Abstract.We have developed a 3D magnetohydrodynamics simulation code for applications in the solar convection zone and photosphere. The code includes a non-local and non-grey radiative transfer module and takes into account the effects of partial ionization. Its parallel design is based on domain decomposition, which makes it suited for use on parallel computers with distributed memory architecture. We give a description of the equations and numerical methods and present the results of the simulation of a solar plage region. Starting with a uniform vertical field of 200 G, the processes of flux expulsion and convective field amplification lead to a dichotomy of strong, mainly vertical fields embedded in the granular downflow network and weak, randomly oriented fields filling the hot granular upflows. The strong fields form a magnetic network with thin, sheetlike structures extending along downflow lanes and micropores with diameters of up to 1000 km which form occasionally at vertices where several downflow lanes merge. At the visible surface around optical depth unity, the strong field concentrations are in pressure balance with their weakly magnetized surroundings and reach field strengths of up to 2 kG, strongly exceeding the values corresponding to equipartition with the kinetic energy density of the convective motions. As a result of the channelling of radiation, small flux concentrations stand out as bright features, while the larger micropores appear dark in brightness maps owing to the suppression of the convective energy transport. The overall shape of the magnetic network changes slowly on a timescale much larger than the convective turnover time, while the magnetic flux is constantly redistributed within the network leading to continuous formation and dissolution of flux concentrations.

Based on comparative analyses of spatial and temporal patterns of high and mediumpotassic basaltic eruptions in the Central Mongolia and marine survey records of Sr isotopes, it is revealed that the start of the recent geodynamic stage in the Central Mongolia correlates with the starting point of its global manifestation, which gives an evidence of a close rela tionship between magmatic occurrences in the region under study and processes of global convergence. The magmatic occur rences are considered as representing the recent geodynamic evolution of the past 90 Ma with milestones of ~66, 40-37, ~32 and 17-15 Ma ago. Global changes, except those ~32 Ma ago, are shown in marine records of Sr isotopes. The Late Plesto cene -Holocene natural and climate setting is reconstructed from radiocarbon datings of various geological and paleobi ological objects. Changes of the natural environment and climate of the Northern hemisphere are plotted with account of strong magma eruptions, attacks of asteroids and meteorites, changes of lithological compositions of sedimentary complexes and species compositions of fauna at the given time interval.Key words: Cenozoic, Central Asia, geochronology, cyclicity, volcanism, paleoclimate. T h e 6 5 t h A n n i v e r s a r y o f t h e I n s t i t u t e o f t h e E a r t h ' s C r u s t , S B R Инcтитут земной коры CО PАН, Иpкутcк, РоccияАннотация: Приведены результаты исследований, выполненных в лаборатории изотопии и геохронологии и лабора тории кайнозоя ИЗК СО РАН в рамках проектов СО РАН: ИМП № 77 «Изучение закономерностей проявления опас ных природных процессов в исторически обозримом прошлом для разработки основ прогноза их поведения на бли жайшие десятилетия» (РК 01201282598) и Пр. VIII.69.1. «Факторы, определяющие изменение среды и климата Цен тральной Азии в кайнозое». На основе сравнительного анализа пространственновременного распределения высоко и умеренно калиевых базальтовых извержений в Центральной Монголии и морских записей изотопов Sr выявлено соответствие начала новейшего геодинамического этапа в Центральной Монголии точке отсчета его глобального выражения, свидетельствующее о тесной связи магматических событий региона с глобальными процессами конвер генции. Эти магматические события рассматриваются как представительные для новейшей геодинамической эволю ции литосферы за последние 90 млн лет, в ходе которой определена важнейшая роль рубежей ~66, 40-37, ~32 и 17- 81

No abstract

Results of a 3D MHD simulation of a sunspot with a photospheric size of about 20 Mm are presented. The simulation has been carried out with the MURaM code, which includes a realistic equation of state with partial ionization and radiative transfer along many ray directions. The largely relaxed state of the sunspot shows a division in a central dark umbral region with bright dots and a penumbra showing bright filaments of about 2 to 3 Mm length with central dark lanes. By a process similar to the formation of umbral dots, the penumbral filaments result from magneto-convection in the form of upflow plumes, which become elongated by the presence of an inclined magnetic field: the upflow is deflected in the outward direction while the magnetic field is weakened and becomes almost horizontal in the upper part of the plume near the level of optical depth unity. A dark lane forms owing to the piling up of matter near the cusp-shaped top of the rising plume that leads to an upward bulging of the surfaces of constant optical depth. The simulated penumbral structure corresponds well to the observationally inferred interlocking-comb structure of the magnetic field with Evershed outflows along dark-laned filaments with nearly horizontal magnetic field and overturning perpendicular ('twisting') motion, which are embedded in a background of stronger and less inclined field. Photospheric spectral lines are formed at the very top and somewhat above the upflow plumes, so that they do not fully sense the strong flow as well as the large field inclination and significant field strength reduction in the upper part of the plume structures.