Dynamics of ionospheric and telluric currents during large events of geomagnetically induced currents

<p>Geomagnetic variations are mainly produced by external currents in the ionosphere and magnetosphere, and secondarily by induced (internal/telluric) currents in the conducting Earth. Large geomagnetically induced currents (GIC) are associated with large time derivatives of the horizontal magnetic field. Recent results show that the time derivative is typically dominated by the contribution from the telluric currents. Our study aims to find measures to quantify the behaviour of external and internal currents and their time derivatives during large GIC events. Results of this study show that strong external currents have quite narrow directional distributions. Angular variation is larger for internal currents, and especially for their time derivatives. For external currents angular variation is larger at higher latitudes. Similar behaviour is not seen with internal currents.</p>

Comparative Study on Numerical Calculation of 2-D Random Sea Surface Based on Fractal Method and Monte Carlo Method

Based on fifty one groups of data on direction distribution measured from buoy sites, several important spectrum parameters including distribution characteristics of the measured data’s spectrum, the Wen’s direction spectrum and the Donelan function are analyzed from the perspectives of standard deviation of directional distribution function and statistical results. Then, a numeric calculation model based on the Monte Carlo method is proposed in this work. At the same time—based on Weierstrass self-affine fractal function—numeric simulation of random sea surface is conducted by modifying the bilateral power law. The analysis of the numeric calculation results under different wind directions, speeds and fetches proves that both methods can be adopted for different water directional distributions and target spectrum models. In addition, this study compares the characteristic wave within different distribution frequency domains in the main wave direction and in its orthogonal direction. It is proved that the fractal method cannot fully reflect the anisotropy of gravity wave and tension wave in the superposition direction, however, it can maintain the similarity of overall energy part with the rough length of the waves. Moreover, there are still limitations of the fractal method in the numeric modeling of undeveloped sea surface.

Giant Gaussian process models of geomagnetic palaeosecular variation: a directional outlook

SUMMARY Assessment of long-term palaeosecular variation (PSV) of the geomagnetic field is frequently based on simplified versions of a class of statistical models known as giant Gaussian processes (GGP) used to represent temporal variations in spherical harmonic descriptions of the field. Here we propose a new type of analysis to assess the shape and dispersion of the directional distributions caused by PSV. The quantities analysed in this study are equal-area coordinates of rotated distributions of palaeomagnetic directions, ${x_E}$ (east−west) and ${x_N}\ $(north−south) and their standard deviations (${\sigma _E}$ and ${\sigma _N}$). These are easy to determine, and can readily be numerically predicted for any GGP model, avoiding the need for the numerous simulations generally used to determine the scatter and/or elongation of directional distributions. Mean predictions of $\overline {{x_N}} $ for a simplified GGP model are different from the expected geocentric axial dipole (GAD) directions, in agreement with inclination differences noted in previous studies. The best estimates for palaeomagnetic inclination are the expected directions from the mean of virtual geomagnetic poles (VGPs) calculated using an iterative angular cut-off process. Predictions of ${\sigma _{\rm E}}$ and ${\sigma _{\rm N}}$ vary with latitude and are symmetric about the Equator. The N–S direction (${\sigma _{\rm N}}$) is always larger than E–W (${\sigma _{\rm E}}$), but the difference decreases from a maximum at the Equator to the poles, where ${\sigma _{\rm N}} = \ {\sigma _{\rm E}}$. A simplified GGP model is used to show that the parameter α (affecting variances in all Gauss coefficients) is positively correlated with ${\sigma _{\rm E}}$ and ${\sigma _{\rm N}}\ $ while the β parameter, the ratio of dipole to quadrupole family standard deviations, modifies the latitudinal dependence of ${\sigma _{\rm E}}$ and ${\sigma _{\rm N}}$. Experimental error in ${\sigma _{\rm E}}$ and ${\sigma _{\rm N}}$ can be accommodated using the common statistical parameters found in palaeomagnetic data sets, as ${\alpha _{95}}$ from site-mean directions. Predictions of simplified GGP models are compared with both numerical simulations and real data spanning the last 10 Ma. The latitudinal dependence of the proposed measures of PSV (${\sigma _{\rm E}}$ and ${\sigma _N}$) provide useful diagnostics for testing the validity of a GGP model. For the past 10 Ma the best-fitting GGP model with a mean GAD field set to $g_1^0 = \ - 18\ \mu T$ has α = 6.7 µT and β = 4.2. These new directional diagnostics will be used to investigate changes in overall geomagnetic field behaviour over other geological time intervals.

The Changes of Theoretical Wave Power from Offshore to Coast in the South-western Black Sea

This study concentrates on the changes of theoretical wave power from offshore to coastal regions of south-western Black Sea. The investigation also offers a long-term (31-year) wave power quantification analysis between 1979 and 2009 using the SWAN version 41.01AB numerical wave model. The wave resource assessment is performed in terms of its seasonal and monthly variability of wave power, annual wave power directional distributions and the comparison of the maximum and median values of some important wave power parameters in the west of Istanbul a major city in Turkey that straddles Europe and Asia across the Bosphorus Strait. For this analysis, 10 point locations distributed on two perpendicular lines (KA and KE) to the coastline with five different depths (5, 25, 50, 75, and 100 m) in the areas of interest were selected. The data needed was extracted from the dataset produced by [1, 2] using a calibrated nested layered wave hindcast model SWAN forced with CFSR winds. The results show that the wave energy resource in the study area is high, and the potential locations can be considered for extracting wave electrical power.

Relative train length and the infrastructure required to mitigate delays from operating combinations of normal and over-length freight trains on single-track railway lines in North America

Distributed power locomotives have facilitated longer heavy-haul freight trains that improve the efficiency of railway operations. In North America, where the majority of mainlines are single track, the potential operational and economic advantages of long trains are limited by the inadequate length of many existing passing sidings (passing loops). To alleviate the challenge of operating trains that exceed the length of passing sidings, railways preserve the mainline capacity by extending passing sidings. However, industry practitioners rarely optimize the extent of infrastructure investment for the volume of over-length train traffic on a particular route. This paper investigates how different combinations of normal and over-length trains, and their relative lengths, relate to the number of siding extensions necessary to mitigate the delay performance of over-length train operation on a single-track rail corridor. The experiments used Rail Traffic Controller simulation software to determine train delay for various combinations of short and long train lengths under different directional distributions of a given daily railcar throughput volume. Simulation results suggest a relationship between the ratio of train lengths and the infrastructure expansion required to eliminate the delay introduced by operating over-length trains on the initial route. Over-length trains exhibit delay benefits from siding extensions while short trains are relatively insensitive to the expanded infrastructure. Assigning directional preference to over-length trains improves the overall average long-train delay at the expense of delay to short trains. These results will allow railway practitioners to make more informed decisions on the optimal incremental capital expansion strategy for the operation of over-length trains.