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1.
Two modes of dipole events in tropical Indian Ocean 总被引：1，自引：0，他引：1
By analyzing the distributions of subsurface temperature and the surface wind stress anomalies in the tropical Pacific and
Indian Oceans during the Indian Ocean Dipole (IOD) events, two major modes of the IOD and their formation mechanisms are revealed.
(1) The subsurface temperature anomaly (STA) in the tropical Indian Ocean during the IOD events can be described as a “<”
-shaped and west-east-oriented dipole pattern; in the east side of the “<” pattern, a notable tongue-like STA extends westward
along the equator in the tropical eastern Indian Ocean; while in the west side of the “<” pattern, the STA has opposite sign
with two centers (the southern one is stronger than the northern one in intensity) being of rough symmetry about the equator
in the tropical mid-western Indian Ocean. (2) The IOD events are composed of two modes, which have similar spatial pattern
but different temporal variabilities due to the large scale air-sea interactions within two independent systems. The first
mode of the IOD event originates from the air-sea interaction on a scale of the tropical Pacific-Indian Ocean and coexists
with ENSO. The second mode originates from the air-sea interaction on a scale of the tropical Indian Ocean and is closely
associated with changes in the position and intensity of the Mascarene high pressure. The strong IOD event occurs when the
two modes are in phase, and the IOD event weakens or disappears when the two modes are out of phase. Besides, the IOD events
are normally strong when either of the two modes is strong. (3) The IOD event is caused by the abnormal wind stress forcing
over the tropical Indian Ocean, which results in vertical transports, leading to the upwelling and pileup of seawater. This
is the main dynamic processes resulting in the STA. When the anomalous easterly exists over the equatorial Indian Ocean, the
cold waters upwell in the tropical eastern Indian Ocean while the warm waters pileup in the tropical western Indian Ocean,
hence the thermocline in the tropical Indian Ocean is shallowed in the east and deepened in the west. The off-equator component
due to the Coriolis force in the equatorial area causes the upwelling of cold waters and the shallowing of the equatorial
India Ocean thermocline. On the other hand, the anomalous anticyclonic circulations and their curl fields located on both
sides of the equator, cause the pileup of warm waters in the central area of their curl fields and the deepening of the equatorial
Indian Ocean thermocline off the equator. The above three factors lead to the occurrence of positive phase IOD events. When
anomalous westerly dominates over the tropical Indian Ocean, the dynamic processes are reversed, and the negative-phase IOD
event occurs.
Supported by National Natural Science Foundation of China (Grant No. 40776013), National Basic Research Program of China (Grant
No. 2006CB403601) and the Knowledge Innovation Project of Chinese Academy of Sciences (Grant No. KZCX-SW-222) 相似文献
2.
Interannual variability in the Biannual Rossby waves in the tropical Indian Ocean and its relation to Indian Ocean Dipole and El Nino forcing 总被引：1，自引：0，他引：1
The interannual variability of the tropical Indian Ocean is studied using Simple Ocean Data Assimilation (SODA) sea surface
height anomalies (SSHA) and Hadley Centre Ice Sea Surface Temperature anomalies. Biannual Rossby waves (BRW) were observed
along the 1.5° S and 10.5° S latitudes during the Indian Ocean Dipole (IOD) years. The SODA SSHA and its BRW components were
comparable with those of Topex/Poseidon. The phase speed of BRW along 1.5° S is −28 cm/s, which is comparable with the theoretical
speed of first mode baroclinic (equatorially trapped) Rossby waves. This is the first study to show that no such propagation
is seen along 1.5° S during El Nino years in the absence of IOD. Thus the westward propagating downwelling BRW in the equatorial
Indian Ocean is hypothesized as a potential predictor for IOD. These waves transport heat from the eastern equatorial Indian
Ocean to west, long before the dipole formation. Along 10.5° S, the BRW formation mechanisms during the El Nino and IOD years
were found to be different. The eastern boundary variations along 10.5° S, being localized, do not influence the ocean interior
considerably. Major portion of the interannual variability of the thermocline, is caused by the Ekman pumping integrated along
the characteristic lines of Rossby waves. The study provides evidence of internal dynamics in the IOD formation. The positive
trend in the downwelling BRW (both in SODA and Topex/Poseidon) is of great concern, as it contributes to the Indian Ocean
warming. 相似文献
3.
《中国科学:地球科学(英文版)》2015,(8)
Based on the merged satellite altimeter data and in-situ observations,as well as a diagnosis of linear baroclinic Rossby wave solutions,this study analyzed the rapidly rise of sea level/sea surface height(SSH)in the tropical Pacific and Indian Oceans during recent two decades.Results show that the sea level rise signals in the tropical west Pacific and the southeast Indian Ocean are closely linked to each other through the pathways of oceanic waveguide within the Indonesian Seas in the form of thermocline adjustment.The sea level changes in the southeast Indian Ocean are strongly influenced by the low-frequency westward-propagating waves originated in the tropical Pacific,whereas those in the southwest Indian Ocean respond mainly to the local wind forcing.Analyses of the lead-lag correlation further reveal the different origins of interannual and interdecadal variabilities in the tropical Pacific.The interannual wave signals are dominated by the wind variability along the equatorial Pacific,which is associated with the El Ni?o-Southern Oscillation;whereas the interdecadal signals are driven mainly by the wind curl off the equatorial Pacific,which is closely related to the Pacific Decadal Oscillation. 相似文献
4.
Using reanalysis data, the role of initial signals in the tropical Pacific Ocean in predictions of negative Indian Ocean Dipole (IOD) events were analyzed. It was found that the summer predictability barrier (SPB) phenomenon exists in predictions, which is closely related to initial sea temperature errors in the tropical Pacific Ocean, with type-1 initial errors presenting a significant west-east dipole pattern in the tropical Pacific Ocean, and type-2 initial errors showing the opposite spatial pattern. In contrast, SPB-related initial sea temperature errors in the tropical Indian Ocean are relatively small. The initial errors in the tropical Pacific Ocean induce anomalous winds in the tropical Indian Ocean by modulating the Walker circulation in the tropical oceans. In the first half of the prediction year, the anomalous winds, combined with the climatological winds in the tropical Indian Ocean, induce a basin-wide mode of sea surface temperature (SST) errors in the tropical Indian Ocean. With the reversal of the climatological wind in the second half of the prediction year, a west-east dipole pattern of SST errors appears in the tropical Indian Ocean, which is further strengthened under the Bjerknes feedback, yielding a significant SPB. Moreover, two types of precursors were also identified: a significant west-east dipole pattern in the tropical Pacific Ocean and relatively small temperature anomalies in the tropical Indian Ocean. Under the combined effects of temperature anomalies in the tropical Indian and Pacific oceans, northwest wind anomalies appear in the tropical Indian Ocean, which induce a significant west-east dipole pattern of SST anomalies, and yield a negative IOD event. 相似文献
5.
XiaoYuan Hong HaiBo Hu XiuQun Yang Yuan Zhang GuoQiang Liu Wei Liu 《中国科学:地球科学(英文版)》2014,57(11):2616-2627
Both the tropical Indian and tropical Pacific Oceans are active atmosphere-ocean interactive regions with robust interannual variability, which also constitutes a linkage between the two basins in the mode of variability. Using a global atmosphereocean coupled model, we conducted two experiments(CTRL and PC) to explore the contributions of Indian Ocean interannual sea surface temperature(SST) modes to the occurrence of El Ni?o events. The results show that interannual variability of the SST in the Indian Ocean induces a rapid growth of El Ni?o events during the boreal autumn in an El Ni?o developing year. However, it weakens El Ni?o events or even promotes cold phase conversions in an El Ni?o decaying year. Therefore, the entire period of the El Ni?o is shortened by the interannual variations of the Indian Ocean SST. Specifically, during the El Ni?o developing years, the positive Indian Ocean Dipole(IOD) events force an anomalous Walker circulation, which then enhances the existing westerly wind anomalies over the west Pacific. This will cause a warmer El Ni?o event, with some modulations by ocean advection and oceanic Rossby and Kelvin waves. However, with the onset of the South Asian monsoon, the Indian Ocean Basin(IOB) warming SST anomalies excite low level easterly wind anomalies over the west tropical Pacific during the El Ni?o decaying years. As a result, the El Ni?o event is prompted to change from a warm phase to a cold phase. At the same time, an associated atmospheric anticyclone anomaly appears and leads to a decreasing precipitation anomaly over the northwest Pacific. In summary, with remote forcing in the atmospheric circulation, the IOD mode usually affects the El Ni?o during the developing years, whereas the IOB mode affects the El Ni?o during the decaying years. 相似文献
6.
南印度洋副热带偶极模（Subtropical Dipole Pattern,SDP）是印度洋存在的另一种很明显的偶极型海温差异现象,在年际和年代际尺度上均有十分明显的表现.而目前有关印度洋海气相互作用的研究主要集中在赤道印度洋地区,针对南印度洋地区的工作还比较少,特别是有关南印度洋海温与ENSO（El NiDo-Southern Oscillation）事件关系的研究.本文初步探讨了年际尺度上南印度洋副热带偶极型海温变化差异与ENSO事件的关系,发现SDP与ENSO事件有密切的联系,SDP事件就像连接正负ENSO位相转换的一个中间环节,SDP事件前后期ENSO的位相刚好完全相反.进一步,本文通过分析SDP事件前后期海温、高低层风、低层辐合辐散、高空云量和辐射等的变化特征研究了南印度洋偶极型海温异常在ENSO事件中的作用,结果表明：SDP在ENSO事件中的作用不仅涉及海气相互作用的正负反馈过程,还与热带和副热带大气环流之间的相互作用有关,特别是与东南印度洋海温变化所引起的异常纬向风由赤道印度洋向赤道太平洋传播的过程等有十分直接的关系;同时,SDP对ENSO事件的影响在很大程度上还依赖于大尺度平均气流随季节的变换. 相似文献
7.
The tropical Indian Ocean experiences an interannual mode of climatic variability, known as the Indian Ocean Dipole (IOD). The signature of this variability in ocean salinity is hypothesized based on modeling and assimilation studies, on account of scanty observations. Soil Moisture and Ocean Salinity (SMOS) satellite has been designed to take up the challenge of sea surface salinity remote sensing. We show that SMOS data can be used to infer the pattern of salinity variability linked with the IOD events. The core of maximum variability is located in the central tropical basin, south of the equator. This region is anomalously salty during the 2010 negative IOD event, and anomalously fresh during the 2011 positive IOD event. The peak-to-peak anomaly exceeds one salinity unit, between late 2010 and late 2011. In conjunction with other observational datasets, SMOS data allow us to draw the salt budget of the area. It turns out that the horizontal advection is the main driver of salinity anomalies. This finding is confirmed by the analysis of the outputs of a numerical model. This study shows that the advent of SMOS makes it feasible the quantitative assessment of the mechanisms of ocean surface salinity variability in the tropical basins, at interannual timescales. 相似文献
8.
The tropical Indian Ocean experiences an interannual mode of climatic variability, known as the Indian Ocean Dipole (IOD). The signature of this variability in ocean salinity is hypothesized based on modeling and assimilation studies, on account of scanty observations. Soil Moisture and Ocean Salinity (SMOS) satellite has been designed to take up the challenge of sea surface salinity remote sensing. We show that SMOS data can be used to infer the pattern of salinity variability linked with the IOD events. The core of maximum variability is located in the central tropical basin, south of the equator. This region is anomalously salty during the 2010 negative IOD event, and anomalously fresh during the 2011 positive IOD event. The peak-to-peak anomaly exceeds one salinity unit, between late 2010 and late 2011. In conjunction with other observational datasets, SMOS data allow us to draw the salt budget of the area. It turns out that the horizontal advection is the main driver of salinity anomalies. This finding is confirmed by the analysis of the outputs of a numerical model. This study shows that the advent of SMOS makes it feasible the quantitative assessment of the mechanisms of ocean surface salinity variability in the tropical basins, at interannual timescales.
相似文献9.
Seasonal and interannual patterns of sea surface temperature in Banda Sea as revealed by self-organizing map 总被引：1，自引：0，他引：1
Seasonal and interannual variations of sea surface temperature (SST) in the Banda Sea are studied for the period of January 1985 through December 2007. A neural network pattern recognition approach based on self-organizing map (SOM) has been applied to monthly SST from the Advanced Very High Resolution Radiometer (AVHRR) Oceans Pathfinder. The principal conclusions of this paper are outlined as follows. There are three different patterns associated with the variations in the monsoonal winds: the southeast and northwest monsoon patterns, and the monsoon-break patterns. The southeast monsoon pattern is characterized by low SST due to the prevailing southeasterly winds that drive Ekman upwelling. The northwest monsoon pattern, on the other hand, is one of high SST distributed uniformly in space. The monsoon-break pattern is a transitional pattern between the northwest and southeast monsoon patterns, which is characterized by moderate SST patterns. On interannual time-scale, the SST variations are significantly influenced by the El Niño-Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) phenomena. Low SST is observed during El Niño and/or positive IOD events, while high SST appears during La Niña event. Low SST in the Banda Sea during positive IOD event is induced by upwelling Kelvin waves generated in the equatorial Indian Ocean which propagate along the southern coast of Sumatra and Java before entering the Banda Sea through the Lombok and Ombai Straits as well as through the Timor Passage. On the other hand, during El Niño (La Niña) events, upwelling (downwelling) Rossby waves associated with off-equatorial divergence (convergence) in response to the equatorial westerly (easterly) winds in the Pacific, partly scattered into the Indonesian archipelago which in turn induce cool (warm) SST in the Banda Sea. 相似文献
10.
B. H. Vaid C. Gnanaseelan P. S. Polito P. S. Salvekar 《Pure and Applied Geophysics》2007,164(8-9):1765-1785
The sea-surface height anomalies derived from Simple Ocean Data Assimilation (SODA) during 1958–2001, Topex/Poseidon satellite
during 1993–2001 and the SODA heat content anomalies (125 m depth) during 1958–2001 are filtered into annual and biennial
Rossby wave components using a two-dimensional Finite Impulse Response filter. The filtered Rossby wave components (both annual
and biennial) in the southern Pacific and Indian Oceans have considerable strength and variability. The propagation of annual
and biennial Rossby waves in the Indonesian through-flow region [12.5°S–7.5°S] of the Indian Ocean is in phase with the southern
Pacific Ocean waves. So it is speculated that the Pacific Ocean influences the Indian Ocean, especially through the region
17.5°S to 7.5°S and thus the southern Pacific Rossby waves could be an unexplored contributor to the Indian Ocean Rossby waves.
We also carried out Fast Fourier Transform (FFT) and wavelet analysis on the tide gauge sea-level data along the Australian
coast to support our claim. Filtered annual and biennial components of SODA heat content anomalies (125 m depth) also support
these findings. 相似文献
11.
印度洋海表温度（Sea Surface Temperature，简称SST）的方差分析和相关分析表明南印度洋也存在一个海温偶极子型振荡，并定义了一个南印度洋海表温度异常偶极子指数.夏、秋季（南半球冬、春）的南印度洋偶极子指数与后期热带500hPa和100hPa高度场异常有显著而持续的相关，在冬、春达到最大，并可以持续到次年夏、秋.前期夏、秋季节的南印度洋偶极模对次年我国大陆东部夏季降水异常有显著的影响，对应偶极子正位相，次年夏季印度洋、南海（东亚）夏季风偏弱；副高加强且南撤、西伸，南亚高压偏强且位置偏东，易形成我国长江流域降水偏多，华南降水偏少；负位相年反之.后期冬季西太平洋暖池是联系南印度洋偶极子与次年我国夏季降水异常关系的一条重要途径.南印度洋偶极子表现出了明显的独立于ENSO（El Nio Southern Oscillation，简称ENSO）的特征. 相似文献
12.
Multi-scale variability of the tropical Indian Ocean circulation system revealed by recent observations 总被引：1，自引：0，他引：1
Ke HUANG Dongxiao WANG Weiqiang WANG Qiang XIE Ju CHEN Lingfang CHEN Gengxin CHEN 《中国科学:地球科学(英文版)》2018,(6)
The tropical Indian Ocean circulation system includes the equatorial and near-equatorial circulations, the marginal sea circulation, and eddies. The dynamic processes of these circulation systems show significant multi-scale variability associated with the Indian Monsoon and the Indian Ocean dipole. This paper summarizes the research progress over recent years on the tropical Indian Ocean circulation system based on the large-scale hydrological observations and numerical simulations by the South China Sea Institute of Oceanology(SCSIO), Chinese Academy of Sciences. Results show that:(1) the wind-driven Kelvin and Rossby waves and eastern boundary-reflected Rossby waves regulate the formation and evolution of the Equatorial Undercurrent and the Equatorial Intermediate Current;(2) the equatorial wind-driven dynamics are the main factor controlling the inter-annual variability of the thermocline in the eastern Indian Ocean upwelling;(3) the equatorial waves transport large amounts of energy into the Bay of Bengal in forms of coastal Kelvin and reflected free Rossby waves. Several unresolved issues within the tropical Indian Ocean are discussed:(i) the potential effects of the momentum balance and the basin resonance on the variability of the equatorial circulation system, and(ii) the potential contribution of wind-driven dynamics to the life cycle of the eastern Indian Ocean upwelling. This paper also briefly introduces the international Indian Ocean investigation project of the SCSIO, which will advance the study of the multi-scale variability of the tropical Indian Ocean circulation system, and provide a theoretical and data basis to support marine environmental security for the countries around the Maritime Silk Road. 相似文献
13.
Porathur V. Joseph 《Surveys in Geophysics》2014,35(3):723-738
Asian summer monsoon sets in over India after the Intertropical Convergence Zone moves across the equator to the northern hemisphere over the Indian Ocean. Sea surface temperature (SST) anomalies on either side of the equator in Indian and Pacific oceans are found related to the date of monsoon onset over Kerala (India). Droughts in the June to September monsoon rainfall of India are followed by warm SST anomalies over tropical Indian Ocean and cold SST anomalies over west Pacific Ocean. These anomalies persist till the following monsoon which gives normal or excess rainfall (tropospheric biennial oscillation). Thus, we do not get in India many successive drought years as in sub-Saharan Africa, thanks to the ocean. Monsoon rainfall of India has a decadal variability in the form of 30-year epochs of frequent (infrequent) drought monsoons occurring alternately. Decadal oscillations of monsoon rainfall and the well-known decadal oscillation in SST of the Atlantic Ocean (also of the Pacific Ocean) are found to run parallel with about the same period close to 60 years and the same phase. In the active–break cycle of the Asian summer monsoon, the ocean and the atmosphere are found to interact on the time scale of 30–60 days. Net heat flux at the ocean surface, monsoon low-level jetstream (LLJ) and the seasonally persisting shallow mixed layer of the ocean north of the LLJ axis play important roles in this interaction. In an El Niño year, the LLJ extends eastwards up to the date line creating an area of shallow ocean mixed layer there, which is hypothesised to lengthen the active–break (AB) cycle typically from 1 month in a La Niña to 2 months in an El Niño year. Indian monsoon droughts are known to be associated with El Niños, and long break monsoon spells are found to be a major cause of monsoon droughts. In the global warming scenario, the observed rapid warming of the equatorial Indian ocean SST has caused the weakening of both the monsoon Hadley circulation and the monsoon LLJ which has been related to the observed rapid decreasing trend in the seasonal number of monsoon depressions. 相似文献
14.
We studied the structure of the Indian Ocean(IO)Meridional Overturning Circulation(MOC)by applying a nonlinear inertia theory and analyzed the coupled relationship between zonal wind stress and MOC anomalies.Our results show that the inertia theory can represent the main characteristics of the IO MOC:the subtropical cell(STC)and cross-equator cell(CEC).The stream function in equatorial and northern IO changes a sign from winter to summer.The anomalies of the zonal wind stress and stream function can be decomposed into summer monsoon mode,winter monsoon mode,and abnormal mode by using the singular vector decomposition(SVD)analysis.The first two modes correlate with the transport through 20°S and equator simultaneously whereas the relationship obscures between the third mode and transports across 20°S and equator,showing the complex air-sea interaction process.The transport experiences multi-time scale variability according to the continuous power spectrum analysis,with major periods in inter-annual and decadal scale. 相似文献
15.
The characteristics and variability of the East India Coastal Current (EICC), the western boundary current in the Bay of Bengal (BoB) during the Indian Ocean Dipole (IOD) years between 2006 and 2012 have been investigated using the high-resolution Regional Ocean Modeling System (ROMS). The evolution of temperature, mixed layer depth (MLD), and seasonal basin scale circulation in the upper ocean simulated by the model agrees well with the observations. The EICC in BoB is characterized by a seasonal reversal flow: the poleward EICC during February?May and the equatorward EICC during August?December. A long-term simulation from 2006 to 2012 suggest that the circulation pattern, boundary current structure, and transport in the western BoB are completely different in positive and negative IOD years. As IOD is mainly phase-locked to the seasonal cycle with most significant influence in the Borel autumn, the equatorward EICC is affected during the IOD years. It is found that the strength of this EICC is ~?5 Sv in October 2010 and a weaker EICC dominated by the presence of eddies is observed in October 2006. We also quantified the local and remote forcing effects on the variability of EICC and found that the seasonal coastal Kelvin waves (KWs) play a dominant role in the development of the EICC. During positive IOD year 2006, due the absence of second downwelling KW, the EICC is completely disorganized and dominated by the eddies, whereas in the negative IOD year 2010, the strong second downwelling KW plays a key role in developing organized and stable EICC in the western BoB. 相似文献
16.
Ocean Dynamics - The present study focuses on the variability of subsurface ocean temperature and associated planetary waves (oceanic Kelvin and Rossby waves) in the Indian Ocean during the boreal... 相似文献
17.
本文分析了夏季西北太平洋大气环流异常特征及其与海温变化的关系,发现夏季西北太平洋异常反气旋/气旋(WNPAC/WNPC)是西北太平洋地区对流层中低层存在的重要大气环流异常现象,与东亚-西北太平洋低纬度至高纬度的经向PJ波列及欧亚中高纬度东西纬向波列的变化有关,通过与中高纬度环流变化的联系,对东亚及欧亚中高纬度气候有重要影响.夏季WNPAC/WNPC与热带海温变化的关系存在明显的不对称性,显著的WNPAC一般出现在El Niño衰减年夏季,与前期El Niño成熟年冬季的赤道东太平洋暖海温异常和El Niño衰减年春夏季印度洋海盆尺度的暖海温异常有明显的正相关关系,进一步表明了WNPAC在El Niño事件影响夏季气候中的重要桥梁作用;而夏季显著的WNPC与前期和同期热带海温变化的关系存在明显的不确定性,主要与夏季热带印度洋和赤道中东太平洋之间东暖西冷的热力差异异常引起的孟加拉湾-赤道西太平洋西风异常有关.进一步分析WNPAC/WNPC与海温变化关系不对称的可能原因,发现El Niño和La Niña衰减年夏季热带印度洋和太平洋海温变化所引起的印-太之间海温(热力)差异的一致性特征可能是导致WNPAC/WNPC与海温变化关系不对称的主要原因. 相似文献
18.
Pramanik Saikat Sil Sourav Mandal Samiran Dey Dipanjan Shee Abhijit 《Ocean Dynamics》2019,69(11):1253-1271
Role of equatorial forcing on the thermocline variability in the Bay of Bengal (BoB) during positive and negative phases of the Indian Ocean Dipole (IOD) and El Niño Southern Oscillation (ENSO) was investigated using the Regional Ocean Modeling System (ROMS) simulations during 1988 to 2015. Two numerical experiments were carried out for (i) the Indian Ocean Model (IOM) with interannual open boundary conditions and (ii) the BoB Model (BoBM) with climatological boundary conditions. The first mode of Sea Surface Height Anomalies (SSHA) variability showed a west-east dipole nature in both IOM and altimetry observations around 11°N, which was absent in the BoBM. The vertical section of temperature along the same latitude showed a sharp subsurface temperature dipole with a core at ~ 100 m depth. The positive (negative) subsurface temperature anomalies were observed over the whole northeastern BoB during NIOD (PIOD) and LN (EN) composites due to stronger (weaker) second downwelling Kelvin Waves. During the negative phases of IOD and ENSO, the cyclonic eddy on the southwestern BoB strengthened due to intensified southward coastal current along the western BoB and local wind stress. The subsurface temperature dipole was at its peak during October–December (OND) with 1-month lag from IOD and was evident from the Argo observations and other reanalysis datasets as well. A new BoB dipole index (BDI) was defined as the normalized difference of 100-m temperature anomaly and found to be closely related to the frequency of cyclones and the surface chlorophyll-a concentration in the BoB.
相似文献19.
Tide gauge data collected from Sri Lanka (three stations) and Western Australia (eleven stations) during the Indian Ocean tsunamis, which occurred in December 2004, March 2005, July 2006, and September 2007, and incorporated five tsunamis, were examined to determine tsunami behaviour during these events. During the December 2004 tsunami, maximum wave heights of 3.87 m and 1.75 m were recorded at Colombo (Sri Lanka) and Bunbury (Western Australia), respectively. The results indicated that although the relative magnitudes of the tsunamis varied, the tsunami behaviour at each station was similar. This was due to the effect of the local and regional topography. At all tide gauges, the spectral energy corresponding to periods between 20 and 85 minutes increased during the tsunami. The sea-level data obtained from the west and south coasts of Sri Lanka (Colombo and Kirinda) indicated the importance of wave reflections from the Maldives Island chain, which produced the maximum wave two to three hours after the arrival of the first wave. In contrast, Trincomalee on the east coast did not show evidence of a reflected wave. Similarly, along the west coast of Australia, the highest waves occurred 15 hours after the arrival of the first wave. Here, based on travel times, we postulated that the waves were reflected from the Mascarene Ridge and/or the Island of Madagascar. Reflected waves were not present in the 2006 tsunami, where the primary waves propagated away from topographic features. One of the main influences of the tsunami was to set up oscillations at the local resonance frequency. Because Sri Lanka and Western Australia have relatively straight coastlines, these oscillations were related to the fundamental period of the shelf oscillation. For Colombo, this corresponded to 75-minute period, whereas in Geraldton and Busselton (Australia), the four-hour period was most prominent; at Jurien Bay and Fremantle, the resonance period was 2.7 hours. 相似文献
20.
This paper presents tsunami intensity mapping and damage patterns along the surveyed coast of Tamilnadu (India) of the deadly
Indian Ocean tsunami of December 26, 2004. The tsunami caused severe damage and claimed many victims in the coastal areas
of eleven countries bordering the Indian Ocean. A twelve-stage tsunami intensity scale proposed by Papadopoulos and Imamura
(2001) was followed to assign the intensity at the visited localities. Along the coast of the Indian mainland, tsunami damage
sustained exclusively. Most severe damage was observed in Nagapattinam Beach, Nabiyarnagar, Vellaipalyam, and the Nagapattinam
Port of Nagapattinum District on the east coast and Keelamanakudy village of Kanyakumari District on the western coast of
Tamilnadu. The maximum assigned tsunami intensity was X+ at these localities. Minimum intensity V+ was received along the coast of Thanjavur, Puddukkotai and Ramnathpuram Districts in Palk Strait. The general observation
reported by many people was that the first arrival was a tsunami crest. The largest tsunami waves were first arrivals on the
eastern coast and the second arrivals on the western coast. Along the coast, people were unaware of the tsunami, and no anomalous
behavior of ocean animals was reported. Good correlation was observed between the severity of damage and the presence of shadow
zone of Sri Lanka, reflected waves from Sri Lanka and the Maldives Islands, variation in the width of the continental shelf,
elevation of the coast and the presence of breakwaters. The presence of medu (naturally elevated landmass very close to the
sea shore and elongated parallel to the coast) reduced the impact of the tsunami on the built environment. 相似文献