EY60回声探测仪在青海湖鱼类资源量评估中的应用   总被引：4，自引：1，他引：3  

谭细畅  史建全  张宏  陶江平  杨建新  祁洪芳  李新辉 《湖泊科学》2009,21(6):865-872

2006年8月16-18日通过使用回声探测仪(Simrad公司EY60型,200kHz换能器)对青海湖的鱼类资源进行了探测评估.结果表明:青海湖裸鲤(Gymnocypris przewalski)水平分布具不均匀性,有小型鱼群聚集现象;在不同的设定分区,鱼类密度在0.168-12.8ind./1000m~3之间,均值为1.16 ind./1000m~3;布哈河口鱼类较为密集,密度最大值为12.8ind./1000m~3.初步估算青海湖裸鲤达可捕规格(体长大于20cm)个体数量为6.5×10~7ind.,95%置信度区间为35.6×10~7-118.4×10~7ind.,应用资源密度体积法估算青海湖裸鲤的可捕资源量约为1 5275t.探测实验还证实,EY60回声探测仪在青海湖中进行鱼类资源评估时探测效果良好,分析软件Sonar5可以对鱼类个体自动识别、计数,便于进行鱼类资源量评估.  相似文献   

全球海洋高频波动主振荡周期的纬向带状分布特征   总被引：2，自引：2，他引：0  

乔方利  TAL Ezer  袁业立 《海洋学报》2004,26(3):1-7

基于1992年10月至2000年12月的TOPEX/Poseidon和ERS-1/2卫星高度计资料,分析了周期短于150d的高频波动及其能量的空间分布特征.在功率谱密度计算基础上,分析特定频段所含能量占周期短于150d的高濒波动总能量的百分比,发现该频段最强振荡(下文称主振荡)所对应的周期从近赤道的1个月逐步增加至南北纬30°附近的4个月,进一步分析表明主振荡周期的这种变化是连续的,与西向行星Rossby波的相速随纬度增加而变慢相对应.主振荡所对应的周期在全球海洋中呈显著的带状分布.进而表明在14°N(S)附近60d周期的振荡除通常所认为的由于潮汐混淆所造成的虚假信号之外,主要是行星Rossby波形态的真实信号.  相似文献   

Relativistic Fe Kα features in the XMM‐Newton spectrum of the intermediate Seyfert galaxy 4U 1344‐60     

E. Jimnez‐Bailn  E. Piconcelli  M. Snchez‐Portal  M. Guainazzi  A. Martocchia  M. Motch  A. Schroder  S. Bianchi  G. Matt 《Astronomische Nachrichten》2006,327(10):1059-1062

We present the analysis of optical and X‐ray XMM‐Newton data of the source 4U 1344‐60. On the basis of the optical data we propose to classify 4U 1344‐60 as a Seyfert 1.5 galaxy and we measured a redshift value z = 0.012 ± 0.001. The observed X‐ray spectrum is complex. The continuum emission can be described as a power law obscured by two neutral absorption components. 4U 1344‐60 exhibits a broad and skewed iron line at 6.4 keV most likely originated in a few gravitational radius of an accretion disc. The analysis also reveals the presence of two narrow emission line‐like features at ∼4.9 keV and ∼5.3 keV. Assuming that hot spots on the surface of the accretion disc, orbiting very close to the black hole is responsible of these emission lines, the accretion disc would present an inclination of 20° and the active regions would be located in the 6–10 R _g radius range. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

Short time-scale wind forced variability in the Río de la Plata Estuary and its role on ichthyoplankton retention     

C.G. Simionato  A. Berasategui  V.L. Meccia  M. Acha  H. Mianzan 《Estuarine, Coastal and Shelf Science》2008

The Río de la Plata Estuary presents a strong bottom salinity front located over a submerged shoal. Apparently favored by retention processes, it is a spawning ground for several coastal fishes. This estuary is very shallow and essentially wind driven and, moreover, in time scales relevant to biota, estuarine circulation is wind dominated and highly variable. Two intriguing questions are, therefore, how this system can favor retention and what the involved mechanisms are. This paper qualitatively explores mechanisms involved in the estuary where retention is favored applying numerical simulations in which neutral particles – simulating fish eggs and early larvae – are released along the bottom frontal zone and tracked for different wind conditions. Results suggest that retentive features can be a consequence of estuarine response to natural wind variability acting over bathymetric features. For winds from most directions, particles either remain trapped near their launching position or move northeastward to southwestward along the shoal. As alternation of winds that favor along-shoal motion is the dominant feature of wind variability in the region, a retentive scenario results from prevailing wind variability. Additionally, winds that tend to export particles with a poor chance of being restored to the front are neither frequent nor persistent. Results show, therefore, that physical forcing alone might generate a retentive scenario at the inner part of this estuary. The physical retention mechanism is more effective for bottom than for surface launched particles. Wind statistics indicate that the proposed mechanism has different implications for retention along the seasons. Spring is the most favorable season, followed by summer, when particles would have a larger propensity to reach the southern area of the estuary (Samborombón Bay). Fall and winter are increasingly less favorable. All these features are consistent with patterns observed in the region in organisms having different life history traits.  相似文献   

热带大气季节内振荡和ENSO的相互关系   总被引：30，自引：2，他引：30       下载免费PDF全文

李崇银  周亚萍 《地球物理学报》1994,37(1):17-26

通过观测资料的分析和数值模拟，研究了热带大气季节内振荡与ＥＮＳＯ的相互关系．一方面，在Ｅ１Ｎｉｎｏ事件发生之前，热带大气季节内振荡（尤其是在赤道中西太平洋地区）异常偏强，通过海一气相互作用它可能是Ｅ１Ｎｉｎｏ的一种重要激发机制．同时，赤道中西太平洋地区大气季节内振荡的异常加强同东亚中高纬度地区３０-６０天振荡的加强和强东亚冬季风有关．另一方面，ＥＮＳＯ对热带大气季节内振荡也有重要影响，在Ｅ１Ｎｉｎｏ期间，热带大气季节内振荡明显减弱；其结构明显趋于正压性．  相似文献   

COMPARISON STUDY ON THE INTRASEASONAL VARIATIONS IN CIRCULATIONS AND PRECIPITATION MODULATED BY THE TROPICAL CYCLOGENESIS OVER SOUTH CHINA SEA–WESTERN PACIFIC DURING GUANGDONG FLOODING PERIOD     

李春晖  万齐林  郑彬 《热带气象学报(英文版)》2011,17(4):363-374

Based on tropical cyclone datasets from Shanghai Typhoon Institute of China Meteorological Administration, the National Centers for Environmental Prediction (NCEP, USA) reanalysis data and the rainfall records from 743 stations in China, the impacts of cyclogenesis number over the South China Sea and the western Pacific are studied on the 30-60-day oscillations in the precipitation of Guangdong during the flooding period. The year with more-than-normal (less-than-normal) tropical cyclogenesis is defined as a ‘high year’ (‘low year’). In light of the irregular periodic oscillations, the method used to construct the composite life cycle is based on nine consecutive phases in each of the cycles. Phases 1, 3, 5, and 7 correspond to, respectively, the time when precipitation anomalies reach the minimum, a positive transition (negative-turning-to-positive) phase, the maximum, and a negative transition phase. The results showed that the precipitation of the 30-60-day oscillations is associated with the interaction between a well-organized eastward propagation system from the Arabian Sea/Bay of Bengal and a westward-propagating system (with cyclonic and anticyclonic anomalies in the northwest-southeast direction) from the South China Sea to western Pacific during the high years, whereas the precipitation is affected during a low year by the circulation over the South China Sea and western Pacific (with cyclonic and anticyclonic anomalies in the northeast-southwest direction). During the high year, the warm and wet air mass from the ocean to the west and south are transported to Guangdong by westerly anomalies and an enclosed latitudinal cell, which ascends in the Northern Hemisphere low latitudes and descends in the Southern Hemisphere low latitudes. During the low year, the warm and wet air mass from the ocean to the south is transported to Guangdong by southwesterly wind anomalies and local ascending movements. Because the kinetic energy, westerly, easterly shift, vertical velocity and vapor transportation averaged over (109–119° E, 10–20° N) is stronger in high years than those in low years, the precipitation of the 30-60-day oscillations in Guangdong is higher in high years than that in low years.  相似文献   

基于机载LiDAR数据的鄱阳湖地区高精度DEM生产研究     

李明  孙彬淳  张俊  胡芬 《测绘与空间地理信息》2016,(3)

大面积湖泊周边地势平坦,利用航空摄影等常规手段实现此类地区精细DEM生产,需要依靠外业控制和大量人工编辑,作业周期长,成本高。本文结合国家基础航空摄影项目,基于ALS60完成了鄱阳湖地区大面积机载LiDAR数据的获取及预处理,并通过地面检校和精度验证,对传感器的系统误差进行修正,在此基础上对点云数据进行精细化处理及DEM高效生产,产品精度满足测绘相关规范要求。该项目的成功开展,为基于航空新型技术手段的大面积湖泊周边等常规作业困难地区的高精度测绘提供了借鉴。  相似文献   

Meridional Propagation of the 30- to 60-day Variability of Precipitation in the East Asian Subtropical Summer Monsoon Region: Monitoring and Prediction     

Jinhai He  Hua Chen 《大气与海洋》2015,53(2):251-263

The meridional propagation of the 30- to 60-day intraseasonal variability (ISV) of precipitation in the East Asian subtropical summer monsoon (EASSM) region and its monitoring and prediction are investigated in the current study. Based on a multivariate empirical orthogonal function (MV-EOF) analysis of precipitation and relative vorticity at 700?hPa in East Asia, a bivariate index referred to as the EASSM-ISV index is designed using the two leading MV-EOF modes, with the objective of real-time monitoring of the 30- to 60-day variability of precipitation in the EASSM region. It is found that this index, with its eight phases, can explain the meridional propagation of the 30- to 60-day ISV in precipitation and circulation in the EASSM region. Based on a singular value decomposition technique, a statistical forecast model is developed in which the EASSM-ISV indices from the preceding five pentads are used to predict the indices in five pentads in the future. Meanwhile, the indices are used to predict the meridional propagation of the 30- to 60-day precipitation anomaly in the EASSM region. This model thus provides a useful tool for intraseasonal prediction of precipitation during the rainy season in China.  相似文献   

ZONALLY SYMMETRICAL EKMAN-CISK MECHANISM AND 30—60-DAY LOW FREQUENCY OSCILLATION NEAR THE EQUATOR     

薛洪斌  钟中  薛峰 《Acta Meteorologica Sinica》2002,(4)

Based on the baroclinic semi-geostrophic model,the effects of zonally symmetrical Ekman-CISK mechanism on the characteristics of 30—60-day low frequency oscillation(LFO)near theequator are investigated.It is found that the theoretical results are in good agreement with theobservational features of LFO.Besides,the planetary-scale LFO with the period of 30—60 d couldbe triggered by the Ekman-CISK mechanism,and the growth rate of perturbation with wavenumber 1 is in order of O (10~(-6)s~(-1)).The zonal propagation of LFO and the correspondinglongitudinal-height structure of physical quantities are also discussed in detail.  相似文献   

太平洋北赤道流区上层海洋季节内振荡及斜压稳定性   总被引：6，自引：0，他引：6       下载免费PDF全文

刘秦玉  潘爱军  刘征宇 《海洋与湖沼》2003,34(1):94-100

根据全球高分辨率的海洋环流模式 (POCM)的数值模拟结果 ,发现北赤道流区上层海洋流的季节内变化是以准 60天振荡为主 ,该准 60天振荡的振幅有年际变化。利用 2 .5层海洋模式 ,确定了NEC区纬向Rossby波解的频散关系。该关系表明 :北赤道流区行星波和波长小于 5 70km的Rossby波都为稳定波 ;波长小于 2 0 0 0km ,大于 5 70km的Rossby为不稳定波 ;最不稳定波的相速度和波长分别为 - 0 .1 45m·s- 1 和 785km。斜压不稳定是北赤道流区上层海洋准 60天振荡的主要形成机制  相似文献