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1.
The Asian Seas International Acoustics Experiment (ASIAEX) included two major field programs, one in the South China Sea (SCS) and the other in the East China Sea (ECS). This paper summarizes results from the work conducted during April and May 2000 and 2001 over the continental shelf and slope in the northeastern South China Sea, just east of Dongsha Island (Pratis Reef). The primary emphasis of the field program was on water-column variability and its impact on acoustic propagation loss. The reader is steered to the appropriate paper within this Special Issue when more information on a specific topic is desired.  相似文献   

2.
The wide-band source (WBS) signals measured in the Asian Seas International Acoustics Experiment (ASIAEX) in the East China Sea (ECS) were used to invert for geoacoustic parameters. Sound speed and density were inverted using the matched-field processing method combined with the vertical reflection coefficients and sea-bed attenuation coefficients were inverted from the vertical correlation data. For a half infinite liquid sea-bottom model, the inverted equivalent bottom sound speed is 1610/spl plusmn/12 m/s and the bottom density is 1.86 g/cm/sup 3/. The inverted attenuation coefficients are well described by a nonlinear relationship of the form /spl alpha//sub b/=0.28f/sup 1.58/ dB/m (f is in units of kilohertz) in the frequency range of 100-600 Hz.  相似文献   

3.
This paper discusses the results of geoacoustic inversion carried out using explosive charge data from the Asian Seas International Acoustic Experiment (ASIAEX) East China Sea (ECS) Experiment. A multifrequency incoherent matched-field inversion processor and a genetic algorithm (GA) are used for the inversion. A multistep matched field inversion approach is presented, which makes use of the varying sensitivities of wave fields at various frequencies to reduce the inversion problem into a sequence of smaller inversions with fewer unknowns to estimate at each stage. Different parameters are estimated using data at different frequencies according to their sensitivities. Inversion results for different areas in the ECS region are summarized and compared with core data.  相似文献   

4.
A case study of internal solitary wave propagation during ASIAEX 2001   总被引：1，自引：0，他引：1  
During the recent Asian Seas International Acoustics Experiment (ASIAEX), extensive current meter moorings were deployed around the continental shelf-break area in the northeastern South China Sea. Thirteen RADARSAT SAR images were collected during the field test to integrate with the in situ measurements from the moorings, ship-board sensors, and conductivity/temperatire/depth (CTD) casts. Besides providing a synoptic view of the entire region, satellite imagery is very useful for tracking the internal waves, locating surface fronts, and identifying mesoscale features. During ASIAEX in May 2001, many large internal waves were observed at the test area and were the major oceanic features studied for acoustic volume interaction. Based on the internal wave distribution maps compiled from satellite data, the wave crests can be as long as 200 km with an amplitude of 100 m. Environmental parameters have been calculated based on extensive CTD casts data near the ASIAEX area. Nonlinear internal wave models have been applied to integrate and assimilate both synthetic aperture radar (SAR) and mooring data. Using SAR data in deep water as an initial condition, numerical simulations produced the wave evolution on the continental shelf and compared reasonably well with the mooring measurements at the downstream station. The shoaling, turning, and dissipation of large internal waves at the shelf break have been studied and are very important issues for acoustic propagation.  相似文献   

5.
A high-resolution, regional, numerical-model-based, real-time ocean prediction system for the northern South China Sea, called the Northern South China Sea Nowcast/Forecast System (NSCSNFS), has been used to investigate subtidal mesoscale flows during the time period of the Asian Seas International Acoustic Experiment (ASIAEX) field programs. The dynamics are dominated by three influences; 1) surface wind stress, 2) intrusions of the Kuroshio through Luzon Strait, and 3) the large-scale cyclonic gyre that occupies much of the northern South China Sea. Each component primarily drives currents in the upper ocean, so deep currents are rather weak. Wind stress is especially effective at forcing currents over the shallow China shelf. The Kuroshio intrusion tends to flow westward until it meets the northern edge of the large-scale cyclonic gyre. Together, these currents produce an intense, narrow jet directed northwest toward the continental slope, often in the region of the ASIAEX field programs. Upon reaching the slope, the current splits with part flowing northeastward along the slope and part flowing southwestward, producing large horizontal and vertical shears and making this region dynamically very complicated and difficult to simulate. The Kuroshio intrusion tends to be stronger (weaker) when the northeasterly winds are strong (weak) and the large-scale gyre is farther south (north), consistent with conclusions from previous model studies. At the northern boundary, the model produces a persistent northward flow through Taiwan Strait into the East China Sea. Data assimilation in the NSCSNFS model is shown to dampen the system, extracting energy and causing the entire system to spin down.  相似文献   

6.
Acoustic transmission loss (TL) and supporting ocean environmental data collected during the Asian Seas International Acoustics Experiment (ASIAEX) on June 3, 2001, in the East China Sea (ECS), in a water depth of approximately 100 m are presented. Objectives of the data analysis are to explore the stochastic nature of TL in terms of the mean$(mu_ TL)$and the fluctuations around the mean (as described by the standard deviation$(sigma_ TL)$and higher order statistics). In particular, we conjecture that$mu_ TL$robustly reflects the macrostate of the ocean, including the bottom, whereas uncertainties in TL as measured by$sigma_ TL$are related to the microstate of the ocean, again including the bottom. Comparisons are made to TL data at a similar location, 200 km from the ASIAEX site, in waters of the same depth, by the Harsh Environment Program in September 1997. The TL is shown to be approximately horizontally isotropic with exception to a discrete anisotropic feature likely caused by internal waves. Various mechanisms of uncertainty are discussed to describe the microstate. These were not sufficiently resolved to identify the primary cause of variability.  相似文献   

7.
As a part of the Asian Seas International Acoustic Experiment (ASIAEX) in the East China Sea, sound propagation signals from wideband explosive sources were measured using a 32-element vertical line array. Measurements were made as a function of range in two perpendicular tracks. Sea-bed geoacoustic parameters based on a fluid half-space geoacoustic model (sound speed, density, and attenuation) are inverted from the sound propagation in the frequency range 100-500 Hz. The sea-bed sound speed and density were first derived from mode arrival time differences which were obtained using a spatial mode filtering technique. Sea-bed acoustic attenuation was subsequently estimated by comparing measured transmission loss with model results.  相似文献   

8.
Solitons northeast of Tung-Sha Island during the ASIAEX pilot studies   总被引：7，自引：0，他引：7  
In a recent study, satellite images have shown that internal solitons are active in the northern South China Sea (SCS). During the Asian Seas International Acoustic Experiment (ASIAEX) pilot studies, current profiler and thermistor chain moorings were deployed in the spring of 1999 and 2000 to investigate internal solitons northeast of Tung-Sha Island on the continental slope of the northern SCS. Most of the observed internal solitons were first baroclinic mode depression waves. The largest horizontal current velocity, vertical displacement, and temperature variation induced by the internal solitons were around 240 cm/s, 106 m, and 11/spl deg/C, respectively, while the estimated nonlinear phase speed was primarily westward at 152 /spl plusmn/ 4 cm/s. The observed internal solitons could be categorized as four types. The first type is the incoming wave from deep water and can be described reasonably well with the KdV equation. The second and third types are in the transition zone before and close to the turning point (where the upper and lower layer depths are equal), respectively. These two types of solitons were generally near the wave-breaking stage. The fourth type of soliton is a second baroclinic mode and probably was locally generated. The time evolutions are asymmetric, especially at the middle depths. A temperature kink following the main pulse of the soliton is often seen. Higher order nonlinear and shallow topographic effects could be the primary cause for these features. The appearance/disappearance of internal solitons coincides mostly with spring/neap tide. The internal soliton is irregularly seen during the neap tide period and its amplitude is generally small. The time interval between two leading solitons is generally around 12 h. The first baroclinic mode of the semidiurnal tide has a larger amplitude than the diurnal tide and could redistribute its energy into the soliton.  相似文献   

9.
The shallow refracted path through sea floor sediments plays a significant role in the transmission of acoustic energy at low frequencies. For bottom grazing angles of 90/spl deg/ to 25/spl deg/, low-frequency acoustic energy was observed to come from reflected paths. For bottom grazing angles of 25/spl deg/ to 10/spl deg/ the dominant source of low-frequency acoustic energy is from shallow refracted paths through the sediments. At angles less than 10/spl deg/, low-frequency acoustic energy is received from both the refracted and the reflected paths. The refracted path is possible because of the positive gradient within the sediment. The sudden emergence of the refracted arrival is related to the overall sound path length in the sediment and sediment absorption of sound. Since sediment absorption is directly proportional to frequency, only low-frequency energy is transmitted via this path. The refracted path may well exist where unconsolidated sediments of at least a few hundred feet are present.  相似文献   

10.
The three-dimensional structures of summer precipitation over the South China Sea （SCS） and the East China Sea （ECS） are investigated based on tropical rainfall measurement mission （TRMM）. The primary results are as follows. First, both the convective and stratiform precipitation rates in the SCS are much higher than those of the ECS. The contribution of the convective cloud precipitation to the surface precipitation is primarily over the SCS and the ECS with a proportion of about 70%, but the contribution of convective cloud precipitation is slightly larger in the SCS than the ECS. The contribution of stratus precipitation is slightly larger in the ECS than that in the SCS. Second, the content of cloud particles and precipitation particles in the ECS in June was greater than that in the SCS, while in July and August, the content of cloud and precipitation particles in the ECS was less than that in the SCS. Third, the latent heat profile of the ECS is quite different from that of the SCS. In June, the peak values of evaporation and condensation latent heating rates in the ECS are greater than those in the SCS. In July and August, however, the peak values of evaporation and condensation latent heating rates in the ECS are about 0.05°/h less than those in the SCS.  相似文献   

11.
利用高分辨率遥感海表温度和海表面风场数据,通过经验正交分解(EOF)和合成分析等方法对春季(3—5月)东海黑潮海温暖舌和海表面风场的年代际变化特征进行分析。结果表明:春季黑潮海温暖舌存在明显的年代际变化特征,在1996/1997年发生由弱到强的位相转换,该年代际变化主要受到北太平洋涡旋振荡(NPGO)的调制。进一步研究表明,与气候态相反,春季黑潮海表温度和风场散度在年代际尺度上表现出显著的负相关关系,合成分析表明,该现象主要是由黑潮西侧东海陆架海域海温的异常增暖所造成。  相似文献   

12.
Determinations of bottom scattering strength in the decade below 1 kHz under downward refracting conditions have been made using acoustic reverberation and transmission data from the 2001 East China Sea Asian Seas International Acoustic Experiment (ASIAEX). The measurements were performed using explosive sources and receiving hydrophones in ship-suspended vertical-line arrays. The focus of this paper has been the dependence of bottom scattering strength on the frequency and characterization of the uncertainties associated with the extraction of scattering strength from reverberation. The derived bottom scattering strength gradually rises with frequency from 100-300 Hz and then more rapidly above 300 Hz. A potential explanation suggests that the frequency variation results from two scattering mechanisms, rough layer scattering at the low end of the band and sediment near-surface volume scattering at the high end. The spatial extrapolation of these results is explored by comparing them with similarly derived scattering strengths using data obtained under the Navy's Harsh Environments Program at a somewhat separated site (56 km) under environmental conditions similar to those during ASIAEX. In the ASIAEX analysis, it has been found that the largest source of uncertainty in the scattering-strength frequency dependence arises from persistence of finite-amplitude effects associated with the source signal.  相似文献   

13.
近20 a来,东海近岸海域频繁爆发了大规模的东海原甲藻藻华,造成了该海域生态系统的严重失衡。2013年前的调查研究显示东海原甲藻藻华发源于台湾暖流锋面,随台湾暖流锋面入侵近海而发展扩大,但受调查范围限制未能明确该藻华最早发生位置。本研究往南扩展了调查断面,于2013年春、夏季,在24°N～30°N海域进行了4次大面调查。结果显示东海原甲藻藻华最早发生于台湾海峡北端,且随台湾暖流锋面推进向北及近岸扩展。这不仅再次证实了台湾暖流锋面为东海原甲藻藻华的发生提供种源,而且明确了在东海区域东海原甲藻藻华最初发生的位置。这为该藻华的监控提供了重要的科学依据,为其他类似藻华的发生、发展提供了参考。  相似文献   

14.
黑潮对邻近中国海的影响和琉球海流研究在物理海洋学是一个很重要的、有趣的课题。为了深入地阐明由中国科学家自2010年7月至2015年5月期间所作研究的进展,本文在以下三个方面进行评述。第一方面是关于黑潮入侵南海以及在吕宋海峡周围的环流,分为以下二个很重要论题做阐述:黑潮入侵的季节和年际变化以及黑潮入侵的机制;黑潮对吕宋海峡海流和南海北部环流的影响。第二方面是关于黑潮及其对东海相互作用的变化,分为以下四个有趣的论题来阐述:东海黑潮研究的评述;黑潮入侵东海,水交换以及动力因子;由于黑潮作用营养物质通量在下游增加;从卫星遥感的应用对黑潮入侵东海对陆地物质通量的影响。第三方面,琉球海流与东海黑潮相互作用也被讨论。最后本文主要点作了总结,对今后进一步需要研究也被讨论。  相似文献   

15.
The Yellow Sea(YS)and East China Sea(ECS)are important marginal seas of the western Pacific.Understanding the dynamics of methane(CH4)in the YS and ECS are esse...  相似文献   

16.
东海沿海季节性海平面异常成因   总被引：1，自引：0，他引：1  
Based on the analysis of sea level, air temperature, sea surface temperature(SST), air pressure and wind data during 1980–2013, the causes of seasonal sea level anomalies in the coastal region of the East China Sea(ECS) are investigated. The research results show:(1) sea level along the coastal region of the ECS takes on strong seasonal variation. The annual range is 30–45 cm, larger in the north than in the south. From north to south, the phase of sea level changes from 140° to 231°, with a difference of nearly 3 months.(2) Monthly mean sea level(MSL)anomalies often occur from August to next February along the coast region of the ECS. The number of sea level anomalies is at most from January to February and from August to October, showing a growing trend in recent years.(3) Anomalous wind field is an important factor to affect the sea level variation in the coastal region of the ECS. Monthly MSL anomaly is closely related to wind field anomaly and air pressure field anomaly. Wind-driven current is essentially consistent with sea surface height. In August 2012, the sea surface heights at the coastal stations driven by wind field have contributed 50%–80% of MSL anomalies.(4) The annual variations for sea level,SST and air temperature along the coastal region of the ECS are mainly caused by solar radiation with a period of12 months. But the correlation coefficients of sea level anomalies with SST anomalies and air temperature anomalies are all less than 0.1.(5) Seasonal sea level variations contain the long-term trends and all kinds of periodic changes. Sea level oscillations vary in different seasons in the coastal region of the ECS. In winter and spring, the oscillation of 4–7 a related to El Ni?o is stronger and its amplitude exceeds 2 cm. In summer and autumn, the oscillations of 2–3 a and quasi 9 a are most significant, and their amplitudes also exceed 2 cm. The height of sea level is lifted up when the different oscillations superposed. On the other hand, the height of sea level is fallen down.  相似文献   

17.
The main processes of interaction between the coastal water, shelf water and Kuroshiowater in the Huanghai Sea (HS) and East China Sea (ECS) are analyzed based on the observation and study results in recent years. These processes include the intrusion of the Kuroshio water into the shelf area of the ECS, the entrainment of the shelf water into the Kuroshio, the seasonal process in the southern shelf area of the ECS controlled alternatively by the Taiwan Strait water and the Kuroshio water intruding into the shelf area, the interaction between the Kuroshio branch water, shelf mixed water and modified coastal water in the northeastern ECS, the water-exchange between the HS and ECS and the spread of the Changjiang diluted water.  相似文献   

18.
东海及其邻近海区是受热带气旋影响较为严重的区域,研究该海域的热带气旋风灾风险有助于防灾减灾。选取1980—2019年影响该海域的587个热带气旋资料,利用Holland经验风场模型获得该海域热带气旋风场数据集,参照Simpson风灾指数方法,构建联合风速及其累计时间的风灾指数。结果表明:(1)东海及其邻近海区大部分海域受热带气旋影响,都会出现最大风速超过30 m/s。(2)进入20世纪,东海热带气旋风速有增强的趋势,每10 a的平均增速约1.6 m/s。(3)近岸海域最大风速主要发生在7月中旬至9月中旬。(4)从宁德至温州近岸海域的风灾等级相对较高,且风灾等级向南北两侧呈递减趋势。  相似文献   

19.
A common problem in sonar system prediction is that the ocean environment is not well known. Utilizing probabilistic based results from geoacoustic inversions we characterize parameters relevant to sonar performance. This paper describes the estimation of transmission loss and its statistical properties based on posterior parameter probabilities obtained from inversion of ocean acoustic array data. This problem is solved by first finding an ensemble of relevant environmental model parameters and the associated posterior probability using a likelihood based inversion of the acoustic array data. In a second step, each realization of these model parameters is weighted with their posterior probability to map into the transmission loss domain. This approach is illustrated using vertical-array data from a recent benchmark data set and from data acquired during the Asian Seas International Acoustics Experiment (ASIAEX) 2001 in the East China Sea. The environmental parameters are first estimated using a probabilistic-based geoacoustic inversion technique. Based on the posterior probability that each of these environmental models fits the ocean acoustic array data, each model is mapped into transmission loss. This enables us to compute a full probability distribution for the transmission loss at selected frequencies, ranges, and depths, which potentially could be used for sonar performance prediction.  相似文献   

20.
Surface maps of nitrate, phosphate and silicate of the East China Sea (ECS) have been constructed and are described. Reports on exchanges of material between the ECS and the South China Sea (SCS) through the Taiwan Strait are reviewed. Recent advances seem to have reversed the earlier view that the SCS exports nutrients to the ECS through the Taiwan Strait. This is because the northward flow of seawater in the summer carries little nutrient. On the other hand, the waters flowing southward along the coast of China in winter carry orders of magnitude higher nutrient concentrations. The outflow of subsurface waters from the SCS, however, is the major source of new nutrients to the ECS continental shelves because these subsurface waters flow out of the Luzon Strait, join the northwardly flowing Kuroshio and enter the Okinawa trough. Around 10% of the nutrients exported from the SCS through the Luzon Strait upwell onto the ECS shelf. These inputs are larger than the aggregate of all the rivers that empty into the ECS, contributing 49% of the externally sourced nitrogen, 71% of the phosphorous, and 54% of the silica for the ECS.  相似文献   

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