Dominant acceleration processes of ambient energetic protons (E ⩾ 50 keV) at the Bow Shock: Conditions and limitations

Energetic proton (E_p ? 50 keV) and magnetic field observations during crossings of the Earth's Bow Shock by the IMP-7 and 8 spacecraft are incorporated in this work in order to examine the effect of the Bow Shock on a pre-existing proton population under different “interplanetary magnetic field-Bow Shock” configurations, as well as the conditions for the presence of the Bow Shock associated energetic proton intensity enhancements. The presented observations indicate that the dominant process for the efficient acceleration of ambient energetic particles to energies exceeding ~ 50 keV is by “gradient-B” drifting parallel to the induced electric field at quasi-perpendicular Bow Shocks under certain well defined limitations deriving from the finite and curved Bow Shock surface. It is shown that the proton acceleration at the Bow Shock is most efficient for high values of the upstream magnetic field (in general B₁ > 8γ), high upstream plasma speed and expanded Bow Shock fronts, as well as for directions of the induced electric field oriented almost parallel to the flanks of the Bow Shock, i.e. when the drift distance of protons parallel to the electric field at the shock front is considerably smaller than the local radius of curvature of the Bow Shock. The implications of the presented observations of Bow Shock crossings as to the source of the energetic proton intensity enhancements are discussed.     

Newtonian and post-newtonian tidal theory: Variable G and earthquakes

A mathematical analysis of the Newtonian and parametrized Post-Newtonian tidal stresses is applied to tidal triggering mechanism for earthquakes. We investigate a possible correlation.The procedure used for calculating the solid earth tidal stress is described by the Newtonian theory and the parametrized Post-Newtonian metric. We calculate tidal stress histories for earthquakes between 1908 and 1991 in Greek area. Although no significant tidal correlation was found for the entire data set, which contained earthquakes of magnitudeM 6.0, a fairly striking correlation was observed for an earthquake-tide correlation by computing tidal functions at the time and place of the earthquake events. A successful correlation as used in this paper means that: earthquake events occur during a certain part of the tidal cycle.Also, we have studied a variation of the gravitational constant according to the variation of the velocity of the Earth and the uniform velocity of the Solar System with respect to a preferred Universal rest frame.This work has been supported by the Greek General Secretariat of Research and Technology under Grant No. 89e160.     

Integrals of motion in the elliptic three-dimensional restricted three-body problem

Three integrals of motion have been found in the three-dimensional elliptic restricted three-body problem for small eccentricitye of the relative orbit of the primaries and small distancer and eccentricitye of the orbit of the third body around a primary. The integrals are given in the form of formal series in the mass-ratio , the eccentricitiese, e and the coordinates and velocities. These integrals depend periodically on the time.     

Multispacecraft observations of the east-west asymmetry of solar Energetic Storm Particle events

Multispacecraft observations of energetic protons (E _p 500 keV) were obtained by the APL/JHU instruments on board the IMP-7 and 8 spacecraft and the Voyager-1 and 2 deep space probes, in order to study the generation of solar flare Energetic Storm Particle (ESP) events at widely separated locations on the same shock front. These locations are presumably characterized, on the average, by different interplanetary magnetic field-shock front configurations, i.e. quasi-perpendicular (quasi-parallel) shocks for eastern (western) solar flare sites. The multispacecraft energetic proton observations show that substantial differences in the ESP proton intensity enhancements (defined as the ratio of intensity increases near the shock over the ambient solar proton population) are detected at these energies for locations on the shock front with wide heliolongitude separations. In particular, large ESP proton intensity enhancements are detected at locations on the shock front for which the solar flare site generating the shock is to the east of the spacecraft meridian, whereas only weak ESP events are observed at locations on the same shock for which the flare site is to the west of the spacecraft meridian. The results indicate that acceleration of ESP protons to E _p 500 keV takes place exclusively at the quasi-perpendicular shock front domain, consistent with the shock drift acceleration mechanism (Armstrong et al., 1977).     

On the E-W asymmetry of Forbush decreases (Ep ≥ 35 MeV)

A ten-year survey of the effects of solar flare-generated shock-waves on the ambient cosmic rays (E 35 MeV) as well as on the solar particle population at low energies (E 300 keV) shows that the quasi-perpendicular side of the expanding shock front (sola flare site to the east of the Sun-spacecraft line) gives rise to prominent Forbusch decreases and large ESP events, whereas the presumably turbulent quasi-parallel part of the large-scale shock front-IMF configurations (source site to the west of the Sun-spacecraft line) is associated, on the average, with small (4%) or no Forbush decreases and weak or no ESP events. The role of grad-B drifts of the particles at quasi-perpendicular shocks is suggested as a common cause for both the ESP events and the Forbush decreases. The observations indicate that turbulence is not a dominant factor in the above shock effects on the energetic particle populations both at low and high energies.     

The influence of pumping parameters in fluid‐driven fractures in weak porous formations

In this work, we investigate the main pumping parameters that influence a fluid‐driven fracture in cohesive poroelastic and poroelastoplastic weak formations. These parameters include the fluid viscosity and the injection rate. The first parameter dominates in the mapping of the propagation regimes from toughness to viscosity, whereas the second parameter controls the storage to leak‐off dominated regime through diffusion. The fracture is driven in weak permeable porous formation by injecting an incompressible viscous fluid at the fracture inlet assuming that the fracture propagates under plane strain conditions. Fluid flow in the fracture is modeled by lubrication theory. Pore fluid movement in the porous formation is based on the Darcy law. The coupling follows the Biot theory, whereas the irreversible rock deformation is modeled with the Mohr–Coulomb yield criterion with associative flow rule. Fracture propagation criterion is based on the cohesive zone approach. Leak‐off is also considered. The investigation is performed numerically with the FEM to obtain the fracture opening, length, and propagation pressure versus time. We demonstrate that pumping parameters influence the fracture geometry and fluid pressures in weak formations through the viscous fluid flow and the diffusion process that create back stresses and large plastic zones as the fracture propagates. It is also shown that the product of the propagation velocity and fluid viscosity, µv that appears in the scaling controls the magnitude of the plastic zones and influences the net pressure and fracture geometry. These findings may explain partially the discrepancies in net pressures between field measurements and conventional model predictions for the case of weak porous formation. Copyright © 2014 John Wiley & Sons, Ltd.     

Observation of shock-accelerated protons by GIOTTO and IMP-8 under solar minimum conditions in February 1986

Solar and shock-accelerated protons were observed by the interplanetary S/C GIOTTO and aboard the Earth orbiting satellite IMP-8 during solar minimum conditions in February 1986. Forward and reverse shock configurations developed on 9–11 February, 1986 and could be recognized by sunward and anti-sunward proton propagation. The results are consistent with a general east-west asymmetry in particle fluxes observed within a distance of 1 AU from the Sun and caused by quasi-perpendicular and quasi-parallel shock configurations in the interplanetary magnetic field. The high-energy protons (>1 GeV) measured simultaneously by ground-based neutron monitors showed a complementary enhanced amplitude in the diurnal variation on 9 February, 1986.     

Stochastic analysis of flux and head moments in a heterogeneous aquifer system

This study investigates the behavior of flux and head in a strongly heterogeneous three-dimensional aquifer system. The analyses relied on data from 520 slug tests together with 38,000 one-foot core intervals lithological data from the site of the General Separations Area in central Savannah River Site, South Carolina, USA. The skewness in the hydraulic conductivity histograms supported the geologic information for the top two aquifers, but revealed stronger clay content, than was reported for the bottom aquifer. The log-normal distribution model described adequately the hydraulic conductivity measurements for all three aquifers although, other distributions described equally well the bottom aquifer measurements. No apparent anisotropy on the horizontal plane was found for the three aquifers, but ratios of horizontal to vertical correlation lengths between 33 and 75 indicated a strong stratification at the site. Three-dimensional Monte Carlo stochastic simulations utilized a grid with larger elements than the support volume of measurements, but of sub-REV (representative elementary volume) dimensions. This necessitated, on one hand, the use of upscaled hydraulic conductivity expressions, but on the other hand did not allow for the use of anisotropic effective hydraulic conductivity expressions (Sarris and Paleologos in J Stoch Environ Res Risk Assess 18: 188–197, 2004). Flux mean and standard deviations components were evaluated on three vertical cross-sections. The mean and variance of the horizontal flux component normal to a no-flow boundary tended to zero at approximately two to three integral scales from that boundary. Close to a prescribed head boundary both the mean and variance of the horizontal flux component normal to the boundary increased from a stable value attained at a distance of about five integral scales from that boundary. The velocity field 〈q_x〉 was found to be mildly anisotropic in the top two aquifers, becoming highly anisotropic in the bottom aquifer; 〈q_y〉 was anisotropic in all three aquifers with directions of high continuity normal to those of the 〈q_x〉 field; finally, 〈q_z〉 was highly anisotropic in all three aquifers, with higher continuity along the east–west direction. The mean head field was found to be continuous, despite the high heterogeneity of the underlying hydraulic conductivity field. Directions of high continuity were in alignment with field boundaries and mean flow direction. Conditioning did not influence significantly the expected value of the flux terms, with more pronounced being the effect on the standard deviation of the flux vector components. Conditioning reduced the standard deviations of the horizontal flux components by as much as 50% in the bottom aquifer. Variability in the head cross-sections was affected only marginally, with an average 10% reduction in the respective standard deviation. Finally, the location of the conditioning data did not appear to have a significant effect on the surrounding area, with uniform reduction in standard deviations.     

Impact of recent climatic change on growth of low elevation eastern Mediterranean forest trees

Evidence is presented of how Pinus halepensis Miller from dry habitats at <300 m elevation of four Greek island regions have responded to climatic conditions of the last two centuries. We compared historical periods of low growth due to low precipitation with the recent period of significant precipitation decline. In all cases trees?? growth patterns across the twentieth century were consistent with trends in annual (rather than seasonal) precipitation, with lowest values in both precipitation and radial growth during the last two decades of the twentieth century, the worst conditions for tree growth in more than 200 years. The data are compared with trends across different vegetation belts of the northern Mediterranean basin. Drought related tree mortality in Greece in 2000 and 2007 coincided with the most severe fire outbreaks on record. IPCC WG I (2007) climate scenarios for the Mediterranean suggest a further decline in precipitation, particularly in the eastern regions. Should this occur, growth reduction in trees, tree mortality and damage from forest fires are likely to become more severe.