Sea level extremes in Marseille (NW Mediterranean) during 1885–2008     

Camille Letetrel  Marta Marcos  Belén Martín Míguez  Guy Woppelmann 《Continental Shelf Research》2010

Sea level extremes and their temporal variability have been explored based on the hourly measurements at Marseille tide gauge for the period 1885–2008. A careful quality check has first been applied to the observations to ensure consistency of the record by eliminating outliers and datum shifts. Yearly percentiles have been used to investigate long-term trends of extremes revealing that secular variations in extremes are linked to mean sea level changes. The associated decadal changes show discrepancies between mean sea level trend and extreme fluctuations, due to the influence of the atmospheric forcing. A local regression model based on the generalized Pareto distribution has been applied to derive trends in return levels. The 50-years return levels reach values between 80 and 120 cm. The most significant changes in return levels are characterized by an increase since the 1970s.  相似文献   

Assessing changes in extreme sea levels: Application to the English Channel, 1900–2006     

Ivan Haigh  Robert Nicholls  Neil Wells 《Continental Shelf Research》2010

A recently extended and spatially rich English Channel sea level dataset has been used to evaluate changes in extreme still water levels throughout the 20th century. Sea level records from 18 tide gauges have been rigorously checked for errors and split into mean sea level, tidal and non-tidal components. These components and the interaction between surge and tide have been analysed separately for significant trends before determining changes in extreme sea level. Mean sea level is rising at 0.8–2.3 mm/year, depending on location. There is a small increase (0.1–0.3 mm/year) in the annual mean high water of astronomical tidal origin, relative to mean sea level, and an increase (0.2–0.6 mm/year) in annual mean tidal range. There is considerable intra- and inter-decadal variability in surge intensity with the strongest intensity in the late 1950s. Storm surges show a statistically significant weak negative correlation to the winter North Atlantic Oscillation index throughout the Channel and a stronger significant positive correlation at the boundary with the southern North Sea. Tide–surge interactions increase eastward along the English Channel, but no significant long-term changes in the distribution of tide–surge interaction are evident. In conclusion, extreme sea levels increased at all of the 18 sites, but at rates not statistically different from that observed in mean sea level.  相似文献   

Stream turbidity responses to storm events in a pristine rainforest watershed on the Coral Coast of southern Fiji     

《国际泥沙研究》2016,(4):279-290

On the Coral Coast of Viti Levu Island in Fiji, inadequate knowledge of suspended sediment delivery patterns in small pristine coastal watersheds hinders any future assessment of accelerated erosion in disturbed areas nearby. This study adopts a rainfall–stream turbidity monitoring approach in the Votua Creek, which drains a small, steep but minimally-disturbed coastal rainforest catchment. Storm rainfall characteristics, stream depth and water turbidity were continuously monitored over one complete Fiji wet season from October 2009 to April 2010. The aim was to evaluate whether these parameters provide sufficient information to illustrate basic features of storm–sediment transport responses, in the case of limited stream gauging and very simple sediment rating curves. This is important because Pacific Island nations like Fiji do not have the resources to initiate long-term gauging and sediment sampling pro-grammes across numerous small catchments.
A significant power function demonstrates that turbidity (T) is a suitable proxy for total suspended solids (TSS) for turbidity measurements above 5 NTU, with TSS?0.930T1.111 (r?0.98, Po0.001). Over the study period, 10 individual storms 11.2–120.1 mm in size produced a‘significant turbidity response’ (STR) in the Votua Creek. Rainfall parameters (totals and intensities) showed positive linear relationships (r ? 0.72–0.94) with stream turbidity parameters (mean, maximum, duration), whilst relationships of similar strength (r ? 0.76–0.98) were also derived between stream flow depth and turbidity. This implies that for small rainforest watersheds in Fiji, rainfall parameters offer no substantial disadvantage over flow as predictors of stream sediment responses to major storms. Event-based analysis revealed that negative (anticlockwise) hysteresis is a typical flow–turbidity pattern for STR events. Negative hysteresis is produced when secondary episodes of renewed (heavy) rainfall occur after maximum intensity, in the later phase of storm events. Tropical Cyclone Mick in December 2009 generated the largest flood and the greatest turbidity response (Tmax ? 1021 NTU, Tmean ? 207 NTU). This concurs with earlier work confirming that tropical cyclones are the most important events for sediment transport in Fiji stream networks.  相似文献   

强龙卷超级单体风暴特征分析与预警研究   总被引：26，自引：12，他引：14       下载免费PDF全文

郑媛媛  朱红芳  方翔  张雪晨  方翀  姚晨  郝莹 《高原气象》2009,28(3):617-625

利用多普勒雷达资料,对发生在安徽的3次强烈龙卷过程进行了分析.重点研究了导致F2～F3级强龙卷的3次超级单体风暴多普勒雷达回波特征及其与强冰雹超级单体风暴的差异.另外,利用安徽省、市、县气象报表、历年气候评价灾情资料(部分来自民政部门的灾情报告),对1960年至今的龙卷天气的时空分布及变化趋势、产生龙卷的环流形势特征进行了分析,结果表明:(1)龙卷主要出现在淮北东部和江淮之间东部地势平坦地区,7月份出现龙卷的概率最高.(2)超级单体龙卷产生在中等大小的对流有效位能和强垂直风切变条件下,同时抬升凝结高度较低.(3)3次F2～F3级龙卷在发生前、发生时在多普勒雷达上都探测到强中气旋和龙卷涡旋特征TVS.与非龙卷超级单体风暴相比,导致强龙卷的中气旋底高明显偏低,基本在1 km以下.同时风暴结构也有所不同,造成龙卷天气的超级单体风暴最大反射率因子与风暴质心高度接近,基本在3 km左右,反射率因子在50～60 dBz.造成强冰雹的超级单体风暴在冰雹产生前,风暴最大反射率因子高于风暴质心的高度;当风暴开始降雹时,最大反射率因子高度开始降低,而风暴质心的高度变化不大,高于最大反射率因子高度,基本保持在5km左右,反射率因子在60～70 dBz.  相似文献   

"2006.10"云南严重秋季连阴雨水汽输送特征和湿Q矢量分析   总被引：2，自引：1，他引：1  

鲁亚斌  普贵明  赵宁坤  李屏  郭荣芬 《气象科学》2009,29(1):64-70

应用常规气象资料通过诊断分析和湿Q矢量分析,探讨了2006年10月上旬云南严重连阴雨期间的水汽输送特征,进一步分析了期间持续性暴雨、大雨的落区分布,结果表明:连阴雨期间,ITCZ异常活跃,先后有4个热带气旋活动,200616号强台风"象神"横穿中南半岛进入孟加拉湾,减弱之后再度发展成孟加拉湾低压,由此提供了孟加拉湾水汽通道;ITCZ水汽通过副高外围气流向中南半岛输送,提供了第二条水汽通道,两条水汽通道呈"人"字形,为连阴雨发生发展提供了有利的水汽条件.湿Q矢量辐合中心在对流层中低层700～640 hPa之间,700 hPa上湿Q矢量散度辐合区与暴雨区对应较好;随着湿Q矢量辐合区加强、移动和减弱,暴雨随之发展、移动和结束.  相似文献   

Long-Term and Short-Term Variations of Sea Level in Eastern Canada: A Review     

Karim Hilmi  Tad Murty  Mohammed I. El Sabh  Jean-Pierre Chanut 《Marine Geodesy》2013,36(1-2):61-78

This is a review of sea level data performed at three selected stations (Québec-Lauzon, Harrington Harbour,and Halifax) in eastern Canada in order to investigate the seasonal trends and other long-term and short-term changes which occurred since the beginning of the 20th century. Stations situated in riverine or estuarine regions (e.g., Québec-Lauzon) are significantly affected by freshwater flow in their annual cycle of sea level changes and exhibit a definite maximum in spring and minimum in autumn-winter. Other stations situated in the eastern half of the Gulf of St. Lawrence (e.g., Harrington Harbour) or near the open Atlantic coast (Halifax) mainly follow the general cycle of subarctic regions, with lows in spring-summer and highs in autumn-winter. Such seasonal variations appear to be related to the atmospheric pressure and baroclinic current variations. Secular trends in mean sea level in eastern Canadian waterbodies show a mean rise of about 2.56 mm/yr -1 due to tectonic motions, that is, land subsidence. At several stations in eastern Canada, evidence is found for the influence of the nodal tide (18.6 years), the sunspot cycle (10.8 years), the lunar perigee (8.47 years), the pole tide (14.5 months), the annual cycle (12 months), and semiannual tidal cycle (6 months) in sea level records. Beside long-term oscillations with periods of more than one year, evidence is found for high energetic semidiurnal and diurnal tides where they contribute largely (from 90-95%) to short term variability of sea level. In the residual signal (variations of sea level--tidal variations), short-term variations between 2 to 30 days can be attributed to meterological forcing (atmospheric pressure and winds), longitudinal seiches (2-10 h), atmospheric tides (12 h and 24 h) and inertial oscillations (16-18 h). A regressive model showed that the water discharge from the St. Lawrence River contributes 29% to the monthly residual sea level at Québec-Lauzon. The atmospheric pressure and winds contribute respectively 8.1% and 8.9% at this station. They contribute 52.1% and 7.7% at Harrington Harbour and 41.8% and 14.3% at Halifax. The regression coefficients of residual sea level on atmospheric pressure are respectively estimated to be -1.507 cm. ( hPa ) -1 ( - 0.345 cm. ( hPa ) -1 ), -0.776 cm. ( hPa ) -1 ( - 0.112 cm. ( hPa ) -1 ) and -0.825 cm. ( hPa ) -1 ( - 0.008 cm. ( hPa ) -1 ) at the three stations. Compared to the coefficient of the inverted barometer, estimated to be -1 cm. ( hPa ) -1 , these effects of the atmospheric pressure on sea level variations seem to be amplified at Que´bec-Lauzon by the wind effects (and water discharge) while they are reduced at Harrington Harbour and Halifax.  相似文献   

Effect of Salinity and Currents on Sea Level Variation Along the Indian Coast: A Numerical Study     

A. D. Rao  S. V. Babu  S. K. Dube 《Marine Geodesy》2013,36(1-2):145-158

The process of upwelling/sinking and associated sea level variations are seen as a response of coastal ocean to pure wind stress forcing. Further,precipitation and monsoonal floods, apart from the marine meteorological parameters, are expected to influence the sea level fluctuations along the coast. This study comprises determining the sea level from the various parameters together with the pure wind stress forcing, which is compared with the observed cycle. However, it is found that there is considerable difference between the computations and observations. This suggests that the sea level is dependent not just on the local forcing alone, but also on the induced background circulation as well. For example, the sea level changes along the east coast of India, particularly the northern region, are more sensitive to freshwater discharge from various rivers joining the Bay of Bengal. This is due to more frequently occurring pre- and postmonsoon cyclonic storms and the associated surges in the Bay of Bengal as compared to the Arabian Sea. Hence the salinity effects are particularly important in the coastal waters off the east coast of India during monsoon months (June-September). For the west coast of India, however, it is expected that the large-scale coastal circulation may play a role in determining sea level changes in addition to other forcings. The salinity effects are negligible along the west coast in the absence of any major river systems that join the Arabian Sea. The local advection currents caused by the offshore directed freshwater discharge from various estuaries joining the coastal bay also seemed to influence the sea level. In order to elucidate the essential dynamics involved and to study the effect of the remote forcing, a three-dimensional baroclinic, nonlinear numerical model is used with appropriate open boundary conditions. The local effect of the current has been incorporated in the west coast model by means of opening a channel at Cochin through which the rainwater is carried away to the model ocean. The low saline plume, cascading from north along the east cost of India, has been incorporated in the east coast model through a proper forcing applied at the northern boundary of the model. With the inclusion of these remote forcings in the models, the disagreement between the simulations and the observations is minimized.  相似文献   

一次南方春季强对流过程中影响对流发展的环境场特征分析   总被引：4，自引：0，他引：4  

陈涛  张芳华  宗志平 《高原气象》2012,31(4):1019-1031

利用地面自动站资料、多普勒雷达资料、FY-2E卫星云图及NCEP FNL 1°×1°逐6h分析场资料,分析了2010年5月5-7日我国南方春季大范围强对流天气过程中尺度对流系统(MesoscaleConvective System,MCS)的发生、发展特征,重点探讨了环境条件差异及其对MCS的影响。结果表明,由于环境场三维动力结构、水汽条件和热力不稳定条件配置的差异,造成对流发展的多样化特征。利用相对风暴螺旋度分析了环境场动力特征对MCS组织结构的影响。重庆上空中高层较干且具有较强的垂直切变,环境场气旋式旋转相对深厚,随着锋面强迫抬升克服对流抑制作用后,局地激发出相对孤立的类似超级单体的强对流风暴,造成冰雹和雷暴大风等天气;而贵州湿层相对深厚,高低空急流的耦合机制更明显,贵州北部的多单体对流风暴组织程度较高,MCS尺度相对较大,局地短时强降水较明显;广东具有最强的垂直切变和深厚湿层,在浅薄冷空气的触发机制下,发展出深厚湿对流形式的中尺度对流复合体,出现了高度组织化的线状对流带,MCS尺度大、持续时间长,造成较强的降水。  相似文献   

Coastal flooding: impacts of coupled wave–surge–tide models     

Judith Wolf 《Natural Hazards》2009,49(2):241-260

Wind waves and elevated water levels together can cause flooding in low-lying coastal areas, where the water level may be a combination of mean sea level, tides and surges generated by storm events. In areas with a wide continental shelf a travelling external surge may combine with the locally generated surge and waves and there can be significant interaction between the propagation of the tide and surge. Wave height at the coast is controlled largely by water depth. So the effect of tides and surges on waves must also be considered, while waves contribute to the total water level by means of wave setup through radiation stress. These processes are well understood and accurately predicted by models, assuming good bathymetry and wind forcing is available. Other interactions between surges and waves include the processes of surface wind-stress and bottom friction as well as depth and current refraction of waves by surge water levels and currents, and some of the details of these processes are still not well understood. The recent coastal flooding in Myanmar (May 2008) in the Irrawaddy River Delta is an example of the severity of such events, with a surge of over 3 m exacerbated by heavy precipitation. Here, we review the existing capability for combined modelling of tides, surges and waves, their interactions and the development of coupled models.  相似文献   

黄河水下三角洲硬壳层特征及其液化过程研究     

常方强  贾永刚  张建  张衍涛  单红仙 《工程地质学报》2009,17(3):349-356

为揭示黄河口水下三角洲硬壳层的土性特征和风浪作用下的液化破坏状况,选择典型研究区,在现场利用普氏贯入仪测试硬壳层的强度特征,原位取1m原状样进行室内土工试验;利用重锤锤击荷载板的方式模拟波浪对硬壳层的动力作用,通过孔压探头和普氏贯入仪实时监测土体内孔压和振动前后强度的变化;通过理论计算研究硬壳层在不同风浪等级下的液化深度。通过研究发现,（1）硬壳层土体基本上处于超固结状态,且超固结比随深度增加而减小,大王北和刁口地区硬壳层强度约是新滩和广利港的两倍,离河口近的地区强度的变异系数比远的地区要大;（2）根据孔压随振次的变化关系,现场土体在振动过程中,孔压的增长经历了4个阶段,即初始阶段、增长阶段、稳定阶段和衰减阶段,且表层土体达到液化,深层的未液化;（3）大王北硬壳层在6~10级风浪下的平均液化深度仅为7~11cm,新滩和广利港硬壳层在6~10级风浪作用下的液化深度达32~42cm。强度高的硬壳层液化深度小,低的液化深度大,这种液化深度的差异性造成了地貌上的凹凸不平。  相似文献