The global joule heat production rate and the AE index

The accuracy of the AE index as a measure of the joule heat production rate is examined for a typical substorm event on 18 March 1978 by estimating the global joule heat production rate, as a function of time, using data obtained from the IMS six meridian chains. In spite of the fact that the AE index had had an initial slow growth which was followed by a rapid growth, the joule heat production rate attained a high level during the slow growth and thus their variations were considerably different from those of the AE index. Therefore, although the AE index is statistically linearly related to the global joule heat production rate, one should be cautious in assuming that details of time variations of the AE index during individual events represent those of the joule heat production rate.     

Velocity fields associated with the magnetic component of solar faculae

The StokesV asymmetries observed in solar faculae can be interpreted by invoking the presence of magnetic and velocity fields variations along the line-of-sight. By means of a perturbative approach, we develop the theoretical dependence on magnetic and velocity fields of the StokesV profile around its zero-crossing point. We find that the empirical curves of growth for theV zero-crossing point and the slope, as well as the curve of growth for the integral (previously derived by Sánchez Almeidaet al., 1989, through the same approach), are reproduced quite well with a single atmosphere which assumes such simultaneous variations.The depth dependence of the fields that give the best fit in our model presents several striking properties which cannot be released without totally compromising the goodness of the fit. Namely, the magnetic field strength increases towards the observer while the downflowing velocity field decreases. Both variations must occur co-spatially, in the same atmospheric layers. This fact seems to contradict theoretical models for the fanning out parts of magnetic concentrations which foresee a sharp separation between a static magnetic layer and a deep zone with velocity fields. We discuss a possible solution of such contradiction in terms of a finite optical thickness of the boundary layer between zones with and without magnetic field in faculae.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.     

Warping modes in discs around accreting neutron stars

The origin and stability of a thin sheet of plasma in the magnetosphere of an accreting neutron star are investigated. First, the radial extension of such a magnetospheric disc is explored. Then a mechanism for magnetospheric accretion is proposed, reconsidering the bending wave explored by Agapitou, Papaloizou & Terquem, that was found to be stable in ideal magnetohydrodynamics. We show that this warping becomes unstable and can reach high amplitudes, in a variant of Pringle's radiation-driven model for the warping of active galactic nucleus accretion discs. Finally, we discuss how this mechanism might give a clue to explain the observed X-ray kilohertz quasi-periodic oscillation of neutron star binaries.     

On the Relationship of the 27-day Variations of the Solar Wind Velocity and Galactic Cosmic Ray Intensity in Minimum Epoch of Solar Activity

We study the relationship of the 27-day variations of the galactic cosmic ray intensity with similar variations of the solar wind velocity and the interplanetary magnetic field based on observational data for the Bartels rotation period # 2379 of 23 November 2007 – 19 December 2007. We develop a three-dimensional (3-D) model of the 27-day variation of galactic cosmic ray intensity based on the heliolongitudinally dependent solar wind velocity. A consistent, divergence-free interplanetary magnetic field is derived by solving Maxwell’s equations with a heliolongitudinally dependent 27-day variation of the solar wind velocity reproducing in situ observations. We consider two types of 3-D models of the 27-day variation of galactic cosmic ray intensity, i) with a plane heliospheric neutral sheet, and ii) with the sector structure of the interplanetary magnetic field. The theoretical calculations show that the sector structure does not significantly influence the 27-day variation of galactic cosmic ray intensity, as had been shown before, based on observational data. Furthermore, good agreement is found between the time profiles of the theoretically expected and experimentally obtained first harmonic waves of the 27-day variation of the galactic cosmic ray intensity (with a correlation coefficient of 0.98±0.02). The expected 27-day variation of the galactic cosmic ray intensity is inversely correlated with the modulation parameter ζ (with a correlation coefficient of −0.91±0.05), which is proportional to the product of the solar wind velocity V and the strength of the interplanetary magnetic field B (ζ∼VB). The high anticorrelation between these quantities indicates that the predicted 27-day variation of the galactic cosmic ray intensity mainly is caused by this basic modulation effect.     

Maximum Entropy and Random Forest Modeling of Mineral Potential: Analysis of Gold Prospectivity in the Hezuo–Meiwu District,West Qinling Orogen,China

Natural Resources Research - This study tested and compared the mineral potential mapping capabilities of the random forest (RF) and maximum entropy (MaxEnt) algorithms using gold deposit...     

Martian rampart crater ejecta: Experiments and analysis of melt-water interaction

Viking images of Martian craters with rampart-bordered ejecta deposits reveal distinct impact ejecta morphology when compared to that associated with similar-sized craters on the Moon and Mercury. Topographic control of distribution, lobate and terraced margins, cross-cutting relationships, and multiple stratigraphic units are evidence for ejecta emplacement by surface flowage. It is suggested that target water explosively vaporized during impact alters initial ballistic trajectories of ejecta and produces surging flow emplacement. The dispersal of particulates during a series of controlled steam explosions generated by interaction of a thermite melt with water has been experimentally modeled. Preliminary results indicate that the mass ratio of water to melt and confining pressure control the degree of melt fragmentation (ejecta particle size) and the energy and mode of melt-ejecta dispersal. Study of terrestrial, lobate, volcanic ejecta produced by steam-blast explosions reveals that particle size and vapor to clast volume ratio are primary parameters characterizing the emplacement mechanism and deposit morphology. Martian crater ramparts are formed when ejecta surges lose fluidizing vapors and transported particles are deposited en masse. This deposition results from flow yield strength increasing above shear stress due to interparticle friction.     

The impact of salt on the late Messinian to recent tectonostratigraphic evolution of the Cyprus subduction zone

Messinian evaporites of locally more than 3‐km thickness occupy the subduction zone between Cyprus and Eratosthenes Seamount. Based on a dense grid of seismic reflection profiles, we report on compressional salt tectonics and its impact on the Late Miocene to Quaternary structural evolution of the Cyprus subduction zone. Results show that evaporites have experienced significant post‐Messinian shortening along the plate boundary. Shortening has initiated allochthonous salt advance between Cyprus and Eratosthenes Seamount, representing an excellent example of salt which efficiently escapes subduction and accretion. Further east, between Eratosthenes Seamount and the Hecataeus Rise, evaporites were compressionally inflated without having advanced across post‐Messinian strata. Such differences in the magnitude of salt tectonic shortening may reflect a predominately north–south oriented post‐Messinian convergence direction, raising the possibility of a later coupling between the motion of Cyprus and Anatolia than previously thought. Along the area bordered by Cyprus and Eratosthenes Seamount a prominent step in the seafloor represents the northern boundary of a controversially debated semi‐circular depression. Coinciding with the southern edge of the salt sheet, this bathymetric feature is suggested to have formed as a consequence of compressional salt inflation and seamount‐directed salt advance. Topographic lows on top of highly deformed evaporites are locally filled by up to 700 m of late Messinian sediments. The uppermost 200 m of these sediments were drilled in the course of ODP Leg 160 and interpreted to represent Lago Mare‐type deposits (Robertson, Tectonophysics, 1998d, 298 , 63‐82). Lago Mare deposits are spatially restricted to the western part of the subduction zone, pinching out towards the east whereas presumably continuing into the Herodotus Basin further west. We suggest a sea level control on late Messinian Lago Mare sedimentation, facilitating sediment delivery into basinal areas whereas inhibiting Lago Mare deposition into the desiccated Levant Basin. Locally, early salt deformation is believed to have provided additional accommodation space for Lago Mare sedimentation, resulting in the presently observed minibasin‐like geometry.     

Decorrelated GRACE time-variable gravity solutions by GFZ,and their validation using a hydrological model

We have analyzed recent gravity recovery and climate experiment (GRACE) RL04 monthly gravity solutions, using a new decorrelating post-processing approach. We find very good agreement with mass anomalies derived from a global hydrological model. The post-processed GRACE solutions exhibit only little amplitude damping and an almost negligible phase shift and period distortion for relevant hydrological basins. Furthermore, these post-processed GRACE solutions have been inspected in terms of data fit with respect to the original inter-satellite ranging and to SLR and GPS observations. This kind of comparison is new. We find variations of the data fit due to solution post-processing only within very narrow limits. This confirms our suspicion that GRACE data do not firmly ‘pinpoint’ the standard unconstrained solutions. Regarding the original Kusche (J Geod 81:733–749, 2007) decorrelation and smoothing method, a simplified (order-convolution) approach has been developed. This simplified approach allows to realize a higher resolution—as necessary, e.g., for generating computed GRACE observations—and needs far less coefficients to be stored.     

Gravity anomaly interpretation of 2D fault morphologies by means of nonplanar fault planes and exponential density contrast model: a space domain technique

Boundary faults associated with thick sedimentary basins are more often curved in cross section rather than planar. We develop a space domain-based automatic gravity inversion technique to quantify such listric fault sources from a set of observed gravity anomalies. The density contrast within the hanging wall of fault morphology is presumed to be known according to a prescribed exponential law. Furthermore, the fault plane is described by a polynomial function of arbitrary but specific degree, whose coefficients become the unknown parameters to be estimated from a set of observed gravity anomalies in addition to the thickness of the fault structure. Using a set of characteristic anomalies, the present inversion identifies approximate parameters pertaining to the origin of fault plane and depth to decollement horizon. Based on the errors between the observed and model gravity anomalies of the structure, the algorithm constructs and solves a system of normal equations to estimate the improvements in depth and coefficients of the polynomial in an iterative approach until one of the specified convergence criteria is fulfilled. The efficacy of the algorithm is shown with the analysis of gravity anomalies attributable to a synthetic model of a listric fault source in the presence of pseudorandom noise. Application of the proposed inversion technique on the observed gravity anomalies of the Ahri-Cherla master fault of the Godavari subbasin in India using the derived exponential density contrast model has yielded an interpretation that is consistent with the available/reported information.