Initial backscatter occurrence statistics from the CUTLASS HF radars

A statistical study of the occurrence of ground and ionospheric backscatter within the fields-of-view of the CUTLASS HF radars, at an operating frequency of 10 MHz, during the first 20 months of operation has been undertaken. The diurnal variation of the occurrence of backscatter and the range at which such backscatter is observed is found to be highly dependent on seasonal changes of the ionospheric electron density in both the E and F region, determined from ionosonde observations. In general, ionospheric backscatter is observed at far ranges during the local day in winter months and at near ranges during the local night in summer months. The Iceland radar observes more near-range E region backscatter than the Finland radar as a consequence of its more zonal look-direction. The dependence of the occurrence of backscatter on geomagnetic activity and radar operating frequency are also investigated. The occurrence of ground and ionospheric backscatter is discussed in terms of HF propagation modes and ionospheric electron densities as well as geophysical processes. A brief assessment of the possible impact of solar cycle variations on the observations is made and frequency management is discussed. Such a study, with its focus on the instrumental aspect of backscatter occurrence, is essential for a full interpretation of HF coherent radar observations.     

On the origin of the fourth zonal geopotential harmonic

Summary It has been proved that the fourth geopotential (Stokes) parameter J₄ of the actual Earth can be explained by its long-term rotational distortions. However, this is not the case of the sixth zonal prameter J₆; its origin should be explained geophysically in another way.Dedicated to the Memory of Professor Karel P     

Gravitational potential energy of terrestrial planets

Summary The gravitational potential energies of Mercury, Venus and Mars have been computed on the basis of density models and compared to that of the Earth. It has been stated that the specific potential energy per unit mass is very close as regards the pair Earth and Venus, as well as the pair Mercury and Mars.Dedicated to the Memory of K. P     

The global and local correlation between the Venus gravity field and its topography

The correlation between the undulations of the equipotential and topography surface of Venus have been investigated over 16 meridional sections as well as, in the global scale. The correlation is, in general high. However, the figure parameters of the ellipsoids best fitting the surface in question differ significantly. The global features like figures of the best-fitting ellipsoids are mutually strange.     

Multi‐scale assessment of overflow‐driven lateral connectivity in floodplain and backwater channels using LiDAR imagery

Overflow‐driven lateral connectivity significantly influences the spatial distribution and diversity of floodplain habitats and biota. Proper understanding of lateral connectivity in floodplain and backwater channels is therefore critical for assessment of river quality and for targeting management or restoration actions. In this study, we present a methodological framework for spatial and temporal assessments of overflow‐driven lateral connectivity at two spatial scales: bypass reach and backwater channel. Firstly, we compute the relative elevations, as well as overflow discharge, duration, and frequency using a simple, raster‐based method that uses a LiDAR digital elevation model (DEM), rating curves, and streamflow time series. Subsequently, we analyse the accuracy of this approach with respect to the accuracy of a DEM and evaluate its further applications. Altogether, four 10‐km‐long bypass reaches and 11 backwater channels are analysed, located along the Rhône River corridor in France. The results proved the precision of the method to be affected by the LiDAR DEM accuracy, which was on average more precise in a typically homogeneous floodplain setting rather than for backwater channel plugs with pronounced topographic complexity and usually riparian forest canopy. Amongst the four studied reaches, Brégnier Cordon proved to have the greatest flooding dynamics, followed by Belley and Chautagne. The hydrological connectivity pattern of Pierre Bénite differed significantly. Three longitudinal patterns of hydrological connectivity of backwater channels displayed stepwise advancement of the water. The presented results can be used to assess ecological potential of floodplain habitats and their historic and prospective evolution through time. Copyright © 2014 John Wiley & Sons, Ltd.     

An assessment of the length and variability of Mercury's magnetotail

We employ Mariner 10 measurements of the interplanetary magnetic field in the vicinity of Mercury to estimate the rate of magnetic reconnection between the interplanetary magnetic field and the Hermean magnetosphere. We derive a time-series of the open magnetic flux in Mercury's magnetosphere, from which we can deduce the length of the magnetotail. The length of the magnetotail is shown to be highly variable, with open field lines stretching between 15R_H and 850R_H downstream of the planet (median 150R_H). Scaling laws allow the tail length at perihelion to be deduced from the aphelion Mariner 10 observations.     

Cosmic Rays and Solar Coronal Emissions: Cross-Correlations of the Time Series

The cosmic-ray (CR) time series were compared with the green 530.3 nm coronal emission line intensity over the period 1951–2003. There is a clear asymmetry in the cross-correlation between the cosmic rays and green emission corona for the even- and odd-numbered solar cycles, where a time lag is ranging between 0 and 380 days. While over the period 1954–1964 and 1978–1985 the time lag is above 200 days, over the period 1965–1976 and 1986–1995 the time lag is below 130 days. A possible reason for the lag asymmetry is discussed. The cross-correlations between the cosmic rays and Wolf sunspot number over the period 1951–2003 is also presented.     

Stark Broadening Data for Stellar Plasma Research

Results of an effort to provide to astrophysicists and physicists a set of Stark broadening parameters that is as complete as possible are presented. Such parameters are needed for stellar opacity calculations, stellar atmosphere modelling, abundance determinations, and diagnostics of various plasmas in astrophysics, physics, and plasma technology. The Stark broadening was treated using a semiclassical perturbation and modified semiempirical approaches.