István Lemperger

GYROSURFING ACCELERATION OF IONS IN FRONT OF EARTH's QUASI-PARALLEL BOW SHOCK

It is well known that shocks in space plasmas can accelerate particles to high energies. However, many details of the shock acceleration mechanism are still unknown. A critical element of shock acceleration is the injection problem; i.e., the presence of the so called seed particle population that is needed for the acceleration to work efficiently. In our case study, we present for the first time observational evidence of gyroresonant surfing acceleration in front of Earths quasi-parallel bow shock resulting in the appearance of the long-suspected seed particle population. For our analysis, we use simultaneous multi-spacecraft measurements provided by the Cluster spacecraft ion (CIS), magnetic (FGM), and electric field and wave instrument (EFW) during a time period of large inter-spacecraft separation distance. The spacecraft were moving toward the bow shock and were situated in the foreshock region. The results show that the gyroresonance surfing acceleration takes place as a consequence of interaction between circularly polarized monochromatic (or quasi-monochromatic) transversal electromagnetic plasma waves and short large amplitude magnetic structures (SLAMSs). The magnetic mirror force of the SLAMS provides the resonant conditions for the ions trapped by the waves and results in the acceleration of ions. Since wave packets with circular polarization and different kinds of magnetic structures are very commonly observed in front of Earths quasi-parallel bow shock, the gyroresonant surfing acceleration proves to be an important particle injection mechanism. We also show that seed ions are accelerated directly from the solar wind ion population.

Increasing the effectiveness of electrical resistivity tomography using γ11n configurations

A new array type, the γ11n arrays are introduced in this paper, in which the sequence of the current(C) and potential (P) electrodes is CPCP and the distance between the last two electrodes is n times the distance between the first two ones and that of the second and third one. These arrays are called quasi null arrays because they are – according to their array and behaviour – between the traditional and null arrays. It is shown by numerical modelling that in detection of small-effect inhomogeneities these configurations may be more effective than the traditional ones including the optimised Stummer configuration. Certain γ11n configurations – especially the γ112, γ113 and γ114 – produced better results both in horizontal and vertical resolution investigations. On the basis of the numerical studies, the γ11n configurations seem to be very promising in problems where the anomalies are similar to the numerically investigated ones, that is they can detect and characterise, for example,tunnels, caves, cables, tubes, abandoned riverbeds or discontinuity in a clay layer with greater efficacy than those of the traditional configurations. γ11n measurements need less data than traditional configurations therefore also the time demand of electrical resistivity tomography (ERT) measurements can be shortened by their use.

Pricking Probe as a Complementary Technique in Archeological Prospecting

We present an original geophysical method, the so-called pricking probe, and demonstrate its usefulness in an archaeological prospecting study. By using this technique, we easily found in the subsurface the remnants of a Paleochristian sepulchral chapel, in spite of dense undergrowth. Later, in the same, already mopped-up area we carried out detailed and systematic pricking probe measurements, and also geoelectric, magnetic and georadar mappings. As we found in the given field experiment, the pricking probe technique is competitive to other methods, considering both its imaging and economic properties. It proved to be the first-second most powerful method. The main advantages of the pricking probe method are as follows. 1. its field procedure and data processing are simple, cheap and quick; 2. the method can be applied even among the most unfavourable field conditions (bad weather, extreme topography, dense undergrowth, etc.), 3. it is nature-friendly (the area has not to be mopped-out), 4. it is effective. Moreover, it provides complementary information to the geoelectric and georadar maps. On the basis of our experiments we recommend a combined application of the pricking probe technique and of one of the relevant standard geophysical method.