Evolutionary Changes in the Configuration of the Magnetic Field of the Solar Corona in the Epoch of the Minimum

Geomagnetism and Aeronomy - The evolution of the magnetic configuration in the solar corona is studied. The curvature of the K-corona helmets obtained from an analytical approximation of the...     

Temporal Variations of the Magnetic Flux in the Solar Photosphere

The problem of the transport and transformation of magnetic fields from the generation zone to the photosphere is studied in this paper. For this purpose, the temporal variations of parameters of bipolar magnetic regions are analyzed based on the magnetic synoptic maps of the Wilcox Solar Observatory (WSO) for the declining phase of cycle 22. A 150-day modulation of the magnetic flux value in bipolar regions and a variation in their rotation velocity with a duration of 80–100 days have been found. Such variations in the parameters are interpreted as a result of action of supergiant and giant convection cells. The magnetic flux from the generation zone emerges through the local channels formed by the supergiant convection cells. From the level of 0.95 R_Sun, the flux is redistributed by giant cells, which form bipolar magnetic regions on the photosphere.     

Interhemispheric distinctions between the polar vortex positions in the winter stratosphere and mesosphere from measurements with a SABER instrument aboard the TIMED satellite

Distinctions between the longitudinal structures of circulation in the stratosphere and mesosphere/lower thermosphere of the Northern and Southern hemispheres are investigated on the basis of the temperature and geopotential distributions obtained with a SABER instrument (TIMED satellite) in the months of February and August in 2002–2005. The positions of the winter cyclone and polar vortex at stratospheric and mesospheric heights in 2002–2005 are compared to the climatic data over 1978–1998. At stratospheric heights, the mean position of the polar vortex’s center over several years changed insignificantly during the specified years (several degrees in latitude and longitude) in both the Southern and Northern hemispheres. At mesosphere/lower thermosphere heights, the polar vortex occupies the same position in the Southern Hemisphere each year during 2002–2005, and this position agrees with the estimates for 1996–1997. Parameters of stationary planetary waves with the zonal wave number 1 (SPW1) in the fields of temperature, geopotential, and wind are calculated from data on the temperature and geopotential. The height profiles of SPW1 amplitudes and phases calculated from the SABER instrument data for August in the Southern Hemisphere are in good agreement with the profiles of amplitudes and phases obtained from the direct wind measurements with HRDI and WINDII instruments. A strong interannual variability of SPW1 parameters is observed in the Northern Hemisphere. The calculation of the Eliassen-Palm flux and its divergence has shown that SPW1 penetrates into the mesosphere mainly from the stratosphere and slows down the zonal mean flux. However, in the Southern Hemisphere, there is a regular additional SPW1 source with the center at a height of about 65 km and a latitude of 55°S. Such a SPW1 source is, on average, absent in the Northern Hemisphere during 2002–2005; however, in some years (for example, in February 2004), its existence is possible.     

Manifestations in the Solar Corona of the Process of Magnetic-Field Generation

Geomagnetism and Aeronomy - The situation with the reliability of calculations of the magnetic field of the solar corona remains a topic of discussion. There is, in particular, the problem of...     

Formation Conditions and Energetics of Solar Nanoflares

The energy potential of solar nanoflares is estimated with a new approach proposed by the author. This approach is based on the drift mechanism for the formation of a dense loop structure in the magnetic field of a bipolar source. The densification process is assumed to proceed until the appearance of unmagnetized protons. These protons produce a current that heats the loop structure. The presence of bipolar sources is associated with local amplification of the background magnetic field by mesogranulation cells. The calculations conducted with the proposed model, which take into account observational data, yield a nanoflare energy range of 10²⁴–10²⁶ erg. The same estimates are obtained from the observed emission of nanoflare radiation. This fact is evidence, on the one hand, that the proposed model is adequate to the given process and, on the other hand, that there are no significant fluxes of the energy of this process as thermal conductivity and nonthermal particle beams. This situation is characterized by a maximum possible nanoflare energy release at a level of ≈10²⁷ erg during the mesogranule lifetime (≈10⁴ s), which yields an intensity of the energy flux of ≈10⁵ erg/s cm². This flux is insufficient to heat even the quiet regions of solar corona.     

Height-latitude structure of the vertical component of the migrating semidiurnal tide in the upper mesosphere and lower thermosphere region (80–100 km)

The height-latitude distributions of parameters of the vertical wind component of the semidiurnal tide were calculated for the mesosphere and lower thermosphere (MLT) region (80–100 km) on the basis of empirical height-latitude distributions of the monthly mean parameters of variations in the horizontal wind component of the migrating semidiurnal tide. The constructed distributions are compared with the results of a numerical modeling of the migrating semidiurnal tide with the aid of a model of global circulation in the middle and upper atmosphere, as well as with the parameters of semidiurnal temperature variations obtained from the data of satellite measurements. It is shown that different models yield the distributions of parameters of semidiurnal variations, which agree within the errors of their values. The presence of high-latitude regions of local maximal amplitudes is a specific feature of the distributions of parameters of semidiurnal variations in the vertical wind constructed in the course of this work. On the whole, at heights of about 90 km and higher, semidiurnal variations in the vertical wind exceed the prevailing vertical wind in amplitude.     

Geometric properties of the coronal neutral surface

The interrelation between the density inhomogeneity and the magnetic field configuration in the solar corona has been studied. The situation of consistency with the regular cellular magnetic field organization, established by the authors based on polarization data, and helmet-shaped coronal structures has been analyzed. Consistency was found when coronal helmets appeared as projections on the plane of the sky of dense layer folds. It turned out that a dense layer on a regularly deformed neutral surface on a scale of 60° generates coronal shapes typical of solar activity minimum epochs. Threby, a weighty argument for the Molodenskii hypothesis that a dense layer is formed on the neutral surface has been obtained and it has been determined that one can find the 3D geometry of the coronal neutral surface based on modeling the visible shape of coronal helmets. The study of this geometry based on the observed coronal structures in the epoch of minimum and low solar activity indicated that the neutral surface longitudinal deformation scale remains stable and the surface latitudinal amplitude at the corona base reaches 50°–70° latitudes and tends to increase with increasing solar activity. This amplitude decreases as a power function with a variable index close to ?1 with increasing distance from the Sun. In addition, a 10° small-scale deformation of the studied surface with a predominant latitudinal flexure direction has been revealed.     

Interhemispheric distinctions in wind-regime parameters in the polar mesosphere-lower thermosphere

The wind circulations in the mesosphere-lower thermosphere at polar latitudes of the Northern and Southern hemispheres are compared on the basis of long-term monthly-mean data on the prevailing zonal and meridional winds and on the parameters of diurnal and semidiurnal migrating tides obtained from the international network of radar stations. Comparison of the seasonal cycles and vertical profiles of the prevailing winds and tide parameters points to the existence of significant distinctions between the hemispheres. These distinctions are most clearly pronounced, first, in the prevailing meridional winds (for example, the annual mean winds in the polar regions have opposite directions in different hemispheres) and, second, the annual cycles of semidiurnal-tide amplitudes, as well as the character of changes in the tide phase with height, are fundamentally different for the Northern and Southern hemispheres. Along with these, significant distinctions are revealed in the prevailing zonal winds and in the diurnal-tide parameters.     

SOLAR ACTIVITY AS A RESULT OF TWO-WAVE MAGNETIC FLUX GENERATION

Solar activity has been studied by using the time series of the yearly mean Wolf sunspot numbers. It was shown that the long-term variation of solar activity could be interpreted both as a beat between the two wave magnetic flux with 21.5-yr and 19.3-yr periods and the epochs of low solar activity after the phase failure. This magnetic flux is likely to be generated by the torsional oscillations of the transition layer located at the bottom of the Sun's convection zone.The periodicities of solar cycles obtained allow us to predict the Sun's activity in the 21st century with high probability. In particular, cycle 23 is predicted to start in 1999 and its maximum to occur between mid-2005 and mid-2006, the Wolf number being in the interval 50–65.     

The polarization of the solar corona on March 29, 2006

The effect of the auroral ring on the polarization of the solar corona during the solar eclipse of March 29, 2006 is studied. The angle and degree of polarization for emission arising from the combination of two partially polarized components is calculated. The emission of each component is described in terms of the Stokes parameters, and the corresponding parameters added. The position angle and degree of polarization are found for all cases realized in observations of the polarized corona with polarizing filter positions of 0°, 60°, 120° and 0°, 45°, and 90°. These calculations indicate that singular polarization points (saddles with index ?1/2) arise at a distance of about 1R_⊙ from the limb. A model for the total emission of the corona is constructed, which is used to calculate deviations of the polarization plane from the tangential direction (with respect to the limb).