Beach erosion has occurred globally in recent decades due to frequent and severe storms.Dongsha beach,located in Zhujiajian Island,Zhejiang Province,China,is a typical embayed sandy beach.This study focused on the mor...Beach erosion has occurred globally in recent decades due to frequent and severe storms.Dongsha beach,located in Zhujiajian Island,Zhejiang Province,China,is a typical embayed sandy beach.This study focused on the morphodynamic response of Dongsha beach to typhoon events,based on beach topographies and surficial sediment characteristics acquired before and after four typhoon events with varying intensities.The four typhoons had different effects on the topography and sediment characteristics of Dongsha beach.Typhoons Ampil and Danas caused the largest(-51.72 m3/m)and the smallest erosion(-8.01 m3/m),respectively.Remarkable alongshore patterns of beach profile volumetric changes were found after the four typhoon events,with more erosion in the southern and central parts of the beach and few changes in the northern part.Grain size coarsening and poor sorting were the main sediment patterns on the beach influenced by different typhoons.Typhoons that occurred in the same year after another typhoon enhanced the effect of the previous typhoon on sediment coarsening and sorting variability,but this cumulative effect was not found between typhoons that occurred during different years.A comparison of the collected data revealed that the topographic state of the beach before the typhoon,typhoon characteristics,and tidal conditions were possible reasons for the difference in the responses of Dongsha beach to typhoon events.More severe beach erosion was caused by typhoons with higher intensity levels and longer durations,and high tide levels during typhoons can determine the upper limit of the beach profile erosion site.Taken together,these results can be used to improve beach management for storm prevention.展开更多
Statistic and typical-year composition methods are used to study the northwest Pacific typhoonactivities in relation with the El Nino and La Nina events. The result indicates that the typhoon tends to be inactive in t...Statistic and typical-year composition methods are used to study the northwest Pacific typhoonactivities in relation with the El Nino and La Nina events. The result indicates that the typhoon tends to be inactive in the El Nino years and active in the La Nina years and it is also dependent on the onset and ending time andintensity of the events and areas of genesis of typhoons. With statistic features of the frequency of typhoon activity in the EI Nino and La Nina years and the time-lag correlation between the frequency and sea surface temperature (SST), useful information is provided for the prediction of typhoon occurrence. In addition, the singularvalues disassemble (SVD) method is applied to study the correlation between the geopotential field and SST fief(l.The result shows that the air-sea coupling in the EI Nino years is unfavorable for the typhoon to develop. whichtake place with a smaller number. Opposite situations are found with the La Nina years.展开更多
By using data of serially numbered typhoons in northwestern Pacific and NOAA OLR data andNCEP/NCAR reanalysis data of wind field, based on the statistics and study of the relationship between thecalendar years with mo...By using data of serially numbered typhoons in northwestern Pacific and NOAA OLR data andNCEP/NCAR reanalysis data of wind field, based on the statistics and study of the relationship between thecalendar years with more (or fewer) summer typhoons and ENSO events, we compared the composites of OLReigenvectors and tropical summer wind fields during El Nio and La Nio events with more or fewer thannormal summer typhoons, respectively. The results show that, in summer, without remarkable systematicanomalies of Mascarene High and Australia High in South Hemisphere, the anomaly of Walker circulation willdominate and follow the rule of ENSO impacts to atmospheric circulation and typhoon frequency. Otherwise,when systematic anomalies of Australia High appear during the El Nio events, circulation anomalies in theSouth Hemisphere will dominate, and many more typhoons will occur. In 1999, which is a special year of LaNia events, northward and eastward monsoon was induced by the stronger Mascarene High, and fewertyphoons arose. The typhoon source are regions where weak vertical wind shear, warm pool in western Pacificand the area with monsoon troughs are overlapping with each other. Finally, this paper analyzes and comparesthe source locations and ranges of more (fewer) typhoons in the events of El Nio and La Nio, respectively.展开更多
A generalized wave-activity density,which is defined as an absolute value of production of three-dimensional vorticity vector perturbation and gradient of general potential temperature perturbation,is introduced and i...A generalized wave-activity density,which is defined as an absolute value of production of three-dimensional vorticity vector perturbation and gradient of general potential temperature perturbation,is introduced and its wave-activity law is derived in Cartesian coordinates. Constructed in an agoestrophic and nonhydrostatic dynamical framework,the generalized wave-activity law may be applicable to diagnose mesoscale weather systems leading to heavy rainfall. The generalized wave-activity density and wave-activity flux divergence were calculated with the objective analysis data to investigate the character of wave activity over heavy-rainfall regions.The primary dynamical processes responsible for disturbance associated with heavy rainfall were also analyzed. It was shown that the generalized wave-activity density was closely correlated to the observed 6-h accumulative rainfall. This indicated that the wave activity or disturbance was evident over the frontal and landfall-typhoon heavy-rainfall regions in middle and lower troposphere. For the landfall-typhoon rainband,the portion of generalized wave-activity flux divergence,denoting the interaction between the basic-state cyclonic circulation of landfall typhoon and mesoscale waves,was the primary dynamic process responsible for the evolution of generalized wave-activity density.展开更多
In sandy sediments, scour and fill is the key process contributed to mine burial. The scour processes surrounding the cylinder mines freely resting on the sandy seabed under the 12-hr combined action of tidal currents...In sandy sediments, scour and fill is the key process contributed to mine burial. The scour processes surrounding the cylinder mines freely resting on the sandy seabed under the 12-hr combined action of tidal currents and wind-generated waves, especially over typhoon events are numerically simulated using the DRAMBUIE model. The East China Sea is a good case study due to the dominant impact of summer typhoon events on sediment transport and scour. The numerical results show that the scour depth generally increases with time under the combined current and wave stresses exerted on the seabed, while the depth of the scour pit depends on infill once the currents subside. There is a positive relationship between the scour depth and the bottom orbital velocity after experiencing 12-hr wave action including storm waves, while the relation is not linear. The experimental results also display an elevated trend for scour depth with the increase of orbital velocity. The numerical results reveal a surprising phenomenon: the mobility of sand altering with the increasing bed shear stress larger than the certain threshold, which is also manifested as the curves of scour depth with the different grain size might cross each other. For laboratory experiments, the variability of sand mobility does not occur, likely because typhoon storm waves cannot be reproduced in the flume. More numerical tests indicate that the intersection will be triggered by the division of critical Shields parameter. The preliminary analysis suggests that the phenomenon never documented is likely generated from the error of empirical formulae.展开更多
基金The Zhejiang Provincial Natural Science Foundation of China under contract No.LHZ22D060001the Scientific Research Funds of the Second Institute of Oceanography,Ministry of Natural Resources under contract Nos JG2315 and XRJH2309the National Key R&D Program of China under contract No.2022YFC3106200.
文摘Beach erosion has occurred globally in recent decades due to frequent and severe storms.Dongsha beach,located in Zhujiajian Island,Zhejiang Province,China,is a typical embayed sandy beach.This study focused on the morphodynamic response of Dongsha beach to typhoon events,based on beach topographies and surficial sediment characteristics acquired before and after four typhoon events with varying intensities.The four typhoons had different effects on the topography and sediment characteristics of Dongsha beach.Typhoons Ampil and Danas caused the largest(-51.72 m3/m)and the smallest erosion(-8.01 m3/m),respectively.Remarkable alongshore patterns of beach profile volumetric changes were found after the four typhoon events,with more erosion in the southern and central parts of the beach and few changes in the northern part.Grain size coarsening and poor sorting were the main sediment patterns on the beach influenced by different typhoons.Typhoons that occurred in the same year after another typhoon enhanced the effect of the previous typhoon on sediment coarsening and sorting variability,but this cumulative effect was not found between typhoons that occurred during different years.A comparison of the collected data revealed that the topographic state of the beach before the typhoon,typhoon characteristics,and tidal conditions were possible reasons for the difference in the responses of Dongsha beach to typhoon events.More severe beach erosion was caused by typhoons with higher intensity levels and longer durations,and high tide levels during typhoons can determine the upper limit of the beach profile erosion site.Taken together,these results can be used to improve beach management for storm prevention.
文摘Statistic and typical-year composition methods are used to study the northwest Pacific typhoonactivities in relation with the El Nino and La Nina events. The result indicates that the typhoon tends to be inactive in the El Nino years and active in the La Nina years and it is also dependent on the onset and ending time andintensity of the events and areas of genesis of typhoons. With statistic features of the frequency of typhoon activity in the EI Nino and La Nina years and the time-lag correlation between the frequency and sea surface temperature (SST), useful information is provided for the prediction of typhoon occurrence. In addition, the singularvalues disassemble (SVD) method is applied to study the correlation between the geopotential field and SST fief(l.The result shows that the air-sea coupling in the EI Nino years is unfavorable for the typhoon to develop. whichtake place with a smaller number. Opposite situations are found with the La Nina years.
基金Science and Technology Bureau of Xiamen (40275016)
文摘By using data of serially numbered typhoons in northwestern Pacific and NOAA OLR data andNCEP/NCAR reanalysis data of wind field, based on the statistics and study of the relationship between thecalendar years with more (or fewer) summer typhoons and ENSO events, we compared the composites of OLReigenvectors and tropical summer wind fields during El Nio and La Nio events with more or fewer thannormal summer typhoons, respectively. The results show that, in summer, without remarkable systematicanomalies of Mascarene High and Australia High in South Hemisphere, the anomaly of Walker circulation willdominate and follow the rule of ENSO impacts to atmospheric circulation and typhoon frequency. Otherwise,when systematic anomalies of Australia High appear during the El Nio events, circulation anomalies in theSouth Hemisphere will dominate, and many more typhoons will occur. In 1999, which is a special year of LaNia events, northward and eastward monsoon was induced by the stronger Mascarene High, and fewertyphoons arose. The typhoon source are regions where weak vertical wind shear, warm pool in western Pacificand the area with monsoon troughs are overlapping with each other. Finally, this paper analyzes and comparesthe source locations and ranges of more (fewer) typhoons in the events of El Nio and La Nio, respectively.
基金National Basic Research Program of China (2009CB421505)National Natural Sciences Foundations of China (40875032)
文摘A generalized wave-activity density,which is defined as an absolute value of production of three-dimensional vorticity vector perturbation and gradient of general potential temperature perturbation,is introduced and its wave-activity law is derived in Cartesian coordinates. Constructed in an agoestrophic and nonhydrostatic dynamical framework,the generalized wave-activity law may be applicable to diagnose mesoscale weather systems leading to heavy rainfall. The generalized wave-activity density and wave-activity flux divergence were calculated with the objective analysis data to investigate the character of wave activity over heavy-rainfall regions.The primary dynamical processes responsible for disturbance associated with heavy rainfall were also analyzed. It was shown that the generalized wave-activity density was closely correlated to the observed 6-h accumulative rainfall. This indicated that the wave activity or disturbance was evident over the frontal and landfall-typhoon heavy-rainfall regions in middle and lower troposphere. For the landfall-typhoon rainband,the portion of generalized wave-activity flux divergence,denoting the interaction between the basic-state cyclonic circulation of landfall typhoon and mesoscale waves,was the primary dynamic process responsible for the evolution of generalized wave-activity density.
文摘In sandy sediments, scour and fill is the key process contributed to mine burial. The scour processes surrounding the cylinder mines freely resting on the sandy seabed under the 12-hr combined action of tidal currents and wind-generated waves, especially over typhoon events are numerically simulated using the DRAMBUIE model. The East China Sea is a good case study due to the dominant impact of summer typhoon events on sediment transport and scour. The numerical results show that the scour depth generally increases with time under the combined current and wave stresses exerted on the seabed, while the depth of the scour pit depends on infill once the currents subside. There is a positive relationship between the scour depth and the bottom orbital velocity after experiencing 12-hr wave action including storm waves, while the relation is not linear. The experimental results also display an elevated trend for scour depth with the increase of orbital velocity. The numerical results reveal a surprising phenomenon: the mobility of sand altering with the increasing bed shear stress larger than the certain threshold, which is also manifested as the curves of scour depth with the different grain size might cross each other. For laboratory experiments, the variability of sand mobility does not occur, likely because typhoon storm waves cannot be reproduced in the flume. More numerical tests indicate that the intersection will be triggered by the division of critical Shields parameter. The preliminary analysis suggests that the phenomenon never documented is likely generated from the error of empirical formulae.
