Observation of saturnian stream particles in the interplanetary space

In January 2004 the dust instrument on the Cassini spacecraft detected the first high-velocity grain expelled from Saturn - a so-called stream particle. Prior to Cassini’s arrival at Saturn in July 2004 the instrument registered 801 faint impacts, whose impact signals showed the characteristic features of a high-velocity impact by a tiny grain. The impact rates as well as the directionality of the stream particles clearly correlate with the sector structure of the interplanetary magnetic field (IMF). The Cosmic Dust Analyser (CDA) registered stream particles dominantly during periods when the IMF direction was tangential to the solar wind flow and in the prograde direction. This finding provides clear evidence for a continuous outflow of tiny dust grains with similar properties from the saturnian system. Within the compressed part of co-rotating interaction regions (CIRs) of the IMF, characterized by enhanced magnetic field strength and compressed solar wind plasma, CDA observed impact bursts of faster stream particles. We find that the bursts result from the stream particles being sped up inside the compressed CIR regions. Our analysis of the stream-particle dynamics inside rarefaction regions of the IMF implies that saturnian stream particles have sizes between 2 and 9 nm and exit the saturnian systems closely aligned with the planet’s ring plane with speeds in excess of 70 km s⁻¹.     

Search for Phobos and Deimos gas/dust tori using in situ observations from Mars Global Surveyor MAG/ER

More than 490 elliptical aerobraking and science phasing orbits made by Mars Global Surveyor (MGS) in 1997 and 1998 provide unprecedented coverage of the solar wind in the vicinity of the orbits of the martian moons Phobos and Deimos. We have performed a comprehensive survey of magnetic field perturbations in the solar wind to search for possible signatures of solar wind interaction with dust or gas escaping from the moons. A total of 1246 solar wind disturbance events were identified and their distribution was examined relative to Phobos, the Phobos orbit, and the Deimos orbit. We find that the spatial distribution of solar wind perturbations does not increase near or downstream of Phobos, Phobos’ orbit, or Deimos’ orbit, which would have been expected if there is significant outgassing or dust escape from the martian moons. Of the 1246 magnetic field perturbation events found in the MGS data set, 11 events were found within 2000 km of the Phobos orbit, while three events were found within 2000 km of the Deimos orbit. These events were analyzed in detail and found to likely have other causes than outgassing/dust escape from the martian moons. Thus we conclude that the amount of gas/dust escaping the martian moons is not significant enough to induce detectable magnetic field perturbations in the solar wind. In essence we have not found any clear evidence in the MGS magnetic field data for outgassing or dust escape from the martian moons.     

Influence of Wind on Dynamics and Flushing of Shallow Estuaries

Observations of two small estuaries in Cape Cod, U.S.A. indicate large variations in salinity structure that are forced by variations in along-estuary wind stress. During onshore winds, the estuarine circulation is reduced, and the along-estuary salinity gradient increases as freshwater accumulates. During offshore winds, the surface outflow is enhanced, freshwater is flushed out of the estuary, and the along-estuary salinity gradient becomes weak. Constrictions block the wind-induced flushing, resulting in strong salinity fronts across the constrictions. The residence time of one of the estuaries varies by more than a factor of three in response to variations in wind-induced flushing. The other estuary has little variation of flushing associated with winds, due to a constriction at the mouth that inhibits the wind-induced exchange. The strong influence of winds on the flushing of these estuaries is due in part to their shallow depths, which accentuates the influence of wind stress relative to the effects of the horizontal density gradient. In addition, the residence times of the estuaries are comparable to the time scale of wind forcing, allowing large changes in water properties during wind events.     

定常风场和吞吐流对乌梁素海流场的影响

风场和吞吐流是浅水湖泊运动的主要驱动力,影响着湖区污染物的迁移转化。基于二维非结构网格,构建了乌梁素海水动力模型。通过对比定常风作用下湖流的方向、环流的分布及形式与无风条件下的区别,模拟不同算例吞吐流作用下湖区流速及环流结构的差异,探究了定常风和吞吐流对乌梁素海流场的影响。结果表明:乌梁素海在无风条件下出现大面积的滞流区;风场会增加湖流的流速,影响区域主要在西大滩区、东大滩区及湖区南部明水区,产生明显环流,风场是乌梁素海主要的驱动力; SSW与ENE向风场作用下,典型区域产生的环流位置、形态结构相近,方向相反;吞吐流量的增加会增大湖区整体流速,对湖区流场形态、结构影响较小;定常风条件下,吞吐流量的增加(一定范围)会导致环流强度减弱。研究结果为乌梁素海营养盐、污染物质输移规律研究奠定基础。     

Tides in the Tongan Region of the Pacific Ocean

Tidal levels and currents in the Tongan region of the Pacific were simulated using a two-dimensional frequency-domain finite element model. The eight major diurnal and semidiurnal tidal constituents were modeled successfully, using open boundary conditions taken from a global tidal model based on the Topex/Poseidon satellite altimeter. Comparison of model results with observations from the single tide gauge site in the area were later used to adjust the boundary conditions. The validity of omitting horizontal eddy viscosity from the finite element model was checked by running an equivalent finite difference model. The results show that although the submarine Tongan ridge does not appear to trap tidal energy, there are residual tidal currents and possible recirculations which are capable of influencing biological productivity around Tonga. The model results are reduced to a simple method for predicting tidal heights in outlying areas, based only on the tidal calendar for the capital, Nuku'alofa.     

Three sipunculan species (two new) from New Zealand

Two new species of Sipuncula arc described from New Zealand; Phascolion temporariae from, the empty tubes of the polychaete Temporaria inexpectata (Mestayeri), and Phascolion tortum from the shells of four species of molluscs. Specimens of Golfingia improvisa (Theel) are also reported from the empty frustules of the foraminiferan Ammodiscoides mestayeri (Cushman) and the sandy tubes of the foraminifera Rhizammina sp. All the species were dredged at depths of 370–660 m from Taiaroa and Papanui Canyons, off the Otago Peninsula, New Zealand. The body cavity of several specimens of G. improvisa contained the larval stage of a nematode.     

基于LSTM的海洋表面短期风速预测研究

为实现对海面风速精确的短期预测,提出了一种基于长短期记忆(LSTM,longshort-termmemory)神经网络的短期风速预测模型,选取OceanSITES数据库中单个浮标站点采集的风速历史数据作为模型输入,经过训练设置最佳参数等步骤,实现了以LSTM方法,对该站点所在海区海面风速在各季节性代表月份海面风速的24 h短期预测。同时通过不同预测时长的实验以及与BP(back propagation)神经网络神经网络和径向基函数神经网络(radialbasisfunctionneuralnetwork,RBF)的预测效果对比实验,证明了LSTM预测方法相比上述两种神经网络预测方法,在海表面风速预测应用中的优越性。最后通过多个海域对应的站点风速数据预测实验,证明了LSTM神经网络模型的普遍适用性,由相关系数和预测误差的分析可知该方法具备应对急剧变化数据的预测稳定性,可以作为海洋表面风速短期预测的一种可靠方法。     

In situ measurements of wind‐driven salt fluxes through constructed channels in a coastal wetland ecosystem

A suite of instruments was deployed in a coastal wetland ecosystem in the Albemarle estuarine system, North Carolina (USA), to characterize wind‐driven transport of saltwater through a constructed (man‐made) channel. Flow velocity, electrical conductivity, and stage were measured in a representative channel over a 2‐month period from May to July 2014, during which 4 wind tides were observed. Collected data show that thousands of metric tons of salt were advected through the channel into coastal wetlands during each event, which lasted up to 4 days. The results reveal that as much as 36% of advected salts accumulated in the wetlands, suggesting that the cumulative effects of these events on the health of coastal wetlands in the Albemarle system may be substantial due to the abundance of constructed channels and the frequency of wind‐driven tidal events. This study is the first to quantify wind‐driven salt fluxes through constructed channels in coastal wetland settings.     

凤城市赛马镇风洞洞穴特征及发育基本条件

赛马镇风洞是我国东北规模较大的岩溶洞穴,洞长在2000m以上,已探测长度1265m.风洞具有纵坡降较小、支洞繁多、形态奇异及国内罕见的溶蚀景观“天锅”等特征.岩性、构造、水文地质特征等是控制洞穴发育的基本条件.风洞的发育约始于中更新世40万年前.     

Linking moisture and near-surface wind with winter temperature to reveal the Holocene climate evolution in arid Xinjiang region of China

An increasing number of palaeo-climatic records have been reported to identify the Holocene climate history in the arid Xinjiang region of northwest China. However, few studies have fully considered the internal linkages within the regional climate system, which may limit our understanding of the forcing mechanisms of Holocene climate change in this region. Here, we systematically consider three major issues of the moisture/precipitation, temperature and near-surface wind relevant to the Holocene climate history of Xinjiang. First, despite there still has debated for the Holocene moisture evolution in this region, more climatic reconstructions from lake sediments, loess, sand-dunes and peats support a long-term regional wetting trend. Second, temperature records from ice cores, peats and stalagmites demonstrate a long-term winter warming trend during the Holocene in middle- to high-latitudes of Asia. Third, recent studies of aeolian sedimentary sequences reveal that the near-surface winds in winter gradually weakened during the Holocene, whereas the winter mid-latitude Westerlies strengthened in the Tienshan Mountains. Based on this evidence, in the arid Xinjiang region we propose an early to middle Holocene relatively cold and dry interval, with strong near-surface winds; and a warmer, wetter interval with weaker near-surface winds in the middle to late Holocene during winter. Additionally, we develop a conceptual model to explain the pattern of Holocene climate changes in this region. From the early to the late Holocene, the increasing atmospheric CO₂ content and winter insolation, and the shrinking of high-latitude continental ice-sheets, resulted in increasing winter temperatures in middle to high latitudes in the Northern Hemisphere. Subsequently, the increased winter temperature strengthened the winter mid-latitude Westerlies and weakened the Siberian high-pressure system, which caused an increase in winter precipitation and a decrease in near-surface wind strength. This scenario is strongly supported by evidence from geological records, climate simulation results, and modern reanalysis data. Our hypothesis highlights the important contribution of winter temperature in driving the Holocene climatic evolution of the arid Xinjiang region, and it implies that the socio-economic development and water resources security of this region will face serious challenges presented by the increasing winter temperature in the future.