚夏季风边缘摆动区陆面能量时空分布规律及其与气候环境的关系

东亚夏季风边缘摆动区既是气候敏感区,也是生态脆弱区和农牧交错带,其特殊陆面能量空间分布格局和演变特征对理解该区域天气和气候变化有重要意义。然而受限于陆面观测资料缺乏,对这部分陆面特征的认识仍非常有限。通过对34 a陆面模拟集成产品的分析,发现夏季风边缘摆动区内潜热和感热通量在空间上表现出明显的过渡特征,由摆动区外的相对均衡状态进入到摆动区内的“突变转换”;陆面能量平衡具有明显的区域特征,能量平衡各分量在纬向和经向都表现出了“阶梯型”的变化。就演变而言,区域平均感热和潜热没有表现出规律性的递减或递增趋势,波动幅度在±20%以内,但在20世纪末存在一个较为明显的摆动相位转换:1997年之前夏季风边缘摆动区夏季风相对活跃,潜热通量总体高于其气候值而感热通量则低于其气候值,之后出现了相反的现象。此外,区内感热和潜热通量对气候环境干湿性质非常敏感,两者存在明显的线性关系。      

Regional trends in recent precipitation indices in China

Summary Regional characteristics of recent precipitation indices in China were analyzed from a daily rainfall dataset based on 494 stations during 1961 to 2000. Some indices such as precipitation percentiles, precipitation intensity, and precipitation persistence were used and their inter-decadal differences were shown in this study. Over the last 40 years, precipitation indices in China showed increasing and decreasing trends separated into three main regions. A decreasing trend of annual precipitation and summer precipitation was observed from the southern part of northeast China to the mid-low Yellow River valley and the upper Yangtze River valley. This region also showed a decreasing trend in precipitation intensity and a decreasing trend in the frequency of persistent wet days. On the other hand, increasing trends in precipitation intensity were found in the Xinjiang region (northwest China), the northern part of northeast China, and southeast China, mainly to the south of the mid-low Yangtze River. The indices of persistent wet days and strong rainfall have contributed to the increasing frequency of floods in southeast China and the Xinjiang region in the last two decades. Persistent dry days and weakening rainfall have resulted in the increasing frequency of drought along the Yellow River valley including North China. Regional precipitation characteristics and trends in precipitation indices indicate the climate state variations in the last four decades. A warm-wet climate state was found in northwest China and in the northern part of northeast China. A warm-dry climate state extends from the southern part of northeast China to the Yellow River valley, while a cool-wet summer was found in southeast China, particularly in the mid-low Yangtze River valley over the last two decades.     

青藏高原与周边地区近四十年区域夏季地表气温变化趋势的异同及归因分析

欧亚大陆夏季地表气温在近四十年有显著的升温趋势,本文基于ERA5再分析数据研究了1979～2019年间欧亚大陆不同区域的夏季地表气温的变化特征,并利用气候反馈响应分析方法揭示了各区域变暖原因的异同。作为全球海拔最高的大地形,青藏高原在过去四十年经历了显著的增温过程。青藏高原周边相对低海拔的地区（如北非—南欧地区、蒙古地区、东北亚地区）同样表现出明显的变暖特征,而高原南侧的南亚地区的地表气温却变化不明显。青藏高原夏季积雪融化引起的地表反照率减小使得更多短波辐射到达地表,放大高原地表增暖。北非—南欧地区增暖则主要源于大气气溶胶含量减少造成的入射短波辐射增加。同时,大气温度升高导致的向下长波辐射增强对北非—南欧地区以及蒙古地区的增暖都有显著贡献。此外,东北亚地区云的减少是造成其地表增暖最主要的过程,而南亚地区则是水汽增加和感热通量减少造成的增温与云和气溶胶增加造成的降温相抵消,因而温度变化幅度不大。     

东北地区作物生长季降水异常特征分析

采用东北地区52个测站1951-2000年4-9月降水量资料,对东北地区作物生长季降水异常进行了诊断分析。结果表明：东北地区生长季降水存在减少趋势,旱灾略多于涝灾,主要存在3-7、12和30a左右的周期变化;可划分为7个降水异常区,其中相邻的3个区（东北中部、南部和东部的大范围地区）有变旱倾向,辽西地区的旱涝灾害最频繁。根据降水减少的趋势,提倡发展旱作农业和节水农业。     

北京郊区草地夏季能量收支平衡的数值模拟

北京郊区地表能量分配可能影响北京地区的天气和气候。为了进一步检验陆面过程模式对北京郊区具有代表性的稀疏草地地表能量分配的模拟能力,利用原版和改进版简化生物圈模式(SiB2,Simple Biosphere Model 2)模拟了2010年7月22日-8月5日期间北京郊区阳坊镇坦克打靶场草地的辐射平衡、能量收支以及地表热通量。并将模拟结果与实际测量的数据进行对比,结果表明:1)原版SiB2低估净辐射11.32%,改进版SiB2则低估净辐射5.81%,主要原因是改进版SiB2更新了土壤热传导率计算方法,从而提高了土壤温度(包括地表温度)模拟结果的精度,进而改善了地表向上的长波辐射模拟结果的准确性;2)改进版SiB2同时改善了感热通量和潜热通量的模拟结果,但是原版SiB2和改进版SiB2均低估了土壤热通量。     

海洋环流对全球增暖趋势的调制：基于FGOALS-s2的数值模拟研究

在工业革命以来全球长期增暖趋势背景下,全球平均表面气温还同时表现出年代际变化特征,二者叠加在一起使得全球平均气温在某些年份增暖相对停滞(如1999～2008年)或者增暖相对较快(如1980～1998年).利用中国科学院大气物理研究所大气科学和地球流体力学数值模拟国家重点实验室(LASG)发展的耦合气候模式FGOALS-s2历史气候和典型路径浓度(RCPs)模拟试验结果研究了可能造成全球增暖的年代际停滞及加速现象的原因,特别是海洋环流对全球变暖趋势的调制作用.该模式模拟的全球平均气温与观测类似,即在长期增暖趋势之上,还叠加了显著的年代际变化.对全球平均能量收支分析表明,模拟的气温年代际变化与大气顶净辐射通量无关,意味着年代际表面气温变化可能与能量在气候系统内部的重新分配有关.通过对全球增暖加速和停滞时期大气和海洋环流变化的合成分析及回归分析,发现全球表面气温与大部分海区海表温度(SST)均表现出几乎一致的变化特征.在增暖停滞时期,SST降低,更多热量进入海洋次表层和深层,使其温度增加;而在增暖加速时期,更多热量停留在表层,使得大部分海区SST显著增加,次表层海水和深海相对冷却.进一步分析表明,热带太平洋表层和次表层海温年代际变化主要是由于副热带—热带经圈环流(STC)的年代际变化所致,然后热带太平洋海温异常可以通过风应力和热通量强迫作用引起印度洋、大西洋海温的年代际变化.在此过程中,海洋环流变化起到了重要作用,例如印度尼西亚贯穿流(ITF)年代际异常对南印度洋次表层海温变化起到关键作用,而大西洋经圈翻转环流(AMOC)则能直接影响到北大西洋深层海温变化.     

Future projections of the surface heat and water budgets of the Mediterranean Sea in an ensemble of coupled atmosphere–ocean regional climate models

Within the CIRCE project “Climate change and Impact Research: the Mediterranean Environment”, an ensemble of high resolution coupled atmosphere–ocean regional climate models (AORCMs) are used to simulate the Mediterranean climate for the period 1950–2050. For the first time, realistic net surface air-sea fluxes are obtained. The sea surface temperature (SST) variability is consistent with the atmospheric forcing above it and oceanic constraints. The surface fluxes respond to external forcing under a warming climate and show an equivalent trend in all models. This study focuses on the present day and on the evolution of the heat and water budget over the Mediterranean Sea under the SRES-A1B scenario. On the contrary to previous studies, the net total heat budget is negative over the present period in all AORCMs and satisfies the heat closure budget controlled by a net positive heat gain at the strait of Gibraltar in the present climate. Under climate change scenario, some models predict a warming of the Mediterranean Sea from the ocean surface (positive net heat flux) in addition to the positive flux at the strait of Gibraltar for the 2021–2050 period. The shortwave and latent flux are increasing and the longwave and sensible fluxes are decreasing compared to the 1961–1990 period due to a reduction of the cloud cover and an increase in greenhouse gases (GHGs) and SSTs over the 2021–2050 period. The AORCMs provide a good estimates of the water budget with a drying of the region during the twenty-first century. For the ensemble mean, he decrease in precipitation and runoff is about 10 and 15% respectively and the increase in evaporation is much weaker, about 2% compared to the 1961–1990 period which confirm results obtained in recent studies. Despite a clear consistency in the trends and results between the models, this study also underlines important differences in the model set-ups, methodology and choices of some physical parameters inducing some difference in the various air-sea fluxes. An evaluation of the uncertainty sources and possible improvement for future generation of AORCMs highlights the importance of the parameterisation of the ocean albedo, rivers and cloud cover.     

Seasonal variability of air-sea fluxes in two contrasting basins of the North Indian Ocean

Latent Heat Flux (LHF) and Sensible Heat Flux (SHF) are the two important parameters in air-sea interactions and hence have significant implications for any coupled ocean-atmospheric model. These two fluxes are conventionally computed from met-ocean parameters using bulk aerodynamic formulations; or the Coupled Ocean Atmosphere Response Experiment (COARE) bulk flux algorithms. Here COARE 3.5 algorithm is used to estimate the heat flux from two Ocean Moored Buoy Network for northern Indian Ocean (OMNI) buoy met-ocean observations in Arabian Sea (AS) and the Bay of Bengal (BoB). The AS and BoB are two ocean basins which are situated in same latitudinal range, but experience drastically differing in their met-ocean conditions, especially during the monsoon seasons. In this study, we have computed and compared the LHF and SHF at two different buoy locations in the AS and BoB and analysed their variability during three different seasons from November 2012 to September 2013. Additionally, 20 years (1998–2017) of Objectively Analysed (OA) Flux data sets collocated with the OMNI buoy locations were also utilised to the analyse the long period seasonal variabilities. The flux terms show strong seasonal variability with several peaks during the monsoon seasons in both the ocean basins. LHF varies directly with wind speed (WS) and inversely with relative humidity (RH). The correlation of LHF with WS is greater than 0.7 and RH is nearly -0.6 with few exceptions during pre-monsoon season in the AS and southwest monsoon in the BoB. However, SHF is less correlated with WS (∼0.3 to 0.5). The difference of sea surface temperature and air temperature (denoted as SST-AT) plays a significant role in determining SHF with a correlation greater than 0.6 in both the basins.     

Impact of clouds on the surface radiation balance of the Arctic Ocean

Summary The relationship between clouds and the surface radiative fluxes over the Arctic Ocean are explored by conducting a series of modelling experiments using a one-dimensional thermodynamic sea ice model. The sensitivity of radiative flux to perturbations in cloud fraction and cloud optical depth are determined. These experiments illustrate the substantial effect that clouds have on the state of the sea ice and on the surface radiative fluxes. The effect of clouds on the net flux of radiation at the surface is very complex over the Arctic Ocean particularly due to the presence of the underlying sea ice. Owing to changes in surface albedo and temperature associated with changing cloud properties, there is a strong non-linearity between cloud properties and surface radiative fluxes. The model results are evaluated in three different contexts: 1) the sensitivity of the arctic surface radiation balance to uncertainties in cloud properties; 2) the impact of interannual variability in cloud characteristics on surface radiation fluxes and sea ice surface characteristics; and 3) the impact of climate change and the resulting changes in cloud properties on the surface radiation fluxes and sea ice characteristics.With 11 Figures     

夏季我国干旱、半干旱区陆面过程能量平衡及其局地大气环流

利用NCEP资料分析得出,夏季我国干旱,半干旱区在整个欧亚大陆上是陆面感热通量最强的地方,与此对应的陆面潜热通量则最弱.陆面所接收的太阳短波辐射主要以感热和长波辐射的能量形式释放.该区降水量很少,降水量的年际变率也很弱;因此,该区的陆面热量通量都显出很弱的年际变率;然而,这些通量的年代际变率信号则比较显著.我国干旱、半干旱区大气环流的热力过程与其陆面过程特征密切相关.该区对流层大气的辐射冷却很强,达-3 K d-1.由于缺乏水汽和上升运动,大尺度凝结加热率、深对流加热率、浅对流加热率都非常弱.因此,600hPa以上的大气以绝热下沉加热来平衡辐射冷却;600hPa以下,陆面感热引起的垂直扩散加热率非常强,多达8 K d-1,它除了平衡辐射冷却以外还制造对流层低层的对流运动,以绝热上升冷却来平衡多余的垂直扩散加热.总之,我国干旱、半干旱区的陆面过程特征决定了该区大气运动的特殊垂直结构,即对流层低层对流上升运动及其上层的下沉运动.我国干旱、半干旱区陆面能量平衡及其局地大气环流的年代际变率,是全球气候系统年代际变率的必然结果.     

基于SPI指数的当前及未来中国东北地区干旱时空演变特征分析

基于降水量历史观测数据和气候模式预估数据,采用标准化降水量指数(Standandized Precipitation Index, SPI)识别干旱事件,从干旱发生的频率和强度特征分析其危险性,研究东北地区当前及未来不同气候变化情景下干旱时空变化特征。结果显示:(1)bcc-csm1-1对东北地区降水的模拟效果较好;(2)东北地区年降水量东南多西部少,未来远期较近期降水增幅更为明显,中、西部地区降水增幅略高于其他地区;(3)仅在RCP8.5情景下未来近期研究区中部地区干旱有加重的趋势,主要源于该时段夏季降水的变化,其余时段皆呈干旱危险性减弱。     

全球变暖趋缓背景下辽宁夏季降水变化及水汽输送特征

利用中国气象数据网提供的中国地面气候资料日值数据集（V3.0）中的降水数据以及ERA-Interim逐月再分析资料对全球变暖趋缓背景下（1998年后）辽宁夏季降水变化特征及水汽输送对其的影响进行研究。结果表明：全球增暖减缓背景下,辽宁夏季降水量存在一定的增加趋势,但趋势较弱,其中辽宁南部降水的增加趋势较其他地区显著,对辽宁整体降水变化的贡献程度相对较高。辽宁南北边界的夏季水汽通量与降水量呈现高度的正相关性。其中,南边界的相关性程度最显著。辽宁上空纬向水汽净输入量对降水的贡献较小,经向水汽通量对于降水的贡献较纬向高且其高值区主要位于辽宁东部及南部地区的对流层低层,对当地降水存在影响。辽宁南部对流层整层的经向水汽通量与辽宁降水量存在显著正相关,通过分析大气环流背景场的变化对辽宁经向水汽输送的影响分析,西太平洋副热带高压脊线的逐渐北移是造成辽宁经向水汽通量增加的重要因素,从而直接影响辽宁降水量的变化趋势,导致辽宁夏季降水在全球变暖减缓背景下存在一定的增加趋势。     

Variability of surface characteristics and energy flux patterns of sunn hemp (Crotalaria juncea L.) under well-watered conditions

There is not much information in the literature about the energy partitioning and micrometeorological features of sunn hemp. Therefore, in this study, the variations in the energy-balance components and plant characteristics such as aerodynamic and surface conductance, crop coefficient, albedo, short- and long wave down- and upward radiation have been measured and estimated for the time period from August to October 2004 over an irrigated sand field at the Arid Land Research Center in Tottori, Japan. The Bowen ratio energy-balance method was used to calculate the partitioning of heat fluxes of sunn hemp. The Bowen ratio values at the first growing stages in August were found to be higher than the Bowen ratio values at the latest growing stages in September and October because of the heavy rain and high soil-water content. The daytime averaged Bowen ratio was 0.19. During the measurement period, the daytime average net radiation, and soil, latent and sensible heat fluxes were approximately 231, 28, 164, and 39 W m^–2, respectively. The net radiation and soil heat flux showed decreasing trends from the beginning to the end of the experiment period due to the atmospheric and crop growth conditions. The daytime averages of aerodynamic and surface conductance for sunn hemp were around 31 and 17 mm s^–1, respectively. Also, the daytime average albedo of sunn hemp was around 19%. Finally, the high precipitation amount due to typhoons, high soil-water content, low available energy and low vapor-pressure deficit lead to decreasing trend of the energy fluxes during the generative phase of sunn hemp.