Pavel Hejda

CONTROL VOLUME METHOD FOR THE DYNAMO PROBLEM IN THE SPHERE WITH THE FREE ROTATING INNER CORE

A model of thermally driven dynamo in the Boussinesq approximation in the spherical shell with the free rotating inner core is considered. To solve equations we use a new in dynamo modeling control volume technique (for details of this method for hydrodynamics see Patankar, 1980). The main advantage of this method over previous attempts to solve magnetohydrodynamics equations in the spherical grids is that no filtering of high harmonics in the pole regions is needed. We present the results of simulations for the self-consistent dynamo system evolution over the diffusion time and longer periods. Different ways of stabilizations of magnetohydrodynamics equations, when convective terms are of the same order (or larger) as conductive ones, are considered.

Association Between Extraterrestrial Phenomena And Weather Changes In The Northern Hemisphere In Winter

This paper includes a discussion of the validity of theobjections which are usuallyraised against the physical plausibility of the correlationsbetween extraterrestrialphenomena and changes in circulation in the lower atmosphere.The behaviour of the winterlower troposphere in the Northern Hemisphere was analysed bothon a month-to-month timescale and on a day-to-day time scale. The mechanisms which cansatisfactorily explainthe behaviour of the winter lower troposphere on these timescales have been described.The basic features of the results presented were explained bymeans of a mechanism basedon the propagation of planetary waves. Attention was focussedon studying the connectionsamong the changes in the pressure and temperature fields, thechanges in solar/geomagnetic activity and QBO phases by the method of composites. It hasbeen found that the compositeswithout considering QBO phases are similar to the QBO-eastpatterns under the highestactivities. Pressure deviations during QBO-west high solaractivity or low geomagneticactivity and temperature deviations during QBO-east/west lowgeomagnetic activity provedto be of negligible statistical significance.

Relation between Northern Hemisphere winter temperatures and geomagnetic or solar activity at different QBO phases

Abstract In our previous work a dominant coupling was shown between solar and geomagnetic activity, and surface air temperature of the QBO-west and east phases, respectively. The aim of the present study is to define ‘typical’ regions of positive and negative deviations from the long-term temperature average, to determine their magnitude and to find the conditions under which such a ‘typical’ distribution of temperature fields occurs.

Experimental determination of magnetic interactions within a system of synthetic haematite particles

Abstract A remanence-based technique, developed recently in magnetic recording media research with the aim of identifying the nature and intensity of interparticle magnetic-interaction fields, is reported. The technique is based on Wohlfarths linear relation linking isothermal remanent magnetization (IRM) acquisition and saturation IRM (SIRM) d.c. demagnetization with the field as a parameter, deviation from the linearity being attributed to many-body effects. Physical interpretation of an interaction-dependent parameter is discussed. The method is demonstrated on artificial samples of synthetic fine-grained haematite with various grain sizes and shapes and different initial magnetic configurations (i.e. the degree of spin-spin ordering). The observed negative character of interactions, yielding a net demagnetizing effect, is attributed to the specific arrangement of magnetic particles in the specimens and/or to a significant portion of superparamagnetic particles in some specimens.

COMPARISON OF SOLAR AND GEOMAGNETIC ACTIVITY EFFECTS ON THE NORTHERN HEMISPHERE WEATHER CHANGES

The changes of pressure and temperature fields in the winter lower troposphere observed in association with changes in solar and/or geomagnetic activity are compared. It is shown that the fact whether it was solar or geomagnetic activity was not so important as whether the levels of the two activities were high or low. The differences between the effects of solar/geomagnetic activity, however, are revealed, the pressure and temperature data being stratified according to the QBO phase. The relationship obtained are discussed from the viewpoint of mechanisms resting upon both the planetary wave propagation and the changes of atmospheric air currents in the global electric circuit.

THE EFFECT OF GEOMAGNETIC AND SOLAR ACTIVITY ON THE DISTRIBUTION OF CONTROLLING PRESSURE FORMATIONS IN THE NORTHERN HEMISPHERE IN WINTER

The distribution of controlling pressure formations, occurring in the Northern Hemisphere during the winters (January and February) of the years 1952 – 1996, has been analysed. It was found that the deepening of the Icelandic and Aleutian pressure lows is connected not only with a particular QBO phase and level of geomagnetic activity (Bochníček et al., 1999) but also with a particular level of solar activity.

Dynamo model with thermal convection and free-rotating inner core

Abstract The 2.5D approach is used to solve the dynamo model in the Boussinesq approximation. Thermal convection in a fast rotating spherical shell with a free-rotating inner core is considered. In all cases the inner core rotates slightly faster than the outer boundary of the shell. The presented dynamo model reverses regularly without any external impulse, and the generated magnetic field has the typical dipole structure at the surface. However, the dipole is aligned rather with the equatorial plane and thus the model can be applied to magnetic fields of Neptune and Uranus.

A possible relation between geomagnetic activity and winter air surface temperatures in Prague

SummaryA possible relation between the 10-day geomagnetic activity, solar activity and temperatures as measured at the meteorological station Prague - Klementinum in 1932–1975 was sought. It was found that: 1) ΣKp correlates with the surface temperature in Prague substantially better than Wolfs number R. 2) The correlation between ΣKp and the surface air temperature is not very close, but is significant at the level p=0.9! 3) If the QBO phase is taken into account, the correlations for the January and February decades of the years 1956–1975 improve as in [27] (van Loon, Labitzke).

Boundary conditions in the hydromagnetic dynamo problem

РезюмеВ урaвненuях в чaсmных nроuзво¶rt;ных, оnuсывaющuх мо¶rt;ельгu¶rt;ромaгнumного ¶rt;uнaмо, крaевое условuе ¶rt;ля векmорa мaгнumноŭ uн¶rt;укцuuВ вырaжaеmся в несmaн¶rt;aрmноŭ форме. Тaк кaк рaзложенuе в ря¶rt; сферuческuхгaрмонuческuх функцuŭ nозволяеm nерэŭmu к крaевым условuям ньюmоновского muna, эmоm меmо¶rt; сmaл сaмым рaсnросmрaненным сnособом рещенuя. Прuнцunuaльно оmлuчaющuŭся чuсленныŭ меmо¶rt; был оnублuковaн в [4, 5]. В nре¶rt;ложенноŭ рaбоmе оnuсывaеmся новыŭ меmо¶rt; рещенuя, uсхо¶rt;ящuŭ uз меmо¶rt;a Ивaновоŭ u нa nросmом nрuмере nрuво¶rt;umся срaвненuе всех mрех чuсленных меmо¶rt;ов.

Incompatible magnetic behaviour of fine-grained natural haematite samples prepared in similar ways

SummaryThe results of a magnetic study of two batches of sized natural haematite fractions (from Kadaň, Czech Republic) are reported. One of the sample batches was prepared by ultrasonic micro precision sieving in propanon (acetone), the other in ethanol (alcohol). Surprisingly, the magnetic behaviour of the ethanol-sieved fractions was much softer (e.g. Hcr ≈ ≈ 20 kA/m) as compared with the propanon-sieved fractions (Hcr > 200 kA/m). Thermomagnetic measurements suggest a maghemite portion is present in the material used for the preparation of the ethanol-sieved samples. Possible causes of this puzzling behaviour are discussed. However, no definite conclusion can be drawn on the basis of the data presently available.