Laboratory modeling and measurement of the acoustic properties of methane-bearing rock samples

The laboratory equipment for simulation of methane-bearing rock samples and study of their acoustic properties (velocities of P- and S-waves) is described briefly. The experimental results are considered.     

Non-linear effects of VLF noise generation by electron beams in the polar magnetosphere

A theory of VLF noise excitation by electron beams in the polar magnetosphere is proposed. Two modes of excited oscillations are considered: waves with frequencies in the vicinity of the lower hybrid resonance (LHR) from about 50 to 1000 kHz and whistler-mode waves in the frequency range of several kHz.The spectral distribution and the level of turbulent noise, having been excited by means of two counterstreaming electron beams, are deduced in magnetized plasma at the LHR frequency. It is also shown that the growth of noise up to the quasistationary level oscillates with time. Energy density of oscillations at the LHR frequency in the region of the dayside polar cusp agrees with the experimental data.The processes of whistler excitation by electron beams are discussed. The growth rate of excitation of whistler-mode by electrostatic oscillations at the LHR frequency is calculated.     

Determination of the Enhancement in Electron Temperature in the Subauroral Ionosphere during Magnetic Storms on a Global Scale

Geomagnetism and Aeronomy - An attempt was made to determine on a global scale the zone of enhanced electron temperature (Te) in the subauroral ionosphere during magnetic storms via the combination...     

Traveltime parameters in a tilted elliptical anisotropic medium‡

In this paper, we derive analytical expressions for one‐way and two‐way kinematical parameters in elliptical tilted transverse isotropy media. We show that the homogeneous elliptical tilted transverse isotropy models result in hyperbolic moveout with a reflection point sideslip x₀, which can be considered as an additional traveltime parameter for one‐way wave propagation. For homogeneous elliptical tilted transverse isotropy models we show that the inversion of one‐way traveltime parameters suffers from the ambiguity for large tilts. It is shown that the accuracy of the inversion is sensitive to the error in x₀. We also derive and invert the traveltime parameters for a vertically heterogeneous elliptical tilted transverse isotropy model with a tilt gradually changing with depth. The a priori knowledge of parameter δ is very important for inversion. The wrong choise of this parameter results in significant errors in inverted model parameters.     

Equipment for the studies of the acoustic properties of hydrate-containing samples in laboratory conditions

Equipment for simulation in laboratory conditions of hydrate-containing artificial samples and measuring their acoustic properties (wave velocities, absorption and attenuation) at different temperature and pressures is designed and constructed. The plant consists of a high-pressure chamber (up to 45 MPa), a measuring system intended for the excitation and reception of acoustic waves, systems for temperature and pressure control (axial and lateral) and for gas/liquid delivery into the sample. The measurements are performed on cylindrical samples with a 30-mm diameter and height of 10–50 mm. A set of successful test experiments was performed, including measurements of acoustic velocities of consolidated (plexiglas, sandstone, and frozen sand) and unconsolidated (dry and wet quartz sand) samples and formation of methane-hydrate bearing samples.     

Structural features of the subauroral ionosphere during the origination of the polarization jet

Narrow jets of rapid westward ion drifts were registered near the plasmapause projection at the F-region altitudes on the Cosmoc-184 satellite and were called “a polarization jet.” In this work, the effect of this polarization jet on the ionospheric structure has been studied, using a three-dimensional model of the high-latitude ionosphere, when strong local magnetospheric electric fields were originated. The calculations indicated that a narrow trough in the latitudinal variations in the electron density at the F-region maximum was formed in the zone where the electric field was switched on. This trough was more pronounced in the early evening hours, when the electron background density was still high, and was less distinct at low back-ground levels during premidnight hours. A comparison of the calculations and experimental data indicated that they were in good agreement with one another, which made it possible to state that the polarization jet was the main mechanism by which narrow electron density troughs were formed in the subauroral ionosphere.     

MAPPING STATISTICAL SURFACES IN SPATIAL ANALYSIS: THE EXAMPLE OF WATER RESOURCE MANAGEMENT

Methods of the compilation and manipulation of statistical surfaces are described in the production of summary maps of water availability. Isopleth maps of water supply (hydrographic potential) and water consumption are compared through the superimposition of their statistical surfaces. A derivative statistical surface is then created which, depending upon the method of transformation employed, depicts either the magnitude of “free” (unused) water resources or the relative completeness (extent) of their utilization. Translated from: Vestnik Moskovskogo Universiteta, geografiya, 1988, No. 2, pp. 64-68 by Natalia B. Barbash, Brooklyn, New York, 11209.     

Formation of a Ring-Shaped Region of Increased Electron Temperature in the Subauroral Ionosphere in Winter

Geomagnetism and Aeronomy - The results of numerical simulations of the electron temperature (Te) are compared with measurement data provided by the CHAMP satellite to show the possibility of the...     

Variations in Ionospheric Parameters during the Formation of a Polarization Jet

Geomagnetism and Aeronomy - The calculation results and experimental data on the formation and development of a polarization jet in subauroral latitudes are compared. It is shown that the...