共查询到20条相似文献，搜索用时 78 毫秒
1.
Auto-correlation analysis of ocean surface wind vectors 总被引：1，自引：0，他引：1
Abhijit Sarkar Sujit Basu A. K. Varma Jignesh Kshatriya 《Journal of Earth System Science》2002,111(3):297-303
The nature of the inherent temporal variability of surface winds is analyzed by comparison of winds obtained through different
measurement methods. In this work, an auto-correlation analysis of a time series data of surface winds measuredin situ by a deep water buoy in the Indian Ocean has been carried out. Hourly time series data available for 240 hours in the month
of May, 1999 were subjected to an auto-correlation analysis. The analysis indicates an exponential fall of the autocorrelation
in the first few hours with a decorrelation time scale of about 6 hours. For a meaningful comparison between satellite derived
products andin situ data, satellite data acquired at different time intervals should be used with appropriate ‘weights’, rather than treating
the data as concurrent in time. This paper presents a scheme for temporal weighting using the auto-correlation analysis. These
temporal ‘weights’ can potentially improve the root mean square (rms) deviation between satellite andin situ measurements. A case study using the TRMM Microwave Imager (TMI) and Indian Ocean buoy wind speed data resulted in an improvement
of about 10%. 相似文献
2.
基于多重互相关函数分析剪切波速 总被引：1，自引：0，他引：1
介绍了一种提高单孔法剪切波速测量精度的新方法-多重互相关函数法。考虑到判断场地剪切波到时差的困难,提出了用多重互相关函数来求得两剪切波的到时差。互相关分析可求取两相似信号的到时差,但当两信号相似性比较差时,所求得到时差的误差较大;自相关函数本身可进行多重自相关分析,互相关函数结合多重自相关函数后,也可以进行多重互相关分析来求取两相似信号的到时差。试验表明：相比互相关函数,多重互相关函数可改善触发信号和井中三分向探头输出信号的相似性及更好地抑制噪声,因此能更精确地计算出触发信号和井中三分向探头输出信号的的到时差。基于此原理设计了剪切波波速的测试系统,此系统能自动分析出测点的剪切波速和形成完整的报告。 相似文献
3.
P. Vethamony V. M. Aboobacker K. Sudheesh M. T. Babu K. Ashok Kumar 《Natural Hazards》2009,49(2):411-420
The Ministry of Shipping desires to revise the inland vessels’ limit (IVL) notification based on scientific rationale to improve
the safety of vessels and onboard personnel. The Mormugao port region extending up to the Panaji was considered for this pilot
study. Measured winds and wave parameters (AWS and moored buoy) as well as NCEP re-analysis and NCMRWF winds were used for
the analysis and input to regional and local models. The results of wave model were validated with measured significant wave
heights (SWHs) and the comparison shows a good match. The analysis indicates that SWHs do not exceed 2.0 m during non-monsoon
months, and in monsoon months exceed 5.0 m, and even 7.0 m, especially during extreme events. In order to draw IVL contours
for Goa coastal region, local model was set up and nearshore waves were simulated for the period May 2004–May 2005. Based
on the nearshore SWH distribution, IVL contours have been fixed for the Mormugao port and Panaji coastal regions. 相似文献
4.
The spectral characteristics of shallow water waves were studied at two locations along the eastern Arabian Sea during 2011. Wave spectra were single-peaked from June to October and predominantly double-peaked during the rest of the year. Even though both locations were subjected to open sea conditions, the percentage of single-peaked spectra was large (63 %) in the southern location compared to a location 350 km north (46 %), because of variation in local winds. Throughout the year, the double-peaked spectra were mostly swell dominated in the southern location. In the northern location, the double-peaked spectra during January to May and December were sea dominated due to the strong local winds blowing from north-west. For the double-peaked wave spectra, the average difference between the spectral peaks was 0.11 Hz, and the average ratio of the spectral energy density at the two peaks was 0.5. Significant wave heights up to 4.2 m and a maximum wave height of 7 m were observed during the south-west monsoon period. Fifty per cent of the waves recorded had spectral peak wave periods between 6 and 12 s. The narrowest directional spectra were found for waves with 10–12-s peak wave periods. Inverse wave age values were biased towards lower values with peaks in the range of 0.2–0.6, indicating a swell-driven wave regime along the eastern Arabian Sea. 相似文献
5.
为了更好地分析探地雷达(GPR)叠前逆时偏移算法对实际地下随机分布介质的成像效果,采用随机过程的谱分解和混合型自相关函数理论构建了不同自相关长度的GPR随机介质模型。基于时域有限差分法(FDTD)构建了GPR叠前逆时偏移成像算法,其中FDTD用于计算正传和反传电磁波场,归一化互相关成像条件用于获取逆时偏移成像剖面。在此基础上,利用该算法对两个随机介质模型的多偏移距正演数据进行计算,并与相应背景介质为均匀介质的逆时偏移结果进行对比。结果表明:电磁波在随机介质中散射强烈,反射波扭曲变形、不连续,形成了明显的随机扰动,致使逆时偏移成像剖面的空间分辨率更低,低频噪声更强;自相关长度是影响随机介质中异常体成像效果的主要因素,自相关长度越小,异常体的成像越清晰,自相关长度越大,异常体的成像效果越差,且不易被识别。 相似文献
6.
波浪增水抬升了岸礁礁坪的平均水位,对岸礁后方陆域安全有重要影响。通过水槽试验,研究了不规则波况下岸礁礁坪的增水。试验组次为3种礁坪水深、4种有效波高和4种谱峰周期的组合。试验结果表明:①岸礁地形上的波浪要素需至少统计200个波才能达到稳定;②不规则波列在岸礁上破碎过程比规则波列复杂,同一波列中波高较大的波以卷破形式在礁前斜坡上破碎,波高较小的波以崩破形式在礁坪上破碎或者不破碎;③礁坪上最大增水值随入射波周期的增大而增大、随礁坪水深的增大而减小,并与入射波波高呈正比。结合试验数据,发现基于规则波试验得出的Gourlay礁坪增水公式,在使用有效波高和谱峰周期作为代表波要素时,公式能良好地预测不规则波在岸礁礁坪上的最大增水值。 相似文献
7.
Two large meteotsunami wave events on Lake Michigan impacted the Chicago coastline within 10 days of each other in 1954. Initial data analysis suggested that the fatal first event (June 26) was caused by a Proudman resonant non-trapped wave, while the second event (July 6) was caused by Greenspan resonant trapped edge waves. In this study, a numerical hydrodynamic model was used to reveal the detailed behavior of these events. For both events, the atmospheric pressure and wind perturbations were found to be essential to explain the magnitude of the wave activity, in contrast to the initial conclusions that the waves were primarily pressure-driven. In the June 26 meteotsunami, Proudman resonance wave was the primary cause of the destructive wave, though the storm also generated edge waves which persisted for many hours, hindering rescue efforts. The maximum wave heights for the July 6 event were found to be the product of a superposition of edge waves and non-trapped waves rather than purely edge waves as originally thought. The results from these events demonstrate the enclosed Lake Michigan basin retained and focused wave energy, leading to their large magnitude, long duration, and destructive nature. 相似文献
8.
The time series BT profiles and surface winds and atmospheric pressure, collected in the deep waters off Ratnagiri and Karwar
during summer monsoon were utilized to document the characteristics of internal waves (IW). Low-frequency (≤2, cycle per day
(cpd)) IW off Ratnagiri are found to propagate at 83 cm/s with wavelengths of 45 km and wave heights upto 40 m. These parameters
for high-frequency (>2 cpd) IW off Karwar correspond to 99 cm/s, 3 km and 23 m. The IW off Karwar appear to leave the station
at 70° (±10°) (measured from the horizontal). The data sets were further analysed to address the harmonic composition of the
IW and identify the possible sources for the observed IW fields. Power spectra of the IW indicated energy peaks at inertial
(0·6 cpd) and tidal (1 and 2 cpd) frequencies off Ratnagiri and in the high-frequency band of 0·5–2·0 cycles per hour off
Karwar. The coherence between the IW and wind/tide is found to be good at several frequencies within the IW spectrum. This
feature probably suggests tides as a source for the IW of tidal frequencies and winds and tides as a joint source for the
IW at the remaining frequencies. 相似文献
9.
Pablo Iribarren Anacona Kevin Norton Andrew Mackintosh Fernando Escobar Simon Allen Bruno Mazzorana Marius Schaefer 《Natural Hazards》2018,92(1):93-112
The rise of total water levels at the coast is caused primarily by three factors that encompass storm surges, tides and wind waves. The accuracy of total water elevation (TWE) forecast depends not only on the cyclonic track and its intensity, but also on the spatial distribution of winds which include its speed and direction. In the present study, the cyclonic winds are validated using buoy winds for the recent cyclones formed in the Bay of Bengal since 2010 using Jelesnianski wind scheme. It is found that the cyclonic winds computed from the scheme show an underestimate in the magnitude and also a mismatch in its direction. Hence, the wind scheme is suitably modified based on the buoy observations available at different locations using a power law which reduces the exponential decay of winds by about 30%. Moreover, the cyclonic wind direction is also corrected by suitably modifying its inflow angle. The significance of modified exponential factor and inflow angle in the computation cyclonic winds is highlighted using statistical analysis. A hydrodynamic finite element-based Advanced Circulation 2D depth integrated (ADCIRC-2DDI) model is used here to compute TWE as a response to combined effect of cyclonic winds and astronomical tides. As contribution of wave setup plays an important role near the coast, a coupled ADCIRC + SWAN is used to perceive the contribution of wind waves on the TWE. The experiments are performed to validate computed surge residuals with available tide gauge data. On comparison of observed surge residuals with the simulations using modified winds from the uncoupled and coupled models, it is found that the simulated surge residuals are better compared, especially with the inclusion of wave effect through the coupled model. 相似文献
10.
The focus of the present study is the assessment of the impact of wind forcing on the spectral wave model MIKE 21 SW in the Indian Ocean region. Three different wind fields, namely the ECMWF analyzed winds, the ECMWF blended winds, and the NCEP blended winds have been used to drive the model. The wave model results have been compared with in-situ observations and satellite altimeter data. This study also evaluated the performance of the wind products during local phenomenon like sea breeze, since it has a significant impact on the wave prediction in the Indian coastal region. Hence we explored the possibility of studying the impact of diurnal variation of winds on coastal waves using different wind fields. An analysis of the model performance has also been made during high wind conditions with the inference that blended winds generate more realistic wave fields in the high wind conditions and are able to produce the growth and decay of waves more realistically. 相似文献
11.
The low frequency oscillation of latent heat flux over the tropical oceans has been studied. The NCEP reanalyzed fields of
wind and humidity alongwith Reynolds SST are used to compute the instantaneous as well as monthly mean surface latent heat
fluxes (LHF) for the year 1999. The procedure of LHF computation is based on bulk method. Spectral analysis shows that significant
energy is contained in Madden Julian Oscillation band in the winds, SST, moisture and in the latent heat flux. The global
distribution of wind, humidity, SST and LHF oscillation on the time scale of 30–50 days are analyzed. Maximum amplitude of
oscillation on this time scale in all the above mentioned parameters were found over the Indian Ocean. The fluctuation of
surface wind speed and moisture controls the latent heat flux on this time scale. The fluctuation of SST on this time scale
does not seem to be important over most of the oceans. 相似文献
12.
The role of intraseasonal oscillations (ISOs) in modulating synoptic and interannual variations of surface winds over the
Indian monsoon region is studied using daily averaged National Centers for Environmental Prediction/National Centre for Atmospheric
Research (NCEP/NCAR) reanalyses for the period 1987–1996. Two dominant ISOs are found in all years, with a period between
30–60 days and 10–20 days respectively. Although the ISOs themselves explain only about 10–25% of the daily variance, the
spatial structure of variance of the ISOs is found to be nearly identical to that of high frequency activity (synoptic disturbances),
indicating a significant control by the ISOs in determining the synoptic variations. Zonal and meridional propagation characteristics
of the two modes and their interannual variability are studied in detail.
The synoptic structure of the 30–60 day mode is similar in all years and is shown to be intimately related to the strong (‘active’)
or weak (‘break’) phases of the Indian summer monsoon circulation. The peak (trough) phase of the mode in the north Bay of
Bengal corresponds to the ‘active’ (‘break’) phase of monsoon strengthening (weakening) the entire large scale monsoon circulation.
The ISOs modulate synoptic activity through the intensification or weakening of the large scale monsoon flow (monsoon trough).
The peak wind anomalies associated with these ISOs could be as large as 30% of the seasonal mean winds in many regions. The
vorticity pattern associated with the 30–60 day mode has a bi-modal meridional structure similar to the one associated with
the seasonal mean winds but with a smaller meridional scale. The spatial structure of the 30–60 day mode is consistent with
fluctuations of the tropical convergence zone (TCZ) between one continental and an equatorial Indian Ocean position. The 10–20
day mode has maximum amplitude in the north Bay of Bengal, where it is comparable to that of the 30–60 day mode. Elsewhere
in the Indian Ocean, this mode is almost always weaker than the 30–60 day mode. In the Bay of Bengal region, the wind curl
anomalies associated with the peak phases of the ISOs could be as large as 50% of the seasonal mean wind curl. Hence, ISOs
in this region could drive significant ISOs in the ocean and might influence the seasonal mean currents in the Bay.
On the interannual time scale, the NCEP/NCAR reanalysed wind stress is compared with the Florida State University monthly
mean stress. The seasonal mean stress as well as interannual standard deviation of monthly stress from the two analyses agree
well, indicating absence of any serious systematic bias in the NCEP/NCAR reanalysed winds. It is also found that the composite
structure of the 30–60 day mode is strikingly similar to the dominant mode of interannual variability of the seasonal mean
winds indicating a strong link between the ISOs and the seasonal mean. The ISO influences the seasonal mean and its interannual
variability either through increased/decreased residence time of the TCZ in the continental position or through occurrence
of stronger/weaker active/break spells. Thus, the ISOs seem to modulate all variability in this region from synoptic to interannual
scales. 相似文献
13.
The paper presents comprehensive statistical analyses of winds and water levels in Mobile Bay, Alabama, based on long-term meteorological and tidal observations at several locations. A procedure has been developed to select the most probable parent distribution function from a list of candidate distributions. The theoretical functions that fit the data best enable us to predict the extreme values of winds and water levels at different return periods. We have demonstrated the importance of dividing the winds into hurricane and nonhurricane seasons and separating astronomical tides from weather-driven water level changes. The statistical analysis suggests that the wind speed averaged over 8 min at Dauphin Island, Alabama, at the 100-year return period would be 48.9 m/s, which is equivalent to a sustained 1-min wind of 205 km/h, a very strong category 3 hurricane on the Saffir-Simpson scale. The probability distribution models predict that the 100-year maximum water level would be 3.23 m above the mean lower low water (MLLW) level at the bay entrance and 3.41 m above the MLLW level near the head of the bay, respectively. Extremely low water levels important to navigation are also found. Application of the predicted extreme winds and surges is illustrated through the development of a storm wave atlas in the estuary. It is expected that the methodology and results presented in this paper will benefit the management and preservation of the ecosystems and habitats in Mobile Bay. 相似文献
14.
东非鲁武马盆地海底水道-朵体体系粗粒浊流沉积物波特征及主控因素 总被引：2，自引：1，他引：1
海底水道-朵体体系内粗粒沉积物波的研究可以深化浊流搬运过程的认识。利用先进的地球物理成像技术,通过地震地貌分析,对东非鲁武马盆地海底水道-朵体体系内这种后期易被改造的特殊沉积体进行识别和解释,结合粗粒沉积物波的形态、尺度、移动方式、厚度变化、平面分布等特征,探讨其成因和影响因素。鲁武马盆地近海底水道-朵体体系内的粗粒浊流沉积物波具有多变的地貌和逆行砂丘的底形。水道内粗粒沉积物波规模较小,分布范围局限;水道-朵体过渡带的粗粒沉积物波规模大,波高约45~110 m,波长可达一千余米,总体规模大于其他地区已识别出的粗粒深水沉积物波。构造活动、超临界流产生的水跃作用、地形地貌的变化以及底流作用是鲁武马盆地粗粒浊流沉积物波形成的主控因素。 相似文献
15.
G. Muraleedharan N. Unnikrishnan Nair P. G. Kurup 《Journal of Earth System Science》1999,108(3):149-153
It is well accepted that the parent distribution for individual ocean wave heights follows the Weibull model. However this
model does not simulate significant wave height which is the average of the highest one-third of some ‘n’ (n- varies) wave heights in a wave record. It is now proposed to redefine significant wave height as average of the highest one-third
of a constant number (n-constant, say,n = 100) of consecutive individual wave heights. The Weibull model is suggested for simulating redefined significant wave height
distribution by the method of characteristic function. An empirical support of 100.00% is established by Χ2-test at 0.05 level of significance for 3 sets of data at 0900, 1200 and 1500 hrs at Valiathura, Kerala coast. Parametric
relations have been derived for the redefined significant wave height parameters such as mean, maximum one-third average,
extreme wave heights, return periods of an extreme wave height and the probability of realising an extreme wave height in
a time less than the designated return period. 相似文献
16.
Influence of waves and horseshoe crab spawning on beach morphology and sediment grain-size characteristics on a sandy estuarine beach 总被引：2，自引：0，他引：2
The effects of wave action and horseshoe crab spawning on the topography and grain-size characteristics on the foreshore of an estuarine sand beach in Delaware Bay, New Jersey, USA were evaluated using data collected over six consecutive high tides. Data were gathered inside and outside a 25 m long exclosure constructed to create a control area free of disturbance by crabs. The density of crabs in the swash zone outside the exclosure was 8·1 organisms m−2. The maximum depth of sediment activation on the upper foreshore where spawning occurred was 0·103 m during periods characterized by low significant wave heights: < 0·08 m. This depth is greater than the depth of activation by waves alone during moderate significant wave heights of 0·16–0·18 m but less than the maximum depth (0·127 m) recorded when spawning occurred during periods of moderate wave heights. Spawning, combined with moderate wave heights, creates a concave upper foreshore that is similar to the type of profile change that occurs during storms, thus lowering the wave-energy threshold for morphological response. Spawning during low wave heights increases the mean grain size and sorting of surface sediments caused by the addition of gravel to the swash. Sedimentological differences are most pronounced on the upper foreshore, and data from this location may be most useful when using grain-size characteristics to interpret the effect of spawning in the sedimentary record. Depths of sediment reworking by horseshoe crabs can be greater than those by subsequent storm waves, so evidence of spawning can be preserved on non-eroding beaches. Greater depth of activation by horseshoe crab spawning than by waves alone, even during moderate-energy conditions, reveals the importance of crab burrowing in releasing eggs to the water column and making them available for shore birds. 相似文献
17.
Estimating palaeowind strength from beach deposits 总被引：1，自引：0，他引：1
Kenneth D. Adams 《Sedimentology》2003,50(3):565-577
Abstract The geological record of past wind conditions is well expressed in the coarse gravel, cobble and boulder beach deposits of Quaternary palaeolakes in the Great Basin of the western USA and elsewhere. This paper describes a technique, using the particle‐size distribution of beach deposits, to reconstruct palaeowind conditions when the lakes were present. The beach particle technique (BPT) is first developed using coarse beach deposits from the 1986–87 highstand of the Great Salt Lake in Utah, combined with instrumental wind records from the same time period. Next, the BPT is used to test the hypothesis that wind conditions were more severe than at present during the last highstand of Lake Lahontan (≈ 13 ka), which only lasted a decade or two at most. The largest 50 beach clasts were measured at nine beach sites located along the north, west and south sides of Antelope Island in the Great Salt Lake, all of which formed in 1986–87. At these sites, the largest clast sizes range from 10 to 28 cm (b‐axis), and fetch lengths range from 25 to 55 km. Nearshore wave height was calculated by assuming that the critical threshold velocity required to move the largest clasts represents a minimum estimate of the breaking wave velocity, which is controlled by wave height. Shoaling transformations are undertaken to estimate deep‐water wave heights and, ultimately, wind velocity. Wind estimates for the nine sites, using the BPT, range from 6·5 to 17·4 m s?1, which is in reasonable agreement with the instrumental record from Salt Lake City Airport. The same technique was applied to eight late Pleistocene beaches surrounding the Carson Sink sub‐basin of Lake Lahontan, Nevada. Using the BPT, estimated winds for the eight sites range from 9·7 to 27·1 m s?1. The strongest winds were calculated for a cobble/boulder beach with a fetch of 25 km. Instrumental wind records for the 1992–99 period indicate that wind events of 9–12 m s?1 are common and that the strongest significant wind event (≥ 9 m s?1 for ≥ 3 h) reached an average velocity of 15·5 m s?1. Based on this preliminary comparison, it appears that the late Pleistocene western Great Basin was a windier place than at present, at least for a brief time. 相似文献
18.
With the rapid expansion of the scale of deep sea net-cage use in the nearshore area of Hainan Island, tropical cyclone-induced wave hazard assessment is urgently needed. In this study, the wind-wave-current coupled ADCIRC?+?SWAN model, which considers the effects of tidal and storm surges, was used to simulate tropical cyclone events over the last 33 years. This model adopts an unstructured high-resolution grid with a nearshore resolution of up to 100 m. The compared simulated results and observations during typhoons JEBI (2013), HAIYAN (2013) and KALMAEGI (2014) were in agreement. This study statistically analyzed maximum significant wave heights on the basis of a large set of simulated storm wave level maps to derive the wave heights of different return periods. Then, the results of nearshore wave hazard classification were obtained by applying the affinity propagation (AP) clustering method to dozens of nearshore profiles. The results demonstrate that the risk at any point in the nearshore area of Hainan Island is dominated by the wave hazard type and water depth condition. The wave hazard assessment method developed for Hainan Island will be significant in assisting government decision-making in the rational planning of deep sea net-cage aquaculture.
相似文献19.
An analytical form for the source function is formulated by comparing the fetch-limited approximation of the Ocean Wave Transport
equation and the empirical equation for the fetch-dependent wave forecast nomograms. The source function thus generated has
been utilised in the numerical model based on Toba’s formulation of wave transport equation and tested for the seas around
the Indian subcontinent (5°S to 25°N latitude; 45°E to 100°E longitude). The grid averaged hindcast wave heights are found
to be moderately matching with the GEOSAT altimeter measured significant wave heights of the 1987–1989 period, particularly
for waves higher than 1 meter. 相似文献
20.
We have begun an investigation of the possible origins of considerable of powerful solar flares. This effect is manifest, first and foremost, in the existence of high-temperature plasma in flare loops over many hours. Analysis of the soft X-ray emission in two energy bands detected by the GOES satellites for about 20 powerful solar flares reveals long time intervals during the decay phase when the source temperature decreases, in general, exponentially. The characteristic time t i for a decrease in the temperature by a factor of ten is 3–10 hours for most powerful events. In addition, another interval of very slow decrease with a characteristic time t i of tens of hours can be identified in some cases. We found a gradual change in the dependence of the temperature on the square root of the emission measure for the source as a whole, which characterizes the transition from purely coronal processes to powerful flares with a prolonged inflow of plasma from the chromosphere. Modeling the energy balance in a loop can yield the requirements for the source of plasma heating in a long-lived arch system. A necessary condition for the development of prolonged flares seems to be a powerful coronal mass ejection, which initiates the formation of a source of plasma heating at coronal heights. Our analysis shows that a considerable fraction of the energy is often released in the region of the cusp, and that systems of giant coronal arches rising to heights of about 100 000 km above the limb are formed in most prolonged events (called dynamical flares in the terminology of Svestka). 相似文献