Strong earthquakes associated with high amplitude daily geomagnetic variations

In this work, we attempt to quantify forces that result from the interaction between the induced Sq-variation currents in the Earth’s lithosphere and the regional Earth’s magnetic field, in order to assess its influence on the tectonic stress field and on seismic activity. The study area is the Sinai Peninsula, a seismically active region where both seismic and magnetic data are available. We show that both short-term and long-term magnetic changes correlate with the seismic activity extending to this area in other previous studies. We also analyze a set of large earthquakes and magnetic data from observatories around the world to deduce a relationship between earthquake magnitude and maximum distance up to which precursory variations of the magnetic field are observed.     

The influence of a local heat source on a borehole temperature curve

Summary The paper describes a simple mathematical method of estimating the location and water yield of an underground water source by measuring the temperature in a borehole.     

Tidal and rotational distortions in figures of Pluto and Charon

The supposition is, the tidal and rotational distortions should be fully responsible for the Pluto's and Charon's figure parameters. The mean polar and equatorial flattenings have been estimated about 10^–3, the second sectorial Stokes parameters about 9 × 10^–5, the differences between equatorial principal moments of inertia about 6 × 10³⁰ kg m² (Pluto) and 2 × 10²⁹ kg m² (Charon).     

Interferometric evidence for the observation of ground backscatter originating behind the CUTLASS coherent HF radars

Interferometric techniques allow the Super-DARN coherent HF radars to determine the elevation angles of returned backscatter, giving information on the altitude of the scatter volume, in the case of ionospheric backscatter, or the reflection altitude, in the case of ground backscatter. Assumptions have to be made in the determination of elevation angles, including the direction of arrival, or azimuth, of the returned signals, usually taken to be the forward look-direction (north) of the radars, specified by the phasing of the antenna arrays. It is shown that this assumption is not always valid in the case of ground backscatter, and that significant returns can be detected from the backward look-direction of the radars. The response of the interferometer to backscatter from behind the radar is modelled and compared with observations. It is found that ground backscatter from a field-of-view that is the mirror image of the forward-looking field-of-view is a common feature of the observations, and this interpretation successfully explains several anomalies in the received backscatter.     

Substorm correlated absorption on a 3200 km trans-auroral HF propagation path

A high-frequency transmitter located at Clyde River, NWT, Canada, and a receiver located near Boston, USA, provide a 3200 km trans-auroral, near-meridional propagation path over which the propagation characteristics have been measured. Out of the fourteen frequencies in the HF band sampled every hour for the duration of the experimental campaign (16 January-8 February 1989), the signal level measurements of 6.800 MHz transmissions were selected in order to determine the extent and occurrence of auroral absorption. The median level of auroral absorption along the path is found to increase with geomagnetic activity, quantified by the index K_p, with the increase being greater in the post-midnight sector than in the pre-midnight sector. This asymmetric behaviour is attributed to the precipitation of high energy electrons into the midnight and morning sector auroral D region. The measured diurnal variation in the median level of absorption is consistent with previous models describing the extent and magnitude of auroral absorption and electron precipitation. Individual substorms, identified from geosynchronous satellite data, are found to cause short-lived absorption events in the HF signal level of \sim30 dB at 6.800 MHz. The occurrence of substorm correlated auroral absorption events is confined to the midnight and morning sectors, consistent with the location of the electron precipitation. The magnitude of absorption is related to the magnetotail stress during the substorm growth phase and the magnetotail relaxation during the substorm expansion phase onset. The absorption magnitude and the occurrence of substorms during the period of the campaign increase at times of high K_p, leading to an increase in median auroral absorption during disturbed periods.     

The tidal force function and tidal torques

Summary The tidal force function of the two-body system is defined. It is formed by two parts, reflecting the direct, as well as, the indirect tidal effects. It enables deriving the tidal torques due to both the tidal effects independently of density distributions. The Stokes parameters of both bodies, the Love numbers and phase lag angles are sufficient for the solution.     

Expanding earth hypothesis and the Earth's gravitational potential energy

Summary The gravitational potential energy of the actual Earth has now been estimated at –2·485 × 10³² J. Three density models of the hypothetical Earth before the hypothetical expansion have been adopted for estimating the internal energy necessary for expanding: 7 × 10³¹ J. No dynamical evidence exists for the origin of this energy in the last 450 × 10⁶ y. The hypothetical increase in the Earth's mass M of about 0·4 M since 2 × 10⁸ y B.P. required for a dynamical balance has also no support in the paleodynamics of the Earth-Moon-Sun system since the M. Ordovician.Dedicated to the Memory of K. P     

Evolution of cultural landscape in the Northern Bohemian Coal mining Region on the background of socio-economic transformations

The NW part of Bohemia belongs to the most intensely exploited territories, both from the functional and ecological standpoints. In a sense, it is an open air laborarory, offering many topics to be discussed, researched and solved. The author strives to give a sociogeographical outline of the current state, with respect to the landscape evolution. This picture focuses on historical developments in recent decades as well.Rapid economic expansion of the examined territory started in the second half of the 19th century, having followed the pre-industrial period. A similar abrupt change of social and economic structures occurred 100 years later, in the post-war period. It was the growth of open-cast brown coal mining and corresponding activities (especially coal-fired plants) which resulted in large scale environmental disturbances, affected the settlement system and harmed the health of the population. Thus, further economic and ecological development should be based on a reclamation of the previous state.