Morphology of low-frequency waves in the solar wind and their relation to ground pulsations

Three classes of low frequency waves (period range 20–80 s) were identified using data from the UCLA fluxgate magnetometer experiment on board the ISEE 2 spacecraft. These are continuous pulsations similar in type to Pc 3, band-limited oscillations distinguished by mixed period fluctuations, and relatively isolated wave bundles. The waves were preferentially observed when the interplanetary magnetic field (IMF) direction was sunward and were most common when the cone angle, i.e. the angle between IMF and the Sun-Earth line (θ_xb) was often between 15° and 45°. Their frequency is proportional to the IMF magnitude.Comparison between the waves observed on board the ISEE 2 spacecraft and the Pc 3–4 recorded simultaneously at a mid-latitude ground station, Oulu (L = 4.5), showed that similarity of spectra of the waves in the spacecraft and on the ground was very rare and that correspondence between the events in space and on the ground was extremely low.     

Mesospheric wind studies during AIDA Act '89: morphology and comparison of various techniques

The Arecibo Initiative in Dynamics of the Atmosphere (AIDA) '89 was a multi-instrument campaign designed to compare various mesospheric wind measurement techniques. Our emphasis here is the comparison of the incoherent scatter radar (ISR) measurements with those of a 3.175 MHz radar operating a s an imaging Doppler interferometer (1131). We have performed further analyses in order to justify the interpretation of the long term IDI measurements in terms of prevailing winds and tides. Initial comparison of 14 profiles by Hines et al., 1993, J. atmos. terr. Phys. 55, 241–288, showed good agreement between the ISR and IDI measurements up to about 80 km, with fair to poor agreement above that altitude. We have compiled statistics from 208 profiles which show that the prevailing wind and diurnal and semidiurnal tides deduced from the IDI data provide a background wind about which both the IDI and ISR winds are normally distributed over the height range from 70 to 97 km. The 3.175 MHz radar data have also been processed using an interferometry (INT) technique [Van Baelen and Richmond 1991, Radio Sts. 26, 1209–1218] and two spaced antenna (SA) techniques [Meek, 1980, J. atmos. terr. Phys. 42, 837–839; Briggs. 1984, MAP Handbook, Vol. 13, pp. 166–186] to determine the three dimensional wind vector. These are then compared with the IDI results. Tidal amplitudes and phases were calculated using the generalized analysis of Groves, 1959, S. atmos. terr. Phys. 16, 344–356, historically used on meteor wind radar data. Results show a predominance of the diurnal S₁¹ tidal mode in the altitude range 70–110 km, reaching a maximum amplitude 45 ms⁻¹ at 95 km, with semidiurnal amplitudes being about 10–15 ms⁻¹ throughout the height range considered. There is evidence of the two day wave in data from 86–120 km, with amplitudes on the order of 20 ms⁻¹.     

Meteor observations by the Arecibo 430 MHz incoherent scatter radar—I. Results from time-integrated observations

The paper discusses an incoherent scatter radar (ISR) power profile interference detection and meteor filtering technique and presents the meteor interference statistics derived from the Arecibo 430 MHz ISR. The statistics obtained from the Arecibo ISR are comparable with the meteor statistics obtained by other radar and optical techniques. Using the hourly rate of meteor flux, the average visual magnitude of the meteors i s estimated to be as faint as + 14, probably, the faintest ever reported. For low echo meteors, the mean ablation height exhibits a logarithmic relationship with the returned power below 105 km. However, once the echo power exceeds a certain threshold, the mean height remains constant at 107 km for all meteors irrespective of their returned power. The unique aspect of the meteor trails reported here is that they are observed in the radial direction of the radar beam. The lack of aspect sensitivity and the high meteor rate detected by the Arecibo 430 MHz system seem to suggest that the scattering mechanism in the UHF range of frequencies may be different from the mechanism operating at VHF. Some future prospects of exploiting; meteor trails to study the neutral wind and other aspects of the meteor region are also proposed.     

A NON-PARAMETRIC APPROACH TO ATTENUATION RELATIONS

Abstract

A non-parametric multidimensional regression method is proposed for the prediction of seismic ground motion parameters. The main features which distinguish the method from standard regression procedures are: (1) The relationship between the input and output variables is not selected a priori by a prediction law, (2) an arbitrary number of input variables Can be taken into account, provided that an appropriate data base exists, and (3) the computational procedure is very simple. The results can be easily updated when new information becomes available. The method has been applied for the derivation of attenuation relations by using a combination of databases compiled by other researchers. In the majority of the cases discussed in this paper, the method was used for the prediction of horizontal peak ground acceleration as a function of magnitude and distance. In some cases, ground conditions were also taken into account. Some results on the attenuation relations of peak ground velocity and displacement, as well as Arias intensity, are also presented.     

Mechanisms and time-scales of the magnetospheric response to the interplanetary magnetic field changes during the 8 May 1986 substorm

On 8 May 1986, between 1113 and 1600 UT, an isolated magnetospheric substorm was observed, during which the AE-index exceeded 700 nT (CDAW 9E event). Three available sets of measurements (a) of the solar-wind parameters (IMP-8 satellite), (b) of the magnetotail energy flux (ISEE-1 spacecraft), and (c) of ground magnetic observatories, allowed us to make a detailed study of the overall magnetospheric response to changes of the interplanetary magnetic field (IMF) direction, during this event of weak solar-wind coupling.In order to study the mechanisms and time-delays of the magnetospheric response to the abrupt increase of the solar-wind energy input, we have evaluated the total magnetospheric energy output U_T following two different methods: (a) Akasofu's method, taking the ring current decay time τ_R constant, and (b) Vasyliunas' method where the values of u_t are independent of the solar-wind energy input as determined from the epsilon parameter. Both methods suggest that the driven system has been considerably developed during this substorm, while an unloading event has been superposed at the expansion onset.     

Space-time structure of the morning aurora inferred from coincident DMSP-F6, -F8, and Søndrestrøm incoherent scatter radar observations

On rare occasions, observations from the DMSP-F6 and -F8 spacecraft and the Søndrestrøm incoherent scatter radar coincide in space. Such coincidence offers a unique opportunity to study temporal vs spatial variations on a small scale. We discuss data from one of those occasions, with observations made in the dawn sector in the presence of moderate auroral precipitation during a magnetically quiet period. The DMSP satellites measured vertical electron and ion flux and cross-track plasma drift while the radar measured the ionospheric electron density distribution and line-of-sight plasma velocities. We combine these data sets to construct a two-dimensional map of a possible auroral pattern above Søndrestrøm. It is characterized by the following properties. No difference is seen between the gross precipitation patterns measured along the DMSP-F6 and -F8 trajectories (separated by 32 km in magnetic east-west direction and some 4 s in travel time in magnetic north-south direction), except that they are not exactly aligned with the L shells. However, F6 and F8 observed minor differences in the small-scale structures. More significant differences are found between small-scale features in the DMSP precipitation measurements and in radar observations of the E-region plasma density distribution. These measurements are separated by 74 km, equivalent to 2.4°, in magnetic longitude, and 0–40 s in time along the spacecraft trajectories (varying with magnetic latitude). Large-scale magnetospheric-ionospheric surfaces such as plasma flow reversal, poleward boundary of the keV ion and electron precipitation, and poleward boundary of E-region ionization, coincide. The combined data suggest that the plasma flow reversal delineates the polar cap boundary, that is, the boundary between precipitation characteristic for the plasma mantle and for the plasma sheet boundary layer.     

Comparison of ionospheric electrical conductances inferred from coincident radar and spacecraft measurements and photoionization models

Height-integrated electrical conductivities (conductances) inferred from coincident Sondrestrom incoherent scatter radar and DMSP-F7 observations in the high-latitude ionosphere during solar minimum are compared with results from photoionization models. We use radar and spacecraft measurements in combination with atmospheric and ionospheric models to distinguish between the contributions of the two main sources of ionization of the thermosphere, namely, solar UV/EUV radiation and auroral electron precipitation. The model of Robinsonet al. (1987, J. geophys. Res.89, 3951) of Pedersen and Hall conductances resulting from electron precipitation appears to be in accordance with radar measurements. Published models of the conductances resulting from photoionization that use the solar zenith angle and the solar 10.7-cm radio flux as scaling parameters are, however, in discrepancy with radar observations. At solar zenith angles of less than 90°, the solar radiation components of the Pedersen and Hall conductances are systematically overestimated by most of these models. Geophysical conditions that have some bearing on the state of the high-latitude thermosphere (e.g. geomagnetic and substorm activity and a seasonal variation of the neutral gas distribution) seem to influence the conductivity distribution but are to our knowledge not yet sufficiently well modelled.     

Simultaneous ground-based observations of polar cap arcs and spacecraft measurements of particle precipitation

In order to investigate the particles which produce the polar cap aurora at the Vostok station in Antarctica, charged particle data obtained by the DMSP satellites for some days in a period from April to August 1985 were surveyed. Due to the satellite orbit the local time range in which the data were available was the morning sector. For all the events when sun-aligned arcs were observed on the ground the simultaneous DMSP measurements on almost the same field line showed an increased integral number flux J. > 10⁸ (cm⁸/s/sr)⁻¹ of the precipitating electrons with energy E_e > 200 eV. The electron spectra with double peaks are typical of intense electron precipitation in the polar cap arcs. The most noticeable feature of ion spectra in the polar cap arcs is the prominent minimum in ion flux in the energy range 0.1 < E_i < 1 keV in contrast with the oval precipitation ; this feature gives the possibility to separate the polar arcs from the aurora in the oval. In some events the satellite crossed the system of two widely separated arcs ; one of them was a sun-aligned arc whereas the other was circular at constant latitude according to the Vostok data. The analysis of the DMSP electron and ion precipitation data has shown that in these events the latitude-oriented arcs are located in the polar cap and not in the auroral oval.     

Implications of Thrown-Out Boulders for Earthquake Shaking

In the source areas of some large shallow earthquakes, we have found many dislodged boulders struck by severe ground shaking. Some boulders were located at quite distances from the former sockets, which remained undisturbed with surrounding clear edges. This fact indicates the possibility that vertically upward seismic acceleration exceeded the earth's gravity (1g). This phenomenon of upthrown boulders is investigated herein by examining the effects of waves, which emanate deep in the ground due to an earthquake, propagate through the ground and boulder, and reflect back to the ground, involving a variety of their interaction. An elastic dynamic analysis is carried out on the basis of a one-dimensional continuum model consisting of the ground and boulder. It is subjected to the input of the Ricker wave, which is intended to simulate an earthquake-generated wave, emanating from the bottom of the model ground. The upthrow of a boulder is taken to occur when the dynamic response at the bottom of the boulder satisfies certain conditions. It turns out that the possibility of upthrow occurrence is high when the period of the Ricker wave coincides with the fundamental period of the ground vibration. It leads to the conclusion that the upthrow takes place due to resonance in the response of the system of the ground and boulder to the external wave input. The upthrow possibility increases as the input acceleration increases. Trial is made of predicting the maximum acceleration and velocity of an earthquake, based on this consideration of the up throw phenomenon.     

Auditory Exostoses in Pre‐Hispanic Populations of the Lower Paraná Wetlands,Argentina

Auditory exostosis (AE) has been characterised from the medical and anthropological perspectives as an adaptive biological response to repeated immersion in cold water as well as exposure to cold environmental temperatures and wind chill. At the archaeological level, the highest prevalence has been found in societies living in coastal environments in areas located at 30–45° north or south latitude with a subsistence pattern based on fishing and mollusc gathering. The region of the lower Paraná River wetlands in Argentina is an area dissected by multiple rivers, streams, and lakes, especially in the Paraná delta near Buenos Aires where these features create a landscape composed of many islands. A variety of archaeological analyses performed on faunal remains, stone tools, bone, and ceramic artefacts are consistent with the interpretation that towards the end of the late Holocene (2000–700 BP), this region was inhabited by hunter–gatherer populations with a subsistence pattern based mainly on fishing and hunting along with the gathering of molluscs. In this work, we present an analysis of 176 crania of individuals recovered from 21 archaeological sites in the region. Results indicate the presence of AE in 6.25% of the cases, with all of these corresponding to adult male individuals. This moderate prevalence coincides with the expected levels for populations where contact with water is frequent in regions located at 30–45° latitude. The absence of female individuals showing evidence of AE allows us to suggest a possible sex‐based division of labour. We hope that this work can contribute to ongoing discussion of the economic and social aspects that characterised pre‐Hispanic life in the study area, while also expanding the available information on AE at the worldwide level. Copyright © 2015 John Wiley & Sons, Ltd.     

Global dynamics of the magnetosphere for northward IMF conditions

Ground-based and spacecraft observations of polar cap geophysical phenomena during periods of northward interplanetary magnetic field (IMF) show specific patterns of electric fields, field-aligned currents, aurora and particle precipitation. These are basically different from those when the IMF is southward. The total combination of observational data for northward IMF indicates rather a closed magnetosphere. This topology has led to the formation of a specific convection pattern in the distant plasma sheet. As different theoretical studies show, the connection of the IMF to geomagnetic flux tubes poleward of the cusp region may serve as the driving mechanism for plasma sheet convection and as the dynamo of current systems. Unfortunately, the direct observations of processes in the distant magnetosphere are too scarce either to accept or reject the concept of a closed magnetosphere. There are also some experimental data that are inconsistent with the closed magnetosphere topology. Definitive open or closed models must await future measurements.     

Size Estimation of Kingsoldier Bream (Argyrops spinifer) and Evidence of Fishing Strategies

This paper provides regression formulae for size estimation of kingsoldier bream (Argyrops spinifer) from measurements taken on bones enabling the reconstruction of the size of fish present in archaeological samples. Bones of Sparidae are commonly recovered from archaeological sites bordering the Arabian Gulf, and, of the species within this family, kingsoldier bream are relatively abundant with the bones also easily identifiable. The marine environment where this fish occurs varies throughout its life cycle, and therefore the reconstructed size of the fish can be used to infer the types of location where past fishing activities took place. Comparison of the estimated size of fish caught from two Late Islamic sites on the northwest coast of Qatar, in combination with other evidence, has been used to indicate differing frequencies of fishing methods at the two sites. This variation in fishing is caused by the topography of the coast in the immediate vicinity of the sites with shallow waters providing a wide tidal zone at the northern of the two with an environment suitable for fishing with stone‐built intertidal fish traps (known in Arabic as al maskar). The topography of the coast at the southern of the two sites is steeper, and the settlement was an important trading port so the coast was utilised primarily as a harbour rather than a fishing ground. The supply of fish at this settlement was provided by fishermen more commonly using basket traps (gargoor) and handlines with fishing taking place from boats. Copyright © 2015 John Wiley & Sons, Ltd.     

In-situ observations of magnetospheric electron scattering by a VLF transmitter

High resolution pitch angle measurements of outer zone electrons in the energy range 12 keV−1.6 MeV were obtained at high altitude in the region of the high power VLF transmitter UMS [300 kW radiated at 17.1 kHz (Watt A. D., 1967, VLF Radio Engineering, Pergamon Press, Oxford)] while a resonant wave-particle interaction was in progress. Additional complementary electron measurements in the range of 36–316 keV were obtained in the drift loss cone by another satellite at low altitude along the drift path 75° east of the interaction region. The data from the low-altitude satellite confirm that UMS was precipitating particles in the inner zone, in the slot, and in the outer zone at the time that the high-altitude satellite was obtaining its data. The high-altitude pitch angle distributions indicate that, for this event, two types of scattering interactions were in progress. Particles with small pitch angles, up to 17.2° at the Equator, were being removed, resulting in an enhanced loss cone. Particles which were mirroring between 6500 km and the altitude of the spacecraft (7200) km were also being strongly scattered, resulting in a relative minimum in the pitch angle distribution around 90°. The data are interpreted as indicating that a cyclotron mode interaction with UMS waves was precipitating electrons with equatorial pitch angles up to 17.2° and that another process, perhaps electrostatic (ES) waves arising from the UMS radiations through a mode-conversion process, was present in the region above 6500 km and was efficiently scattering those particles which mirrored in that region     

Auroral radio absorption as an indicator of magnetospheric electrons and of conditions in the disturbed auroral D-region

In a previous paper we demonstrated a method by which the auroral radio absorption measured with a riometer can be predicted from energetic electron measurements at geosynchronous orbit. The present paper enquires to what extent the process can be inverted: what levels of magnetospheric electron flux, and of D-region production rate, electron density and incremental absorption, are predicted by a given measurement of radio absorption and what reliance can be placed on such predictions?Using data from 45 precipitation features recorded with riometers in Scandinavia and at geosynchronous orbit with GEOS-2, it is shown that electron fluxes in the ranges 20–40,40–80 and 80–160 keV increase with increasing absorption and can be predicted to better than 50% for absorption events of 2 dB or greater. Electrons above 160 keV show little or no correlation with absorption. D-region production rates and electron densities can be predicted to within factors of 2 and √2, respectively.It is more difficult to specify the height of the absorbing region because of uncertainly in the profile of the effective recombination coefficient. Having regard to other data, an α_eff profile is proposed which satisfies rocket and incoherent scatter data as well as the present calculations. It is shown that any day-night variation in auroral absorption is associated with a change of spectrum rather than a change of recombination coefficient.     

Observatory validation of Neolithic tells (“Magoules”) in the Thessalian plain,central Greece,using hyperspectral spectroradiometric data

This paper presents the results obtained from field spectroradiometric campaigns over Neolithic tells (“magoules”) located at the Thessalian region in Greece. In each one of the four archaeological sites selected, three sections were carried out using the GER 1500 handheld spectroradiometer. Spectral profiles of the sections and several vegetation indices such as Normalized Difference Vegetation Indices (NDVI) and Simple Ratio (SR) have been examined in this study. This is one of the first times that ground hyperspectral data are evaluated in such context of archaeological research for the spectral characterization of archaeological features. As it was found, ground spectroradiometric measurements can be efficiently used in order to support and validate satellite imagery results for the detection of archaeological sites.     

Optimum temporal and spectral window for monitoring crop marks over archaeological remains in the Mediterranean region

This paper aims to explore the formation of crops marks over archaeological features using remote sensing data. Crop marks are very important to archaeological research since they can reveal in an indirect way buried archaeological remains. Several researches have been able to locate subsurface relics via interpretation of multispectral and hyperspectral satellite images. However the best phenophase (time-window) where these crop marks are enhanced and which spectral bands are the most capable for this enhancement are still an open question for the scientific community. This study aims to address these fundamental aspects of Remote Sensing Archaeology. For this reason an extensive dataset was used: two control archaeological sites were constructed in two different areas of Cyprus (Alampra and Acheleia). In these areas both barley and wheat, were cultivated. In situ spectroradiometric measurements were taken over a whole phenological cycle (2001–2012) for both areas. More than 30 in situ campaigns were performed and more than 2600 ground measurements were collected. The phenological analysis of these measurements have shown that a period of only 15 days is best suitable for monitoring crop marks which is connected with one phenological stage; during the beginning of the boot stage of the crops. This period can be used in areas having similar climatic condition as Cyprus (Mediterranean region). Also as it was found, this phenological stage of crops might be also influenced by the climatic conditions of the area. The evaluation of a proposed Archaeological Index was performed at the Thessalian plain (central Greece), where several Neolithic settlements are established. The evaluation was made using both Hyperion and Landsat images. The results have shown that the proposed Archaeological Index is suitable for the enhancement of crop marks in satellite imagery.     

A study of wave packets and phase jumps in low latitude Pc3 geomagnetic pulsation

An array of four low latitude induction coil magnetometer stations has been used to study the spatial and temporal characteristics of Pc3 pulsations over a longitudinal range of 17° at L = 1.8 to 2.7 in southeast Australia. A preliminary study of individual Pc3 wave packet structure at the azimuthal stations has established the existence of phase jumps between wave packets at low latitudes, similar to those observed at synchronous orbit and at higher latitude ground stations. However, there did not appear to be any obvious pattern in phase jump occurrences between stations or signal components.     

康熙三十四年建太和殿大木结构研究

本文在王璞子、傅熹年先生的基础上,通过深入研究《太和殿纪事》所记载的大木尺寸,详细测量、分析太和殿木结构的现状尺寸,得出以下结论1、康熙三十四年所建太和殿平面丈尺是用清尺在明代遗留建筑基址上量度确定的,明清大木侧脚设计有所差异;2、太和殿通檐柱高(柱脚至挑檐枋上皮)等于明间开间;3、金柱高(至上层檐)为通檐柱高的1.5倍;4、上下层斗拱在此基础上深化设计、权衡尺寸,总出挑凑足整尺寸,并通盘考虑以适合檐步举架尺寸;5、按照前后挑檐檩间距的1/3确定屋架正心桁之间的总举架高度。     

A model for the electron temperature variation along geomagnetic field lines and its effect on electron density profiles and VLF paths

A realistic model for the temperature variation along geomagnetic field lines is described. For high altitudes (>1500 km) the temperature is taken to increase as the nth power of radial distance (n−2), giving temperatures consistent with those measured in situ by high altitude satellites. For realistic temperatures at low altitude an extra term is included. The temperature gradient along the field line is then 0.9–1.6° km⁻¹ during the day and 0.5–0.7° km⁻¹ during the night at 1000 km, reducing to about half these values at 2000 km, for the latitude range 35–50°. This is consistent with calculations made from nearly simultaneous satellite measurements at 1000 and 2500 km. It is shown that assuming diffusive equilibrium, including the new temperature model, more realistic equatorial electron density profiles result than for isothermal field lines.The temperature gradient model is also purposely formulated to be of a form that enables the temperature modified geopotential height to be obtained without numerical integration. This renders the model particularly suitable for ray-tracing calculations. A ray-tracing model is developed and it is shown that unducted ray paths are significantly altered from the corresponding paths in an equivalent isothermal model; there is greater refraction and magnetospheric reflection takes place at lower altitudes. For summer day conditions, an inter-hemispheric unducted ray path becomes possible from 26° latitude that can reach the ground at the conjugate.