The nature of terrestrial infragravitational “noise”

This paper is focused on analysis of comprehensive experimental research data on the infragravitational range of periods (from 20 s to 10–12 min) obtained by synchronous measurements of fluctuations in deformations of the Earth’s crust and atmospheric and hydrospheric pressure variations. It is established that the identified variations in the period range of 1–4 min are rarely observed in records of a laser nanobarograph and laser instrument for measuring hydrospheric pressure variations (laser hydrophone), while they are frequently observed in records of laser strainmeters at a variation period of 3–4 min. Oscillation excitation in the period ranges of 7–13 min, especially in the period ranges of 8–12 min, is largely related to atmospheric processes in the corresponding periods.     

The relationship between coronal fan structures and oscillations above faculae regions

The power spectra of radial-velocity and intensity oscillations are analyzed using ground-based (the Si I 10 827 Å and He I 10 830 Å lines) and Solar Dynamics Observatory (the Fe I 6173, 1700 Å, He II 304 Å, and Fe IX 171 Å lines) data, with the aim of searching for frequency modes that most efficiently penetrate into the solar corona from the lower layers of solar faculae. Analysis of the spatial distribution of the oscillation power at various heights indicates that fan structures in the corona (at the height of the 171 Å emission) are better reproduced at frequencies of 1–1.5 mHz. This means that oscillations with periods of 10–15 min dominate in coronal loops above faculae regions. The five-minute oscillations that universally dominate in radial-velocity measurements in low layers of faculae are appreciable in coronal loops only in individual compact fragments.     

Short-period variations in the proper motions of sunspots from SOHO (MDI) observations

Short-period (1–60 min) variations in the coordinates of the centers of gravity of isolated sunspots are analyzed. The sunspot coordinated were determined using two sets of observational data—magnetograms and intensities—obtained by SOHO (MDI) on December 6, 1998, from 01:00 to 21:57 UT with temporal resolution 60 s and spatial resolution 0.6″/pixel. A slow drift in the sunspot coordinates was removed using a low-frequency filter with a 61-min integration window. The guiding errors (RMS～0.014″) were determined by analyzing correlated motions in pairs of sunspots, and were removed from the time series before determining the sunspot proper motions. Based on the calculated power spectra for the sunspot proper motions, two period intervals containing appreciable power were identified. One coincides with the well-known 5-min acoustic solar oscillations. The concentration of power in this interval is greater for the coordinate variations derived the magnetograms than those derived from the intensities; the harmonic amplitude for some peaks reaches ～±30 km. The other spectral interval corresponds to periods exceeding 30 min. Overall, the rms short-period variations in the sunspot proper motions are 9.9±2.2 and 16.7±7.6 km (0.014″±0.003″ and 0.024″±0.010″) for the magnetogram and intensity data, respectively.     

Properties of oscillations in sunspot penumbras

Observations of oscillations in the penumbras of seven sunspots are analyzed. High-sensitivity differential measurements of the line-of-sight velocity (11 time series) and variations of the Ni I 4857 Å and H_β line profiles (four series) have provided new data making it possible to improve estimates of the amplitude and spectral characteristics of the oscillations. In the middle penumbras, oscillations of the line-of-sight velocity with fundamental periods of 5 and 8–10 min predominate at the photospheric level; their amplitude does not exceed 40–50 m/s, and the spatial coherence scale in the radial direction is no greater than 5″–10″. At frequencies of 0.5–2.0 mHz, the phase difference between the photosphere and chromosphere (NiI 4857 Å-H_β) is close to 180°. The line-of-sight velocity component due to Evershed motions is responsible for oscillations with periods of 15–35 min, which occur synchronously at both heights.     

Parametric excitation of acoustic oscillations in closed coronal magnetic loops

Quasi-periodic modulations of the microwave emission from solar outbursts at 37 GHz are studied based on 17 events observed in 1989–2000 at the Metsähovi Observatory. Low-frequency modulations with periods of ～5 min were found in approximately 90% of the observed microwave outbursts. The most likely origin of this modulation is modulation of the current flowing along a closed coronal magnetic loop due to the five-minute oscillations of the photospheric-convection velocity. In approximately 70% of the cases, oscillations with periods ～10 min were observed simultaneously with the five-minute oscillations in the same events. In 30% of the cases, simultaneous modulation of the microwave emission by three low-frequency signals with periods of 3, 5, and 10 min was observed. One possible origin of these “double” and “triple” modulations is parametric excitation of acoustic oscillations with periods of 10 and 3 min in a closed coronal magnetic loop as a result of coupling with the five-minute photospheric oscillations. This can occur when the period of the natural acoustic oscillations of the closed magnetic loop is about 10 min (the resonance condition). Since the ten-minute oscillations are excited more easily than the three-minute oscillations at the parametric instability, the latter are observed less frequently. For the same reason, the observed linewidth of the ten-minute oscillations is considerably greater than that of the three-minute oscillations.     

Some aspects of the 30–50 day oscillation

The structure and interannual variability of the 30–50 day oscillation over the Indian region have been studied during the monsoon season. The power spectra of the zonal component of wind show large power in the 30–50 day time scale. The oscillation has a meridional wavelength of about 25° latitude and a slow northward phase speed of about 0.7° latitude per day. The oscillation also has some interannual variability. The periods are somewhat longer during the drought years.     

Manifestation of Earth’s diurnal periods in VLF radiation

Spectral analysis of the registered data of natural VLF noise at the frequencies of 0.7, 1.2, and 5.3 kHz for 1997–2006 as well as of direction-finding data of atmospherics in the frequency range of 3–60 kHz for 2002–2006 has been carried out. The analysis has shown that in VLF noise envelope spectra and direction-finding data there are diurnal maxima that coincide with the periods of the Earth’s rotation relative to the Sun (1440 min) and relative to the stars (1436 min). The highest amplitude in spectral components coincides with the period of the Earth’s rotation relative to the Sun, and it is observed for the radiation registered form the southwesterly direction. It has been shown that not only the X-ray emission the Sun but also the X-ray emission of the galaxy affect the level of ionosphere D layer ionization.     

The properties of long-term sunspot oscillations

It is shown that neglecting the motion of sunspots in the plane of the sky in pixels of SOHO MDI magnetograms obtained for the vertical direction results in false periods of 700–1300 min in the long-term oscillations of the magnetic fields of sunspots observed near the central meridian (the Y artefact). The oscillation mode proposed by Efremov, Parfinenko, and Solov’ev in 2012 to be the lowest-frequency sunspot mode is an artefact. A proposed technique for monitoring this artefact using wavelet transforms can be used to study oscillation periods in the range 15 min < T < 500 min. The observational dependence of the oscillation frequency of the sunspot magnetic field on the field strength is constructed using observations of 45 sunspots. This dependence shows a multimode behavior that is consistent with earlier ground observations. One interpretation of this dependence based on the existence of four geometrical oscillation modes detected earlier is proposed.     

Satellite-based technique for nowcasting of thunderstorms over Indian region

India experiences severe thunderstorms during the months, March–June. But these systems are not predicted well, mainly due to the absence of mesoscale observational network over Indian region and the expert system. As these are short lived systems, the nowcast is attempted worldwide based on satellite and radar observations. Due to inadequate radar network, satellite plays the dominant role for nowcast of these thunderstorms. In this study, a nowcast based algorithm ForTracc developed by Vila et al. (Weather Forecast 23:233–245, 2008) has been examined over the Indian region using Infrared Channel \((10.8~\upmu \hbox {m})\) of INSAT-3D for prediction of Mesoscale Convective Systems (MCS). In this technique, the current location and intensity in terms of Cloud Top Brightness Temperature (CTBT) of the MCS are extrapolated. The purpose of this study is to validate this satellite-based nowcasting technique for Convective Cloud Clusters that helps in optimum utilization of satellite data and improve the nowcasting. The model could predict reasonably the minimum CTBT of the convective cell with average absolute error (AAE) of \({<}7\hbox { K}\) for different lead periods (30–180 min). However, it was underestimated for all the lead periods of forecasts. The AAE in the forecasts of size of the cluster varies from about \(3\times 10^{4}\hbox { km}^{2}\) for 30-min forecast to \(7\times 10^{4}\hbox { km}^{2}\) for 120-min forecast. The mean absolute error in prediction of size is above 31–38% of actual size for different lead periods of forecasts from 30 to 180 min. There is over estimation in prediction of size for 30 and 60 min forecasts (17% and 2.6% of actual size of the cluster, respectively) and underestimation in 90 to 180-min forecasts (–2.4% to –28%). The direct position error (DPE) based on the location of minimum CTBT ranges from 70 to 144 km for 30–180-min forecast respectively.     

Investigation of Cement–Bentonite Slurry Samples Containing PFA in the UCS and Triaxial Apparatus

Three mixtures of cement–bentonite slurry containing 28, 36 and 44 % PFA (as a proportion of cementitious materials) were tested using the unconfined compressive strength and triaxial apparatus to determine the stress–strain and shear strength relationships for samples cured for various periods. The samples were batched using 4 % bentonite and 20 % cementitious materials (by mass of water) and allowed to cure underwater once extruded from sealed moulds. Curing periods of 14, 28 and 90 days were selected to investigate the changes in behaviour at durations commonly specified (28 and 90 days) as well as providing insight into changing behaviour with curing (additional curing periods of 7 and 60 days were investigated on a smaller number of samples to increase understanding). Two rates of displacement were used (1.0 and 1.3 mm/min) and four confining pressures (0, 50, 100 and 200 kPa). Shear strength and strain at peak deviator stress of the samples do not appear to vary considerably with confining pressure. For samples containing 28 % PFA, the majority of physical properties exhibited by the cement–bentonite samples change with curing period up to 60 days, where after the properties become similar to those cured for 90 days.     

Microvariability of line profiles in the spectrum of the star ι Her

We present the results of a search for and analysis of line-profile variations in the spectrum of the star ι Her. The observations were acquired with the 1.8 m telescope of the Bohyunsan Optical Astronomy Observatory (Republic of Korea) in May–June 2004. We obtained 69 spectra of the star with signal-to-noise ratios ≈300 and a time resolution of 5–7 min. Profile variability was revealed for six lines of HI, HeI, and SiIII, in the central parts of the lines. The variability amplitude is ≈(1–2)% in units of the intensity of the adjacent continuum. Evidence was found for cyclic variations of the lines, with periods from ≈7^h to ≈2.9^d. We conclude that ι Her belongs to the group of slowly pulsating stars.     

Variations in Geophysical Fields during Hurricanes and Squalls

Based on complex analysis of the results of instrumental observations during strong atmospheric disturbances, it is shown that hurricanes and squalls are accompanied not only by high wind velocities, but also by high-amplitude microbaric variations, variations in amplitudes of the microseismic background, and the vertical component of the electric field. It is established that 1–4 hours before the onset, squalls and hurricanes are characterized by increased amplitudes of microbaric variations in the range of periods of 2–6 min, as well as by low-frequency variations in the electric field and variations in the microseismic background, which together with the meteorological parameters can be considered as a complex prognostic criterion of an impending hurricane (squall).     

Mesozoic-Cenozoic Tectonics of the Yellow Sea and Oil-Gas Exploration

The purpose of the present study was to study the tectonics of the Yellow Sea. Although oil- gas exploration has been undertaken for more than 30 years in the southern Yellow Sea, the exploration progress has achieved little. There are three tectonic periods with near N–S trending shortening and compression (260–200 Ma, 135–52 Ma and 23–0.78 Ma) and three tectonic periods with near E–W trending shortening and compression (200–135 Ma, 52–23 Ma and 0.78 Ma) at the Yellow Sea and adjacent areas during the Mesozoic and Cenozoic. The Indosinian tectonic period is the collision period between the Sino-Korean and Yangtze Plates, which formed the basic tectonic framework for the Yellow Sea area. There were strong intraplate deformations during the Yanshanian (200–135 Ma) and Sichuanian (135–52 Ma) periods with different tectonic models, which are also the main formation periods for endogenic metallic mineral deposits around the Yellow Sea. The three tectonic periods during the Cenozoic affect important influences for forming oil-gas reservoirs. The Eocene–Oligocene (52–23 Ma) is the main forming period for oil-gas sources. The Miocene–Early Pleistocene (23–0.78 Ma) was a period of favorable passage for oil-gas migration along NNE trending faults. Since the Middle Pleistocene (0.78 Ma) the NNE trending faults are closed and make good conditions for the reservation of oil-gas. The authors suggest that we pay more attention to the oil-gas exploration at the intersections between the NNE trending existing faults and Paleogene– Neogene systems in the southern Yellow Sea area.     

The effect of climate change on the mobility and stability of coastal sand dunes in Ceará State (NE Brazil)

The coast of Ceará State in NE Brazil is covered by vast fields of active and stabilized coastal sand dunes. Its tropical climate is characterized by two seasons, wet and dry, with wind intensity determined by the meridional shift of the Intertropical Convergence Zone. The wind power is negatively correlated with precipitation, and precipitation is negatively correlated with the difference between sea surface temperatures of the tropical Atlantic north and south of the equator. We present a model suggesting that during the Late Pleistocene wind power determined the mobility and stability of the dunes. Sand dunes accumulated during periods of high wind power (as it is today) and stabilized when wind power was low. Once the dunes were stabilized by vegetation they could not be activated even by increased wind power. Samples that were taken for luminescence dating from 25 stabilized dunes along the coasts of Ceará gave ages ranging from135 ka to < 100 yr. We postulate that these luminescence ages fall at the beginning of wet periods in NE Brazil characterized by low wind power. These paleoclimatic wet periods correlate well with the cold periods of stades in Greenland ice-core records.     

Photometry of the intermediate polar 1RXS J062518.2+733433: Characteristics of its periodic brightness variations

We present the results of our photometry of the recently discovered intermediate polar 1RXS J062518.2+733433. The observations were made using the 70 cm telescope of the Astronomical Observatory of the Ural State University with a multichannel photometer, and were carried out during 13 nights in March–May 2004. Our analysis reveals brightness variations with periods of 19.788 ± 0.003 min, corresponding to the rotational period of the white dwarf, 21.273 ± 0.003 min, corresponding to the orbital sideband, and 283.3 ± 0.5 min, which is the orbital period. The variations with the white dwarf’s rotational period show a stable amplitude and a quasi-sinusoidal pulse shape persistent over a long time. In contrast, the orbital-sideband variations have an unstable amplitude and a significantly nonsinusoidal pulse shape that varies with time. Variations of the amplitude and pulse shape of the orbital-sideband variations can be related to structural changes of the accretion disk surrounding the white dwarf.     

Spectral-temporal evolution of low-frequency pulsations in the microwave radiation of solar flares

Low-frequency pulsations of 22 and 37 GHz microwave radiation detected during solar flares are analyzed. Several microwave bursts observed at the Metsähovi Radio Observatory are studied with time resolutions of 100 and 50 ms. A fast Fourier transformation with a sliding window and the Wigner-Ville method are used to obtain frequency-time diagrams for the low-frequency pulsations, which are interpreted as natural oscillations of coronal magnetic loops; the dynamical spectra of the pulsations are synthesized for the first time. Three types of low-frequency fluctuations modulating the flare microwave radiation can be distinguished in the observations. First, there are fast and slow magneto-acoustic oscillations with periods of 0.5–0.8 s and 200–280 s, respectively. The fast magneto-acoustic oscillations appear as trains of narrow-band signals with durations of 100–200 s, a positive frequency drift dν/dt=0.25 MHz/min, and frequency splitting δν=0.01–0.05 Hz. Second, there are natural oscillations of the coronal magnetic loops as equivalent electrical circuits. These oscillations have periods of 0.5–10 s and positive or negative frequency drift rates dν/dt=8×10^?3 Hz/min or dν/dt=?1.3×10^?2 Hz/min, depending on the phase of the radio outburst. Third, there are modulations of the microwave radiation by short periodic pulses with a period of 20 s. The dynamical spectra of the low-frequency pulsations supply important information about the parameters of the magnetic loops: the ratio of the loop radius to its length r/L≈0.1, the plasma parameter β≈10^?3, the ratio of the plasma densities outside and inside the loop ρ_e/ρ_i≈10^?2, and the electrical current flowing along the loop I≈10¹² A.     

Evaluating the impact of artificial groundwater recharge structures using geo-spatial techniques in the hard-rock terrain of Rajasthan,India

Groundwater levels in hard-rock areas in India have shown very large declines in the recent past. The situation is becoming more critical due to a paucity of rainfall, limited surface water resources and an increasing pattern of groundwater extraction in these areas. Consequently, the Ground Water Department with the aid of World Bank has implemented the water structuring programme to mitigate groundwater scarcity and to develop a viable solution for sustainable development in the region. The present study has been undertaken to assess the impact of artificial groundwater recharge structures in the hard-rock area of Rajasthan, India. In this study groundwater level data (pre-monsoon and post-monsoon) of 85 dug-wells are used, spread over an area of 413.59 km². The weathered and fractured gneissic basement rocks act as major aquifer in the area. Spatial maps for pre- and post-monsoon groundwater levels were prepared using the kriging interpolation technique with best fitted semi-variogram models (Spherical, Exponential and Gaussian). The groundwater recharge is calculated spatially using the water level fluctuation method. The entire study period (2004–2011) is divided into pre- (2004–2008) and post-intervention (2009–2011) periods. Based on the identical nature of total monsoon rainfall, two combinations of average (2007 and 2009) and more than average (2006 and 2010) rainfall years are selected from the pre- and post-intervention periods for further comparisons. All of the water harvesting structures are grouped into the following categories: as anicuts (masonry overflow structure); percolation tanks; subsurface barriers; and renovation of earthen ponds/nadis. A buffer of 100 m around the intervention site is taken for assessing the influence of these structures on groundwater recharge. The relationship between the monsoon rainfall and groundwater recharge is fitted by power and exponential functions for the periods of 2004–2008 and 2008–2011 with R ² values of 0.95 and 0.98, respectively. The average groundwater recharge is found to be 18% of total monsoon rainfall prior to intervention and it became 28% during the post-intervention period. About 70.9% (293.43 km²) of the area during average rainfall and more than 95% (396.26 km²) of the area during above-average rainfalls show an increase in groundwater recharge after construction of water harvesting structures. The groundwater recharge pattern indicates a positive impact within the vicinity of intervention sites during both average and above-average rainfall. The anicuts are found to be the most effective recharge structures during periods of above-average rainfall, while subsurface barriers are responded well during average rainfall periods. In the hard-rock terrain, water harvesting structures produce significant increases in groundwater recharge. The geo-spatial techniques that are used are effective for evaluating the response of different artificial groundwater recharge techniques.     

Long-period oscillations of the solar microwave emission

Modulations of the microwave emission of the Sun at 11.7 GHz have been studied using more than 40 events observed in 2001 at the Mets?hovi Radio Observatory. In nearly all the observed events, low-frequency modulations with periods of 3–90 min were detected. As a rule, simultaneous modulation of the emission at several frequencies was observed. One possible origin of such modulations with periods 5–10 min is parametric resonance arising in coronal magnetic loops as a result of interactions with the 5-min photospheric oscillations, while the long-period modulations could be a manifestation of sunspot oscillations. Torsional (ϑ-mode) and radial (r-mode) oscillations have such periods. The frequency of occurrence of oscillations with the determined periods is considered, and a lower limit for the brightness temperature of the oscillations is estimated.     

Effect of Strain Rate on the Strength Characteristics of Soil–Lime Mixture

The effects of rate of strain on strength and deformation characteristics of soil–lime were investigated. Five strain rates (0.1, 0.8, 2.0, 4.0 and 7.0 %/min), five lime contents (0, 3, 6, 9 and 12 %) by dry soil weight and three cell pressures (100, 200 and 340 kN/m²) were carried. Triaxial tests, under unconsolidated condition, were used to study the effect of strain rate on strength and initial modulus of elasticity of soil and soil–lime mixture after two curing periods 7 and 21 days, respectively. A total of 405 triaxial specimens have been tested, where 225 specimens have been tested with first curing period (7 days). The testing program includes nine specimens for each strain rate, and each lime content was carried out, including natural soil with zero lime content. Another set of triaxial tests with a total of 180 specimens for the second curing period (21 days) was prepared at optimum moisture content, and the corresponding maximum dry density was also tested. The effects of strain rate and curing period on each of stress–strain behavior, type of failure, deviator stress at failure, cohesion and angle of internal friction and initial modulus of elasticity were studied thoroughly for the natural soil as well as soil–lime mixtures. For natural soil, the test results showed that the undrained shear strength, the initial modulus of elasticity and the cohesion increase significantly as the strain rate increase, while for soil–lime mixture at different curing periods, the undrained shear strength, initial modulus of elasticity and the cohesion increases to a maximum and then decreases as the strain rate and lime content increase. Also, the same variables and angle of internal friction increase with increasing curing period.     

Moving players,traversing perspectives: Global value chains,production networks and Ghanaian football labour migration

This article examines the production and transnational export of Ghanaian football labour. It does so via a cross-disciplinary approach that utilises perspectives rooted in the sociology of development (global value chains) and economic geography (global production networks). The article is underpinned by two central arguments. Firstly, it contends that the GVC framework is useful in accounting for how Ghanaian players are produced and prepared for the international market, identifying the key agents and agencies involved, mapping the geography of production and export and assessing the institutional context within which the trade operates locally, nationally and internationally. The second draws on the GPN perspective to argue that while Ghanaian football labour migration remains a process contoured by uneven asymmetries of power that favour actors, stakeholders and entities in the global North, there are currently segments of the production–export chain where power is much more diffuse and some benefits are captured in the global South. The paper draws on interview data and observations gleaned from four periods of multi-sited ethnographic fieldwork in Ghana between January 2008 and June 2011.