气候系统内极区热汇与热带海洋热源之间的相互作用(英)

The anomalous change of two polar sea ice and tropical ocean SST is a very important index for global climate monitoring and prediction. In this paper, the wave resonance principle is used to calculate month by month running cross couple correlation coefficient time series between sea ice in different sea area of two Polars, as well as between them and five elements of E1 Nino events, to analyze their variation features, and to find out their resonance periods. The resonance period of two waves is just the strongest interaction period.Some results are concluded as follows. 1) The Arctic sea ice to the Pacific-side (NPI1) and Atlantic-side (NP12) show a strong positive-negative feedback impact each other to the Antarctic Ross Sea ice (SPI2) with equal intensity. 2) Both NPI1 and NPI2 give a strong positive and negative feedback to the Antarctic Wedded Sea ice (SPI3) while it is rather weak in convercse status. It means that, the Arctic sea ice plays a leading and controlling role on the Wedded Sea ice. 3) SST of Nino 4 area in thecentral equatorial Pacific has a best resonance period with SPI2 with cycle period of 132 months. It closely relates to quasi-11 years oscillation period of both SST of Nino 4 area and SPI2. SST of Nino 4 has also a resonance period to SPI3 with cycle of 61 months. There also exist strong interaction periods between the Antarctic sea ice and other elements of ENSO event but weaker than SST of Nino 4 area.     

Physical model tests to determine the mechanism of submarine landslides under the effect of sea waves

Submarine landslides are a common type of disaster which threaten property and the safety of human life. To effectively prevent and control such disasters, we conduct a series of large-scale physical model tests to determine the mechanism of submarine landslides. First, a large-scale physical model test system is designed and developed, including flume test frame, wave-making system, wave-absorbing system, and data monitoring system. In the tests, we investigate the effect of different sea waves by changing the parameters of the wave-making system and the influence of the slope inclination by constructing different models. Data regarding the wave pressure acting on the slope surface, seepage pressure, and displacement are monitored during the test procedure. The test results show that the seepage pressure in the faults varies cyclically with the sea waves and is lower at internal points than at outcrops. If the wave loading time is sufficiently long, the seepage pressure and displacement deformation in the fault zone will gradually increase. In other words, failures in fault zones precede submarine landslides. The weak fault zone provides the preferred sliding surface, and the sea waves supply the external dynamic energy for submarine landslides. The conclusions provide guidelines for similar engineering and research.

     

Sea ice disaster risk assessment index system based on the life cycle of marine engineering

Based on the classification results of marine structure accidents induced by sea ice, the risk assessment index system of sea ice disasters was established. The possibility coefficient of risks was proposed based on risk factors of sea ice disasters, including sea ice conditions, ice risk status, ice resistance in the design phase, the current defense ability in the operation phase, and management behaviors in the freezing period. The severity index should be determined according to the affected scope, the distribution of affected personnel, and the monitoring ability in emergency. According to the case study and expert evaluation method, the scores and levels of sea ice disaster risk assessment indices were determined. Finally, the sea ice disaster risks of two offshore oil platforms and a coastal nuclear power plant were assessed.

     

Influence of sea level variability on a micro-tidal beach

Global climate change in response to buildup of human-induced greenhouse gases in the atmosphere has already resulted in several visible consequences such as an increase in ocean heat content and melting of glaciers. The relative effect of sea level and wave variability on shoreline changes along the coastline of James Town, Ghana (Gulf of Guinea), was investigated between 2013 and 2014. Data were gathered at James Town, over an 8-month period (2013–2014) from nearshore video installation, Era-Interim hindcast, and satellite altimetry. Data were evaluated over daily and monthly timescale variations. Though beach changes are not directly driven by sea level variability, its action is key in modulating waves influence. The results show that the shoreline responds in decreasing order to sea level variations (86%), waves (9%), and tidal cycles (5%) on daily bases. Wind-induced setup has limited effect on the shoreline. The observed most important component of sea level anomaly at this tropical “storm free” coast is the influence from inverse barometer. Decadal observations from satellite show that sea level anomaly is continuously rising in the Gulf of Guinea subregion with expected strong consequence for this urbanized low lying sandy coast.

     

Depositional processes beneath coastal multi‐year sea ice

The extent of multi‐year sea ice impacts climate processes worldwide, such as ocean–atmosphere carbon dioxide exchange and deep ocean current formation. Reconstructing these processes in the past, and assessing the distribution of ecologically and climatically significant features, such as polynas, requires recognition of sediments deposited under multi‐year sea ice, but little is known about their characteristics. Textural analysis of subaerial and sea floor sediment in Explorers Cove, McMurdo Sound, at the mouth of Taylor Valley, Antarctica, augmented with observations of sedimentary structures and faunal components, elucidates how sediment is transported to the sea floor and allows characterization of the deposits. Comparison of grain‐size characteristics of subaerial (moraine, delta and sea‐ice surface) sediment and sea floor sediment from short cores taken at depths of 7 to 25 m indicates that the likely source of the moderately to poorly sorted sea floor sand is deltaic sediment; small glacial meltwater streams have built deltas since Taylor Valley became ice‐free ca 7000 years ago. Windblown sediment accumulating on the multi‐year sea ice close to the coast typically is coarser grained than sediment on the sea floor; this suggests that the transport of sediment through the ice to the sea floor is not the predominant mode of sediment transfer. However, supra‐sea‐ice sediment does move to the sea floor through local fractures. The rate of sedimentation under multi‐year sea ice is low because of limited stream flow and biogenic sedimentation; the ice cover inhibits primary productivity and dampens waves, precluding physical re‐suspension. The upper centimetres of sea floor sediment are churned by epifaunal scallops and brittle stars that leave no telltale biogenic structures and whose calcite ossicles and shells may be poorly preserved. The resulting deposits under multi‐year sea ice are poorly sorted, massive sand that provides little evidence of the bioturbators that have masked the indicators of the original physical depositional processes.     

北冰洋中央密集冰区海冰对太阳短波辐射能吸收的观测研究

太阳辐射能是海冰融化的最主要能源,基于在2008年8月21~27日北极加拿大海盆中部为期8天的冰站考察中海冰光学观测数据,研究了北冰洋中央密集冰区海冰吸收的太阳辐射能。通过现场直接观测,确定了海冰透射率、反照率、吸收率及其随冰厚的变化,得出海冰对太阳短波辐射的吸收率大约为到达冰面太阳辐射的16%,大部分被冰雪表面反射。为期3天的对太阳辐射的观测表明,虽然到达北冰洋中央密集冰区的太阳辐射能并不少,但由于云和雾覆盖的时间所占的比例很大,有将近57%被大气削弱,其余的又有77%左右被冰雪表面反射回太空,海冰吸收的热量只有10.2 W/m²,相当于每天融化2.6 mm的冰,1 m厚海冰全部融化需要380天,不足以为海冰融化提供足够的热量。因此北冰洋中央密集冰区终年被海冰覆盖,即使在北冰洋海冰面积骤减的现状下,那里的海冰密集度仍然接近100%。然而,文章的结果指出：大气中云和雾大幅度减少、积雪层融化、海冰厚度减小、融池的比例增加等因素都会大幅度增加海冰吸收的热量,未来这些过程的发生有可能导致北冰洋密集冰区的海冰快速融化。     

北冰洋中央密集冰区海冰对太阳短波辐射能吸收的观测研究

太阳辐射能是海冰融化的最主要能源,基于在2008年8月21～27日北极加拿大海盆中部为期8天的冰站考察中海冰光学观测数据,研究了北冰洋中央密集冰区海冰吸收的太阳辐射能.通过现场直接观测,确定了海冰透射率、反照率、吸收率及其随冰厚的变化,得出海冰对太阳短波辐射的吸收率大约为到达冰面太阳辐射的16%,大部分被冰雪表面反射.为期3天的对太阳辐射的观测表明,虽然到达北冰洋中央密集冰区的太阳辐射能并不少,但由于云和雾覆盖的时间所占的比例很大,有将近57%被大气削弱,其余的又有77%左右被冰雪表面反射回太空,海冰吸收的热量只有10.2W/m2,相当于每天融化2.6mm的冰,1m厚海冰全部融化需要380天,不足以为海冰融化提供足够的热量.因此北冰洋中央密集冰区终年被海冰覆盖,即使在北冰洋海冰面积骤减的现状下,那里的海冰密集度仍然接近100%.然而,文章的结果指出:大气中云和雾大幅度减少、积雪层融化、海冰厚度减小、融池的比例增加等因素都会大幅度增加海冰吸收的热量,未来这些过程的发生有可能导致北冰洋密集冰区的海冰快速融化.     

A study on reflection pattern of swells from the shoreline of peninsular India

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.     

Shallow water wave spectral characteristics along the eastern Arabian Sea

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.     

Effect of pore connectivity on reflection amplitudes of an inhomogeneous wave in a composite porous solid saturated by two immiscible fluids

Present paper aims to study the phenomenon of reflection and transmission when an inhomogeneous wave strikes some discontinuity in a composite porous medium saturated by two immiscible viscous fluids. The incident wave splits into six reflected and six transmitted waves at the interface. All reflected and transmitted waves are inhomogeneous in nature with different directions of propagation vector and attenuation vector. A dimensionless parameter \(\varsigma \in [0, 1]\) is introduced to represent the extent of connection among the pores at the interface. Expression of Umov–Poynting vector is derived to obtain energy flux vector. Continuity of energy flux vector at the interface gives the required boundary conditions for the system. Connecting parameter \(\varsigma \) is also employed in boundary conditions to model the partial connection of pores at the interstices of two media. For numerical discussion we consider a porous medium composed of sandstone and ice, saturated with oil and water. The effect of parameter \(\varsigma \) and angle of incidence is determined numerically on the amplitude and the energy ratios of reflected and transmitted waves.     

Sea ice disasters and their impacts since 2000 in Laizhou Bay of Bohai Sea, China

Influenced by cold waves and low salinity of sea water, sea ice disasters occurred to Laizhou Bay frequently. The sea ice can be classified into five grades. Usually, sea ices of grade 3?C5 will have more or less impacts on beach shellfishes, mariculture and navigation. There was sea ice of grade 3 in normal winters, and there was sea ice of grade 4?C5 in cold winters. In the twentieth century, sea ice of grade 4 or 5 occurred five times in Laizhou Bay. During the years from 2000 to 2012, sea ice of grade 1 or 1.5 occurred twice, sea ice of grade 2 or 2.5, four times, that of grade 3 or 3.5, four times, and that of grade 4, twice. Among which, the sea ice disasters of 2009/2010 and 2010/2011 led to great damages and inflicted inferior impact on navigation, mariculture and marine organisms. To reduce the economic loss of sea ice disasters and their ecological influences, the authors put forward the countermeasures to sea ice disasters, which include strengthening the research of monitoring and forecasting of sea ice disasters, managing strictly the mariculture, establishing emergent recovery projects of sea ice disasters, constructing emergent recovery systems of sea ice and perfecting them continually.     

Sedimentation in a river dominated estuary

The Mgeni Estuary on the wave dominated east coast of South Africa occupies a narrow, bedrock confined, alluvial valley and is partially blocked at the coast by an elongate sandy barrier. Fluvial sediment extends to the barrier and marine deposition is restricted to a small flood tidal delta. Sequential aerial photography, sediment sampling and topographical surveys reveal a cyclical pattern of sedimentation that is mediated by severe fluvial floods which exceed normal energy thresholds. During severe floods (up to 10x 10³ m³ s^?1), lateral channel confinement promotes vertical erosion ofbed material. Eroded material is deposited as an ephemeral delta in the sea. After floods the river gradient is restored within a few months through rapid fluvial deposition and formation of a shallow, braided channel. Over an extended period (approximately 70 years) the estuary banks and bars are stabilised by vegetation and mud deposition. Subsequent downcutting in marginal areas transforms the channel to an anastomosing pattern which represents a stable morphology which adjusts to the normal range of hydrodynamic conditions. This cyclical pattern of deposition produces multiple fill sequences in such estuaries under conditions of stable sea level. The barrier and adjacent coastline prograde temporarily after major floods as the eroded barrier is reformed by wave action, but excess sediment is ultimately eroded as waves adjust the barrier to an equilibrium plan form morphology. Deltaic progradation is prevented by a steep nearshore slope, and rapid sediment dispersal by wave action and shelf currents. During transgression, estuarine sedimentation patterns are controlled by the balance between sedimentation rates and receiving basin volume. If fluvial sedimentation keeps pace with the volume increase of a basin an estuary may remain shallow and river dominated throughout its evolution and excess fluvial sediments pass through the estuary into the sea. Only if the rate of volume increase of the drowned river valley exceeds the volume of sediment supply are deep water environments formed. Under such conditions an estuary becomes a sediment sink and infills by deltaic progradation and lateral accretion as predicted by evolutionary models for microtidal estuaries. Bedrock valley geometry may exert an important control on this rate of volume increase independently of variations in the rate of relative sea level change. If estuarine morphology is viewed as a function of the balance of wave, tidal and fluvial processes, the Mgeni Estuary may be defined as a river dominated estuary in which deltaic progradation at the coast is limited by high wave energy. It is broadly representative of other river dominated estuaries along the Natal coast and a conceptual regional depositional model is proposed. Refinement of a globally applicable model will require further comparative studies of river dominated estuaries in this and other settings, but it is proposed that river dominated estuaries represent a distinct type of estuarine morphology.     

Sensitivity of the Northern Hemisphere climate system to extreme changes in Holocene Arctic sea ice

The extent of seasonal and perennial sea ice changed dramatically through the Late Quaternary and these changes influenced both the ocean and atmosphere by controlling the exchange of energy, moisture and gases between them, and by altering the planetary albedo. Reconstructing the changing patterns of sea ice distribution in the recent past remains one of the outstanding challenges to the paleo-community. To evaluate the importance of these reconstructions we performed sensitivity tests using NCAR's Community Climate Model (CCM3), and a series of prescribed sea ice extents designed to capture the full range of Arctic sea ice variability under interglacial (Holocene) and full glacial (Last Glacial Maximum) boundary conditions. Our simulations indicate that surface temperatures and sea level pressures in winter (DJF) are most sensitive to changes in sea ice, and that these changes are propagated over the surrounding land masses in the North Atlantic, but that equivalent changes in sea ice produce smaller corresponding changes in temperature or sea level pressure in the North Pacific region. A comparison between CLIMAP (Map Chart Series MC-36, Geological Society of America, Boulder, CO, 1981) and a more realistic assessment of LGM sea ice yields dramatic changes in winter temperatures and precipitation patterns across Eurasia. These differences, forced only by changed sea ice conditions, reinforce the need to develop accurate maps of past sea ice to correctly simulate Late Quaternary environments. Such reconstructions also will be essential to validate the next generation of sea ice models.     

累积海冰密集度及其在认识北极海冰快速变化的作用

为定量分析北冰洋海冰密集度年际差异,提出并采用累积海冰密集度(ASIC)概念。利用SSMR/SSMI的分辨率为25 km的海冰密集度数据,分别研究了1979—2011年北极海冰在融冰期(4~9月)和结冰期(10月至翌年3月)的变化过程以及2个冰期内ASIC的区域差异。研究发现,在1979—1989年、1989—1999年和1999—2009年期间,融冰期海冰发生明显变化的范围都远远大于结冰期海冰发生明显变化的范围。1998—2010年,融冰期内发生加速融化的海区并没有都出现结冰期冰量减小的现象。在此期间融冰期ASIC减小,结冰期ASIC也减小的海域仅集中在楚克奇海、新地岛北部海域以及格陵兰岛东西海岸。融冰期ASIC减小,而结冰期ASIC无明显变化的海域包括波弗特海、东西伯利亚海、拉普捷夫海和喀拉海。这些区域与局地陆地径流侵入的海域重合。研究发现,在这些区域,融冰期ASIC减少是陆地径流增大加速海冰融化引起的。在结冰期,陆地径流加速海水结冰的作用消除融冰期海水吸收大量太阳辐射能后发生推迟结冰的现象,使得ASIC无明显变化。融冰期ASIC减小,而结冰期ASIC增大的区域只有白令海。研究结果证明累积海冰密集度能够去除海冰高频变化而只表现低频变化,能够描述海冰的年际变化特征。同时由于海冰变化与海洋中其他物理参数存在显著关系,变T的ASIC可以更加方便地描述次表层叶绿素最大值层深度的变化。     

Rogue events in spatiotemporal numerical simulations of unidirectional waves in basins of different depth

The evolution of unidirectional nonlinear sea surface waves is calculated numerically by means of solution of the Euler equations. The wave dynamics corresponds to quasi-equilibrium states characterized by JONSWAP spectra. The spatiotemporal data are collected and processed providing information about the wave height probability and typical appearance of abnormally high waves (rogue waves). The waves are considered at different water depths ranging from deep to relatively shallow cases (k _p h > 0.8, where k _p is the peak wavenumber, and h is the local depth). The asymmetry between front and rear rogue wave slopes is identified; it becomes apparent for sufficiently high waves in rough sea states at all considered depths k _p h ≥ 1.2. The lifetimes of rogue events may reach up to 30–60 wave periods depending on the water depth. The maximum observed wave has a height of about three significant wave heights. A few randomly chosen in situ time series from the Baltic Sea are in agreement with the general picture of the numerical simulations.     

Evidence of extreme wave events from boulder deposits on the south-east coast of Malta (Central Mediterranean)

Large boulder accumulations have been observed on various coasts bordering the Mediterranean and have been associated with extreme wave events such as powerful storms or tsunamis. This study provides an in-depth analysis of 430 boulder deposits, located along a 3.5 km stretch of rocky coast situated on the SE of the Maltese Islands. It includes a geomorphometric analysis of the observed boulders and use of numerical modelling to estimate wave height required to initiate boulder movement. Comparisons of aerial imagery over a period of 46 years have made it possible to identify boulder movement that could only be attributed to storm waves, given that no local tsunamigenic event has been recorded over this time period. Positioned in the central Mediterranean, the Maltese Islands are exposed to potential tsunamis generated by seismic activity associated with the Malta Escarpment, and the Calabrian and Hellenic arcs. Although imprints from historic tsunami impact cannot be excluded, results indicate that the area is exposed to strong storm waves that are capable of displacing some of the very large boulders observed on site.

     

基于GPS的海冰实时监测系统及其应用研究

海冰是高纬度海区特有的海洋现象。运动的海冰具有巨大的能量,对冰区的石油平台、港口堤坝、船只等构成了巨大的威胁,因此实时获取准确的海冰运动信息对于海冰灾害的防治有重要的现实意义。我国海冰为一年海冰,冰体较薄,用于极地的海冰跟踪设备并不适用于我国北方海域。设计并提出了一种基于GPS的海冰定位跟踪系统,系统包含冰上定位发射和接收两个部分。冰上部分质量较轻且外形增加了防滑设计,接收端接收到数据后自动入库,并与地图匹配显示。监测系统于2015-2016年冬季在辽东湾海域进行了应用测试,应用试验表明,该方法能够较好地进行海冰定位与跟踪,定位误差在5 m以内,运行时间较久,较适用于我国薄冰海域。     

北极海冰减退引起的北极放大机理与全球气候效应

自20世纪70年代以来,全球气温持续增高,对北极产生了深刻的影响。21世纪以来,北极的气温变化是全球平均水平的2倍,被称为"北极放大"现象。北极海冰覆盖范围呈不断减小的趋势,2012年北极海冰已经不足原来的40%,如此大幅度的减退是过去1 450年以来独有的现象。科学家预测,不久的将来,将会出现夏季无冰的北冰洋。全球变暖背景下北极内部发生的正反馈过程是北极放大现象的关键,不仅使极区的气候发生显著变化,而且对全球气候产生非常显著的影响,导致很多极端天气气候现象的发生。北极科学的重要使命之一是揭示这些正反馈过程背后的机理。北极放大有关的重大科学问题主要与气—冰—海相互作用有关,海冰是北极放大中最活跃的因素,要明确海冰结构的变化,充分考虑融池、侧向融化、积雪和海冰漂移等因素,将海冰热力学特性的改变定量表达出来。海洋是北极变化获取能量的关键因素,是太阳能的转换器和储存器,要认识海洋热通量背后的能量分配问题,即能量储存与释放的联系机理,认识淡水和跃层结构变化对海气耦合的影响。全面认识北极气候系统的变化是研究北极放大的最终目的,要揭示气—冰—海相互作用过程、北极海洋与大气之间反馈的机理、北极变化过程中的气旋和阻塞过程、北极云雾对北极变化的影响。在对北极海冰、海洋和气候深入研究的基础上,重点研究极地涡旋罗斯贝波的核心作用,以及罗斯贝波变异的物理过程,深入研究北极变化对我国气候影响的主要渠道、关键过程和机理。     

Coastal flooding in the Maldives: an assessment of historic events and their implications

With many inhabited islands only at about 1 m above mean sea level, the Maldives is among the nations most threatened by coastal flooding and sea level rise. However, the understanding of recent coastal flood events in the Maldives is limited and is important to understanding future flood threats. This paper assesses (1) the sea level and wave climate of the Maldives, (2) the sea level and wave conditions during recent coastal flood events, and (3) the implications for flood management and future research. The analysis uses observed still water levels (1987–2015) and hindcast wave conditions (1979–2015). Two significant flood events on 10–13 April 1987 and 15–17 May 2007 are examined in detail. This shows that coastal flooding in the Maldives occurs due to multiple interacting sources. These include long-period (up to 20 s) energetic waves generated in the Southern Ocean combined with spring tides. Wave run-up (mainly wave set-up) appears an essential mechanism for a flood, but is currently poorly quantified. However, as sea levels continue to rise the conditions that produce a flood will occur more frequently, suggesting that flooding will become common in the Maldives. This analysis is a starting point for future research and highlights the need to continue research on flood sources, pathways and receptors, and plan adaptation measures. Priorities include monitoring of waves, sea levels and flood events, and a better understanding of set-up (and other shallow water processes over reefs).     

Attenuation of Gravity Waves in Fast Ice

Doklady Earth Sciences - The attenuation coefficients of sea waves in ice in the coastal zone of the Sea of Okhotsk with periods from 4 to 30 s were estimated as a function of their wavelength...