The mean curvature of the external equipotential surface and the vertical gravity gradient as functions of stokes's constants

Summary The mean curvature of the equipotential surface and the vertical gradient of gravity are expressed in terms of a development into a series of spherical harmonics [1, 2, 4], neglecting terms of the order of 10^–8. The curvature anomalies have been computed using the satellite data [3]. The symbols used are the same as in [5].Dedicated to 90th Birthday of Professor Frantiek Fiala     

Dynamic properties of the probe for measuring the temperature gradient

Summary The paper analyses the behaviour of a probe for direct measurements of temperature increase with depth in boreholes and derives transient characteristics of a gradient probe using the electrothermal analogy.     

Triaxiality of Halley's Comet

There are many aspects of observational evidence that cometary nuclei have irregular or nonspherical shape. The triaxial figure of the Halley's Comet nucleus is a well known fact. Therefore, the nucleus shape plays a significant role in consideration of the formation and evolution of comets and several attempts have been made to explain their nonsphericity. These studies were mainly based on the random-walk schemes for the aggregation processes. Although some results indeed lead to irregularities and deviation from sphericity, the spherical or irregular shape seem to be prevailing results. On the other hand the triaxial figure can be formed by the tidal and rotational forces. Thus, the assumption that the shape of the cometary nucleus due to some of these effects is in principle acceptable. In here assumed scenario already evolved cometary nucleus is situated as a satellite in the gravitation field of a planetary-like body. Since the rigidity of the nucleus is low, it may be easily transferred in the state of a synchronous satellite and in its shape could be imprinted the dynamical effects from this epoch. Here presented results indicate, that such a possibility should be seriously considered. The theory of this process is applied to the nucleus of comet Halley. It is shown, that the nucleus might be synchronously orbiting around a planetary-like hypothetical body with a period of 0.7 days. The minimal bulk tensile strength of the cometary material of about 10² N m^–2 is estimated.     

Electromagnetic induction in a half-space with a cylindrical inhomogeneity

Summary The problem of electromagnetic induction in a half-space with a cylindrical inhomogeneity is treated. Solutions for TE and TM polarization of the exciting electromagnetic field are given, which can be used for computing sounding and profiling curves. The anisotropy of the surface impedance is pointed out, as well as a whole series of other interesting properties of the magnetotelluric field in this model; some of them are also demonstrated on the computed theoretical curves.     

Complex system approach to interpretation of monitoring time series: two case histories from NW Bohemia

Ever wider implementation of information technologies is flooding us by monitoring data. To an efficient risk management, those data have to be processed and assessed in the same rate as they are recorded and transported. Paper demonstrates some methods dealing with intrinsic, nonlinear dynamics of slope system for computerized safety assessment of monitoring time series, their modeling and early warning launching. Analysis and modeling of phase changes – i.e. specific transient states between different developmental stages of dynamics of unstable slope systems, enabled to fix new types of precursors for rock fall warning and to enhance time prediction of rock fall occurrence. Mathematically well based, novel numerical and topological methods from the toolbox of complex system theory were successfully implemented to that challenge. Their pattern-recognition ability, i.e., diagnostic sensitivity, and more realistic results of modeling of time series relevant patterns have reached beyond ranges of regularly used—both the idea- and the data-driven—methods. Moreover, results yielded by phase space analyses are in good agreement with the ones by numerical fractal analyses. Obtained results have strengthened the primary, mainly theoretically based hypothesis; the dynamics of an unstable rock slope has to be considered as behavior of nonlinear, dissipative, non-equilibrium, self-organizing complex system. Correspondingly to the theoretical assumptions, two qualitatively different types of slope system dynamics—near to equilibrium and far from equilibrium states, were identified. All field monitoring data used originated in practice of highly automated, integrated IT system of monitoring assessment, and management of rock fall hazard at sandstone rock walls in the NW Bohemia.     

CUTLASS Finland radar observations of the ionospheric signatures of flux transfer events and the resulting plasma flows

The CUTLASS Finland radar has been run in a two-beam special scan mode, which offered excellent temporal and spatial information on the flows in the high-latitude ionosphere. A detailed study of one day of this data revealed a convection reversal boundary (CRB) in the CUTLASS field of view (f.o.v) on the dayside, the direction of plasma flow either side of the boundary being typical of a dawn-cell convection pattern. Poleward of the CRB a number of pulsed transients are observed, seemingly moving away from the radar. These transients are identified here as the ionospheric signature of flux transfer events (FTEs). Equatorward of the CRB continuous backscatter was observed, believed to be due to the return flow on closed field lines. The two-beam scan offered a new and innovative opportunity to determine the size and velocity of the ionospheric signatures associated with flux transfer events and the related plasma flow pattern. The transient signature was found to have an azimuthal extent of 1900 ± 900 km and an poleward extent of 250 km. The motion of the transient features was in a predominantly westward azimuthal direction, at a velocity of 7.5 ± 3 km.     

Large-scale distribution of magnetic fields,green corona and prominences during an extended activity cycle

The interrelations of the latitudinal distribution of the coronal green emission maxima, maximal numbers and areas of prominences, magnetic fields, sunspots, and polar faculae in the 20th and 21st sunspot cycles have been investigated. It is again demonstrated how the behaviour of all studied data depends on their heliographic latitude. In the polar zone, well separated from the equatorial we observe following polarity magnetic fields transported only polewards, while the equatorial zone is occupied mostly by leading polarity fields, developed there, moving equatorwards, and crossing the equator to the other hemisphere with the new cycle during the minimum of sunspot activity.This magnetic field distribution is well emphasized by the places of maximal occurrence of prominences and by the distribution of coronal green emission maxima which also differ in dependence on latitude.The question of identifying the first and last evolutionary stages of an extended cycle of activity is discussed and the existence of a magnetic activity cycle lasting 15–17 years is suggested.     

Secular variations in the curvature of equipotential surfaces and directions of verticals due to geodynamic phenomena

Summary Formulae and numerical estimates are given for the non-periodical variations in the curvature of equipotential surfaces, horizontal forces and directions of the vertical, caused by the decrease in the second zonal geopotential harmonic, by the decrease in the angular velocity of the Earth's rotation and by secular polar motion.

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