The effect of static stress perturbations due to an intermediate depth intraslab earthquake on seismic cycles of large interplate earthquakes at a subduction zone is examined through a numerical simulation using a laboratoryderived friction law. The frictional stress on a plate interface in a two-dimensional uniform elastic half-space model is assumed to obey a rate- and state-dependent friction law, and the plate interface is loaded by a steady plate motion, resulting in recurrence of large interplate earthquakes in the model. Static stress perturbations on the plate interface due to an intermediate depth intraslab earthquake with reverse fault type is introduced to the model. This model is set up so as to simulate seismic cycles at the Miyagi-Oki subduction zone, northeastern Honshu, Japan, where a large interplate earthquake is expected to occur and an intraslab earthquake of M = 7.1 took place in May, 2003. The simulation result indicates that the static stress changes due to the intraslab earthquake promote slip just below the interplate seismogenic zone, accelerating aseismic sliding there. This aseismic sliding generates stress concentration at the bottom of the seismogenic zone, often advancing the occurrence time of the next interplate earthquake. The shear-stress increases at aseismic slip regions with velocity-strengthening frictional property cannot be held and then aseismic sliding should take place to relax the increased stress. The present simulation result suggests that the promotion of aseismic sliding around the source area is important for evaluating the triggering effects of earthquakes. The conventional Coulomb failure stress approaches to the evaluation of the effect of static stress changes on seismic activity may be insufficient when static stress changes influence aseismic slip rates.

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We usually use the Brownian distribution, lognormal distribution, Gamma distribution, Weibull distribution, and exponential distribution to calculate long-term probability for the distribution of time intervals between successive events. The values of two parameters of these distributions are determined by the maximum likelihood method. The difference in log likelihood between the proposed model and the stationary Poisson process model, which scores both the period of no events and instances of each event, is considered as the index for evaluating the effectiveness of the earthquake probability model. First, we show that the expected value of the log-likelihood difference becomes the expected value of the logarithm of the probability gain. Next, by converting the time unit into the expected value of the interval, the hazard is made to represent a probability gain. This conversion reduces the degrees of freedom of model parameters to 1. We then demonstrate that the expected value of the probability gain in observed parameter values ranges between 2 and 5. Therefore, we can conclude that the long-term probability calculated before an earthquake may become several times larger than that of the Poisson process model.

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The nonlinear system of equations for solving GPS atmospheric sounding's bending angles are normally solved using Newton's method. Because of the nonlinear nature of the equations, Newton's method applies linearization and iterations. The method assumes the refraction angle to be small enough such that the dependency of the doppler shift on these angles are linear. The bending angles are then solved iteratively. Since the approach assumes the dependency of doppler shift on bending angles to be linear, which in actual sense is not, some small nonlinearity error is incurred. The Newton's iterative method is often used owing to the bottleneck of solving in exact form the nonlinear system of equations for bending angles. By converting this system of trigonometric nonlinear equations into algebraic, the present contribution proposes an analytic (algebraic) algorithm for solving the bending angles and presents the geometry of the solution space. The algorithm is tested by computing bending angles of three CHAMP occultation data and the results compared to those of iterative Newton's approach. Occultation 133 of 3rd May 2002 is selected as it occurred during diurnal solar radiation maximum past afternoon. During this time, the effect of ionospheric noise is high. Occultations number 3 of 14th May 2001 and number 6 of 2nd February 2002 were selected since they occurred past mid-night, a time of low solar activity and thus less effect of ionospheric noise. The results for occultation 133 of 3rd May 2002 indicate that the nonlinearity errors in bending angles increase with decrease in height to a maximum absolute value of 0.00069° (0.1%) for the region 5-40 km during period of high solar activity. Such nonlinearity errors are shown to impact significantly on the computed impact parameters to which the bending angles are referred. During low solar activity period, the nonlinearity error was relatively small for occultation number 3 of 14th May 2001 with maximum absolute value of 0.00001°. The analytical algorithm thus provide an independent method for controlling classical iterative procedures and could be used where very accurate results are desired.

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In this paper, we show that the Virtual Geomagnetic Pole (VGP) distribution used in paleomagnetic studies is only one of the 2D spherical projections of a 3D paleomagnetic directional data set. Therefore, in principle, the VGP distribution does not by itself completely represent the paleomagnetic directional data set. We suggest that it is necessary to include in the analyses another 2D spherical projection of a 3D paleomagnetic directional data set - the Equatorial Virtual Pole (EVP) distribution. The EVP is defined as the point 90° from the VGP along the great circle through the VGP and the site. The VGP and EVP distributions represent different aspects of the directional data sets and information not carried in the VGP distribution is carried by the EVP distribution. Ideal VGP and EVP distributions depict different aspects of the characteristics of the geomagnetic field as such that, while the VGPs tend to distribute symmetrically around the regions where the field is perpendicular to the earth's surface, the EVPs concentrate about the nodal or null flux lines.

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Turbulent motions in the core, being highly anisotropic because of the influence of the Earth's rotation and its magnetic field, cause the eddy diffusion of large-scale fields much more effectively than the molecular diffusion. Reliable estimates of the eddy diffusivities, or the subgrid-scale fluxes, are therefore of significance. In this paper, scale similarity of magnetohydrodynamic turbulence in a rapidly rotating system is investigated to model subgrid-scale processes, as used in large-eddy simulations. The turbulent flux has been computed by taking an ensemble average of results of direct numerical simulations, which are to be employed in this paper, over the computational box which represents a small region in the Earth's core. The anisotropy of turbulent flux computed after averaging over segments into which the box is divided remains unchanged even when the size of segments changes. Dependence of turbulent flux computed from fields to which a spatial filter is applied on its width indicates that subgrid-scale flux can be evaluated through extrapolation. This method will be useful for performing global geodynamo simulations taking into account subgrid-scale processes.

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In this paper, we report the responses of the low latitude ionosphere near the longitude 120°E to the April 2000 geomagnetic storm using Digisonde data measured at Chungli (25.0°N, 121.2°E, Mag. 13.8°N), Wuhan (30.6°N, 114.4°E, Mag. 19.3°N), and Kokubunji (35.7°N, 139.5°E, Mag. 25.7°N). At these three stations, the significant ionospheric responses are near-simultaneous height disturbances after the sudden storm commencement (SSC) on April 6, 2000 and wave-like disturbances in the daytime on April 7. The ionospheric height disturbances in the nighttime after the SSC at these stations are suggested to be caused by the storm related perturbed electric fields, and the followed wave-like disturbances may be caused by storm induced atmospheric gravity waves. The vertical effective winds derived from Digisonde measurements imply the existence of significantly large vertical drifts during this storm, which are in agreement with the perturbed zonal electric fields predicted by the model of Fejer and Scherliess (1997) and Scherliess and Fejer (1997). Finally, the storm time derivations of foF2 from its monthly median level at these stations are used to validate the predication ability of the empirical model of Araujo-Pradere et al. (2002), which has included in the International Reference Ionosphere model IRI2000.

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We present the values of a ratio β of the solar radiation pressure force to the solar gravity on the finite circular cylindrical grains, as functions of an aspect ratio of the cylinder and an incident angle Θ of the solar radiation. By using the resulting formula of β(Θ), the trajectory of the Kepler orbit for the rotating silicate cylinder is computed associated with a spin motion under the assumption that the spin axis is along the shortest axis of the cylinder and points to the direction perpendicular to the solar radiation. We found for the silicate cylinder grain with a mass equivalent to a sphere with a radius of 0.15 μm, and the aspect ratio of 2.0 that a heliocentric distance of the grain varies periodically with a time, having an amplitude of the fluctuation in the heliocentric distance of about 0.02 AU, where the spin velocity is 0.25 rotation/day and the initial orbit has a semi-major axis 3.0 AU and an eccentricity 0. In addition, during such a fluctuation of the heliocentric distance, the instantaneous eccentricity of the orbit also varies simultaneously from 0 to 1.6 with the rotation of the grain. This implies that the in-situ measurements of orbital elements of impact grains on the dust detector may record those instantaneous orbital elements related to the phase of the grain's rotation.

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The phenomenon of quasi-stable trapping of charged particles in the keV to MeV energy range within the polar cusp region of the Earth's magnetosphere is explored. The remote equatorial magnetic field lines on the dayside magnetosphere are compressed by the solar wind and exhibit two local minima in the geomagnetic field strength along the field line in high latitudes. These minima, on both sides of the equator, result in stable confinement structures. Numerical modeling of charged particle orbits that pass through the regions of these local field minima has been carried out using different seasonal Earth tilt and different magnetospheric disturbance level. These orbit tracings show when and where these off-equatorial trapped radiation zones would be situated. The existence and extent of these confinement zones depend on the tilt angle. Indeed, the northern cusp confinement zone appears only at the northern summer solstice, while the southern cusp particle capture zone appears around winter solstice. The particle orbits that pass through opposite off-equatorial field minimum during solstices reveal a bound of the geomagnetic equatorial plane on the day sector. During equinox, the particle confinement zones exist in both cusps at times of disturbed magnetosphere conditions. The trapped particles drift within the trapping zones with periods of the several minutes, conserving the 1st and 2nd adiabatic invariants.

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