The Canary Eddy Corridor: A major pathway for long-lived eddies in the subtropical North Atlantic

We report, from remote sensing and in situ observations, a new type of permanent structure in the eastern subtropical Atlantic Ocean, that we call the “Canary Eddy Corridor”. The phenomenon, is a zonal long-lived (>3 months) mesoscale eddy corridor, whose source is the flow perturbation of the Canary Current and the Trade Winds at the Canary Islands. The latitudinal range of the corridor spans 22°N–29°N and extends from the Canaries to at least 32ºW, near the mid-Atlantic. This is the main region of long-lived westward-propagating eddies in the subtropical northeast Atlantic. From a age-distribution study we observe that at least 10% of mesoscale eddies in this region are long-lived, with a dominance of anticyclones over cyclones. Another four westward-propagating eddy corridors were also detected: two small corridors north and south of the Azores Front; a small zonal corridor located near 31ºN, south of the island of Madeira; and a small corridor located near the Cape Blanc giant filament. The existence of these corridors may change, at least for the northeastern subtropical Atlantic, the general idea that mesoscale eddies are disorganized, ubiquitous structures in the ocean. The Canary Eddy Corridor constitutes a direct zonal pathway that conveys water mass- and biogeochemical properties offshore from the Canary Island/Northwest Africa upwelling system, and may be seen as a recurrent offshore pump of organic matter and carbon to the oligotrophic ocean interior. Estimates of volume and mass transport indicate that Canary Eddy Corridor westward transport is more than one-fourth of the southward transport of the Canary Current. The westward transport of kinetic energy by the eddies of the Canary Corridor is as important as the southward transport by the Canary Current. The total primary production related to the Corridor may be as high as the total primary production of the northwest Africa upwelling system for the same latitude range.     

On the frequency contents of local events: source or path effect?

Local events which occurred in the Timanfaya volcanic field are analysed and their spectral contents are interpreted as being due to the effect of a finely layered medium with large impedance contrast, the presence of which is well known from well-logging data. By considering the layered medium as a filter, its spectral response (amplitude and phase) is computed from different randomly generated values of its parameters (total thickness, mean thickness of the individual layers and impedance contrast), showing that this stratigraphic filter acts as a low-pass filter. This effect can be correctly modelled by means of an exponential correlation function. However, in some cases resonant peaks appear in the spectrum superimposed on the low-pass filter effect, which can only be attributed to resonant scattering. An analysis of the phase and group delay associated with the amplitudes is made and strongly suggests that it is necessary to incorporate the theory of resonant scattering for the retrieval of medium properties. From the point of view of the amplitudes, the superposition of both effects, low-pass filter and resonant peaks, allows us to reproduce the gross features that are usually attributed to source effects. The need for a careful analysis of the local site response previous to any interpretation of the spectral features in terms of source characteristics is thus emphasized.     

Study of the transfer between libration point orbits and lunar orbits in Earth–Moon system

This paper is devoted to the study of the transfer problem from a libration point orbit of the Earth–Moon system to an orbit around the Moon. The transfer procedure analysed has two legs: the first one is an orbit of the unstable manifold of the libration orbit and the second one is a transfer orbit between a certain point on the manifold and the final lunar orbit. There are only two manoeuvres involved in the method and they are applied at the beginning and at the end of the second leg. Although the numerical results given in this paper correspond to transfers between halo orbits around the \(L_1\) point (of several amplitudes) and lunar polar orbits with altitudes varying between 100 and 500 km, the procedure we develop can be applied to any kind of lunar orbits, libration orbits around the \(L_1\) or \(L_2\) points of the Earth–Moon system, or to other similar cases with different values of the mass ratio.     

Spatial collinear restricted four-body problem with repulsive Manev potential

We outline some aspects of the dynamics of an infinitesimal mass under the Newtonian attraction of three point masses in a symmetric collinear relative equilibria configuration when a repulsive Manev potential (\(-1/r +e/r^{2}\)), \(e>0\), is applied to the central mass. We investigate the relative equilibria of the infinitesimal mass and their linear stability as a function of the mass parameter \(\beta \), the ratio of mass of the central body to the mass of one of two remaining bodies, and e. We also prove the nonexistence of binary collisions between the central body and the infinitesimal mass.     

Post‐fire hydrological response and suspended sediment transport of a terraced Mediterranean catchment

In July 2013, a wildfire severely affected the western part of the island of Mallorca (Spain). During the first three post‐fire hydrological years, when the window of disturbance tends to be more open, the hydrological and sediment delivery processes and dynamics were assessed in a representative catchment intensively shaped by terracing that covered 37% of its surface area. A nested approach was applied with two gauging stations (covering 1.2 km² and 4.8 km²) built in September 2013 that took continuous measurements of rainfall, water and sediment yield. Average suspended sediment concentration (1503 mg L^?1) and the maximum peak (33 618 mg L^?1) were two orders of magnitude higher than those obtained in non‐burned terraced catchments of Mallorca. This factor may be related to changes in soils and the massive incorporation of ash into the suspended sediment flux during the most extreme post‐fire event; 50 mm of rainfall in 15 min, reaching an erosivity of 2886 MJ mm ha^?1 h^?1. Moreover, hysteretic counter‐clockwise loops were predominant (60%), probably related to the increased sensitivity of the landscape after wildfire perturbation. Though the study period was average in terms of total annual precipitation (even higher in intensities), minimal runoff (2%) and low sediment yield (6.3 t km^?2 y^?1) illustrated how the intrinsic characteristics of the catchment, i.e. calcareous soils, terraces and the application of post‐fire measures, limited the hydrosedimentary response despite the wildfire impact. Copyright © 2017 John Wiley & Sons, Ltd.     

Identifying Variable γ-ray Sources Through Radio Observations

We present preliminary results of a campaign undertaken with different radio interferometers to observe a sample of the most variable unidentified EGRET sources. We expect to detect which of the possible counterparts of the γ-ray sources (any of the radio emitters in the field) varies in time with similar timescales as the γ-ray variation. If the γ-rays are produced in a jet-like source, as we have modelled theoretically, synchrotron emission is also expected at radio wavelengths. Such radio emission should appear variable in time and correlated with the γ-ray variability.     

Predicting strain using forward modelling of restored cross-sections: Application to rollover anticlines over listric normal faults

A strategy to predict strain across geological structures, based on previous techniques, is modified and evaluated, and a practical application is shown. The technique, which employs cross-section restoration combined with kinematic forward modelling, consists of restoring a section, placing circular strain markers on different domains of the restoration, and forward modelling the restored section with strain markers until the present-day stage is reached. The restoration algorithm employed must be also used to forward model the structure. The ellipses in the forward modelled section allow determining the strain state of the structure and may indirectly predict orientation and distribution of minor structures such as small-scale fractures. The forward model may be frozen at different time steps (different growth stages) allowing prediction of both spatial and temporal variation of strain. The method is evaluated through its application to two stages of a clay experiment, that includes strain markers, and its geometry and deformation history are well documented, providing a strong control on the results. To demonstrate the method's potential, it is successfully applied to a depth-converted seismic profile in the Central Sumatra Basin, Indonesia. This allowed us to gain insight into the deformation undergone by rollover anticlines over listric normal faults.