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1.
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
2.
K. V. S. R. Prasad S. V. V. Arun Kumar Ch. Venkata Ramu P. Sreenivas 《Natural Hazards》2009,49(2):347-360
The nearshore parameters, viz., wave runup, wave setup, and wave energy have been estimated during storm and normal conditions
of SW monsoon (June–September) and NE monsoon (November–February) by empirical parameterization along Visakhapatnam coast.
These results were compared with the field observations during three storms of SW monsoon season in the year 2007. The higher
nearshore wave energies were observed at R.K. Beach, Jodugullapalem beach, and Sagarnagar beach during both the seasons. During
storm events, the higher wave energies associated with higher wave runups cause severe erosion along the wave convergence
zones. The storm wave runups (SWRUs) were higher at R.K. Beach, Palm beach, Jodugullapalem beach, and Sagarnagar Beach. The
yearly low wave energy was observed at Lawson’s Bay with lowest wave runup, considered as safest zone. R.K. Beach, Palm beach,
and Jodugullapalem beach are identified as vulnerable zones of wave attack. It is noteworthy that in addition to wave energies,
wave runups and wave setups also play a vital role in endangering the coast. 相似文献
3.
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
4.
The cyclone wave parameters are predicted using Young’s parametric hurricane wave prediction model. The input cyclone tracks
for this work are obtained from Fleet Naval Meteorology and Oceanography Center, USA. Extreme value analysis is carried out
to obtain the wave heights and periods for 1 in 5, 10, 50 and 100 years return periods, respectively. The deep-water hindcast
wave corresponding to 100 years from probable directions are allowed to propagate to Visakhapatnam coastal waters using nearshore
spectral wind-wave mode. The offshore wave height for one in 100-year return period is 11.9 m, and the corresponding nearshore
wave height at 10-m water depth varies between 4.6 and 5.6 m depending on the directional spreading. Weibull distribution
is chosen to fit the 24 cyclonic data sets over a total period of 30 years (September 1972 to November 2002). This paper demonstrates
usefulness of Young’s wave model for deep-water extreme wave hindcasting. Further, the results of the present study would
be highly useful for assessing the design wave height for Visakhapatnam coast. 相似文献
5.
Cyclone-generated surface waves are simulated using state-of-art SWAN (Simulating WAves Nearshore) model coupled with hydrodynamic
model inputs. A severe cyclonic storm passed over the Arabian Sea during 4–9th November 1982 is selected from UNISYS track
records. The cyclone lasted for nearly 6 days and subsided with a land fall at Gujarat coast, west coast of India. In this
study, cyclonic wind fields are generated using a well-established relationship suggested by Jelesnianski and Taylor (1973). The associated water level variations due to storm surge and surge generated currents are simulated using POM (Princeton
Ocean Model). The outputs are one-way coupled with the wave model SWAN for simulating wave parameters off Gujarat, north-east
basin of Arabian Sea. An extensive literature review is carried out on the progress and methodology adopted for storm wave
modelling and analysis. The results presented in this paper reveal the severity of the storm event and would be highly useful
for assessing the extreme wave event/climate especially for the south coast of Gujarat. 相似文献
6.
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
7.
The disastrous effects of numerous winter storms on the marine environment in the North Sea and the Baltic Sea during the
last decade show that wind waves generated by strong winds actually represent natural hazards and require high quality wave
forecast systems as warning tools to avoid losses due to the impact of rough seas. Hence, the operational wave forecast system
running at the German Weather Service including a regional wave model for the North Sea and the Baltic Sea is checked extensively
whether it provides reasonable wave forecasts, especially for periods of extraordinary high sea states during winter storms.
For two selected extreme storm events that induced serious damage in the area of interest, comprehensive comparisons between
wave measurements and wave model forecast data are accomplished. Spectral data as well as integrated parameters are considered,
and the final outcome of the corresponding comparisons and statistical analysis is encouraging. Over and above the capability
to provide good short-term forecast results, the regional wave model is able to predict extreme events as severe winter storms
connected with extraordinary high waves already about 2 days in advance. Therefore, it represents an appropriate warning tool
for offshore activities and coastal environment. 相似文献
8.
Summary. The purpose of this paper is to establish a dynamic constitutive model of fracture normal behaviour, based on laboratory tests
of artificial fractures cast by cement mortar. A series of tests are systematically carried out under quasi-static (10−1 MPa/s) up to highly dynamic (103 MPa/s) monotonic loading conditions. The normal stress-fracture closure response is measured at different loading rates.
Based on the measured curves, a nonlinear (hyperbolic) dynamic model of fracture normal behaviour, termed as dynamic BB model,
is proposed. The dynamic model is modified from the existing BB model of static normal behaviour of fractures by taking into
account the loading-rate effect. Two important dynamic parameters of fractures, FSC
d
(dynamic fracture stiffness constant, which describes the incremental ratio of dynamic initial stiffness) and FCC
d
(dynamic fracture closure constant, which describes the decremental ratio of dynamic maximum allowable closure), are identified.
They indicate the quantitative degree of loading-rate effect on fracture normal behaviour subjected to dynamic loads. For
practical application, the new model is incorporated into the Universal Distinct Element Code (UDEC) and subsequently, UDEC
modelling of normally incident P-wave transmission across single fractures with the dynamic BB model is conducted. Wave transmission
coefficient is obtained for various combinations of fracture dynamic parameters, as well as different wave amplitudes and
frequencies. The numerical results show that wave transmission coefficient for a fracture with the dynamic BB model is greater
than that for a fracture with the static BB model. In addition, a fracture with higher values of FSC
d
and FCC
d
leads to higher transmission (lower attenuation).
Author’s address: J. Zhao, Ecole Polytechnique Federale de Lausanne (EPFL), Rock Mechanics Laboratory, 1015 Lausanne, Switzerland 相似文献
9.
近年来随着极端天气/气候事件的频发,应对极端天气/气候事件的要求极其紧迫。目前气象资料对极端天气/气候事件的研究相对较短,由此作者提出利用石笋记录重建历史年际、年代际极端天气/气候事件的构想。通过对目前已有的石笋极端天气/气候事件研究实例分析总结,认为洞穴石笋沉积速率相对较快,石笋中标志性结构构造特征的存在,有利于石笋记录到极端天气/气候事件。同时就目前的研究现状,作者提出建立准确年代标尺、选择生长速率相对较快和存在标志性结构构造特征、能记录到极端气候的石笋,以及提高采样分辨率和与其他记录相互验证等作为石笋极端气候研究的工作要求,同时就文石笋研究极端天气/气候事件提出文石笋可能更加容易记录到极端天气/气候事件的个人新认识。 相似文献
10.
Impact of sea breeze on wind-seas off Goa, west coast of India 总被引:1,自引:0,他引:1
After withdrawal of the Indian Summer Monsoon and until onset of the next monsoon, i.e., roughly during November–May, winds
in the coastal regions of India are dominated by sea breeze. It has an impact on the daily cycle of the sea state near the
coast. The impact is quite significant when large scale winds are weak. During one such event, 1–15 April 1997, a Datawell
directional waverider buoy was deployed in 23 m water depth off Goa, west coast of India. Twenty-minute averaged spectra,
collected once every three hours, show that the spectrum of sea-breeze-related ‘wind-seas’ peaked at 0.23 ±0.05 Hz. These
wind-seas were well separated from swells of frequencies less than 0.15 Hz. The TMA spectrum (Bouwset al 1985) matched the observed seas spectra very well when the sea-breeze was active and the fetch corresponding to equilibrium
spectrum was found to be 77±43 km during such occasions. We emphasize on the diurnal cycle of sea-breeze-related sea off the
coast of Goa and write an equation for the energy of the seas as a function of the local wind 相似文献
11.
Mohammed Taaouati Driss Nachite Javier Benavente Abdelmounim Elmrini 《Environmental Earth Sciences》2011,64(5):1225-1236
The morphodynamic behavior of a mesotidal sandy beach was monitored during both calm and energetic conditions. Two years of
seasonal surveys were carried out on Charf el Akab, a gently sloped beach in the North Atlantic coast of Morocco. The method
of survey consisted of a 3D study of the beach morphological changes and provided 2 cm vertical accuracy. During the surveyed
period, Charf el Akab beach underwent very energetic wave conditions, and the breaking wave height was of H
b ≥ 1.5 m. The beach is characterized by a nonpermanent swash bar and composed of well-sorted medium sand. The application
of environmental parameters revealed a dissipative state with very low beach gradient which did not vary significantly over
the studied period. Morphological changes consist of beach erosion and bar decay under high-energy waves, whereas the intertidal
bar re-established and the beach recorded an accentuated accretion due to relatively fair weather conditions. The beach volume
reveals a seasonal behavior; the sand accumulated during summer is dramatically removed during winter season. The range in
beach sand volume from the most accreted to the most eroded conditions observed is about −5,493 m3. The average sand volume flux between surveys reaches −1 and 0.4 m2/day during peak erosion and accretion periods. The relationships between the wave forcing and the sand volume adjustments
were examined. The sand volume change was found to be highly correlated (0.91) with the wave energy flux. The highest correspondence
(0.95) was found between the sand flux rate and the wave energy flux. The wave forcing is expected to be the main factor governing
beach morphodynamics at Charf el Akab site. 相似文献
12.
Progress in Researches on Ensemble Forecasting of Extreme Weather Based on Numerical Models 总被引:1,自引:1,他引:0
Under the background of climate change, extreme weather events (e.g., heavy rainfall, heat wave, and cold damage) in China have been occurring more frequently with an increasing trend of induced meteorological disasters. Therefore, it is of great importance to carry out research on forecasting of extreme weather. This paper systematically reviewed the primary methodology of extreme weather forecast, current status in development of ensemble weather forecasting based on numerical models and their applications to forecast of extreme weather, as well as progress in approaches for correcting ensemble probabilistic forecast. Nowadays, the forecasting of extreme weather has been generally dominated by methodology using dynamical models. That is to say, the dynamical forecasting methods based on ensemble probabilistic forecast information have become prevailing in current operational extreme weather forecast worldwide. It can be clearly found that the current major directions of research and development in this field are the application of ensemble forecasts based on numerical models to forecasting of extreme weather, and its improvement through bias correction of ensemble probabilistic forecast. Based on a relatively comprehensive review in this paper, some suggestions with respect to development of extreme weather forecast in future were further given in terms of the issues of how to propose effective approaches on improving level of identification and forecasting of extreme events. 相似文献
13.
近年来随着极端天气/气候事件的频发,应对极端天气/气候事件的要求极其紧迫。目前气象资料对极端天气/气候事件的研究相对较短,由此作者提出利用石笋记录重建历史年际、年代际极端天气/气候事件的构想。通过对目前已有的石笋极端天气/气候事件研究实例分析总结,认为洞穴石笋沉积速率相对较快,石笋中标志性结构构造特征的存在,有利于石笋记录到极端天气/气候事件。同时就目前的研究现状,作者提出建立准确年代标尺、选择生长速率相对较快和存在标志性结构构造特征、能记录到极端气候的石笋,以及提高采样分辨率和与其他记录相互验证等作为石笋极端气候研究的工作要求,同时就文石笋研究极端天气/气候事件提出文石笋可能更加容易记录到极端天气/气候事件的个人新认识。 相似文献
14.
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
15.
Characteristics of high impact weather and meteorological disaster in Shanghai,China 总被引:3,自引:2,他引:1
This paper discusses the characteristics of high-impact weather events based on available data during 1960–2009, including
the frequency and extreme value of rainstorm, typhoon, thunderstorm, strong wind, tornado, fog, haze and hot days in Shanghai,
China. The frequency and spatial distribution of meteorological disasters and their impacts on both human and property during
1984–2009 are also discussed. Examination of the frequency indicates a decreasing trend in the occurrence of typhoon, thunderstorm,
strong wind, tornado and fog, and an increasing trend in the occurrence of rainstorm, haze and hot days. The number of casualties
caused by meteorological disasters appears to show a slight decreasing trend while the value of direct economic loss is increasing
slightly during 1984–2009, and the number of collapsed or damaged buildings and the area of affected crops have no significant
trend in Shanghai. These results can be attributed to the great efforts for prevention and mitigation of meteorological disasters
made by Shanghai government in recent 60 years. With global climate change, urbanization and rapid economic development, Shanghai
has become more vulnerable to high-impact weather and meteorological disaster, especially precipitation extreme, summer high
temperature, haze and typhoon, so more strategies of mitigation and/or adaptation of natural disasters are quite useful and
necessary for local government and the public in the future. 相似文献
16.
R. Rajesh Kumar B. Prasad Kumar A. N. V. Satyanarayana D. Bala Subrahamanyam A. D. Rao S. K. Dube 《Natural Hazards》2009,49(2):213-224
This work reports an efficient bulk formulation of sea surface drag that incorporates effect of dynamic stability under varied
atmospheric forcing. The proposed formulation exhibits a polynomial dependence of wind speed on air–sea temperature difference
based on statistical analysis. Quality checked meteorological and oceanographic data from four shallow water buoys located
off Korean seas having measurements at an interval of every 1 h were used for this study. The analyses of in situ records
for this region suggest stability ranging from highly stable to very unstable conditions. Importance of this proposed formulation
is better reflected during unstable condition where other popular bulk formulations fail. In addition, importance and impact
of such a study on wind-wave growth using the state-of-art wave model was also investigated. Finally, we advocate a new drag
formulation, which accounts for varied atmospheric stability and suggest that this should be considered as an essential pre-requisite
for ocean modeling studies. 相似文献
17.
Two surface‐sediment sampling campaigns were carried out in November and December 2003, before and after a strong swell event, in the back‐reef area of a microtidal fringing reef on the western coast of La Reunion, Indian Ocean. The spatial distributions of the mean grain size, sorting and skewness parameters are determined, and grain‐size trend analysis is performed to estimate the main sediment transport pathways in the reef. The results of this analysis are compared with hydrodynamic records obtained in the same reef area during fair weather conditions and during swell events. Sediment dynamics inferred from the hydrodynamic records show that significant sediment erosion and transport occur only during swell events and under strongly agitated sea states. Under normal wave conditions, there is a potential for onshore sediment transport from the reef‐flat to the back‐reef, but this transport is episodic and occurs principally during high‐tide stages. Sediment transport trends revealed by the grain‐size trend analysis method show onshore and alongshore low‐energy transport processes that are in agreement with the hydrodynamic records. The grain‐size trend analysis method also provides evidence of an offshore high‐energy transport trend that could be interpreted as a real physical process associated with return flow from the shore to the reef. The impact of swell on the reef sediment dynamics is clearly demonstrated by onshore and alongshore transport. Considering different combinations of the vector transport trends computed through the grain‐size trend analysis approach, more realistic and pertinent results can be obtained by applying an exclusive OR operation (XOR case) on the vectors. The main results presented here highlight a trend towards the accumulation of carbonate sands in the back‐reef area of the fringing reef. These sediments can only be resuspended during extreme events such as storms or tropical cyclones. 相似文献
18.
Atlanta’s urban heat island under extreme heat conditions and potential mitigation strategies 总被引:2,自引:0,他引:2
The urban heat island (UHI), together with summertime heat waves, foster’s biophysical hazards such as heat stress, air pollution,
and associated public health problems. Mitigation strategies such as increased vegetative cover and higher albedo surface
materials have been proposed. Atlanta, Georgia, is often affected by extreme heat, and has recently been investigated to better
understand its heat island and related weather modifications. The objectives of this research were to (1) characterize temporal
variations in the magnitude of UHI around Metro Atlanta area, (2) identify climatological attributes of the UHI under extremely
high temperature conditions during Atlanta’s summer (June, July, and August) period, and (3) conduct theoretical numerical
simulations to quantify the first-order effects of proposed mitigation strategies. Over the period 1984–2007, the climatological
mean UHI magnitude for Atlanta-Athens and Athens-Monticello was 1.31 and 1.71°C, respectively. There were statistically significant
minimum temperature trends of 0.70°C per decade at Athens and −1.79°C per decade at Monticello while Atlanta’s minimum temperature
remained unchanged. The largest (smallest) UHI magnitudes were in spring (summer) and may be coupled to cloud-radiative cycles.
Heat waves in Atlanta occurred during 50% of the years spanning 1984–2007 and were exclusively summertime phenomena. The mean
number of heat wave events in Atlanta during a given heat wave year was 1.83. On average, Atlanta heat waves lasted 14.18 days,
although there was quite a bit of variability (standard deviation of 9.89). The mean maximum temperature during Atlanta’s
heat waves was 35.85°C. The Atlanta-Athens UHI was not statistically larger during a heat wave although the Atlanta-Monticello
UHI was. Model simulations captured daytime and nocturnal UHIs under heat wave conditions. Sensitivity results suggested that
a 100% increase in Atlanta’s surface vegetation or a tripling of its albedo effectively reduced UHI surface temperature. However,
from a mitigation and technological standpoint, there is low feasibility of tripling albedo in the foreseeable future. Increased
vegetation seems to be a more likely choice for mitigating surface temperature. 相似文献
19.
Extreme climate and weather events are increasingly being recognized as key aspects of climate change. Pre-monsoon season
(March–May) is the hottest part of the year over almost the entire South Asian region, in which hot weather extremes including
heat waves are recurring natural hazards having serious societal impacts, particularly on human health. In the present paper,
recent trends in extreme temperature events for the pre-monsoon season have been studied using daily data on maximum and minimum
temperatures over a well-distributed network of 121 stations for the period 1970–2005. For this purpose, time series of extreme
temperature events have been constructed for India as a whole and seven homogeneous regions, viz., Western Himalaya (WH),
Northwest (NW), Northeast (NE), North Central (NC), East coast (EC), West coast (WC) and Interior Peninsula (IP). 相似文献
20.
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