The earliest datable observation of the aurora borealis

F Richard Stephenson, David M Willis and Thomas J Hallinan document observations of the aurora borealis from a Babylonian clay tablet from more than 2500 years ago – probably the earliest reliable account.     

Early observation of the aurora australis: AD 1640

David M Willis, José M Vaquero and F Richard Stephenson cast a critical eye over evidence of auroral observations in 17th-century Chile.     

地基观测的夜侧极光对行星际激波的响应

行星际激波与地球磁层相互作用通常会导致日侧极光活动增强,随后沿着极光卵的晨昏两侧向夜侧扩展的激波极光. 行星际激波也可能直接导致夜侧扇区极光活动增强,甚至沉降粒子能通量的数量级可以与典型亚暴相比拟. 本文首次利用我国南极中山站和北极黄河站连续多年积累的极光观测数据,对行星际激波与地球磁层相互作用期间地面台站在夜侧扇区(18—06 MLT)观测的极光响应进行了分析. 对18个极光观测事件的分析结果表明:行星际激波与磁层相互作用可以在夜侧触发极光爆发和极光微弱增强或静态无变化事件;太阳风-磁层能量耦合的效率以及磁层空间的稳定性决定着行星际激波能否触发极光爆发.     

An analogue model study of electromagnetic induction in the eastern coastal region of North America

The behavior of electric and magnetic field variations over the eastern coastal region of North America is studied using a scaled laboratory electromagnetic analogue model. The model source frequency used simulates a period of 1 h in the geophysical scale. The results indicate that deflection and conductive channelling of induced electric current is important for both the E-polarization (northeast-southwest direction of the electric field of the source) and the H-polarization (northwest-southeast) of the source field. In the model, conductive channelling occurs through the Strait of Belle Isle, Cabot Strait, and in the St. Lawrence River. Current deflection is particularly prevalent around the southeast coast of Newfoundland for both E- and H-polarization, and around the northeast coastline of Nova Scotia for E-polarization. The model results also show current deflection by cape and bay coastal features, as well as by ocean depth contours.A comparison of model measurements for the cases of a uniform source field and a line current source indicate that the nature of the source field has a measurable but surprisingly small effect on the vertical to horizontal magnetic field ratio for both E- and H-polarizations, and negligible effect on the magnetotelluric ratio for coastal regions.The model fields in coastal regions were found to be strongly influenced by induced currents, deflected and channelled by the coastline and ocean bathymetry, and were dependent on the nature and particularly the polarization of the source field. Thus, along the complex coastline of eastern North America, a wide range of electric and magnetic field values should be expected. In some regions the coast effect, measured by the vertical to horizontal magnetic field ratio at the coast, could be expected to be extremely small or absent, while in other regions the ratio could approach a value as large as unity for variations of 1 h period.     

An unconventional proterozoic paleomagnetic polar wander path for North America and its advantages

Statistically-contoured paleomagnetic poles for the Proterozoic of North America trace a sub-equatorial polar wander path that differs from more-conventional APW tracks. This path is modified by two types of hairpins, those that close in the northern hemisphere and are closely synchronous with the Hudsonian and the Grenvillian events, and those that close in the southern hemisphere and do not appear to have tectonic significance. The north-closing hairpins correspond to major shearing through the continent. The most plausible displacement of North America during the Proterozoic is an anti-clockwise rotation along a small circle centered close to the equator. A major reorganization of the APW path in the late Proterozoic probably corresponds to the beginning of subduction processes.     

Predictability of the Rate of Seismic Energy in North America

Izvestiya, Physics of the Solid Earth - Abstract—The predictability of the rate of seismicity and strong earthquakes of North America is assessed based on the catalog of the U.S. Geological...     

Radiocarbon dating of small terrestrial gastropod shells in North America

Fossil shells of small terrestrial gastropods are commonly preserved in wetland, alluvial, loess, and glacial deposits, as well as in sediments at many archeological sites. These shells are composed largely of aragonite (CaCO₃) and potentially could be used for radiocarbon dating, but they must meet two criteria before their ¹⁴C ages can be considered to be reliable: (1) when gastropods are alive, the ¹⁴C activity of their shells must be in equilibrium with the ¹⁴C activity of the atmosphere, and (2) after burial, their shells must behave as closed systems with respect to carbon. To evaluate the first criterion, we conducted a comprehensive examination of the ¹⁴C content of the most common small terrestrial gastropods in North America, including 247 AMS measurements of modern shell material (3749 individual shells) from 46 different species. The modern gastropods that we analyzed were all collected from habitats on carbonate terrain and, therefore, the data presented here represent worst-case scenarios. In sum, ～78% of the shell aliquots that we analyzed did not contain dead carbon from limestone or other carbonate rocks even though it was readily available at all sites, 12% of the aliquots contained between 5 and 10% dead carbon, and a few (3% of the total) contained more than 10%. These results are significantly lower than the 20–30% dead carbon that has been reported previously for larger taxa living in carbonate terrain. For the second criterion, we report a case study from the American Midwest in which we analyzed fossil shells of small terrestrial gastropods (7 taxa; 18 AMS measurements; 173 individual shells) recovered from late-Pleistocene sediments. The fossil shells yielded ¹⁴C ages that were statistically indistinguishable from ¹⁴C ages of well-preserved plant macrofossils from the same stratum. Although just one site, these results suggest that small terrestrial gastropod shells may behave as closed systems with respect to carbon over geologic timescales. More work on this subject is needed, but if our case study site is representative of other sites, then fossil shells of some small terrestrial gastropods, including at least five common genera, Catinella, Columella, Discus, Gastrocopta, and Succinea, should yield reliable ¹⁴C ages, regardless of the local geologic substrate.     

中国华北峰值加速度的衰减特性及与北美东部的比较

利用唐山强余震的强地面运动记录,研究了近场强地面运动水平峰值加速度的衰减特性,得到了唐山地区的衰减关系(土层、土层与基岩)．此外,还得到了北美东部的衰减关系,并将其与中国华北的衰减进行了比较,认为两者的衰减趋势是比较一致的．中国华北的衰减特性可供北美东部参考．      

Attenuation characteristics of peak acceleration in North China and comparison with those in the eastern part of North America

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Many-year level variations in the Great Lakes of Eurasia and North America

Regularities in the secular variations of water level in the Great Lakes of Eurasia and North America under natural climate and anthropogenic impacts are studied.     

Development of site-specific design ground motions in Western and Eastern North America

This paper presents results recently obtained for generating site-specific ground motions needed for design of critical facilities. The general approach followed in developing these ground motions using either deterministic or probabilistic criteria is specification of motions for rock outcrop or very firm soil conditions followed by adjustments for site-specific conditions. Central issues in this process include development of appropriate attenuation relations and their uncertainties, differences in expected motions between Western and Eastern North America, and incorporation of site-specific adjustments that maintain the same hazard level as the control motions, while incorporating uncertainties in local dynamic material properties. For tectonically active regions, such as the Western United States (WUS), sufficient strong motion data exist to constrain empirical attenuation relations for M up to about 7 and for distances greater than about 10–15 km. Motions for larger magnitudes and closer distances are largely driven by extrapolations of empirical relations and uncertainties need to be substantially increased for these cases.

For the Eastern United States (CEUS), due to the paucity of strong motion data for cratonic regions worldwide, estimation of strong ground motions for engineering design is based entirely on calibrated models. The models are usually calibrated and validated in the WUS where sufficient strong motion data are available and then recalibrated for applications to the CEUS. Recalibration generally entails revising parameters based on available CEUS ground motion data as well as indirect inferences through intensity observations. Known differences in model parameters such as crustal structure between WUS and CEUS are generally accommodated as well. These procedures are examined and discussed.     

Some appearances of the aurora borealis in Greece

Summary Some observations of the aurora borealis in Greece are given with the sources from which they were taken. It was found that the appearances of this phenomenon are not exceptionally rare. These appearances coincide with the years of maximun of solar activity and especially 1–2 years after it, while in the years of minimum of solar activity or near these years none of the described cases belong here. Except of two appearances of this phenomenon all the others were observed in Spring and Autumn or near these seasons. The southest geographical latitude of which edges of the aurora borealis have been observed in Greece is the latitude of 35 N.     

A study of energy,generation and conversion over North America

The energy conversion between potential and kinetic energy and the generation of available potential energy are computed over North America. The relative contribution from each latitude belt within the region, for each field, have been discussed.     

Landscape and climate change threats to wetlands of North and Central America

North and Central America has a combined total of 2.5 million km² of wetlands, with 51 % in Canada, 46 % in the USA, and the remainder in subtropical and tropical Mexico and Central America. Loss rates are well known for the conterminous USA and for parts of Canada but poorly understood for Mexico and Central America. Wetlands of North America continue to be threatened due to drainage for agriculture and urban development, extreme coastal and river management, water pollution from upstream watersheds, peat mining, waterfowl management, and more recently climate change. Human use of wetlands in this region are many, including receiving ecosystem services such as water purification, flood regulation, climate regulation, and direct provisioning benefits for many cultures living in and among wetlands, especially in the Louisiana Delta and in Mexico and Central America. Climate change affects will cause wetland impacts on coastal wetlands due to sea level rise and on inland wetlands due to changes in precipitation, air temperature, and river discharges. Wetlands, in turn, have a major role in the storage of carbon in boreal regions of Canada and with carbon sequestration in temperate and tropical wetlands of the Americas.     

Crustal and upper mantle structure of stable continental regions in North America and northern Europe

From an analysis of many seismic profiles across the stable continental regions of North America and northern Europe, the crustal and upper mantle velocity structure is determined. Analysis procedures include ray theory calculations and synthetic seismograms computed using reflectivity techniques. TheP wave velocity structure beneath the Canadian Shield is virtually identical to that beneath the Baltic Shield to a depth of at least 800 km. Two major layers with a total thickness of about 42 km characterize the crust of these shield regions. Features of the upper mantle of these region include velocity discontinuities at depths of about 74 km, 330 km, 430 km and 700 km. A 13 km thickP wave low velocity channel beginning at a depth of about 94 km is also present.A number of problems associated with record section interpretation are identified and a generalized approach to seismic profile analysis using many record sections is described. TheS wave velocity structure beneath the Canadian Shield is derived from constrained surface wave data. The thickness of the lithosphere beneath the Canadian and Baltic Shields is determined to be 95–100 km. The continental plate thickness may be the same as the lithospheric thickness, although available data do not exclude the possibility of the continental plate being thicker than the lithosphere.     

The craton: Its effect on the distribution of seismicity and stress in North America

The gross distribution of seismicity in North America suggests the interior platform and shield provinces are relatively stable and significantly affect the intraplate stress field. Focal mechanisms and in-situ stress measurements indicate the cratonic areas of North America must be relatively immobile with respect to the eastern and western portions of the continent. Simple kinematic models are presented to illustrate the importance of the craton in any attempt to explain the general pattern of intraplate stress and seismicity in North America.     

苏北平原井下摆观测效果的讨论

文章以江苏省大丰台、盐城台、淮阴台、海安台，射阳台井下摆观测为例。比较它们的观测结果，分析认为井下摆的观测效果不仅与地面复盖层的厚度有关，而且与井下摆周围的环境干扰，观测用井的质量有关。为了提高井下摆观测效果，应尽量减少环境干扰，并注意井的垂直度和固井，文章还指出，沿海地区井下摆受海浪干扰相当显著的。     

琼北GPS流动观测数据质量检核

利用TEQC软件,对琼北GPS流动观测网7个测点2011—2018年8期数据进行质量检核,给出检核结果统计表,就数据有效率、多路径误差及观测值和周跳比等,综合分析测点周围观测环境、仪器稳定性是否发生变化,为测点及周围观测环境的维护及升级改造提供参考。     

Spatial texture based automatic classification of dayside aurora in all-sky images

A spatial texture based representation method including features of intensity, shape and texture, was utilized to characterize all-sky auroral images. The combination of the local binary pattern (LBP) operator and a delicately designed block partition scheme achieved both global shapes and local textures capabilities. The representation method was used in automatic recognition of four primary categories of discrete dayside aurora using observations between years 2003–2009 at the Yellow River Station, Ny-Ålesund, Svalbard. The supervised classification results on labeled data in 2003 were in accordance with the labeling by scientists considering both spectral and morphological information. The occurrence distributions of the four categories were obtained through automatic classification of data between 2004–2009, which confirm the multiple-wavelength intensity distribution of dayside aurora, and further provide morphological interpretation of auroral types.