On the nature of the apparent response of the vorticity area index to the solar magnetic field

The apparent response of the vorticity area index to the solar magnetic field is confined to tropospheric regions of intense circulation. Discussions and calculations that include larger volumes of the troposphere would not be expected to show a significant Sun-weather effect. Analysis of the effect in time intervals outside the original 1963–73 is also discussed. An assessment of this Sun-weather effect at the present time is given.Proceedings of the 14th ESLAB Symposium on Physics of Solar Variations, 16–19 September 1980, Scheveningen, The Netherlands.     

The effect of intergalactic dust on the measurement of the cosmological deceleration parameterq 0

In a recent attempt to explain the cosmic microwave background without the big bang, a thermalization mechanism involving intergalactic whisker grains of graphite was proposed. The effect of absorption by the intergalactic medium in general, and of the above type in particular, on the measurement of the deceleration parameterq ₀ of the expanding universe is discussed. Its effect is shown to be comparable in magnitude but opposite to that of the luminosity evolution in galaxies. A consequential selection effect is also discussed.     

The role of the Yoshizawa effect in the Archontis dynamo

The generation of mean magnetic fields is studied for a simple non-helical flow where a net cross-helicity of either sign can emerge. This flow, which is also known as the Archontis flow, is a generalization of the Arnold–Beltrami–Childress flow, but with the cosine terms omitted. The presence of cross-helicity leads to a mean-field dynamo effect that is known as the Yoshizawa effect. Direct numerical simulations of such flows demonstrate the presence of magnetic fields on scales larger than the scale of the flow. Contrary to earlier expectations, the Yoshizawa effect is found to be proportional to the mean magnetic field and can therefore lead to its exponential instead of just linear amplification for magnetic Reynolds numbers that exceed a certain critical value. Unlike α effect dynamos, it is found that the Yoshizawa effect is not notably constrained by the presence of a conservation law. It is argued that this is due to the presence of a forcing term in the momentum equation, which leads to a non-zero correlation with the magnetic field. Finally, the application to energy convergence in solar wind turbulence is discussed.     

The visco-resistive stability of arcades in the corona of the Sun

The stability of ballooning modes in coronal arcades is studied using linear visco-resistive MHD. Rigid wall conditions are adopted for modelling the photospheric line-tying of the magnetic field. The full Braginskii viscosity stress tensor is used and particular attention is given to the effect of the viscosity coefficient ₃ which was left out of an earlier investigation by Van der Linden, Goossens, and Hood (1987, 1988). The numerical results for shearless arcades show that the coefficient ₃ has a stabilizing effect. However, for realistic values of the equilibrium quantities the stabilizing effect by ₃ can be neglected in comparison with the strong stabilizing effect of the perpendicular viscosity. The effect of magnetic field strength and mode number on stability are determined. In particular it is found that there exists a critical field strength for every mode number such that the mode is stable for weaker fields and unstable for stronger fields.     

The unique frequency spectrum of the Blazhko RRc Star LS Her

The Blazhko effect in RR Lyrae stars is still poorly understood theoretically. Stars with multiple Blazhko periods or in which the Blazhko effect itself varies are particularly challenging. This study investigates the Blazhko effect in the RRc star LS Her. Detailed CCD photometry in the   V , R _C  and I _C band has been performed on 63 nights during six months. LS Her is confirmed to have a Blazhko period of  12.75 ± 0.02  d. However, where normally the side frequencies of the Blazhko triplet are expected, an equidistant group of three frequencies is found on both sides of the main pulsation frequency. As a consequence, the period and amplitude of the Blazhko effect itself vary in a cycle of  109 ± 4  d. LS Her is a unique object turning out to be very important in the verification of the theories for the Blazhko effect.     

The effects on the MHD stability of field line tying to the end faces of a cylindrical magnetic loop

We examine the magnetohydrodynamic (MHD) stability of a magnetic loop, taking into account field line tying at its foot points. We use the ideal MHD energy equation to derive a stability equation for a specific class of perturbations.We found that for a loop with large aspect ratio (10) the field line tying effect is negligible to the m = 1 kink mode but important to the localized modes. The stability criterion for high m localized modes is derived and compared with the Suydam criterion. The result shows that for the perturbation of the class studied, there are two effects of field line tying; one is a field line bending effect which is always stabilizing and the other is a shear effect which is stabilizing or destabilizing depending on the sign of the gradient of potential magnetic field. The net effect of field line tying is determined by the sum of these two effects.The result of this work is contrary to the result of Hood and Priest, in which they found that the field line tying effect is significant to the m = 1 mode. We believe that the contradiction comes from their incomplete minimization of the energy equation.     

The evolution of the atmosphere of the earth

Computer simulations of the evolution of the Earth's atmospheric composition and surface temperature have been carried out. The program took into account changes in the solar luminosity, variations in the Earth's albedo, the greenhouse effect, variation in the biomass, and a variety of geochemical processes. Results indicate that prior to two billion years ago the Earth had a partially reduced atmosphere, which included N₂, CO₂, reduced carbon compounds, some NH₃, but no free H₂. Surface temperatures were higher than now, due to a large greenhouse effect. When free O₂ appeared the temperature fell sharply. Had Earth been only slightly further from the Sun, runaway glaciation would have occured at that time. Simulations also indicate that a runaway greenhouse would have occured early in Earth's history had Earth been only a few percent closer to the Sun. It therefore appears that, taking into account the possibilities of either runaway glaciation or a runaway greenhouse effect, the continously habitable zone about a solar-type star is rather narrow, extending only from roughly 0.95 to 1.01 AU.     

A full-sky prediction of the Sunyaev–Zeldovich effect from diffuse hot gas in the local universe and the upper limit from the WMAP data

We use the Point Source Catalogue Redshift Survey galaxy redshift catalogue combined with constrained simulations based on the IRAS 1.2-Jy galaxy density field to estimate the contribution of hot gas in the local universe to the Sunyaev–Zeldovich (SZ) effect on a large scale. We produce a full-sky healpix map predicting the SZ effect from clusters as well as diffuse hot gas within  80  h ⁻¹ Mpc  . Performing cross-correlation tests between this map and the WMAP data in pixel, harmonic and wavelet space we can put an upper limit on the effect. We conclude that the SZ effect from diffuse gas in the local universe cannot be detected in current cosmic microwave background (CMB) data and is not a large-scale contaminating factor  (ℓ < 60)  in studies of CMB angular anisotropies. We derive an upper limit for the mean temperature decrement of  Δ T < 0.33 μK  at the 2σ confidence level for the 61-GHz frequency channel. However, for future high-sensitivity experiments observing at a wider range of frequencies, the predicted large-scale SZ effect could be of importance.     

Some results on the global dynamics of the regularized restricted three-body problem with dissipation

We perform an analysis of the dynamics of the circular, restricted, planar three-body problem under the effect of different kinds of dissipation (linear, Stokes and Poynting–Robertson drags). Since the problem is singular, we implement a regularization technique in the style of Levi–Civita. The effect of the dissipation is often to decrease the semi-major axis; as a consequence the minor body collides with one of the primaries. In general, it is quite difficult to find non-collision orbits using random initial conditions. However, by means of the computation of the Fast Lyapunov Indicators (FLI), we obtain a global view of the dynamics. Precisely, we detect the regions of the phase space potentially belonging to basins of attraction. This investigation provides information on the different regions of the phase space, showing both collision and non-collision trajectories. Moreover, we find periodic orbit attractors for the case of linear and Stokes drags, while in the case of the Poynting–Robertson effect no other attractors are found beside the primaries, unless a fourth body is added to counterbalance the dissipative effect.     

Hydrodynamical simulations of the Sunyaev–Zel'dovich effect: the kinetic effect

We use hydrodynamical N -body simulations to study the kinetic Sunyaev–Zel'dovich effect. We construct sets of maps, one square degree in size, in three different cosmological models. We confirm earlier calculations that on the scales studied the kinetic effect is much smaller than the thermal (except close to the thermal null point), with an rms dispersion smaller by about a factor of 5 in the Rayleigh–Jeans region. We study the redshift dependence of the rms distortion and the pixel distribution at the present epoch. We compute the angular power spectra of the maps, including their redshift dependence, and compare them with the thermal Sunyaev–Zel'dovich effect and with the expected cosmic microwave background anisotropy spectrum as well as with determinations by other authors. We correlate the kinetic effect with the thermal effect both pixel-by-pixel and for identified thermal sources in the maps to assess the extent to which the kinetic effect is enhanced in locations of strong thermal signal.     

Source–lens clustering effects on the skewness of the lensing convergence

The correlation between source galaxies and lensing potentials causes a systematic effect on measurements of cosmic shear statistics, known as the source–lens clustering (SLC) effect. The SLC effect on the skewness of lensing convergence, S ₃, is examined using a non-linear semi-analytic approach and is checked against numerical simulations. The semi-analytic calculations have been performed in a wide variety of generic models for the redshift distribution of source galaxies and power-law models for the bias parameter between the galaxy and dark matter distributions. The semi-analytic predictions are tested successfully against numerical simulations. We find the relative amplitude of the SLC effect on S ₃ to be of the order of  5–40  per cent. It depends significantly on the redshift distribution of sources and on the way in which the bias parameter evolves. We discuss possible measurement strategies to minimize the SLC effects.     

The Effect of the CCD Gate Structure in the Determination of the Undersampled Point Spread Function

Using numerical simulations, we evaluated the gate structure effect of the front-illuminated (FI) charge-coupled device (CCD) on determining the point spread function (PSF) from the analysis of undersampled experimental data. The PSF of the Soft X-ray Telescope onboard Yohkoh was studied as a model case. Its full-width at half-maximum is about one pixel size, and the FI CCD was equipped in the telescope as a detector. Of the three emission lines used during the pre-launch experiment, the data from the lowest-energy line (carbon K-line, 0.28 keV) were significantly influenced by the gate structure. The results from previous studies regarding the analysis of pre-launch data were examined and compared with the results from our simulation, and the expected error ranges of the gate structure effect are discussed. We found that the error caused by the effect of the gate structure is significant; at an energy of 0.28 keV, the error may lead to a too sharp PSF by about a few tens of percent.     

Determination of the electromagnetic field produced by a magnetic oblique-rotator

The inertial effect on the structure of the magnetosphere of a rotating star is investigated, in the corotation approximation for a surrounding quasi-neutral plasma. The equation of motion reduces to a usual static balance equation between the electromagnetic and the centrifugal forces, in the rotating frame. However the MHD condition, which can be regarded as a special form of the generalized Ohm's law, is modified by the inclusion of inertial effect, with a violation of the frozen-in condition in case of a general (i.e., not restricted to corotation) plasma motion. The inertial effect on the electromagnetic field is summarized in a partial scalar potential named the non-Backus potential, which is proportional to the centrifugal potential in the corotation approximation.An approximate solution of this corotation problem is given, in which another characteristic radiusr _M appears besides the light radiusr _L . This radius defines a distance beyond which the inertial effect becomes dominant over the electromagnetic one, and is useful in estimating the magnitude of the terminal velocity of a centrifugal wind. A few examples of the modification of dipole magnetic field due to the inertial effect are visualized. In an oblique-rotation case, it can be seen that such a warp of the neutral sheet (the surface ofB _r =0) is reproduced as observed in the Jovian magnetosphere.     

Predictions on the application of the Hanle effect to map the surface magnetic field of Jupiter

In this paper we evaluate the possibility of detecting, for the first time, the surface magnetic field of Jupiter (∼1 bar level) by observing the change of linear polarization induced by the Hanle effect on the H Lyman-alpha (Lyα) emission line of the planet. We find that, indeed, the Hanle effect, which results from the interaction between a local magnetic field and the atomic polarization induced by absorption of anisotropic radiation, is sensitive to relatively weak values of the strength of the magnetic fields expected on planets. First, we show that for the Lyα emission backscattered by atomic H in the presence of a magnetic field, the Hanle effect is polarizing. This new result is in total contrast to the depolarizing effect predicted and observed for emission lines scattered at right angles in solar prominences. Additionally, to estimate the polarization rate for the case of Jupiter, we have considered three magnetic field models: a dipole field for reference, an O₄ based model [Connerney, J.E.P., 1981. The magnetic field of Jupiter—A generalized inverse approach. J. Geophys. Res. 86, 7679-7693], and finally, an O₆ based model [Khurana, K.K., 1997. Euler potential models of Jupiter's magnetospheric field. J. Geophys. Res. 102, 11295-11306]. In all models, we show that for the jovian backscattered Lyα line, the Hanle effect does enhance the Lyα linear polarization; the polarization rate may exceed 2% at specific regions of the jovian disc, making detection possible either remotely or from an orbiter around Jupiter. In general, depending on the instrumental sensitivity and the observing strategy used, we show that accurate mapping of the linear polarization rate at the planetary surface (thermosphere) or off-disc (corona) may provide a rather accurate estimate of the jovian total magnetic field strength on large area scales.     

Influence of the east-west component of the interplanetary magnetic field on the intensity of the auroral electrojet

Analysis of interplanetary data has been made to evaluate the influence of the Biny component of the IMF on the magnitude of the AL index, especially with reference to the contribution of B_y in the reconnection process between the IMF and geomagnetic fields in the dayside part of the magnetosphere. The results of the analysis showed that the effect of Biny on AL is predominantly of a different type from that expected by the current theory of reconnection, and the B_y effect of the latter type was found to be much less significant in magnitude than the theory predicts. The discrepancy may be resolved if the region where the reconnection takes place has an elongated shape.     

Apsidal precession of the outer solar planetary orbits due to the pioneer anomaly

Despite the now common position that the Pioneer anomaly is not a real gravitational effect but an effect due to the on-board thermal recoil forces – for curiosity’s sake, we here take the suggestion of Nyambuya (2015) where it has been assumed that the Pioneer anomaly – can, in-principle, be attributed to a gravitational effect due to these spacecrafts accreting some material from a rarefied Interplanetary Medium (IPM) in the domain where the Pioneer anomaly has manifested [20 AU ≲ r ≲ 70 AU]. If this assumption is correct, then, the expected Pioneer acceleration of these spacecrafts maybe much smaller than the Pioneer acceleration to cause as noticeable apsidal precession of the outer Solar planets Uranus, Neptune and Pluto, thus making it difficult to rule-out a gravitational origin of the Pioneer anomaly.     

Origin and sustainability of the population of asteroids captured in the exterior resonance 1:2 with Mars

At present, approximately 1500 asteroids are known to evolve inside or sticked to the exterior 1:2 resonance with Mars at a ? 2.418 AU, being (142) Polana the largest member of this group. The effect of the forced secular modes superposed to the resonance gives rise to a complex dynamical evolution. Chaotic diffusion, collisions, close encounters with massive asteroids and mainly orbital migration due to the Yarkovsky effect generate continuous captures to and losses from the resonance, with a fraction of asteroids remaining captured over long time scales and generating a concentration in the semimajor axis distribution that exceeds by 20% the population of background asteroids. The Yarkovsky effect induces different dynamics according to the asteroid size, producing an excess of small asteroids inside the resonance. The evolution in the resonance generates a signature on the orbits, mainly in eccentricity, that depends on the time the asteroid remains captured inside the resonance and on the magnitude of the Yarkovsky effect. The greater the asteroids, the larger the time they remain captured in the resonance, allowing greater diffusion in eccentricity and inclination. The resonance generates a discontinuity and mixing in the space of proper elements producing misidentification of dynamical family members, mainly for Vesta and Nysa-Polana families. The half-life of resonant asteroids large enough for not being affected by the Yarkovsky effect is about 1 Gyr. From the point of view of taxonomic classes, the resonant population does not differ from the background population and the excess of small asteroids is confirmed.     

A comparative analysis of the volcanic impact on the climates of the Earth and Mars

The climatic impact of volcanic activity on the Earth and Mars is considered and a comparative analysis is made. The effect of gaseous components and of aerosols, formed in the process of the evolution of volcanic cloud, on the greenhouse effect and climate on the Earth and Mars is analyzed. A numerical modelling has shown that the climatic impact of volcanic activity depends on the optical properties (the extent of opacity of the atmospheric gaseous components and on the intensity of volcanic activity). In connection with sporadic variations in the intensity of volcanic activity, a temporal modulation of climate takes place with alternating periods of warming and cooling. An important role of SO₂ and volcanic aerosols in the formation of climate in the presence of evolution of the Earth and Mars is revealed.