Minicomets in the Solar system and in the Earth’s atmosphere and related phenomena

We consider the history of discovery and justify the existence in the Solar system of a new class of bodies—minicomets, i.e., bodies of cometary nature and composition but of low mass. Two classes of minicomets are distinguished: icy ones similar to the Tunguska meteorite, and snow ones, which break up at high altitudes.     

Alfvén Reflection and Reverberation in the Solar Atmosphere

Magneto-atmospheres with Alfvén speed [a] that increases monotonically with height are often used to model the solar atmosphere, at least out to several solar radii. A?common example involves a uniform vertical or inclined magnetic field in an isothermal atmosphere, for which the Alfvén speed is exponential. We address the issue of internal reflection in such atmospheres, both for time-harmonic and for transient waves. It is found that a mathematical boundary condition may be devised that corresponds to perfect absorption at infinity, and, using this, that many atmospheres where a(x) is analytic and unbounded present no internal reflection of harmonic Alfvén waves. However, except for certain special cases, such solutions are accompanied by a wake, which may be thought of as a kind of reflection. For the initial-value problem where a harmonic source is suddenly switched on (and optionally off), there is also an associated transient that normally decays with time as $\mathcal{O}(t^{-1})$ or $\mathcal{O}(t^{-1}\ln t)$ , depending on the phase of the driver. Unlike the steady-state harmonic solutions, the transient does reflect weakly. Alfvén waves in the solar corona driven by a finite-duration train of p-modes are expected to leave such transients.     

Information from the Kinematics of F and G Stars in the Solar Neighborhood

We have calculated the orbital parameters for 90 stars in Chen et al. and updated the kinematic data for stars in Edvardsson et al. by using the accurate Hipparcos parallaxes and proper motions, and recalculated the \\\\\\\\\\\\-element abundances in Edvardsson et al. in a way consistent with Chen et al. The two sets of data are combined in a study of stellar populations and characteristics of F & G stars in the solar neighborhood. We confirm the result of Chen et al. that a distinguishable group of stars may belong to the thick disk rather than the thin disk. The ages for the stars are determined using the theoretical isochrones of VandenBerg et al. The age-metallicity relation is investigated for different subgroups according to distance from the sun and galactic orbital parameters. It is found that a mixing of stars with different orbital parameters significantly affect the age-metallicity relation for the disk. Stars with orbits confined to the solar circle all have metallicities [Fe/H] > -0.3 irresp     

On the Positronium Continuum and 0.511 MeV Line in Solar Flares

We have studied the influence of the density of the annihilation region on the positronium continuum. A relation between the ratio 3γ/2γ and the densityis explicitly given, with which one can derive directly from the observed 3γ/2γ the density where the annihilation occurs. A unique solution may be found from the observed width of the 0.511MeV line. We applied the method to three flares observed by GRS/SMM. It is shown that due to the measuring uncertainties in the 0.511 MeV line width, we cannot distinguish a chromospheric source from a coronal source, though both accurately localized. To improve the measuring accuracy of the 0.511MeV line and the ratio 3γ/2γ will be an important step for a better understanding of the annihilation process in solar flares.     

The Solar Cycle 23?�C?24 Minimum. A Benchmark in Solar Variability and Effects in the Heliosphere

Given the numerous ground-based and space-based experiments producing the database for the Cycle 23??C?24 Minimum epoch from September 2008 to May 2009, we have an extraordinary opportunity to understand its effects throughout the heliosphere. We use solar radiative output in this period to obtain minimum values for three measures of the Sun??s radiative output: the total solar irradiance, the Mg ii index, and the 10.7 cm solar radio flux. The derived values are included in the research summaries as a means to exchange ideas and data for this long minimum in solar activity.     

Which are the dwarfs in the Solar System?

The International Astronomical Union recently adopted a new definition of planets in our Solar System. A new category of objects was introduced: a “dwarf planet.” This is “a celestial body that has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape and has not cleared the neighborhood around its orbit.” In a footnote, the resolution says: “An IAU process will be established to assign borderline objects into either “dwarf planet” and other categories." In order to contribute to the establishment of this classification procedure, we analyze the problem of the minimum mass required to become a “dwarf planet,” either from the theoretical and the observational perspective. We propose classification criteria for “dwarf planets” based on the available information on the shape and size of asteroids and TNOs, principally the direct or indirect estimates of the diameter and the estimate of the shapes from the lightcurves. We compile the available observational data on large asteroids and TNOs. According to our classification scheme there is only one rocky “dwarf planet” and 12 icy “dwarf planets” among the already discovered objects.     

Energy Buildup,Flux Confinement and Helicity Accumulation in the Solar Corona

Starting from a dipole field and a given distribution of footpoint displace- ment of field lines on the photosphere,we find axisymmetric,force-free field solutions in spherical coordinates that have the same distribution of normal field on the photo- sphere and magnetic topology as the dipole field.A photospheric shear is introduced in the azimuthal direction in a region that strides across the equator and ends at latitude γ_s.The footpoint displacement has a sine distribution in latitude and a peak amplitude of (?)_m.The magnetic energy E,azimuthal flux F_(?),and magnetic helicity H_T in the solar corona are then calculated for each force-free field solution.It is found that for a given shear region range γ_s,all of the three quantities increase monotoni- cally with increasing (?)_m.In particular,both F_(?) and H_T have a linear dependence on (?)m.When (?)_m reaches a certain critical value (?)_(mc),the force-free field loses equilib- rium,leading to a partial opening of the field and the appearance of a current sheet in the equatorial plane.At this point,E,F_(?)and H_T reach their maximum values, E_c,F_((?)c) and H_(Tc).E_c increases,and F_((?)c) and H_(Tc)decrease with decreasing λ_s.It is found that E_c is always smaller than the open field energy,in agreement with the Aly conjecture.Of the three critical parameters,E_c has the weakest dependence on λ_s.Therefore,if one is interested in the transition of a magnetic configuration from a stable state to a dynamic one,the magnetic energy is probably the most appropriate marker of the transition.     

Cross Helicity and Turbulent Magnetic Diffusivity in the Solar Convection Zone

In a density-stratified turbulent medium, the cross helicity 〈u′⋅B′〉 is considered as a result of the interaction of the velocity fluctuations and a large-scale magnetic field. By means of a quasilinear theory and by numerical simulations, we find the cross helicity and the mean vertical magnetic field to be anti-correlated. In the high-conductivity limit the ratio of the helicity and the mean magnetic field equals the ratio of the magnetic eddy diffusivity and the (known) density scale height. The result can be used to predict that the cross helicity at the solar surface will exceed the value of 1 gauss km s⁻¹. Its sign is anti-correlated to that of the radial mean magnetic field. Alternatively, we can use our result to determine the value of the turbulent magnetic diffusivity from observations of the cross helicity.     

Combined Analysis of Solar Neutrino and Solar Irradiance Data: Further Evidence for Variability of the Solar Neutrino Flux and Its Implications Concerning the Solar Core

A search for any particular feature in any single solar neutrino dataset is unlikely to establish variability of the solar neutrino flux since the count rates are very low. It helps to combine datasets, and in this article we examine data from both the Homestake and GALLEX experiments. These show evidence of modulation with a frequency of 11.85 year⁻¹, which could be indicative of rotational modulation originating in the solar core. We find that precisely the same frequency is prominent in power spectrum analyses of the ACRIM irradiance data for both the Homestake and GALLEX time intervals. These results suggest that the solar core is inhomogeneous and rotates with a sidereal frequency of 12.85 year⁻¹. From Monte Carlo calculations, it is found that the probability that the neutrino data would by chance match the irradiance data in this way is only 2 parts in 10 000. This rotation rate is significantly lower than that of the inner radiative zone (13.97 year⁻¹) as recently inferred from analysis of Super-Kamiokande data, suggesting that there may be a second, inner tachocline separating the core from the radiative zone. This opens up the possibility that there may be an inner dynamo that could produce a strong internal magnetic field and a second solar cycle.     

Solar Magnetism and the Activity Telescope at HSOS

A new solar telescope system is described, which has been operating at Huairou Solar Observing Station (HSOS), National Astronomical Observatories, Chinese Academy of Sciences (CAS), since the end of 2005. This instrument, the Solar Magnetism and Activity Telescope (SMAT), comprises two telescopes which respectively make measurements of full solar disk vector magnetic field and Hα observation. The core of the full solar disk video vector magnetograph is a birefringent filter with 0.1  bandpass, installed in the tele-centric optical system of the telescope. We present some preliminary observational results of the full solar disk vector magnetograms and Hα filtergrams obtained with this telescope system.     

Why Do Temperature and Velocity Have Different Relationships in the Solar Wind and in Interplanetary Coronal Mass Ejections?

In-situ observations of the solar wind (SW) show temperature increasing with the wind speed, whereas such a dependence is not observed in interplanetary coronal mass ejections (ICMEs). The aim of this paper is to understand the main origin of this correlation in the SW and its absence in ICMEs. For that purpose both the internal-energy and momentum equations are solved analytically with various approximations. The internal-energy equation does not provide a strong link between temperature and velocity, but the momentum equation does. Indeed, the observed correlation in the open magnetic-field configuration of the SW is the result of its acceleration and heating close to the Sun. In contrast, the magnetic configuration of ICMEs is closed, and moreover the momentum equation is dominated by magnetic forces. This implies no significant correlation between temperature and velocity, as observed.     

The Relation between the Amplitude and the Period of Solar Cycles

The maximum amplitudes of solar activity cycles are found to be well anti-correlated (r = -0.72) with the newly defined solar cycle lengths three cycles before (at lag -3) in 13-month running mean sunspot numbers during the past 190 years. This result could be used for predicting the maximum sunspot numbers. The amplitudes of Cycles 24 and 25 are estimated to be 149.5±27.6 and 144.3±27.6, respectively.     

Magnetic Activity and the Enhanced 5303 Å Emission in Solar Active Regions

Analysis of the intensity maps of Fexiv emission at =5303 Å obtained from the observations of ground-based coronagraphs during the sunspot minimum period 1985 and 1986 shows the persistent presence of localized strong emissions. Typical emission intensities associated with the active regions were found to be about 5 to 20 times stronger than the unperturbed corona. Using Stanford magnetograms we identified strong magnetic field gradients in those active regions, with a minimum threshold gradient of 3 × 10^–5 G km^–1, associated with such strong emissions. From our sample we infer that the flux emergence within or in the vicinity of a persistent active region seems to play an important role in the activity associated with the enhancement in 5303 Å emission.     

Algorithm Design and Test of the Solar Guide Telescope

The Solar Guide Telescope (SGT), an important solar attitude sensor of the SST (Space Solar Telescope, a space solar observing instrument being developed in China), can accurately produce pointing error signals of the SST for attitude control at high speed. We analyze in detail the error algorithm of the heliocentric coordinates and the edge judging of solar images. The measuring accuracy of ±0.5 arcsec of the SGT is verified by experiments on the tracking of the Sun and by testing a sun simulator. Some factors causing the pointing errors are examined.     

Coronal Holes and Solar Wind High-Speed Streams: I. Forecasting the Solar Wind Parameters

We analyze the relationship between the coronal hole (CH) area/position and physical characteristics of the associated corotating high-speed stream (HSS) in the solar wind at 1 AU. For the analysis we utilize the data in the period DOY 25 – 125 of 2005, characterized by a very low coronal mass ejection (CME) activity. Distinct correlations between the daily averaged CH parameters and the solar wind characteristics are found, which allows us to forecast the solar wind velocity v, proton temperature T, proton density n, and magnetic field strength B, several days in advance in periods of low CME activity. The forecast is based on monitoring fractional areas A, covered by CHs in the meridional slices embracing the central meridian distance ranges [−40°,−20°], [−10°,10°], and [20°,40°]. On average, the peaks in the daily values of n, B, T, and v appear delayed by 1, 2, 3, and 4 days, respectively, after the area A attains its maximum in the central-meridian slice. The peak values of the solar wind parameters are correlated to the peak values of A, which provides also forecasting of the peak values of n, B, T, and v. The most accurate prediction can be obtained for the solar wind velocity, for which the average relative difference between the calculated and the observed peak values amounts to %. The forecast reliability is somewhat lower in the case of T, B, and n ( , 30, and 40%, respectively). The space weather implications are discussed, including the perspectives for advancing the real-time calculation of the Sun – Earth transit times of coronal mass ejections and interplanetary shocks, by including more realistic real-time estimates of the solar wind characteristics.     

Changes in Quasi-periodic Variations of Solar Photospheric Fields: Precursor to the Deep Solar Minimum in Cycle 23?

Possible precursor signatures in the quasi-periodic variations of solar photospheric fields were investigated in the build-up to one of the deepest solar minima experienced in the past 100 years. This unusual and deep solar minimum occurred between Solar Cycles 23 and 24. We used both wavelet and Fourier analysis to study the changes in the quasi-periodic variations of solar photospheric fields. Photospheric fields were derived using ground-based synoptic magnetograms spanning the period 1975.14 to 2009.86 and covering Solar Cycles 21, 22, and 23. A hemispheric asymmetry in the periodicities of the photospheric fields was seen only at latitudes above ±?45^° when the data were divided into two parts based on a wavelet analysis: one prior to 1996 and the other after 1996. Furthermore, the hemispheric asymmetry was observed to be confined to the latitude range of 45^° to 60^°. This can be attributed to the variations in polar surges that primarily depend on both the emergence of surface magnetic flux and varying solar-surface flows. The observed asymmetry along with the fact that both solar fields above ±?45^° and micro-turbulence levels in the inner-heliosphere have been decreasing since the early- to mid-nineties (Janardhan et al. in Geophys. Res. Lett. 382, 20108, 2011) suggest that around this time active changes occurred in the solar dynamo that governs the underlying basic processes in the Sun. These changes in turn probably initiated the build-up to the very deep solar minimum at the end of Cycle 23. The decline in fields above ±?45^°, for well over a solar cycle, would imply that weak polar fields have been generated in the past two successive solar cycles, viz. Cycles 22 and 23. A continuation of this declining trend beyond 22 years, if it occurs, will have serious implications for our current understanding of the solar dynamo.