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1.
Algal bloom observed using Indian Remote Sensing Satellite IRS-P4 Ocean Color Monitor (OCM) derived chlorophyll images during December 23, 2003–January 8, 2004, off the Oman coast. High chlorophyll concentration (～20 mg m?3) patches were observed. MODIS-Aqua data of January 1, 2004, were analyzed to generate normalized water leaving radiance (nLw) images for seven visible channels: 412, 443, 488, 531, 551, 667 and 678 nm. The channels 667 and 678 nm showed interesting algal bloom features. The bloom features were detected in OCM image of January 2, 2004, using Subramanian's Trichodesmium detection Protocol. MODIS-Aqua retrieved Sea Surface Temperature (SST) around the bloom patches was observed to be >240°C. The OCM chlorophyll mean observed to be very high (>10.0 mg m?3) in two bloom pockets. Quickscat scatterometer derived wind speed was found to be optimum in the range of 3–5 m/sec.  相似文献   

2.
南海东北部是寡营养海域，夏季浮游植物叶绿素浓度较低，热带气旋“风泵”效应带来的上层海洋扰动可能引起表层浮游植物的显著增长。以往的研究通常关注热带气旋风应力和海洋中尺度涡对上层海洋浮游植物的影响，本文利用航次CTD、实测叶绿素a浓度、Argo温盐剖面和遥感数据，探讨了台风“风泵”和黑潮共同作用下真光层内浮游植物的变化特征及其成因。结果表明，2015年台风“莲花”过境1周后产生向吕宋海峡西北侧南海海域(A区)入侵的黑潮流套，该入侵的黑潮流套使台风前原有的气旋涡消失，抑制了台风产生的上升流对表层(0～40 m)营养盐供给，使次表层(60～90 m)营养盐富集，进而抑制了表层的叶绿素a增长，促进了次表层叶绿素a的增长；吕宋海峡西侧南海海域(B区)表层的浮游植物叶绿素a浓度增加不仅是源于叶绿素最大层浮游植物的向上输运，更是由于浮游植物的繁殖增长；A区台风引起的流套式的黑潮入侵，促进了B区台风后气旋式流场的形成，产生的持续增强的气旋涡为B区表层叶绿素持续增长提供了充足的营养盐供给。  相似文献   

3.
During the periods of cyclonic activity, tropical cyclones frequently develop in groups partially coinciding in time. In the “atmosphere–ocean” system, the conditions favoring the development of tropical cyclones are limited. In such setting, a “competition struggle” between tropical cyclones suggesting their possible interrelation is possible. As a result of this study, a regression signature illustrating the energetic impact of a group of tropical cyclones on the development of an individual cyclone in this group has been revealed.  相似文献   

4.
Energy interdependence between groups of tropical cyclones separated by time intervals of cyclonic “calm” is investigated. A linear negative interrelation between the total powers of such groups is revealed. The groups consist of real tropical cyclones that occurred within the active cyclonic zone in the northwestern Pacific. The corresponding regression relationships are obtained. Interrelation between the stages of development of seasonal cyclonic activity is revealed. Semidiurnal total powers (power elements) are chosen as “operational” objects with the use of which the sought-for interrelation is established. Regressions were obtained separately for each season: the number of elements and their powers are related by a negative power relation. The result obtained is supposed to serve as a certain basis for the probabilistic prediction of cyclonic activity during the season.  相似文献   

5.
香港经常受到西北太平洋热带气旋的影响,对该地区热带气旋持续时间的研究有助于经济社会的稳定发展。按照气象和天文台警告信号,热带气旋分为不同的强度等级。建立热带气旋持续时间的Poisson-Weibull复合分布模型,相应获得持续时间重现值的求解公式,分别用于不同热带气旋分类下持续时间多年一遇重现值的计算中。基于1987-2016年袭港热带气旋数据的分析结果表明,Poisson-Weibull分布适用于不同的持续时间分类样本;强的热带气旋经常会伴随较长的持续时间,这将会对该地区造成更为严重的破坏,这可为防灾减灾提供参考。  相似文献   

6.
In the winter Kuroshio Extension region, the atmospheric response to oceanic eddies is studied using reanalysis and satellite data. The detected eddies in this region are mostly under the force of northwesterly wind, with the sea surface temperature (SST) anomaly located within the eddy. By examining the patterns of surface wind divergence, three types of atmospheric response are identified. The first type, which occupies 60%, is characterized by significant sea surface wind convergence and divergence at the edge and a vertical secondary circulation (SC) aloft, supporting the “vertical momentum mixing mechanism”. The SCs on anticyclonic eddies (AEs) can reach up to 300 hPa, but those on cyclonic eddies (CEs) are limited to 700 hPa. This can be explained by analyzing vertical eddy heat transport: When northwesterly wind passes the warmer center of an AE, it is from the cold to warm sea surface, resulting in stronger evaporation and convection, triggering stronger upward velocity and moist static heat flux. For the cases of CEs, the wind blows from warm to cold, which means less instability and less evaporation, resulting in weaker SCs. The second type, which occupies 10%, is characterized by divergence and a sea level pressure anomaly in the center, supported by the “pressure adjustment mechanism”. The other 30% are mostly weak eddies, and the atmospheric variation aloft is unrelated to the SST anomaly. Our work provides evidence for the different atmospheric responses over oceanic eddies and explains why SCs over AEs are much stronger than those over CEs by vertical heat flux analysis.  相似文献   

7.
The results of decennial monitoring of the Caspian Sea were summarized, which allowed revealing the “pumping” of nutrients from the euphotic layer to deepwater depressions of the Central and Southern Caspian Sea. In parallel, in the deepwater depressions, growth of hypoxia to values of 0.2–0.5 ml O2/l proceeds. In 2006, hydrogen sulfide was registered in the near-bottom layer of the South Caspian Sea Basin. It is shown that the transformation of the hydrochemical structure was directed towards the conditions observed at the times of Bruevich (1933–1934), but no complete coincidence has yet been reached.  相似文献   

8.
Numerical modeling of extreme sea levels associated with tropical cyclones in the Indian seas has been confined to the northern part of the Bay of Bengal (north of Tamil Nadu). However, limited attempts have been made for modeling of surges along the Tamil Nadu and Sri Lankan coasts. Although, very rarely, cyclones form south of 10°N, there are some instances of severe cyclonic storms hitting these areas and causing widespread destruction to life and property. Keeping this in view, a suitable location-specific, high-resolution, numerical model has been developed for the prediction of storm surges in these regions with a grid resolution of 3 km. Using the model, numerical experiments are performed to simulate the storm surge associated with the 1964 Rameswaram cyclone, the 1978 Batticaloa cyclone, the 1992 Tuticorin cyclone, the 1993 Karaikal cyclone, and the 1994 Madras cyclone. During the years 1964, 1978, and 1992, the cyclones struck both Sri Lanka and Tamil Nadu coasts, while in 1993 and 1994, the cyclones struck only the Tamil Nadu coast. It is found that the computed sea surface elevations are in close agreement with the available observations/estimates.  相似文献   

9.
A characterization of extreme wave parameters during extratropical cyclones in the Northern hemisphere is made from WAM wave model hindcasts. In February 2007 two extratropical storms were observed in the North Atlantic and the wave fields associated with them are modeled in this paper. Wave buoy and satellite altimetry data were used to validate the WAM hindcast results. The distribution of the Benjamin–Feir index (BFI), kurtosis and the ratio of maximum wave height to significant wave height (abnormality index) around the eye of the two extratropical cyclones is studied. It is found that under these conditions the BFI and kurtosis are significantly larger mainly in the fourth quadrant and also when the wind direction is aligned with the wave propagation direction. In these regions the probability of occurrence of abnormal waves is higher.  相似文献   

10.
The expansion of wind fields observed at fixed times (four times daily) in complex empirical orthogonal functions is performed for the Japan Sea area (34°–53° N, 127°–143° E). The wind fields are taken from the 1998–2004 NCEP/NCAR Reanalysis data with better spatial resolution (1° × 1°) than the standard product, which are publicly available on the Internet. Major modes of wind variability in the Japan Sea area are identified. The modes determine a general direction of air-mass transport throughout a year, zonal and meridional modulation, and a cyclonic and an anticyclonic eddy component. Objective classification of wind fields with respect to the prevailing flow direction is performed, and wind stress and wind-curl patterns are obtained for major events in the cold and warm periods of the year. The pattern obtained can be used in hydrodynamic numerical models of the general circulation of the Japan Sea.  相似文献   

11.
Field measurements during the Bay of Bengal Monsoon Experiment (BOBMEX-99), data from a deep sea moored buoy, and satellite altimeter were used to describe variability in the hydrographic and meso-scale features in the Bay of Bengal (BoB) during the summer monsoon of 1999. The thermohaline fields showed two regions of upsloping of isopleths centered at 82°E and 84.75°E, ～110 km and 450 km away from the coast, respectively, followed by downsloping. The upsloping/downsloping of isopleths and the alternating currents was part of cyclonic and anti-cyclonic circulation patterns in the western BoB. In this region, both wind and current were important in the dynamics of coastal upwelling. The observations showed a relationship between the propagating waves and eddy on variability of thermohaline fields. On an annual cycle, four Kelvin waves were observed in the BoB, but only the downwelling Kelvin wave formed during October entered the Arabian Sea. During the monsoon season, four eddies were formed in the western BoB, of which the anticyclonic eddy centered at 15°N, 84°E and the cyclonic eddy centered at 17.5°N, 84.5°E were prominent. The baroclinic instability caused by the opposing currents along the east coast and the wind stress curl favored the formation of eddies. Okhubo-Weiss and Isern-Fontanet parameter confirmed the presence of eddies in the BoB.  相似文献   

12.
利用经验正交函数数据插值法(Data INterpolating Empirical Orthogonal Functions)重构由MODIS-Aqua卫星提供的三级产品叶绿素a质量浓度,得到了从2003—2009年东中国海叶绿素a质量浓度的月平均场。东中国海近岸叶绿素a质量浓度7 a平均值明显高于外海。对叶绿素a质量浓度季节平均场进行分析研究表明,东中国海叶绿素a质量浓度主要受长江径流、海表水温和季风的影响。对叶绿素a质量浓度异常场进行EOF分析表明,第一模态方差贡献为37.8％,空间分布显示,在长江口东北部出现叶绿素a质量浓度异常高值区,时间变化以半年和半年以下周期为主;第二模态方差贡献为21.4％,空间分布显示,在长江口东部出现叶绿素a质量浓度异常高值区,时间系数主要表现为年际变化。  相似文献   

13.
The Aral Sea is an important water area both for monitoring and oceanological studies, because its salinity and salt composition strongly differ from the oceanic. We offer a semiempiric calculation method of electric conductivity and the coefficient of its temperature dependence k judging from the ionic composition of water. The properties of the solution are considered as the sum of properties of seven binary salts taken based on the ionic composition of the solution. The MgSO4 concentration is thought to be the highest possible, which makes the salt concentration nearly unambiguous. In a salinity range of 46–120‰ and temperature range of 5–25°C (2002–2009), the standard deviation of the calculated and measured electric conductivity was 2.9%. To refine the calculation of salinity from electric conductivity measurements using the “oceanic” formula, we suggest its preliminary reduction to a constant temperature (20°C) using the measured or calculated coefficient k.  相似文献   

14.
In general, a mesoscale cyclonic (anticyclonic) eddy has a colder (warmer) core, and it is considered as a cold (warm) eddy. However, recently research found that there are a number of “abnormal” mesoscale cyclonic (anticyclonic) eddies associated with warm (cold) cores in the South China Sea (SCS). These “abnormal” eddies pose a challenge to previous works on eddy detection, characteristic analysis, eddy-induced heat and salt transports, and even on mesoscale eddy dynamics. Based on a 9-year (2000–2008) numerical modelling data, the cyclonic warm-core eddies (CWEs) and anticyclonic cold-core eddies (ACEs) in the SCS are analyzed. This study found that the highest incidence area of the “abnormal” eddies is the northwest of Luzon Strait. In terms of the eddy snapshot counting method, 8 620 CWEs and 9 879 ACEs are detected, accounting for 14.6% and 15.8% of the total eddy number, respectively. The size of the “abnormal” eddies is usually smaller than that of the “normal” eddies, with the radius only around 50 km. In the generation time aspect, they usually appear within the 0.1–0.3 interval in the normalized eddy lifespan. The survival time of CWEs (ACEs) occupies 16.3% (17.1%) of the total eddy lifespan. Based on two case studies, the intrusion of Kuroshio warm water is considered as a key mechanism for the generation of these “abnormal” eddies near the northeastern SCS.  相似文献   

15.
Pockmark-like seabed features located on the Landes Plateau, Bay of Biscay, are depressions up to 1 km across and 50 m deep according to multibeam echo sounder data. Seismic (airgun and TOPAS) profiles show that each feature comprises a stack of identical features which extend down to 300 ms (twt). Three types of depressions, elongate, irregular and circular, appear as non-truncating V-shaped features in the Plio-Quaternary sediments. These features are located above the Parentis Basin where deep faults, basement ridges and diapiric bodies extend upwards across the sedimentary cover, providing ideal migration pathways for any buoyant fluids. Initial inspection suggests that these are classic pockmarks; however, the absence of reflection truncation and the absence of indications of shallow gas beneath the features indicate that they were not formed by the removal of sediment. These are “pockforms” but not “pockmarks”. This paper presents an explanation for the formation of these features, involving collapse and subsidence, sedimentary erosion, and only in some cases the erosion of seabed sediments by probable escaping fluids. These origins are mainly conducted through tectonic fluid dynamics which acted in the area up to the Late Miocene. It might be expected that these features would have been infilled by subsequent sedimentation, but their shape has been preserved because sedimentation in the area mainly comprised muds deposited from low-energy transportation (diluted gravity flows) and settling from hemipelagic suspension.  相似文献   

16.
Spectral wave characteristics were studied based on waves measured for 1 year during 2010 off Gangavaram, Bay of Bengal. Maximum wave height of 5.2 m was observed on 19 May 2010 due to the influence of cyclonic storm LAILA. The wave spectrum was single-peaked during 57 % of the time and the double-peaked spectrum observed was mainly swell-dominated. Low-frequency waves (0.05–0.15 Hz) were predominantly from 150° to 180°, whereas high-frequency waves (>0.15 Hz) during November–January were mainly from 90° to 120°, and during July and August from 180° to 210°. Annual average significant wave height was similar to the value (1 m) observed in the eastern Arabian Sea.  相似文献   

17.
Numerical modeling of extreme sea levels associated with tropical cyclones in the Indian seas has been confined to the northern part of the Bay of Bengal (north of Tamil Nadu). However, limited attempts have been made for modeling of surges along the Tamil Nadu and Sri Lankan coasts. Although, very rarely, cyclones form south of 10°N, there are some instances of severe cyclonic storms hitting these areas and causing widespread destruction to life and property. Keeping this in view, a suitable location-specific, high-resolution, numerical model has been developed for the prediction of storm surges in these regions with a grid resolution of 3 km. Using the model, numerical experiments are performed to simulate the storm surge associated with the 1964 Rameswaram cyclone, the 1978 Batticaloa cyclone, the 1992 Tuticorin cyclone, the 1993 Karaikal cyclone, and the 1994 Madras cyclone. During the years 1964, 1978, and 1992, the cyclones struck both Sri Lanka and Tamil Nadu coasts, while in 1993 and 1994, the cyclones struck only the Tamil Nadu coast. It is found that the computed sea surface elevations are in close agreement with the available observations/estimates.  相似文献   

18.
Eddy activity in the lee of the Hawaiian Islands   总被引：2，自引：0，他引：2  
Persistent northeasterly trade winds have a substantial impact on the oceanic circulation around the Hawaiian Islands. A regional ocean model is applied to understand the effect of different temporal and spatial resolutions of surface momentum forcing on the formation of strong mesoscale vortices and on the simulation of realistic levels of eddy kinetic energy. The higher spatial and temporal resolutions of wind forcing is shown to substantially affect the vorticity and deformation field in the immediate lee of the Hawaiian Islands and produce patterns of eddy kinetic energy similar to observations. This suggests that the surface eddy field in the region is mostly dominated by the local surface momentum forcing. Mesoscale cyclones and anticyclones formed in the lee of the Island of Hawaii are shown to have different propagation patterns. Mesoscale cyclones are more confined to the lee and are hence subject to interactions with the strong wind forcing and deformation field as well as smaller vortices formed in the wake of the other islands. Mesoscale anticyclones show not only a tendency to propagate further westward, but also to persist as coherent features as they propagate, even at relatively lower values of relative vorticity. The large strain rates that affect the propagation of the cyclones cause them to break down into filaments of positive vorticity. Rossby numbers of O(1) within vortices and filaments indicate that nonlinear interactions between the wind stress and the vertical component of the relative vorticity field is potentially important in producing large vertical velocities. Modeled cyclonic eddies show a good resemblance to observations both in terms of vertical structure and propagation patterns.  相似文献   

19.
基于南海东北部1998~2019年的多源卫星遥感数据和风场再分析数据, 较系统地分析了南海东北部涡旋内部叶绿素a浓度的分布特征, 通过量化统计和涡心坐标系参数合成等方法探究了中尺度涡对叶绿素a浓度变化的影响规律及潜在机制。结果表明: (1)南海东北部约有60%的中尺度涡旋内部存在叶绿素a浓度增加和减少的现象。(2)南海东北部中尺度涡内部叶绿素a扰动受到涡旋抽吸和涡致Ekman抽吸机制的共同调控, 其中约有38% (39%)的暖(冷)涡内涡旋抽吸的贡献更大, 21% (24%)的暖(冷)涡内涡致Ekman抽吸的贡献更大。(3)南海东北部中尺度涡生命周期内的海表叶绿素a浓度变化存在显著的阶段性差异, 在冷暖涡的生成期, 涡旋抽吸的作用更为显著, 而在冷暖涡的顶峰和消亡期, 涡致Ekman抽吸的作用更为明显。上述研究结果有助于理解南海东北部初级生产力对中尺度涡的响应过程与机理, 对认识海洋物理-生物耦合过程具有一定的参考价值和研究意义。  相似文献   

20.
Time series of the chlorophyll-a concentration (Chl-a) observed by ocean color satellites from 1998 to 2009 were used to assess eutrophication in Toyama Bay, the Sea of Japan. An overall mean of Chl-a during the 12-year period was used to divide the study area into “high” or “low” Chl-a areas based on a reference condition of 5 mg m?3. The annual maximum monthly mean Chl-a trend was estimated pixel-wise and its significance examined by the Sen slope test at a 90 % confidence level. By combining the level and trend of remotely sensed Chl-a, Toyama Bay was then classified into six eutrophication states: high-increasing, high-no trend, high-decreasing, low-increasing, low-no trend and low-increasing. Our study indicates that the combined use of both the level and trend of remotely sensed Chl-a can be an efficient method to preliminarily assess eutrophication of coastal waters after a quality screening process with level 2 flags and validation with in situ Chl-a data.  相似文献   

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