The solar radiation incident at the top of the atmospheres of Uranus and Neptune

The latitudinal and seasonal variation of the direct solar radiation incident at the top of the atmosphere of Uranus and Neptune has been recalculated by use of updated values for the period of axial rotation and the oblateness. Values for the solar radiation are given in Watt per square meter instead of the unit used in earlier papers (calories per square centimeter per planetary day). The solar radiation averaged over a season and a year as a function of planetocentric latitude has also been reviewed. In addition, attention is made to the ratio of the solar radiation incident on an oblate planet to that incident on a spherical planet.     

Determination of the solar X-ray spectrum by using the atmospheric extinction

Indications about the spectral distribution of the solar radiation below 20 Å are obtained by comparing the atmospheric extinction of the solar radiation measured by three ion chambers in the satellites SOLRAD 7 and 8.The data refer to July 5, 6 and 8, 1965 and July 23, 1966 when the satellites passed from light to darkness into or out of the earth's shadow.The spectral intensity distribution is shown for the four days, and a comparison is made between active and quiet days.     

Combined solar radiation pressure and drag effects on the orbits of artificial satellites

A semi analytical theory is proposed to study the joint effects of direct solar radiation pressure and atmospheric drag on the orbit of an artificial Earth satellite. Making the solar radiation pressure equal to zero the problem is reduced to one already solved by Brouwer and Hori. The solutions are not equivalent, however, since in the Brouwer and Hori theory one has spurious Poisson terms.     

Perturbations of a spheroidal satellite due to direct solar radiation pressure

The orbital accelerations of certain balloon satellites exhibit marked oscillations caused by solar radiation impinging on the surface of the satellites, which, once spherical, have assumed a spheroidal shape producing a component of force at right-angles to the Sun-satellite direction. Given the characteristics and orientation of the satellite, the equations of force are determined by the formulae of Lucas. Otherwise the phase-angle and magnitude of the right-angle force are determined by trial and error, or best-fit techniques. Using a variation of the approach developed by Aksnes, a semi-analytical algorithm is presented for evaluating the perturbations of the Keplerian elements by direct solar radiation pressure on a spheroidal satellite. The perturbations are obtained by summing over the sunlit part of each orbit and allow for a linear variation in the phase-angle. The algorithm is used to determine the orbital accelerations of 1963-30D due to direct solar radiation pressure, and these results are compared to the observed values over two separate periods of the satellite's lifetime.     

A simple algorithm for simulating the solar ultraviolet radiation at the Earth's surface: An application in determining the minimum erythema dose

The purpose of this study is to present a new simple model algorithm for simulating the solar ultaviolet radiation reaching the surface of the Earth. The algorithm is capable of providing both the direct and diffuse solar ultraviolet radiation, for different atmospheric conditions, time, and geographic locations. An application of the model relates to the calculation of the minimum energy input of ultraviolet radiation to be received by a human to allow an erythema development.     

Long-periodic and secular perturbations to the orbits of Explorer 19 and Lageos due to direct solar radiation pressure

A theory for the long-term variations in the orbit of a spherically symmetric satellite due to direct solar radiation pressure is tested using two satellite orbit analyses. The first of these analyses is in terms of mean elements for the balloon satellite Explorer 19. The results are compared with the expected theoretical variations with short-period terms omitted. The second analysis utilises satellite laser ranging observations of the geodetic satellite, Lageos. A novel long-term analysis technique is developed primarily for laser ranging studies. The technique is tested along with the solar radiation pressure perturbation theory by comparing the results from the theory and the analysis.     

Rotational dynamics of a solar system body under solar radiation torques

The rotational dynamics of a small solar system body subject to solar radiation torques is investigated. A set of averaged evolutionary equations are derived as an analytic function of a set of spherical harmonic coefficients that describe the torque acting on the body due to solar radiation. The analysis also includes the effect of thermal inertia. The resulting equations are studied and a set of possible dynamical outcomes for the rotation rate and obliquity of a small body are found and characterized.     

Dust particle in the solar gravitational and electromagnetic fields

The action of the solar electromagnetic radiation (in the form of the Poynting-Robertson effect) on the motion of interplanetary dust particle in the gravitational field of the Sun is discussed from the theoretical point of view. Results are presented to all orders inv/c (c - speed of light,v -orbital velocity of the particle) - general relativistic formula is presented.     

On the increase of solar activity in the southern hemisphere during solar cycle 21

The present paper investigates the north-south asymmetry for major flares (solar cycles 19 and 20), type II radio bursts (solar cycles 19,20 and 21), white light flares (solar cycle 19,20 and 21), and gamma ray bursts, hard X-ray bursts and coronal mass ejections (solar cycle 21). The results are compared with the found asymmetry in favour of the northern hemisphere during solar cycles 19 and 20 in favour of the southern hemisphere during solar cycle 21.     

The interpretation of hard X-ray polarization measurements in solar flares

We review recent observations of polarization of moderately hard X-rays in solar flares and compare them with the predictions of recent detailed modeling of hard X-ray bremsstrahlung production by non-thermal electrons. We find that the recent advances in the complexity of the modeling lead to substantially lower predicted polarizations than in earlier models and more fully highlight how various parameters play a role in determining the polarization of the radiation field. The new predicted polarizations are comparable to those predicted by thermal modeling of solar flare hard X-ray production, and both are in agreement with the observations. In the light of these results, we propose new polarization observations with current generation instruments which could be used to discriminate between non-thermal and thermal models of hard X-ray production in solar flares.     

The effects of sunspots on solar irradiance

Sunspots have an obvious direct effect upon the visible radiant energy falling upon the Earth. We show how to estimate this effect and compare it quantitatively with recent observations of the solar total irradiance (Willson et al., 1981). The sunspots explain about half of the total observed variance of one-day averages. Since the sunspot effect on irradiance produces an asymmetry of the solar radiation, rather than (necessarily) a variation of the total luminosity, we have also estimated the sunspot population on the invisible hemisphere. This extrapolation allows us to estimate the true luminosity deficit produced by sunspots, in a manner that tends toward the correct long-term average value. We find no evidence for instantaneous global re-emission to compensate for the sunspot flux deficit.     

Satellite orbits perturbed by direct solar radiation pressure: General expansion of the disturbing function

An expression is derived for the solar radiation pressure disturbing function on an Earth satellite orbit which takes into account the variation of the solar radiation flux with distance from the Sun's centre and the absorption of radiation by the satellite. This expression is then expanded in terms of the Keplerian elements of the satellite and solar orbits using Kaula's method. The Kaula inclination functions are replaced by an equivalent set of modified Allan inclination functions.The resulting expression reduces to the form commonly used in solar radiation pressure perturbation studies (e.g. Aksnes, 1976), when certain terms are neglected. If, as happens quite often in practice, a satellite's orbit is in near-resonsnce with certain of these neglected terms, these near-resonant terms can cause changes in the satellite's orbital elements comparable to those produced by the largest term in Aksnes's expression. A new expression for the solar radiation pressure disturbing function expansion is suggested for use in future studies of satellite orbits perturbed by solar radiation pressure.     

The dynamics of solar sails with a non-point source of radiation pressure

The form of the solar radiation pressure on a heliocentric orbiting solar sail is obtained for a finite angular sized and limb darkened solar disk by the use of the radiation pressure tensor. It is found that the usual inverse square variation of the solar radiation pressure is modified by the finite angular size, and to a lesser extent by the solar limb darkening. The actual magnitude of the modification is in itself small, except at close heliocentric distances. However, its existence has implications for the dynamical stability of solar sails both in parked and circular orbital configurations and for the accuracy of trajectory calculations, particularly for sails in the inner solar system.     

Elemental diffusion and segregation processes in partially ionized solar plasma

Although diffusion is usually associated with equalizing of the chemical composition, the pressure and temperature gradients inside the Sun cause elemental diffusion segregation. While light hydrogen is flowing up to the solar envelope, helium and heavier elements are settling down to the core. The target of our simulation is an accurate estimation of the settling rate in solar plasma during the course of solar evolution. The rate of helium depletion in the envelope is a key parameter of the solar evolution and depends on position and conditions around the base of the convective mixing zone. The rate of heavy element settling is sensitive to the degree of ionization and interaction with the radiation flux. We estimate the effect of ion ionization on the settling rate for several heavy elements up to iron in the framework of the LTE assumption and the thermodynamic calculation according to SAHA-S EOS.     

Emission of solar radio spikes by beam-driven cyclotron resonance

The generation of bright solar radio spikes by the beam-driven cyclotron resonance maser mechanism (the resonant interaction of an electron beam with a circularly polarized wave in a background plasma under the action of a guide magnetic field) is studied. Nonlinear effects such as radiation damping and gyrophase bunching on electron energy and momentum are responsible for the enhanced direct energy conversion between the beam and the coherent wave. Factors such as beam energy spread and pitch angle distribution are analyzed. The intense maser radiation is carried at the source by the circularly polarized wave propagating along the magnetic field. Due to the magnetic field curvature, the outgoing maser radiation converts into extraordinary and ordinary modes. The extraordinary mode suffers from plasma absorption at the second harmonic layer, whereas the ordinary mode is likely to get through.     

Perturbations of the orbit of Explorer 19 due to solar radiation

The orbit of the balloon satellite, Explorer 19, is analysed to determine the effects of direct solar radiation pressure over one revolution of the satellite (111 min) for MJD 42822 and MJD 42966. At the earlier date, the satellite entered the Earth's shadow, presenting an opportunity to examine the effectiveness of two different shadow models. The reflectivity of the surface of the satellite was estimated from analysis of the variations in orbital eccentricity over a period of 236 days.Although many of the parameters associated with the shape and orientation of the satellite are unknown, the theory for a non-spherical satellite is applied using trial and error methods to determine the parameters of best fit. The paper concludes with an examination of the perturbations in orbital eccentricity and inclination due to incident, specularly reflected, and diffusely reflected radiation.     

The solar spectral irradiance and its action in the atmospheric photodissociation processes

A critical analysis has been made of solar irradiance in the spectral region covering wavelengths from 100 nm upwards; the absorption characteristics of molecules of oxygen and ozone have been taken into account with a view to the direct application of the results to atmospheric photochemistry. The absorption of radiation by these molecules results in the photodissociation of both of them in the homosphere, and it also makes possible the penetration of solar radiation from the thermosphere, through the mesosphere and the stratosphere, down to the troposphere.Special attention has been given to each of the following spectral regions: Lyman-alpha radiation at 121.6 nm, the O₂ Schumann-Runge continuum at wavelengths less than 175 nm, the O₂ Schumann-Runge band system from 200 to 175 nm, and the O₂ Herzberg continuum at 242.4 nm. For absorption by ozone, the solar spectrum has been analysed in the following regions: the Hartley band at wavelengths less than 310 nm, the Huggins bands at wavelengths above 310 nm and the visible Chappuis bands. Finally, for the photodissociation of O₃, particular attention has been given to the transition region (300–320 nm) in which there is a change-over from the production of the excited atom O(¹D) to that of the atom in its ground state O(³p).     

Interplanetary dust particles and solar radiation

The problem of the action of the solar radiation on the motion of interplanetary dust particle is discussed. Differences between the action of electromagnetic solar radiation and that of the solar wind are explained not only from the point of view of the physical nature of these phenomena but also from the point of view of dust particle's orbital evolution. As for the electromagnetic solar radiation, general equation of motion for the particle is written and the most important consequences are: (i) the process of inspiralling toward the Sun is not the only possible motion - even spiralling from the Sun is also possible, and, (ii) the orbital plane of the particle (its inclination) may change in time. As for the solar wind, the effect corresponding to the fact that solar wind particles spread out from the Sun in nonradial direction causes that the process of inspiralling toward the Sun is in more than 50% less effective than for radial spread out; in the region of the asteroid belt (long period orbits) the process of inspiralling is changed into offspiralling. Also shift in the perihelion of dust particle's orbit exists.     

The energy distribution in the solar EUV spectrum and abundance of elements in the solar atmosphere

This paper is a result of the evolution of researches on the prediction and identification of the solar EUV spectrum by Ivanov-Holodny and the author.An absolute calibration of the solar EUV spectrum is given. The corresponding energy distribution is shown in Figure 2. During the minimum solar activity the radiation flux in the range below 1027 Å near the earth is 2.6 erg/cm² sec, in the maximum it is 8 erg/cm² sec.Abundances of fifteen elements in the solar atmosphere were deduced (Table III) from a comparison of predicted and observed intensities of more than 300 lines in the spectral region below 1215 Å.     

Compton effect interpretation of solar red shift

The hypothesis that the solar red shift is due to Compton scattering of solar radiation through the electrons in the solar atmosphere predicts a variation in magnitude of the red shift with position in good agreement with observation. Quasar red shifts may be similarly explained.