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1.
We present data from three acoustic Doppler current profilers (ADCPs) moored off Cuddalore (12°N), Kakinada (16.5°N), and Gopalpur (19°N) on the continental slope of the western Bay of Bengal and one mooring on the slope of the northern bay (89°E, 19°N; referred to as being located at Paradip). The data were collected during May 2009 to March 2013 and the observations show that the seasonal cycle, which includes the annual cycle, the semi-annual cycle, and a peak around 120 days, dominates the observed variability of the East India Coastal Current (EICC). Spectral analysis suggests that the 120-day peak dominates the seasonal variability at Paradip and is strong at Gopalpur and Kakinada. The annual cycle is coherent along the western boundary of the bay, i.e., the east coast of India, but with significant phase differences between moorings. At the semi-annual and 120-day periods, the alongshore coherence is weaker. Intraseasonal variability is weaker than the seasonal cycle, particularly at Cuddalore and Paradip, and it exhibits seasonality: the strongest intraseasonal variation is during spring (February–April). Peaks around 12 and 20–22 days are also seen at Gopalpur, Kakinada, and Cuddalore. A striking feature of the currents is the upward phase propagation, but there are also instances when phase propagates downward. The much lower vertical phase speed in the top ～100 m at Cuddalore leads to a distinct undercurrent at this location; at other locations, the undercurrent, though it exists often, is not as striking. During spring, however, the EICC tends to flow poleward (eastward) at Cuddalore, Kakinada, and Gopalpur (Paradip) over the top ～300 m, which is the maximum depth to which observations were made. The cross-shore component of the EICC is much weaker than the alongshore component at Cuddalore and, except for a few bursts during spring, at Kakinada and Gopalpur. It is only at Paradip, on the slope of the northern boundary, that significant cross-shore flows are seen during spring and the summer monsoon (June–August) and these flows are seen to be associated with eddy-like circulations in the altimeter data. We use the ADCP data to validate popular current data products like OSCAR (Ocean Surface Currents Analyses Real-time), ECCO2 (Estimating the Circulation and Climate of the Ocean, Phase II), and GODAS (Global Ocean Data Assimilation System). The OSCAR currents at Paradip match the observed currents well, but the correlation is much weaker at the other three locations. Both ECCO2 and GODAS fair poorly, particularly the latter because its variability in this boundary-current regime is extremely weak. Though it performs badly at Paradip, ECCO2 does capture the observed variability on occasions at the other locations.  相似文献   

2.
A high resolution model, using the Miami Isopycnic Coordinate Ocean Model (MICOM), has been implemented for the first time to study the seasonal circulation and coastal upwelling off the southwest Indian coast during 1974. This model is part of a model and data assimilation system capable of describing the ocean circulation and variability in the Indian Ocean and its predictability in response to the monsoon system. Along the southwest coast of India the dominant coastal current is the reversing West Indian Coastal Current which is well simulated and described, in addition to the weaker undercurrent of the opposite direction. Upwelling of cold water, 4‡C lower than offshore temperatures appear in April. The upwelling intensifies with the southwest monsoon and is simulated in accordance within situ observations. Upwelling appears to be strongest off Cochin and Quilon, and the upwelling of cold water is seen together with a decrease in salinity in the model simulation.  相似文献   

3.
Monthly-mean winds and currents have been used to identify the driving mechanisms of seasonal coastal circulation in the North Indian Ocean. The main conclusions are: (i) the surface circulation off Arabia is typical of a wind-driven system with similar patterns of longshore current and wind stress; (ii) circulation off the west coast of India is consistent with the dynamics of a wind-driven eastern boundary current only during the southwest monsoon. During the northeast monsoon it is possible that the influence of the interior flow is important. (iii) There are at least three mechanisms that influence the surface circulation off the east coast of India: wind-stress, influence of fresh-water run off and contribution of the interior flow. It is difficult at present to assess the relative importance of these three processes.  相似文献   

4.
The dynamics and thermodynamics of the surface layer of the Arabian Sea, north of about 10N, are dominated by the monsoon-related annual cycle of air-sea fluxes of momentum and heat. The currents in open-sea regime of this layer can be largely accounted for by Ekman drift and the thermal field is dominated by local heat fluxes. The geostrophic currents in open-sea subsurface regime also show a seasonal cycle and there is some evidence that signatures of this cycle appear as deep as 1000 m. The forcing due to Ekman suction is an important mechanism for the geostrophic currents in the central and western parts of the Sea. Recent studies suggest that the eastern part is strongly influenced by the Rossby waves radiated by the Kelvin waves propagating along the west coast of India. The circulation in the coastal region off Oman is driven mainly by local winds and there is no remotely driven western boundary current. Local wind-driving is also important to the coastal circulation off western India during the southwest monsoon but not during the northeast monsoon when a strong (approximately 7 × 106m3/sec) current moves poleward against weak winds. This current is driven by a pressure gradient which forms along this coast during the northeast monsoon due to either thermohaline-forcing or due to the arrival of Kelvin waves from the Bay of Bengal. The present speculation about flow of bottom water (deeper than about 3500 m) in the Arabian Sea is that it moves northward and upwells into the layer of North Indian Deep Water (approximately 1500–3500m). It is further speculated that the flow in this layer consists of a poleward western boundary current and a weak equatorward flow in the interior. It is not known if there is an annual cycle associated with the deep and the bottom water circulation.  相似文献   

5.
The present study investigates the impact of wave energy and littoral current on shorelines along the south-west coast of Kanyakumari, Tamil Nadu, India. The multi-temporal Landsat TM, ETM+ images acquired from 1999 to 2011 were used to demarcate the rate of shoreline shift using GIS-based Digital Shoreline Analysis System. The statistical analysis such as net shoreline movement and end point rate were determined from the multi-temporal shoreline layers. Moreover, the wave energy and seasonal littoral current velocity were calculated for each coastal zone using mathematical equations. The results reveal that the coastal zones, which include Kanyakumari, Kovalam, Manavalakurichi and Thengapattinam coasts, consisting of maximum wave energy along with high velocity of littoral current, have faced continuous erosion processes. The estimated wave energy along these zones ranges from 6.5 to 8.5 kJ/km2 and the observed current velocity varies from 0.22 to 0.32 m/s during south-west and north-east monsoons. The cumulative effect of these coastal processes in the study area leads to severe erosion that is estimated as 300.63, 69.92, 54.12 and 66.11 m, respectively. However, the coastal zones, namely Rajakkamangalam, Ganapathipuram, Muttam and Colachel, have experienced sediment deposits due to current movement during the north-east monsoon. However, the trend changes during the south-west monsoon as a result of sediment drift through backwash. The spatial variation of shoreline and its impact on wave energy and the littoral current have been mapped using the geo-spatial technology. This study envisages the impact of coastal processes on site-specific shorelines. Hence, the study will be effective for sustainable coastal zone management.  相似文献   

6.
A seasonal reconstruction of the Indian Ocean during the last glacial maximum (18,000 yr B.P.) reveals that its surface circulation and sea surface temperature patterns were significantly different from the modern Indian Ocean. This reconstruction is based on the planktonic foraminiferal biogeography and estimated sea surface temperatures in 42 Indian Ocean samples. Compared to modern conditions, the polar front was 5° to 10° latitude further north during the last glacial maximum; the Subtropical Convergence was 2° to 5° latitude further north. The West Australian Current was more intense as part of the West Wind Drift was deflected northward along the coast of Australia. The Agulhas Current was cooler and weaker during the summer and more saline and subtropical during the winter. In general, the low latitudes underwent little temperature change. The western Arabian Sea was warmer which implies less upwelling and a weaker Southwest Monsoon. On the average, the Indian Ocean was 1.9°C cooler in February and 1.7°C cooler in August during the last glacial maximum.  相似文献   

7.
Using the satellite derived sea surface temperature (SST) data for 1979 (bad monsoon) and 1983 (good monsoon), the SST variability for two contrasting monsoon seasons is studied. The study indicates that large negative anomalies off the Somali and Arabian coasts are associated with good monsoon rainfall over India. The strong monsoonal cooling in these regions can be attributed to strong low level winds and intense upwelling. The reappearance of 27°C isotherm off Somali coast in May/June coincides with the onset of southwest monsoon over India. Further, the influence of zonal anomaly of SST off Somalia Coast (SCZASST) and Central Indian Ocean Zonal Anomaly of SST (CIOZASST) with monsoon rainfall over India is brought out. The former is negatively related to the monsoon rainfall over western and central parts of India, whilst CIOZASST is positively related.  相似文献   

8.
王元叶  何青 《水科学进展》2008,19(3):394-399
通过分析声学多普勒流速剖面仪(Acoustic Doppler Current Profiler,ADCP)的声强垂向剖面分布特征,利用数学极值定理,确定床面边界位置,进而确定出ADCP记录的所有在水中的流速单元,将ADCP处理软件"丢弃"的部分近底流速数据或由于底跟踪丢失而损失的流速数据确定出来。利用"六点法"同时、同高度的电磁海流计流速数据对提取出来的ADCP近底流速数据进行验证。验证结果表明,提取出来的ADCP近底流速数据可信、可用。  相似文献   

9.
A review is given of the summer monsoon systems in Africa and India, and of their comparison at different time scales. Features of the circulation are described first, including the main respective meteorological centres of action controlling the annual cycle of the rain bands over these two regions. The main elements of the atmospheric intraseasonal variability are then presented, which controls in particular the onset of these two monsoon systems. Then the sensitivity of these two monsoon systems to oceanic and continental surface conditions in the context of interannual variability is discussed and compared. Consequences in term of predictability are commented. Finally, the Intergovernmental Panel on Climate Change (IPCC4) scenarios of the future climate over these two regions are presented.  相似文献   

10.
During 23–30 September 1997, a rare cyclonic storm has developed close to the Andhra coast, and it has later travelled parallel to coastline northward and finally crossed the land at Chittagong (22°N, 91°E) on 27 September. While translating along the east coast of India, it has produced heavy to very heavy rainfall on the coastal stations causing devastating floods. In this study, we made an attempt to understand the salient causes of this unique cyclone movement. We have analyzed daily fields of wind and relative humidity for 850, 700, 500 hPa and mean daily OLR data to understand the plausible reasons for its movement. The buoy data deployed by National Institute of Ocean Technology, Chennai, Viz. DS5 (15°N, 81°E), DS4 (19°N, 88°E) and SW7 (20°N, 86°E) were analyzed to understand the ocean–atmosphere interaction processes in the west Bay of Bengal during formation of the system. Analysis of OLR over the cyclonic storm region has revealed that the heavy rainfall areas coincide with low OLR (120–180 W m?2). The persistent southward movement of 500 hPa ridge on the eastern wedge of the system along with the steering current at 200 hPa has helped in maintaining the movement of the system parallel to the east coast of India during its life cycle.  相似文献   

11.
Monthly-mean wind stress and its longshore and offshore components have been computed using the bulk aerodynamic method for each of a string of 36 two-degree-latitude by two-degree-longitude squares along the coast of the north Indian Ocean. The data source for the computation is the sixty-year mean resultant winds of Hastenrath and Lamb. The main features exhibited by the components, taking the longshore components as positive (negative) when the Ekman transport is away from (towards) the coast, are: (1) Along the coasts of Somalia and Arabia, the magnitude of the wind stress is among the highest in the north Indian Ocean, and its direction is generally parallel to the coastline. This results in a longshore component which is large (as high as 2·5 dyne/cm2) and positive during the southwest monsoon, and weaker (less than 0·6 dyne/cm2) and negative during the northeast monsoon. (2) Though weak (less than 0·2 dyne/cm2) during the northeast monsoon, the monthly-mean longshore component along the west coast of India remains positive throughout the year. The magnitude of the offshore component during the southwest monsoon is much larger than that of the longshore component. (3) The behaviour of the wind stress components along the east coast of India is similar to that along the Somalia-Arabia coast, but the magnitudes are much smaller.  相似文献   

12.
千年尺度气候变率的研究   总被引：5，自引：0，他引：5  
2 0世纪后期 ,千年 (ka)尺度气候变率的研究取得了重要的进展 ,这表现在以下几个方面 :(1)格陵兰冰芯及深海沉积证明 ,在末次冰期中普遍存在平均周期为 1 5ka的循环 ,有人认为全新世也存在这种循环 ,小冰期就是最近一个循环的冷期。 (2 )每个循环由 1个相对暖期 (间冰阶 )及 1个冷期(冰阶 )组成 ,称为Dansgaard/Oeshger循环 (D/O循环 )。 (3)连续几个D/O循环的冰阶气温愈来愈低 ,海因里希事件 (H事件 )就发生在最冷的冰阶之后。 (4 )自 15kaBP到 6 8kaBP共确定出 6次H事件 ,分别称为H1…H6,有的作者认为新仙女木事件 (YD)与H事件形成机制近似 ,可以称为H0 。 (5 )D/O循环与H事件的成因 ,目前尚无定论。但热盐环流 (THC)变化的学说得到了较多作者的承认。这个学说认为 :北大西洋北部的大量融冰使海面为冷的淡水控制 ,影响了大传送带中海水的下沉 ,从而削弱了深水的形成。北大西洋THC减弱 ,使向北输送的热量减少 ,使北大西洋气候更寒冷。一旦深水形成再次增加 ,完成一个D/O循环。H事件形成的机制与之类似 ,不过过程变化更为激烈。 (6 )这样 ,THC有 3种模态 :现代模 (北大西洋有两个泵 )、冰阶模 (一个泵 ) ,及H事件 (无泵 )。 (7)海洋环流模式已经对THC的变化及模态之间的转换进行了模拟 ,至少在一定程度?  相似文献   

13.
Seasonal variability in heat-related mortality across the United States   总被引：1，自引：1，他引：0  
This study examines the seasonal variability in the heat mortality relationship across 29 US metropolitan areas from 1975 to 2004 to discern the seasonal cycle of the health risk from anomalously high temperatures (relative to the time of season). Mortality data for the 30-year period are standardized to account for population trends and overall seasonal and interannual variability. On days when a city experienced an “oppressive” air mass, mean anomalous mortality was calculated. Results show that while the greatest overall health impact is found mid-summer in many locations due to the peak frequency of hot weather occurring at this time, the relative increase in acute mortality on oppressive air mass days is actually just as large in spring as it is in summer, and in some cases is larger. Late summer and autumn vulnerability to anomalously warm or hot days is much less significant than spring days in all areas except along the Pacific coast. Results show significant spatial variability, with the most consistent results across the more ‘traditionally’ heat vulnerable areas of the Midwestern and northeastern US, along with the Pacific Coast. Elsewhere, the seasonal cycle of the correlation between anomalously high temperatures and human health is more ambiguous.  相似文献   

14.
The 2004 Indian Ocean tsunami had a significant impact on the Tamil Nadu coast in India. In this paper, a range of field survey data collected by different survey teams available in literature have been analyzed and compiled to serve as a basis for validation of numerical tsunami simulations. The individual field surveys reveal a significant scatter in the run-up data between the different teams, which point out that the uncertainty in these data must be taken into account when using them for validation. The inundation of the 2004 Indian Ocean tsunami is simulated for the coastlines of Chennai and Nagapattinam based on high-resolution topography. Different spatially uniform Manning friction as well as heterogeneous friction maps is used. Overall, the simulation results showed a good agreement with the field observations, but there are also some observed spatial variability in the goodness of the fit between the data and simulations. In some areas, clear discrepancies are found. The results obtained using detailed land use maps including spatially variable friction are not significantly more accurate than those employing spatially constant values. For most areas, parameters indicating relatively low friction provided best match with the observations. This may also suggest that the inundation is often strongly governed by local variations in topography.  相似文献   

15.
Information on reflected surface gravity waves from the shoreline is required for understanding the coastal hydrodynamics. We have quantified the reflected swells (frequency band 0.045–0.12 Hz) from the west and east coast of India based on the spectral wave data derived from the directional waverider buoys. Reflection coefficient, ratio of the reflected and incident spectral energy, was used to quantify the reflected waves. Influence of the seasons, cyclone, relative depth, land/sea breeze, tides and tidal current on the reflected waves were examined. For the locations off the west coast of India, seasons have large impact on the reflection coefficient and were relatively less during the monsoon season due to the increase in incident wave energy. Locations off the east coast of India show almost the same reflection coefficient throughout the year and have no significant seasonal variations. The reflection coefficient off Puducherry was higher than that for other locations due to the low incident wave energy. The reflection coefficient was low during the cyclone period, but the reflected energy during cyclone was higher than that during the normal condition due to the high incident wave energy. High-energy reflected waves show large variation with tide due to the trapping and dissipation of reflected wave by bottom friction and this effect cause low reflection in deep water location than shallow water location. The reflection coefficient decreases with increase in relative depth off west coast of India.  相似文献   

16.
The tsunami run-up, inundation and damage pattern observed along the coast of Tamilnadu (India) during the deadliest Indian Ocean tsunami of December 26, 2004 is documented in this paper. The tsunami caused severe damage and claimed many victims in the coastal areas of eleven countries, bordering the Indian Ocean. Along the coast of Indian mainland, the damage was caused by the tsunami only. Largest tsunami run-up and inundation was observed along the coast of Nagapattinam district and was about 10–12 m and 3.0 km, respectively. The measured inundation data were strongly scattered in direct relationship to the morphology of the seashore and the tsunami run-up. Lowest tsunami run-up and inundation was measured along the coast of Thanjavur, Puddukkotai and Ramnathpuram districts of Tamilnadu in the Palk Strait. The presence of shadow of Sri Lanka, the interferences of direct/receded waves with the reflected waves from Sri Lanka and Maldive Islands and variation in the width of continental shelf were the main cause of large variation in tsunami run-up along the coast of Tamilnadu.  相似文献   

17.
我国海洋科学领域的全球变化研究进展   总被引：7，自引：3，他引：7  
简要介绍了属于海洋科学研究领域中的全球变化研究计划,重点介绍了我国在热带海洋和全球大气（TOGA）、世界大洋环流试验（WOCE）、全球海洋通量联合研究（JGOFS）和海洋PAGES研究中所开展的工作及其研究进展。  相似文献   

18.
The intraseasonal tropical variability (ITV) patterns in the tropical troposphere are documented using double space-time Fourier analysis. Madden and Julian oscillations (MJO) as well as equatorial coupled waves (Kelvin and Rossby) are investigated based on the NCEP/NCAR Reanalysis data for the 1977–2006 period and the outputs of an intermediate ocean-atmosphere coupled model named LODCA-OTCM. A strong seasonal dependence of the ITV/ENSO relationship is evidenced. The leading relationship for equatorial Rossby waves (with the correlation of the same order than for the MJO) is documented; namely, it is shown that intensification of Rossby waves in the central Pacific during boreal summer precedes by half a year the peak of El Niño. The fact that MJO activity in spring-summer is associated to the strength of subsequent El Niño is confirmed. It is shown that LODCA-QTCM is capable of simulating the convectively coupled equatorial waves in outgoing long wave radiation and zonal wind at 850 hPa fields with skill comparable to other Coupled General Circulation Models. The ITV/ENSO relationship is modulated at low frequency. In particular the periods of low ENSO amplitude are associated with weaker MJO activity and a cancellation of MJO at the ENSO development phase. In opposition, during the decaying phase, MJO signal is strong. The periods of strong ENSO activity are associated with a marked coupling between MJO, Kelvin and equatorially Rossby waves and ENSO; the precursor signal of MJO (Rossby waves) in the western (central) Pacific is obvious. The results provide material for the observed change in ENSO characteristics in recent years and question whether the characteristics of the ITV/ENSO relationship may be sensitive to the observed warming in the central tropical Pacific.  相似文献   

19.
We analyze the dynamical features and responsible factors of the low-frequency intraseasonal time scales which influenced the nature of onset, intensity and duration of active/break phases and withdrawal of the monsoon during the anomalous Indian summer monsoon of 2002 — the most severe drought recorded in recent times. During that season, persistent warm sea surface temperature anomalies over the equatorial Indian Ocean played a significant role in modulating the strength of the monsoon Hadley circulation. This in turn affected the onset and intense break spells especially the long break during the peak monsoon month of July. Strong low-frequency intraseasonal modulations with significant impact on the onset and active/break phases occurred in 2002 which were manifested as a good association between low-frequency intraseasonal oscillations and the onset and active/break spells. Further, SST anomalies over the equatorial Indo-Pacific region on low-frequency intraseasonal time scales were found to affect the equatorial eastward and thereby off-equatorial northward propagations of enhanced convection over the Indian region. These propagations in turn modulated the active/break cycle deciding the consequent severity of the 2002 drought.  相似文献   

20.
A daily surface soil moisture model described and tested previously with data from the Phoenix, AR (USA) area, has been applied now to climate data collected in semi-arid Botswana over a multi-year period. The physically based model was calibrated with observed surface moisture data from one growing season and validated with data from another. Good overall agreement (r2 = .89) was found between the observed and modelled data. The seasonal variability of precipitation in this region is reflected in the simulated daily surface moisture. The response of the natural savanna vegetation as observed from monthly composites of satellite-derived Normalized Difference Vegetation Index (NDVI) is also monitored for the same period. It is seen that the NDVI peaks at different times during the rainy season from one year to the next, according not only to the total seasonal precipitation, but its temporal distribution as well. It is also seen that there is a delay in intraseasonal vegetation response. While the NDVI is poorly correlated with the current month's average soil moisture, a distinct relationship with the previous month's average soil moisture was found.  相似文献   

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