Polarization of Jupiter: Semiannual variations in the north-south asymmetry

The analysis of the previous (1981–1999) and recent (2000–2007) observations of Jupiter has confirmed the semiannual variations in the north-south asymmetry of polarized radiation in the polar regions of the planet. The processes of polar aerosol formation are modulated by the position of the planet relative to the solar equator.     

Long-term variations in north-south asymmetry of solar activity

We present a new set of data on relative sunspot number (total, northern hemisphere, and southern hemisphere), taken for the 37-yr period 1947 to 1983; this constitutes a particularly coherent and consistent set of data, taken by the same observer (Hisako Koyama) using the same observing instrument. These data are combined with earlier data (White and Trotter, 1977) on the variation of sunspot areas for both solar hemispheres from 1874 to 1971. The combined data, covering 110 years and 10 solar cycles, are examined for periodicity in solar activity north-south asymmetry. We show that, in general, northern hemisphere activity, displayed as either An/(An + As) or Rn/(Rn + Rs), peaks about two years after sunspot minimum. This peak is greater during even cycles, pointing to a 22-yr periodicity in north-south asymmetry in solar activity, suggesting that the asymmetry is related to the 22-yr solar magnetic cycle. We demonstrate that the largest and most protracted period of northern-hemisphere activity excess in the last 110 years has occurred from 1959 to 1970; we show that there is a strong correlation between northern activity excess and a cosmic-ray density gradient perpendicular to the ecliptic plane, pointing southward, which is evident in cosmic-ray diurnal variation data from the Embudo underground cosmic-ray telescope.     

The north-south asymmetry of sunspot areas during solar cycle 22

We have analyzed the asymmetry of sunspot areas during the current solar cycle 22, finding that it has been statistically significant and that the shape of the underlying trend within the full asymmetry time series (1874–1993) indicates that the dominance of solar activity has started to shift, during the current cycle, from the northern hemisphere to the southern one.     

Periodicities in the north-south asymmetry of solar activity

This paper tries to cast additional evidence on the proposed periodic behaviour of the N-S asymmetry in sudden disappearances (SD) of solar prominences (Vizoso and Ballester, 1987). We have performed a Blackman-Tukey power spectrum of the values of the SD N-S asymmetry and the results shows a significant peak, above 95% confidence level, at 12.4 years, another peak at 2.3 years fails to be statistically significant. Moreover, power spectrum performed with the values of N-S asymmetry of flare number and flare index (Vizoso and Ballester (1987) display significant peaks, above 95% confidence level, around 3.1–3.2 years.     

Chaotic behavior of the north-south asymmetry of sunspots?

North-south asymmetry in the distribution of sunspots was examined. Weak correlations between north-south asymmetry and sunspot number were found in several time lags. Higuchi's fractal dimension (1988) was calculated to evaluate irregularity in north-south asymmetry. The fractal dimension obtained is 1.90 ± 0.01 and this implies that the north-south asymmetry is highly irregular. The method of Sugihara and May (1990), based on the nonlinear prediction method, was used to distinguish between deterministic chaos and noise. The results do not confirm the idea that north-south asymmetry is an example of deterministic chaos.     

Near-infrared polarization studies of Saturn and Jupiter

Polarization measurements of Jupiter, Saturn, and Saturn's rings from 1 to 3.5 μm are presented. At 1.6 μm on the discs of the two planets, the radially directed limb polarizations observed in the visible undergo, in some cases, a surprising 90° rotation to a tangential direction, particularly on the poles. The only immediate explanation for this effect is double Mie scattering, due to aerosols which must be of the order of a micrometer in size. On Jupiter the patterns are not uniform and are not stable, reflecting variable aerosol concentrations on the two poles. The ring polarization is uniformly negative (E vector parallel to the ecliptic plane) from the visible through 3.5 μm, and is inversely proportional to the albedo. This is as expected from Wolff's model for scattering from rough solid surfaces; but the degree of polarization seems uncommonly high, exceeding 2% at 3.5 μm.     

Periodic variation of the north-south asymmetry of solar activity phenomena

We report here a study of various solar activity phenomena occurring in both north and south hemispheres of the Sun during solar cycles 8–23. In the study we have used sunspot data for the period 1832–1976, flare index data for the period 1936-1993, Hα flare data 1993–1998 and solar active prominences data for the period 1957–1998. Earlier Verma reported long-term cyclic period in N-S asymmetry and also that the N-S asymmetry of solar activity phenomena during solar cycles 21, 22, 23 and 24 will be south dominated and the N-S asymmetry will shift to north hemisphere in solar cycle 25. The present study shows that the N-S asymmetry during solar cycles 22 and 23 are southern dominated as suggested by Verma.     

Interpretation of the apparent north-south asymmetry and fluctuations of galactic rotation

A model of the apparent north-south asymmetry of the rotation curve of the Galaxy and of the asymmetry appearing for the rotation of its outskirts has been presented, in terms of interaction redshifts. Fluctuations in the rotation curve for neutral hydrogen are discussed and interpreted as expanding motions in the arms. The expansion of the disk of the Galaxy which has been suggested previously as an explanation for the asymmetry has been shown to meet some serious difficulties. A remarkable north-south symmetry both in the spatial distribution and in the kinematics of neutral hydrogen in the subsolar region follows from the present model.     

Evolution and nature of north-south asymmetry in the heliospheric current sheet

The nature and evolution of north-south asymmetry in the heliospheric current sheet (HCS) has been investigated using solar and interplanetary magnetic field (IMF) observations for the past few solar cycles. The mean heliographic latitude of the HCS (averaged over the solar longitude) a ₀ is found to be non-zero during many solar rotations indicating that the large-scale solar magnetic field is more ordered in a system where the origin is shifted away from the centre of the Sun. We have shown that the asymmetry in HCS manifests in different forms depending on the transition heliographic latitude of the reversal of dominant polarity of the IMF ( _T) and the difference in the maximum latitudinal extension of the HCS in the two solar hemispheres (). The classification of the observed asymmetry during 1971–1985 and its effect on IMF observations near Earth has been studied. We have also inferred the sign of _T during 1947–1971 using inferred IMF polarity data. The observed sign reversals of _T suggest the importance of periodicities less than the solar cycle period to be associated with the evolution of asymmetry in HCS. Asymmetry in sunspot activity about the solar equator does not seem to relate consistently well with the asymmetry in HCS about the heliographic equator.     

The north-south asymmetry of solar filaments separately at low and high latitudes in solar cycle 23

We present the results of a study on the north-south asymmetry of solar filaments at low(50°) and high(60°) latitudes using daily filament numbers from January 1998 to November 2008(solar cycle 23). It is found that the northern hemisphere is dominant at low latitudes for cycle 23. However, a similar asymmetry does not occur for solar filaments at high latitudes. The present study indicates that the hemispheric asymmetry of solar filaments at high latitudes in a cycle appears to have little connection with that at low latitudes. Our results support that the observed magnetic fields at high latitudes include two components: one comes from the emergence of the magnetic fields from the solar interior and the other comes from the drift of the magnetic activity at low latitudes.     

Evidence for solar-cycle evolution of north-south flare asymmetry during cycles 20 and 21

The record of flare incidence from January 1969 to October 1988 indicates that the north-south (N-S) distribution of large flares is periodic and approximately in phase with the 11-year sunspot cycle. These data are based on observations of the whole-disk Sun in continuum soft X-rays which commenced in early 1969 and have proceeded without interruption to the present time. The pattern of occurrence, observed for slightly less than two sunspot cycles, is that large flares concentrate in north heliographic latitudes soon after solar minimum and then migrate gradually southward as the cycle progresses. By the end of the cycle, most large flares occur in the south. The degree of N-S asymmetry apparently is a function of the intensity of the flare; the most intense flares show the largest amount of N-S asymmetry. The data suggest that sunspots and flares may be driven by distinctly different excitation mechanisms arising at different levels in the convection zone. This conjecture is supported by recent work of Bai (1987, 1988), who has discovered that the superactive regions producing the majority of flares rotate at a speed substantially different from the Carrington rate, which is based primarily on the observed motion of sunspots.     

Inference of sector polarity of the inter-planetary magnetic field from the cosmic ray north-south asymmetry

The sector polarity of the interplanetary magnetic field has been inferred daily for the period 1971–1973, using ground level cosmic ray observations. The method depends on the sectors directed towards and away from the Sun being associated with different characteristic variations of the cosmic ray north-south asymmetry. The analysis has a simple basis. The difference between the north and south daily mean intensities of directional telescopes at a single observing station is determined and its value relative to the 27-day average is calculated. The sign (negative or positive) of the value thus derived corresponds to the sector polarity on a daily basis. Good (~76%) agreement is obtained between the polarities inferred indirectly by the present method and those observed directly with the spacecraft magnetometers. We therefore suggest that cosmic ray observations can be used for inferring the sector polarity of the magnetic field in interplanetary space.     

The solution for seasonal variations in the Earth's rate of rotation

New physical principles for an explanation of seasonal variations in the Earth's rate of rotation are proposed. It is thought that the variations are caused by a variation of the total energy of the Earth's atmosphere in the course of the planet's revolution about the Sun in elliptic orbit. Jacobi's virial equation for the Earth's atmosphere is derived from the Eulerian equations. The virial theorem is obtained. The existence of the relationship between Jacobi's function and potential energy of the atmosphere is confirmed. In the framework of this relationship, Jacobi's equation is reduced to the equation of unperturbed virial oscillations. The solution of the above-mentioned equation expresses the periodic virial oscillations of Jacobi's function (moment of inertia) of the Earth's atmosphere with time. The solution of the perturbed virial oscillation problem of the atmosphere-solid Earth system is obtained. The perturbation term in Jacobi's virial equation regards, in explicit form, the energy changes occurring in the atmosphere in the course of the planet's revolution about the Sun in elliptic orbit. The annual and semi-annual periodic variations in the Earth's rate of rotation can be considered as an astrometrical result following from the obtained solution. A satisfactory accord of the theoretical results with experimental data is shown.     

Diurnal and seasonal variations of sporadic meteor parameters

Diurnal variations of the median echo durations of sporadic meteor echoes during August and December-January periods are discussed. It is shown that differences between seasonal distributions result from the superposition of simultaneous diurnal effects controlling the electron loss processes in the ionized meteor trail.     

The Cassini-Huygens flyby of Jupiter

The Cassini-Huygens spacecraft flew by Jupiter on December 30, 2000. The instruments aboard the spacecraft started making scientific observations three months earlier. Joint, collaborative observations were carried out with the teams of other spacecraft, notably Galileo, and with Earth-based observers. An operational overview of the flyby is presented and attention drawn to contributions of the eleven papers of this series which follow. Prime achievements of this campaign have been to better define the present state of fundamental elements of the jovian system, confirming many previously tentative conclusions. Particularly noteworthy is that the interactions between the solar wind and the jovian magnetosphere have been explored far deeper than before, along with the link to the morphology and dynamics of the jovian aurora.     

Hydrogen peroxide on Mars: evidence for spatial and seasonal variations

Hydrogen peroxide (H₂O₂) has been suggested as a possible oxidizer of the martian surface. Photochemical models predict a mean column density in the range of 10¹⁵-10¹⁶ cm⁻². However, a stringent upper limit of the H₂O₂ abundance on Mars (9×10¹⁴ cm⁻²) was derived in February 2001 from ground-based infrared spectroscopy, at a time corresponding to a maximum water vapor abundance in the northern summer (30 pr. μm, Ls=112°). Here we report the detection of H₂O₂ on Mars in June 2003, and its mapping over the martian disk using the same technique, during the southern spring (Ls=206°) when the global water vapor abundance was ∼10 pr. μm. The spatial distribution of H₂O₂ shows a maximum in the morning around the sub-solar latitude. The mean H₂O₂ column density (6×10¹⁵ cm⁻²) is significantly greater than our previous upper limit, pointing to seasonal variations. Our new result is globally consistent with the predictions of photochemical models, and also with submillimeter ground-based measurements obtained in September 2003 (Ls=254°), averaged over the martian disk (Clancy et al., 2004, Icarus 168, 116-121).     

Confirmation of the 25.5-day fundamental period of the Sun using the north-south asymmetry of the flare index

Short-term periodicities of solar activity were studied. To perform the study, a north-south asymmetry time series was constructed by using the northern and the southern hemisphere flare index values for solar cycle 22. The statistical significance of this time series was calculated. It indicates that in most of cases the asymmetry is highly significant during cycle 22. Power spectral analysis of this time series reveals a periodicity around 25.5 days, which was announced before as a fundamental period of solar activity (Bai and Sturrock, 1991). To investigate the time agreement between the two hemispheres, the phase distribution was studied and a phase shift of about 0.5 was found. An activity trend from the north to the south was found.     

The free oscillations of Jupiter

The spectrum of free oscillations of Jupiter is calculated for a set of models, each of them fitting all available observational data. Diagnostic capabilities of the spectrum are studied. They could be used, as soon as relevant observations are performed, for both the identification of the observed modes and the improvement of the models themselves. The calculations were made for five-layer models. They differ in the core mass (2–10 M_⊕) and in the molecular-metallic phase transition pressure of hydrogen (1.5–3 Mbar). The spectrum of Jupiter consists of gravitational modes related to density jumps in the planetary interiors and of acoustic modes. The periods of the acoustic modes are calculated for degree up to l=30 and overtone number up to n=20. The investigated models have a characteristic frequency of ≈152–155 μHz. Two outer gravitational modes related to density jumps in the molecular envelope and at the interface with the metallic envelope have nonzero displacements at the planetary surface. These modes have good diagnostic properties. The values of the kinetic energy averaged over the period of oscillation are calculated for a 1-m amplitude of the displacement at the planetary surface. The influence of all effects of rotation on the spectrum is discussed.     

Eccentric Extrasolar Planets: The Jumping Jupiter Model

Most extrasolar planets discovered to date are more massive than Jupiter, in surprisingly small orbits (semimajor axes less than 3 AU). Many of these have significant orbital eccentricities. Such orbits may be the product of dynamical interactions in multiplanet systems. We examine outcomes of such evolution in systems of three Jupiter-mass planets around a solar-mass star by integration of their orbits in three dimensions. Such systems are unstable for a broad range of initial conditions, with mutual perturbations leading to crossing orbits and close encounters. The time scale for instability to develop depends on the initial orbital spacing; some configurations become chaotic after delays exceeding 10⁸ y. The most common outcome of gravitational scattering by close encounters is hyperbolic ejection of one planet. Of the two survivors, one is moved closer to the star and the other is left in a distant orbit; for systems with equal-mass planets, there is no correlation between initial and final orbital positions. Both survivors may have significant eccentricities, and the mutual inclination of their orbits can be large. The inner survivor's semimajor axis is usually about half that of the innermost starting orbit. Gravitational scattering alone cannot produce the observed excess of “hot Jupiters” in close circular orbits. However, those scattered planets with large eccentricities and small periastron distances may become circularized if tidal dissipation is effective. Most stars with a massive planet in an eccentric orbit should have at least one additional planet of comparable mass in a more distant orbit.