An Assessment of ENSO Stability in CAMS Climate System Model Simulations

We present an overview of the El Ni?o–Southern Oscillation(ENSO) stability simulation using the Chinese Academy of Meteorological Sciences climate system model(CAMS-CSM). The ENSO stability was quantified based on the Bjerknes(BJ) stability index. Generally speaking, CAMS-CSM has the capacity of reasonably representing the BJ index and ENSO-related air–sea feedback processes. The major simulation biases exist in the underestimated thermodynamic damping and thermocline feedbacks. Further diagnostic analysis reveals that the underestimated thermodynamic feedback is due to the underestimation of the shortwave radiation feedback, which arises from the cold bias in mean sea surface temperature(SST) over central–eastern equatorial Pacific(CEEP). The underestimated thermocline feedback is attributed to the weakened mean upwelling and weakened wind–SST feedback(μ_a) in the model simulation compared to observation. We found that the weakened μ_a is also due to the cold mean SST over the CEEP.The study highlights the essential role of reasonably representing the climatological mean state in ENSO simulations.     

NUMERICAL PREDICTION OF AN EXTREME RAINSTORM OVER THE PEARL RIVER DELTA REGION ON 7 MAY 2017 BASED ON WRF-ENKF

An ensemble Kalman filter based on the Weather Research and Forecasting Model (WRF-EnKF) is used to explore the effectiveness of the assimilation of surface observation data in an extreme local rainstorm over the Pearl River Delta region on 7 May 2017. Before the occurrence of rainstorm, the signals of weather forecasts in this case are too weak to be predicted by numerical weather model, but the surface temperature over the urban area are high. The results of this study show that the wind field, temperature, and water vapor are obviously adjusted by assimilating surface data of 10-m wind, 2-m temperature, and 2-m water vapor mixing ratio at 2300 BST 6 May, especially below the height of 2 km. The southerly wind over the Pearl River Delta region is enhanced, and the convergence of wind over the northern Guangzhou city is also enhanced. Additionally, temperature, water vapor mixing ratio and pseudoequivalent potential temperature are obviously increased over the urban region, providing favorable conditions for the occurrence of heavy precipitation. After assimilation, the predictions of 12-h rainfall amount, temperature, and relative humidity are significantly improved, and the rainfall intensity and distribution in this case can be successfully reproduced. Moreover, sensitivity tests suggest that the assimilation of 2-m temperature is the key to predict this extreme rainfall and just assimilating data of surface wind or water vapor is not workable, implying that urban heat island effect may be an important factor in this extreme rainstorm.     

一次东北冷涡下槽后强风与飑线后向入流演变及成因分析

本文利用NCEP分析资料、多普勒雷达观测资料、常规气象观测资料以及数值模拟结果,对2016年7月30日发生在华北、辽宁附近的一次强飑线过程中后向入流的演变及成因进行研究。结果表明,此次飑线发生在中纬度新生冷涡槽前,低层有水汽辐合区和地面辐合线对应,且过程中伴有较强的对流有效位能释放。飑线后部中层(冷涡槽后)一直存在α中尺度西风大值带,此大风速带造成了上下层相反的水平涡度,并形成喇叭形环流结构,该结构不同于经典飑线结构。飑线后部水平方向上水平涡度分布不均匀,并形成水平涡度旋度上正下负的分布,即导致中层强风区上部上升运动、下部下沉运动,该下沉运动引发飑线中的后向入流和低层强风速带形成。在中层,飑线的后部边缘始终有较强的风速大值带伴随飑线的发展,该大值带的形成与对流强弱和非热成风涡度有关,对流过程中低层非热成风涡度为负,中上层非热成风涡度为正,导致飑线后部中层西风加速和低层西风减速,有利于后向入流的发展和飑线的维持,当对流减弱时,非热成风涡度与后向入流均减弱。文中给出了后向入流形成演变的概念模式。     

国家数字地震台数据处理研究

为了突显被淹没在噪声背景下的有用信息,对国家数字地震台的数据处理方法进行了研究,并用Matlab程序给出了详细的设计过程。     

额济纳绿洲沙尘暴沉积特征

1 Introduction Oases are unique ecosystems and important residences for our ancestors in arid and semiarid regions of the world, and have deeply been imprinted by human actions, such as Jericho oasis of Jordan Valley, Jarmo oasis of the Euphrates River an…     

安徽齐云山丹霞地貌成因

According to the study of some local scholars (Peng Hua et al., 2000), over 400 sites of Danxia landform have been already discovered in China. Chen Guoda (1935), Zeng Zhaoxuan et al. (1978), Huang Jin et al. (1992; 1994; 1996) and Peng Hua et al. (1998; …     

Small target extraction based on independent component analysis for hyperspectral imagery

IntroductionFeature extraction or transformation is a key stepfor target detection in hyperspectral imagery. Thepurpose is to transform the high-dimensional imageinto low-dimensional image series so that the differ-ences between the targets and the backgr…     

龙骨坡遗址第7水平层石制品新材料

文章记述并分析了20世纪90年代后期重庆巫山龙骨坡遗址出土于第7水平层的16件石制品,包括若干各具特色的工具类型,如原型手镐、原型薄刃斧、大型尖刃器、直刃砍砸器、凸刃砍砸器、长刃石刀、短刃石刀、刮削器、凿刃器等,反映出石器制作者明确的工作目标和为了达到目标所经历的一个又一个中间过程;说明了当时的人类对工具制作的具体需求和适当利用自然环境的事实。研究证据还体现了大约200万年前华南早期人类工具类型的多样性与特殊性,标志着中国早期人类在当时阶段所达到的技术发展水平。龙骨坡遗址很可能是东亚早期人类文化的一个发祥地。     

Effects of soil conservation practices on soil erosion and the size selectivity of eroded sediment on cultivated slopes

Soil conservation practices can greatly affect the soil erosion process, but limited information is available about its influence on the particle size distribution(PSD) of eroded sediment, especially under natural rainfall. In this study, the runoff, sediment yields, and effective/ultimate PSD were measured under two conventional tillage practices, downhill ridge tillage(DT) and plat tillage(PT) and three soil conservation practices, contour ridge tillage(CT), mulching with downhill ridge tillage(MDT), and mulching with contour ridge tillage(MCT) during 21 natural rainfall events in the lower Jinsha River. The results showed that(1) soil conservation practices had a significant effect on soil erosion. The conventional tillage of DT caused highest runoff depth(0.58 to 29.13 mm) and sediment yield(0.01 to 3.19 t hm-2). Compared with DT, the annual runoff depths and sediment yields of CT, MDT and MCT decreased by 12.24%-49.75% and 40.79%-88.30%, respectively.(2) Soil conservation practices can reduce the decomposition of aggregates in sediments. The ratios of effective and ultimate particle size(E/U) of siltand sand-sized particles of DT and PT plots were close to 1, indicating that they were transported as primary particles, however, values lower/greater than 1 subject to CT, MDT and MCT plots indicated they were transported as aggregates. The ratios of E/U of claysized particles were all less than 1 independently of tillage practices.(3) The sediments of soil conservation practices were more selective than those of conventional tillage practices. For CT, MDT and MCT plots, the average enrichment ratios(ERs) of clay, silt and sand were 1.99, 1.93 and 0.42, respectively, with enrichment of clay and silt and depletion of sand in sediments. However, the compositions of the eroded sediments of DT and PT plots were similar to that of the original soil. These findings support the use of both effective and ultimate particle size distributions for studying the size selectivity of eroded sediment, and provide a scientific basis for revealing the erosion mechanism in the purple soil area of China.     

海洋沉积物孔隙水中阴阳离子含量的离子色谱法分析方法

分别采用Metrosep A Supp4-250型阴离子柱和Metrosep C 2-150型阳离子柱,以1.8 mmol/L Na2CO3 1.7 mmol/L NaHCO3和4 mmol/L酒石酸 0.75 mmol/L吡啶二羧酸为阴阳离子淋洗液,用离子色谱仪来测定海洋沉积物孔隙水中阴离子Cl-、Br-和SO42-浓度和阳离子Na 、NH4 、K 、Ca2 、Mg2 的浓度。特别是针对高Cl-和高Na 背景下Br-和NH4 的测定做了专门分析,得到了较理想的结果,建立了一套离子色谱法测定海洋沉积物孔隙水中常见的阴阳离子含量的实验方法。