Powerful solar radio bursts as a global and free tool for testing satellite broadband radio systems,including GPS–GLONASS–GALILEO

We investigated failures in the global positioning system (GPS) performance produced by solar radio bursts with unprecedented radio flux density during the X6.5 and X3.4 solar flares on 6 and 13 December 2006, respectively. The effect of these events on GPS was compared to that of the X17.2 solar flare of 28 October 2003. Significant experimental evidence was found that high-precision GPS positioning on the Earth's entire sunlit side was partially disrupted for more than 10–15 min on 6 and 13 December 2006. The high level of phase slips and count omissions resulted from the wideband solar radio noise emission. Our results provide serious grounds for revising the role of space weather factors in the functioning of modern satellite systems and for considering these factors more carefully in practice. Similar failures in the operation of satellite navigation systems (GPS, GLONASS, and GALILEO) can be fatal for operating safety systems as a whole and lead to great financial losses. Another important conclusion of our investigation concerns the continuous calibrated monitoring of the level of the solar radio emission flux. This monitoring involved a large number of solar radio spectrographs and allowed us to estimate the solar radio noise level in the range of the GPS–GLONASS–GALILEO frequencies.     

Density fluctuations measured by ISEE 1–2 in the Earth’s magnetosheath and the resultant scattering of radio waves

Radio waves undergo angular scattering when they propagate through a plasma with fluctuating density. We show how the angular scattering coefficient can be calculated as a function of the frequency spectrum of the local density fluctuations. In the Earths magnetosheath, the ISEE 1–2 propagation experiment measured the spectral power of the density fluctuations for periods in the range 300 to 1 s, which produce most of the scattering. The resultant local angular scattering coefficient can then be calculated for the first time with realistic density fluctuation spectra, which are neither Gaussian nor power laws. We present results on the variation of the local angular scattering coefficient during two crossings of the dayside magnetosheath, from the quasi-perpendicular bow shock to the magnetopause. For a radio wave at twice the local electron plasma frequency, the scattering coefficient in the major part of the magnetosheath is b(2f_p) 0.5–4 × 10^–9 rad²/m. The scattering coefficient is about ten times stronger in a thin sheet (0.1 to IR_E) just downstream of the shock ramp, and close to the magnetopause.     

Characteristics of Pc4–5 pulsations obtained using the method of bistatic backscatter of HF radio waves,the EISCAT HF heating facility,and ground-based magnetometers

The results of studying the Pc4–5 pulsation parameters based on the method of bistatic backscatter of radio waves, using the EISCAT/Heating HF facility (Tromsø, Norway) and IMAGE ground-based magnetometers (Scandinavia), are presented. The observations were performed during the morning hours on October 3, 2006, when a substorm developed on the nightside. An analysis of the observational data obtained from 1000 to 1020 UT indicated that wave-like disturbances with periods corresponding to Pc4–5 pulsations (80–240 s) existed at that time. The variations in the full vector of the ionospheric irregularity motion and the electric field strength in an artificially disturbed high-latitude ionospheric F region has been reconstructed based on simultaneous Doppler observations on two paths. A general conformity is observed among the time variations in Pc4–5 pulsations in the magnetic and ionospheric data: between the velocity amplitude (|V|) and the X component of the Earth’s magnetic field and between the irregularity motion azimuth and the Y component. Large-scale waves, corresponding to the natural resonances of magnetic field lines (small values of the azimuthal number |m| ～ 2–4), and small-scale waves (large values |m| ～ 17–20) were simultaneously registered during the experiment based on magnetic data. It has been indicated that the periods of wave-like processes registered using the method of bistatic backscatter and ground-based magnetometers were in agreement with one another. The formation of wave-like processes is explained by the nonstationary impact of the solar wind and IMF on the Earth’s magnetosphere. The variations in the IMF, according to the ACE satellite measurements, were characterized by a sharp increase in the solar wind plasma dynamic pressure that occurred at about 09 UT on October 3, 2006, and was accompanied by rapid polarity reversals of the north-ward-southward (B _z) and transverse (B _y) IMF components.     

Flood–ebb and spring–neap variations of mixing,stratification and circulation in Chesapeake Bay

A three-dimensional hydrodynamic model is used to investigate intra-tidal and spring–neap variations of turbulent mixing, stratification and residual circulation in the Chesapeake Bay estuary. Vertical profiles of salinity, velocity and eddy diffusivity show a marked asymmetry between the flood and ebb tides. Tidal mixing in the bottom boundary layer is stronger and penetrates higher on flood than on ebb. This flood–ebb asymmetry results in a north–south asymmetry in turbulent mixing because tidal currents vary out of phase between the lower and upper regions of Chesapeake Bay. The asymmetric tidal mixing causes significant variation of salinity distribution over the flood–ebb tidal cycle but insignificant changes in the residual circulation. Due to the modulation of tidal currents over the spring–neap cycle, turbulent mixing and vertical stratification show large fortnightly and monthly fluctuations. The stratification is not a linear function of the tidal-current amplitude. Strong stratification is only established during those neap tides when low turbulence intensity persists for several days. Residual circulation also shows large variations over the spring–neap cycle. The tidally averaged residual currents are about 50% stronger during the neap tides than during the spring tides.     

Propagation of HF radiowaves on high-latitude radio paths during the magnetically disturbed period of October 24–28, 2003

The behavior of the HF signal parameters during magnetic storms and substorms has bee experimentally studied simultaneously on the Kiruna-Kirkenes auroral path, Kiruna-Longyearbyen polar path, and Murmansk-St. Petersburg subauroral path. The first two paths are equipped with the instruments making it possible to measure the values of the signal-to-noise ratio, Doppler frequency shift, and elevation angle. The method of oblique sounding of the ionosphere (OSI) was used on the Murmansk-St. Petersburg path. Two substantial substorms, a moderate storm, and an intense storm occurred during the studied period. Some new regularities have been revealed. On the Kiruna-Kirkenes and Kiruna-Longyearbyen paths, the signalto-noise ratio increased (due to the transition from the F ₂ signal reflections to the E _s reflections), the elevation angle increased (due to an increase in the ionospheric F ₂ layer height and a decrease in the critical frequency), and the Doppler shift increased (due to the variations in ionization and the appearance of ionospheric irregularities during a substorm) when the signal was reflected from the F ₂ layer close to the moment of the substorm or storm beginning T ₀. It is possible to control the so-called “main effect” in the ionosphere on the Murmansk-St. Petersburg path.     

Attenuation and Shock Waves in Linear Hereditary Viscoelastic Media; Strick–Mainardi,Jeffreys–Lomnitz–Strick and Andrade Creep Compliances

Dispersion, attenuation and wavefronts in a class of linear viscoelastic media proposed by Strick and Mainardi (Geophys J R Astr Soc 69:415–429, 1982) and a related class of models due to Lomnitz, Jeffreys and Strick are studied by a new method due to the author. Unlike the previously studied explicit models of relaxation modulus or creep compliance, these two classes support propagation of discontinuities. Due to an extension made by Strick, either of these two classes of models comprise both viscoelastic solids and fluids. We also discuss the Andrade viscoelastic media. The Andrade media do not support discontinuity waves and exhibit the pedestal effect.     

Seasonal—daily variations in the electromagnetic background of the medium-frequency and high-frequency radio ranges during low solar activity

Based on the data of the long-term monitoring of the electromagnetic background at frequencies of 1–30 MHz in Tomsk, new main regularities of the daily and seasonal variations in this background in different frequency ranges at a low level of solar activity (the annual average values are 68.6 = F _10.7 <= 80.9) have been established.     

Impairment of radio wave signal by rainfall on fixed satellite service on earth–space path at 37 stations in Nigeria

This study investigates the effect of rainfall on horizontally polarized radio waves for fixed satellite service at Ku, Ka and V bands for links to the recently launched Nigeria Communication Satellite one (NigComSat-1), for annual time availabilities of 99–99.99% in an average year for 37 stations in Nigeria. The results obtained at Ku-band downlink shows that 99.99% availability is possible in all the 37-stations in Nigeria. At Ka-band downlink the results also show that only 99.9% availability is practicable in all the 37 stations in Nigeria. At V-band downlink, 99.99% availability is also not possible in all the 37 stations in Nigeria. An availability level of 99.9% is only practicable in the North–West (NW) and North–East (NE) regions, where the attenuation is between 14 and 17.9 dB. Total fade out of signals during rainfall are probable in the South–South (SS), South–East (SE), South–West (SW) and Middle–Belt (MB) regions at 99.9% availability.     

Regional debris-flow and debris-flood frequency–magnitude relationships

Construction of frequency–magnitude (F–M) relationships of debris floods and debris flows is challenging because of few direct observations, discontinuous event occurrence, loss of field evidence, the difficulty of accessing the sediment archive and the challenge of finding suitable statistical methods to analyse the dataset. Consultants often face budget limitations that prohibit application of the full gamut of absolute dating methods, stratigraphic analysis and analytical tools necessary to fully resolve the F–M legacy. In some cases, F–M curves are needed for watersheds without local information, or where obtaining this information is prohibitively expensive. For such watersheds, the F–M relationship may be estimated where several F–M curves have already been assembled in a specific region. Individual F–M curves are normalized by fan area or fan volume, then stratified by process type and geomorphic activity level. This paper describes the development of regional F–M curves for debris flows in southwestern British Columbia and debris flows and debris floods in the Bow River valley near Canmore, Alberta. We apply the regional relationships to other cases in Canada and the United States and demonstrate that the method can be globalized. The regional approach is compared to cases where detailed F–M relationships have been established by other means. Strong negative deviations from the regional debris-flow or debris-flood magnitude trends could signal inherent watershed stability, while strong positive deviations could signal extraordinary landslide processes, or suggest that the fan may be largely of paraglacial origin. We highlight some of these outlying cases and develop a method whereby the regional curves can be meaningfully adjusted, or reliance can be placed on lower or upper confidence bounds of the F–M curves. We caution against the indiscriminate use of the regionally based F–M curves, especially in watersheds where multiple geomorphic processes are active. © 2020 John Wiley & Sons, Ltd.     

Modelling Gravitational Instabilities: Slab Break–off and Rayleigh–Taylor Diapirism

A non-standard new code to solve multiphase viscous thermo–mechanical problems applied to geophysics is presented. Two numerical methodologies employed in the code are described: A level set technique to track the position of the materials and an enrichment of the solution to allow the strain rate to be discontinuous across the interface. These techniques have low computational cost and can be used in standard desktop PCs. Examples of phase tracking with level set are presented in two and three dimensions to study slab detachment in subduction processes and Rayleigh–Taylor instabilities, respectively. The modelling of slab detachment processes includes realistic rheology with viscosity depending on temperature, pressure and strain rate; shear and adiabatic heating mechanisms; density including mineral phase changes and varying thermal conductivity. Detachment models show a first prolonged period of thermal diffusion until a fast necking of the subducting slab results in the break–off. The influence of several numerical and physical parameters on the detachment process is analyzed: The shear heating exerts a major influence accelerating the detachment process, reducing the onset time to one half and lubricating the sinking of the detached slab. The adiabatic heating term acts as a thermal stabilizer. If the mantle temperature follows an adiabatic gradient, neglecting this heating term must be included, otherwise all temperature contrasts are overestimated. As expected, the phase change at 410 km depth (olivine–spinel transition) facilitates the detachment process due to the increase in negative buoyancy. Finally, simple plume simulations are used to show how the presented numerical methodologies can be extended to three dimensions.     

Vertical–vertical controlled-source electromagnetic instrumentation and acquisition

Vertical–vertical controlled-source electromagnetic is an alternative to other techniques for providing three-dimensional resistivity images of the subsurface. It utilizes a large and powerful vertical dipole transmitter and arrays of E-field receivers with vertical and horizontal dipole sensors. The necessary instrumentation and acquisition procedures which differ strongly from other controlled-source electromagnetic methods are described in the paper.     

Pipe–soil interaction and pipeline performance under strike–slip fault movements

The performance of pipelines subjected to permanent strike–slip fault movement is investigated by combining detailed numerical simulations and closed-form solutions. First a closed-form solution for the force–displacement relationship of a buried pipeline subjected to tension is presented for pipelines of finite and infinite lengths. Subsequently the solution is used in the form of nonlinear springs at the two ends of the pipeline in a refined finite element model, allowing an efficient nonlinear analysis of the pipe–soil system at large strike–slip fault movements. The analysis accounts for large strains, inelastic material behavior of the pipeline and the surrounding soil, as well as contact and friction conditions on the soil–pipe interface. The numerical models consider infinite and finite length of the pipeline corresponding to various angles β between the pipeline axis and the normal to the fault plane. Using the proposed closed-form nonlinear force–displacement relationship for buried pipelines of finite and infinite length, axial strains are in excellent agreement with results obtained from detailed finite element models that employ beam elements and distributed springs along the pipeline length. Appropriate performance criteria of the steel pipeline are adopted and monitored throughout the analysis. It is shown that the end conditions of the pipeline have a significant influence on pipeline performance. For a strike–slip fault normal to the pipeline axis, local buckling occurs at relatively small fault displacements. As the angle between the fault normal and the pipeline axis increases, local buckling can be avoided due to longitudinal stretching, but the pipeline may fail due to excessive axial tensile strains or cross sectional flattening. Finally a simplified analytical model introduced elsewhere, is enhanced to account for end effects and illustrates the formation of local buckling for relative small values of crossing angle.     

Moreton wave, “EIT wave”, and type II radio burst as manifestations of a single wave front

We show that a Moreton wave, an “EIT wave,” and a type II radio burst observed during a solar flare of July 13, 2004, might have been a manifestation of a single front of a decelerating shock wave, which appeared in an active region (AR) during a filament eruption. We propose describing a quasi-spheroidal wave propagating upward and along the solar surface by using relations known from a theory of a point-like explosion in a gas whose density changes along the radius according to a power law. By applying this law to fit the drop in density of the coronal plasma enveloping the solar active region, we first managed to bring the measured positions and velocities of surface Moreton wave and “EIT wave” into correspondence with the observed frequency drift rate of the meter type II radio burst. The exponent of the vertical coronal density falloff is selected by fitting the power law to the Newkirk and Saito empirical distributions in the height range of interest. Formal use of such a dependence in the horizontal direction with a different exponent appears to be reasonable up to distances of less than 200 Mm around the eruption center. It is possible to assume that the near-surface shock wave weakens when leaving this radius and finally the active region, entering the region of the quiet Sun where the coronal plasma density and the fast-mode speed are almost constant along the horizontal.     

Excitation of Alfvén waves and vortices in the ionospheric Alfvén resonator by modulated powerful radio waves

A review of the artificial excitation of Alfvén waves and vortices in the ionospheric Alfvén resonator (IAR) is presented. In the framework of simplified models of the IAR and the Alfvén vortex instability, we discuss the main physical phenomena arising under the periodic heating of the ionosphere by a powerful HF radio signal with a modulation frequency F which lies in the range of short-period geomagnetic pulsations (F = 0.1–10 Hz). The amplitudes, frequency spectra, and polarization characteristics of artificial pulsations on the ground are found, and a brief comparison with experimental data is made. The Alfvén vortex instability in the IAR is analysed from the point of view of its artificial triggering. Two ways of such a triggering are discussed. The first suggests the use of two spaced transmitter antenna which produce an ionospheric current being in resonance with Alfvén vortices. Existing heating facilities are suitable for this experiment. The second method is based on the change of macroscopic parameters of the ionosphere, such as the conductivity in the instability region. This method is simple, but requires more powerful heaters.     

Mixed fluid sources involved in diamond growth constrained by Sr–Nd–Pb–C–N isotopes and trace elements

Sub-micrometer inclusions in diamonds carry high-density fluids (HDF) from which the host diamonds have precipitated. The chemistry of these fluids is our best opportunity of characterizing the diamond-forming environment. The trace element patterns of diamond fluids vary within a limited range and are similar to those of carbonatitic/kimberlitic melts that originate from beneath the lithospheric mantle. A convecting mantle origin for the fluid is also implied by C isotopic compositions and by a preliminary Sr isotopic study (Akagi, T., Masuda, A., 1988. Isotopic and elemental evidence for a relationship between kimberlite and Zaire cubic diamonds. Nature 336, 665–667.). Nevertheless, the major element chemistry of HDFs is very different from that of kimberlites and carbonatites, varying widely and being characterized by extreme K enrichment (up to ～ 39 wt.% on a water and carbonate free basis) and high volatile contents. The broad spectrum of major element compositions in diamond-forming fluids has been related to fluid–rock interaction and to immiscibility processes.Elemental signatures can be easily modified by a variety of mantle processes whereas radiogenic isotopes give a clear fingerprint of the time-integrated evolution of the fluid source region. Here we present the results of the first multi radiogenic-isotope (Sr, Nd, Pb) and trace element study on fluid-rich diamonds, implemented using a newly developed off-line laser sampling technique. The data are combined with N and C isotope analysis of the diamond matrix to better understand the possible sources of fluid involved in the formation of these diamonds. Sr isotope ratios vary significantly within single diamonds. The highly varied but unsupported Sr isotope ratios cannot be explained by immiscibility processes or fluid-mineral elemental fractionations occurring at the time of diamond growth. Our results demonstrate the clear involvement of a mixed fluid, with one component originating from ancient incompatible element-enriched parts of the lithospheric mantle while the trigger for releasing this fluid source was probably carbonatitic/kimberlitic melts derived from greater depths. We suggest that phlogopite mica was an integral part of the enriched lithospheric fluid source and that breakdown of this mica releases K and radiogenic Sr into a fluid phase. The resulting fluids operate as a major metasomatic agent in the sub-continental lithospheric mantle as reflected by the isotopic composition and trace element patterns of G10 garnets.     

Dynamic response of structures subjected to pounding and structure–soil–structure interaction

During strong earthquakes, adjacent structures with non-sufficient clear distances collide with each other. In addition to such a pounding, cross interaction of adjacent structures through soil can exchange the vibration energy between buildings and make the problem even more complex. In this paper, effects of both of the mentioned phenomena on the inelastic response of selected steel structures are studied. Number of stories varied between 3 and 12 and different clear distances up to the seismic codes prescribed value are considered. The pounding element is modeled within Opensees. A coupled model of springs and dashpots is utilized for through-the-soil interaction of the adjacent structures, for two types of soft soils. The pounding force, relative displacements of stories, story shears, and plastic hinge rotations are compared for different conditions as the maximum responses averaged between seven consistent earthquakes. As a result, simultaneous effects of pounding and structure–soil–structure interaction are discussed.     

Formation and Suppression of Strike–Slip Fault Systems

Strike–slip faults are a defining feature of plate tectonics, yet many aspects of their development and evolution remain unresolved. For intact materials and/or regions, a standard sequence of shear development is predicted from physical models and field studies, commencing with the formation of Riedel shears and culminating with the development of a throughgoing fault. However, for materials and/or regions that contain crustal heterogeneities (normal and/or thrust faults, joints, etc.) that predate shear deformation, kinematic evolution of strike–slip faulting is poorly constrained. We present a new plane-stress finite-strain physical analog model developed to investigate primary deformation zone evolution in simple shear, pure strike–slip fault systems in which faults or joints are present before shear initiation. Experimental results suggest that preexisting mechanical discontinuities (faults and/or joints) have a marked effect on the geometry of such systems, causing deflection, lateral distribution, and suppression of shears. A lower limit is placed on shear offset necessary to produce a throughgoing fault in systems containing preexisting structures. Fault zone development observed in these experiments provides new insight for kinematic interpretation of structural data from strike–slip fault zones on Earth, Venus, and other terrestrial bodies.     

Role of wave–mean flow interaction in sun–climate connections: Historical overview and some new interpretations and results

Quasi-decadal variations in solar irradiance – termed the 11-year solar cycle (SC) – have been linked to variations in a variety of atmospheric circulation features, including the polar vortex, the Brewer–Dobson circulation, and the quasi-biennial oscillation. These features share an underlying commonality: they are all rooted in wave–mean flow interaction. The purpose of this paper is to provide a historical overview of the connection between the SC and wave–mean flow interaction and to propose a more complete theoretical framework for solar modulated wave–mean flow interaction that includes both zonal-mean and zonally asymmetric ozone as intermediaries for communicating variations in solar spectral irradiance to the climate system. We solve a quasi-geostrophic model using the WKB formalism to highlight the physics connecting the SC to planetary wave-drag. Numerical results show the importance of the zonally asymmetric ozone field in mediating the effects of solar variability to the wave-driven circulation in the middle atmosphere.     

Quasi-geostrophic shallow-water vortex–patch equilibria and their stability

We examine the equilibrium form, properties, stability and nonlinear evolution of steadily-rotating simply-connected vortex patches in the single-layer quasi-geostrophic model of geophysical fluid dynamics. This model, valid for rotating shallow-water flow in the limit of small Rossby and Froude numbers, has an intrinsic length scale L _D called the “Rossby deformation length” relating the strength of the stratification to that of the background rotation. Here, we generate steadily-rotating vortex equilibria for a wide range of γ?=?L/L _D , where L is the typical horizontal length scale of the vortex. We vary both γ (over the range 0.02?≤?γ?≤?10) and the vortex aspect ratio λ (over the range 0?<?λ?<?1). We find two modes of instability arising at sufficiently small aspect ratio λ?<?λ _c (γ): an asymmetric (dominantly wave 3) mode at small γ (or large L _D ) and a symmetric (dominantly wave 4) mode at large γ (or small L _D ). At marginal stability, the asymmetric mode dominates for γ???3, while the symmetric mode dominates for γ???3. The nonlinear evolution of weakly-perturbed unstable equilibria results in major structural changes, in most cases producing two dominant vortex patches and thin, quasi-passive filaments. Overall, the nonlinear evolution can be classified into three principal types: (1) vacillations for a limited range of aspect ratios λ when 5?≤?γ?≤?6, (2) filamentation and a single-dominant vortex for γ???1, and (3) vortex splitting – asymmetric for 1???γ???4 and symmetric for γ???4.