On nonadiabatic waves in the photospheres of cool stars

The coupled set of equations of hydrodynamics and radiative transfer is derived for small disturbances in a plane, grey atmosphere. Only radiative transfer is taken into account in the energy equation; dynamical effects of radiation are ignored. A mean stationary radiative flux through the photosphere is taken into account. The radiative transfer equation is used by assuming the Eddington approximation, moreover, an exponential height profile of the temperature and an analytical opacity formula are supposed. For this model we obtained an asymptotic solution for plane nonadiabatic acoustic waves and radiation waves. The approach provides a detailed discussion of the interaction of nonadiabatic p‐modes and radiation waves in a realistic model of the photosphere of a solar‐like star.     

Turbulent Heat Fluxes in the Atmosphere of Venus

A thermal regime of the troposphere of Venus is mainly determined by the greenhouse effect. A closeness of the real temperature gradient to the adiabatic one indicates that turbulent heat fluxes are also essential. Additional problems arise as only about 11% of the solar radiation absorbed by the planet reaches the surface, and most of it is taken up in the clouds at altitudes of 60–70 km. The present study summarizes experimental data on atmospheric parameters related to turbulence and estimates turbulent fluxes and turbulence characteristics. These data confirm the author's hypothesis of an anomalous downward turbulent heat flux in the free atmosphere. A normal upward turbulent heat flux exists in the planetary boundary layer.     

Turbulence in the troposphere of Venus: Refined characteristics and new estimates

Based on spaceborne experimental data, characteristics of turbulence are calculated for the Venusian troposphere under conditions corresponding to the planet-averaged flux of solar radiation, which is equal to its value at a solar zenith angle of 66°. Additionally, given experimental data on radiation fluxes and their numerical calculations, turbulence characteristics were calculated for a solar zenith angle of 45°. The turbulence pattern is significantly different for small and large solar zenith angles. At large solar zenith angles, there exist an anomalous downward turbulent heat flux above 7–10 km and a normal upward flux at lower heights. At small zenith angles, the turbulent flux is normal throughout the entire troposphere. The dissipation of turbulent energy contributes significantly to the atmospheric heating in a wide range of altitudes. The spectrum of the time and space scales of dissipative processes in the troposphere is very wide and changes with height.Translated from Astronomicheskii Vestnik, Vol. 39, No. 1, 2005, pp. 38–50.Original Russian Text Copyright © 2005 by Izakov.     

Numerical simulation of the general circulation of the Cytherean lower atmosphere

The principal features which distinguish the atmosphere on Venus from that of the Earth are the slow rotation of the planet, the large mass of the atmosphere, and the opacity of the atmosphere to long-wave radiation. The slow rotation of the planet gives rise, first of all, to nongeostrophuc dynamics (the atmosphere gas has a tendency to move along the pressure gradient), with the result that the region of the main influx of solar energy is located on one side of the planet, and the region of maximum cooling on the other. These considerations lead to a much simpler scheme of circulation than that in the Earth's atmosphere.The large mass of the atmosphere is the cause of a high thermal and mechanical inertia, which explains why the atmospheric circulation is asymmetrical relative to the solar-antisolar axis. The daily center of circulation is displaced to the second half of the Cytherean solar day, i.e., to the line of zero budget of thermal energy corresponding to a height of the Sun abobe the horizon of about 20°. The notions of cold and warm regions are very relative for Venus. While the horizontal temperature differences on the Earth may reach 100°, a mean horizontal temperature drop as small as 3° in the Cytherean atmosphere may be looked upon as an exceptional phenomenon. This high thermal homogeneity is due to a very large thermal inertia, with cooling at the poles never manifesting itself in the temperature fields obtained.The opacity of the Cytherean atmosphere to long-wave radiation results in vertical heat transfer by turbulence, mesoscale convection, and large-scale currents. This produces adiabatic stratification in the troposphere and a high temperature in the lower layers.These phenomena were studied in a general manner using two- and three-level models. Steps have recently been undertaken to investigate in greater detail the vertical structure of the troposphere on Venus using ten-level models. It appeared that the vertical dynamic structure of the troposphere is very much dependent on the distribution in height of the solar energy influx. In the greenhouse model, the entire atmosphere is affected by circulation. Pronounced velocity maxima are observed in the lower and upper layers. In a model with adsorption of solar radiation in the upper layer, the velocity is small in the lower layers, but it rapidly increases and changes its direction several times in the upper layers. The mean kinetic energy of the atmosphere proves to be two to three times smaller than in the greenhouse model.Attempts have been made in the calculations to find the principal modes of the statistical fluctuations. The results obtained show that atmospheric circulation may be represented by a global mean basic state following the rotation of the planet with deviations from that basic state which are indeterminate disturbances. The mean basic state exhibits a high degree of symmetry relative to the equator. On account of nonlinearity, the disturbances were observed in all the models independently of space and time resolution. This phenomenon appears to reflect the actual properties of the Cytherean atmosphere and has no bearing on the details of the numerical scheme.     

The effects of reduced land fraction and solar forcing on the general circulation: results from the NCAR CCM

Land fraction and the solar energy at the top of the atmosphere (solar constant) may have been significantly lower early in Earth's history. It is likely that both of these factors played some important role in the climate of the early earth. The climate changes associated with a global ocean(i.e. no continents) and reduced solar constant are examined with a general circulation model and compared with the present-day climate simulation. The general circulation model used in the study is the NCAR CCM with a swamp ocean surface. First, all land points are removed in the model and then the solar constant is reduced by 10% for this global ocean case.Results indicate that a 4 K increase in air temperature occurs with global ocean simulation compared to the control. When solar constant is reduced by 10% under global ocean conditions a 23 K decrease in air temperature is noted. The global ocean warms much of the troposphere and stratosphere, while a reduction in the solar constant cools the troposphere and stratosphere. The largest cooling occurs near the surface with the lower solar constant.Global mean values of evaporation, water vapor amounts, absorbed solar radiation and the downward longwave radiation are increased under global ocean conditions, while all are reduced when the solar constant is lowered. The global ocean simulation produces sea ice only in the highest latitudes. A frozen planet does not occur when the solar constant is reduced—rather, the ice line settles near 30° of latitude. It is near this latitude that transient eddies transport large amounts of sensible heat across the ice line acting as a negative feedback under lower solar constant conditions keeping sea ice from migrating to even lower latitudes.Clouds, under lower solar forcing, also act as a negative feedback because they are reduced in higher latitudes with colder atmospheric temperatures allowing additional solar radiation to reach the surface. The overall effect of clouds in the global ocean is to act as a positive feedback because they are slightly reduced thereby allowing additional solar radiation to reach the surface and increase the warming caused by the removal of land. The relevance of the results to the “Faint-Young Sun Paradox” indicates that reduced land fraction and solar forcing affect dynamics, heat transport, and clouds. Therefore the associated feedbacks should be taken into account in order to understand their roles in resolving the “Faint-Young Sun Paradox”.     

About Hypothesis of the Superconducting Origin of the Saturn’s Rings

Hypothesis of possible superconductivity of the iced matter of the rings of Saturn (based on the data of Voyager and Pioneer space missions) allow us to explain many phenomena which have not been adequately understood earlier. Introducing into planetary physics force of magnetic levitation of the superconducting iced particle of the rings, which interact with magnetosphere of the planet, becomes to be possible to explain origin, evolution, and dynamics of the rings; to show how the consequent precipitation of the rings’ matter upon the planet was concluded; how the rings began their rotation; how they were compressed by the magnetic field into the thin disc, and how this disc was fractured into hundreds of thousands of separated rings; why in the ring B do exist “spokes”; why magnetic field lines have distortion near by ring F; why there is a variable azimuth brightness of the ring A; why the rings reflected radio waves so efficiently; why exists strong electromagnetic radiation of the rings in the 20.4 kHz–40.2 MHz range and Saturnian kilometric radiation; why there is anomalous reflection of circularly polarized microwaves; why there are spectral anomalies of the thermal radiation of the rings; why the matter of the various rings does not mix but preserves its small-scale color differences; why there is an atmosphere of unknown origin nearby the rings of Saturn; why there are waves of density and bending waves within Saturn’s rings; why planetary rings in the solar system appear only after the Belt of Asteroids (and may be the Belt of Asteroids itself is a ring for the Sun); why our planet Earth has no rings of its own.     

Polarization of Microwave Radio Emission of Flare-Producing Solar Active Regions

On the basis of our multiwavelength observations made with the one-dimensional RATAN-600 radio telescope, we study the inversion of the circular polarization in the solar microwave emission at different frequencies. The inversion is detected in the emission of flare-producing active regions (FPARs) at various stages of their development, starting from the pre-flare stage. During the latest 23rd solar cycle maximum, numerous FPARs revealed spectral inhomogeneities in their polarized microwave radiation (Bogod and Tokhchukova, 2003, Astron. Lett. 29, 263). Here, we discuss a particular case of such inhomogeneities, the frequency-dependent double inversion of the sign of circular polarization, which probably reflects some essential processes in FPARs. We consider several mechanisms for the double inversion: linear interaction of waves in the region of a quasitransverse magnetic field, the propagation of waves through a region of zero magnetic field, the scattering of radio waves on waves of high-frequency plasma turbulence, the influence of the current fibrils on the propagation of the radio emission, and the magnetic “dips,” in which the direction of magnetic field lines changes the sign relative to the observer. All of them have shortcomings, but the last mechanism explains the observations the best.     

Response of an optically thin,isothermal atmosphere to a convective overshoot

Radiation is believed to be hostile to the generation of gravity waves by granulation at the base of photosphere where the radiation is effective. A convective overshoot from subphotosphere seems able to penetrate to a height where the solar temperature is minimum and to excite the gravity waves in a stable region there.The response of the solar atmosphere to a Gaussian disturbance characterizing such a convective overshoot is studied in an unbounded isothermal atmosphere. Radiative effects are included, but only in regions which are optically thin. The response is measured in terms of mean vertical kinetic energy density (E _z) and mean vertical external energy flux (Q _z). E _z and Q _z were calculated for a wide range of frequencies centered at the observed 5-min velocity oscillation period. The computed sharp and broad power spectra at the lower chromosphere and the upper photosphere, respectively, are attributed to the combined effects of space damping and source function. Low-frequency waves (2000 s or longer) are found to be not responsible for depositing energy in the upper solar atmosphere.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

A New Way that Planets Can Affect the Sun

We derive a perturbation inside a rotating star that occurs when the star is accelerated by orbiting bodies. If a fluid element has rotational and orbital components of angular momentum with respect to the inertially fixed point of a planetary system that are of opposite sign, then the element may have potential energy that could be released by a suitable flow. We demonstrate the energy with a very simple model in which two fluid elements of equal mass exchange positions, calling to mind a turbulent field or natural convection. The exchange releases potential energy that, with a minor exception, is available only in the hemisphere facing the barycenter of the planetary system. We calculate its strength and spatial distribution for the strongest case (“vertical”) and for weaker horizontal cases whose motions are all perpendicular to gravity. The vertical cases can raise the kinetic energy of a few well positioned convecting elements in the Sun’s envelope by a factor ≤7. This is the first physical mechanism by which planets can have a nontrivial effect on internal solar motions. Occasional small mass exchanges near the solar center and in a recently proposed mixed shell centered at 0.16R _s would carry fresh fuel to deeper levels. This would cause stars like the Sun with appropriate planetary systems to burn somewhat more brightly and have shorter lifetimes than identical stars without planets. The helioseismic sound speed and the long record of sunspot activity offer several bits of evidence that the effect may have been active in the Sun’s core, its envelope, and in some vertically stable layers. Additional proof will require direct evidence from helioseismology or from transient waves on the solar surface.     

Near-surface winds at the Huygens site on Titan: Interpretation by means of a general circulation model

This study aims at interpreting the zonal and meridional wind in Titan's troposphere measured by the Huygens probe by means of a general circulation model. The numerical simulation elucidates the relative importance of the seasonal variation in the Hadley circulation and Saturn's gravitational tide in affecting the actual wind profile. The observed reversal of the zonal wind at two altitudes in the lower troposphere can be reproduced with this model only if the near-surface temperature profile is asymmetric about the equator and substantial seasonal redistribution of angular momentum by the variable Hadley circulation takes place. The meridional wind near the surface is mainly caused by the meridional pressure gradient and is thus a manifestation of the Hadley circulation. Southward meridional wind in the PBL (planetary boundary layer) is consistent with the near-surface temperature at the equator being lower than at mid southern latitudes. Even small changes in the radiative heating profile in the troposphere can substantially affect the mean zonal and meridional wind including their direction. Saturn's gravitational tide is rather weak at the Huygens site due to the proximity to the equator, and does not clearly manifest itself in the instantaneous vertical profile of wind. Nevertheless, the simulated descent trajectory is more consistent with the observation if the tide is present. Because of a different force balance in Titan's atmosphere from terrestrial conditions, PBL-specific wind systems like on Earth are unlikely to exist on Titan.     

The influence of the solar atmospheric stratification on the structure of the acoustic wave field

We investigate the influence of the solar atmospheric temperature stratification on the amplitude of waves at different heights and its dependence on frequency and wave number. Special interest is taken in the influence of atmospheric layers on the appearence of the recently observed p-mode crossing features and their location in the Fourier domain. We consider four stratification models. One of them is the standard model with convection-zone, VAL-atmosphere and corona. The others are modifications of this model in order to discuss the influence of specific layers of the atmosphere. The changes in the temperature structure significantly influence the velocity amplitude at certain frequency-wave number combinations at certain heights.     

Planetary waves on the Sun?

Some recent observations of the Sun suggest a class of wave-like motions moving both eastward and westward at a uniform velocity with respect to the mean solar angular velocity. It is suggested that these may be hydromagnetic planetary waves. An estimate of the mean toroidal magnetic field is made, based on a theoretical treatment of such waves already in the literature, and a slight correction to the mean rate of rotation of the Sun is inferred.     

Atmospheric temperature response to solar cycle UV flux variations

A radiative-convective climate model was used to explore the response of the mean global vertical temperature structure to a variation in the solar UV flux over the solar cycle. The model predicted a cooling of the troposphere and a warming of the stratosphere from solar minimum to solar maximum. The response of the atmospheric temperature to solar UV variations was found to be moderated by a concomitant change in the mean global stratospheric ozone content.     

Dynamics of the chemical evolution of Earth's primitive atmosphere

The course of evolution of Earth's primitive reducing atmosphere is shown to possibly have been determined to a large extent by the effect of thunder shock waves, which is comparable to the effect of solar uv radiation. The major chemical reactions occurring during a thunderstorm in the troposphere were pyrolysis of hydrocarbons, their oxidation by water vapor and their reaction with molecular nitrogen. These reactions were studied by the single-pulse shock tube technique and their rates as well as their product distributions were determined.The greenhouse effect of water vapor and acetylene enhanced oxidation by water vapor and prevented the accumulation of large graphite and polymer deposits on the Earth's surface. This is in accordance with their absence on the contemporary Earth. Changes in the frequency and power of thunderstorms, within reasonable limits, affected the rate of evolution but caused only small changes in the concentration profiles of HCN and aldehydes, which are essential for further chemical evolution in the oceans. The surface temperature and relative hydrogen concentration are shown to be of prime importance in determining the course and outcome of atmospheric evolution.     

Comparative study of ion cyclotron waves at Mars, Venus and Earth

Ion cyclotron waves are generated in the solar wind when it picks up freshly ionized planetary exospheric ions. These waves grow from the free energy of the highly anisotropic distribution of fresh pickup ions, and are observed in the spacecraft frame with left-handed polarization and a wave frequency near the ion’s gyrofrequency. At Mars and Venus and in the Earth’s polar cusp, the solar wind directly interacts with the planetary exospheres. Ion cyclotron waves with many similar properties are observed in these diverse plasma environments. The ion cyclotron waves at Mars indicate its hydrogen exosphere to be extensive and asymmetric in the direction of the interplanetary electric field. The production of fast neutrals plays an important role in forming an extended exosphere in the shape and size observed. At Venus, the region of exospheric proton cyclotron wave production may be restricted to the magnetosheath. The waves observed in the solar wind at Venus appear to be largely produced by the solar-wind-Venus interaction, with some waves at higher frequencies formed near the Sun and carried outward by the solar wind to Venus. These waves have some similarity to the expected properties of exospherically produced proton pickup waves but are characterized by magnetic connection to the bow shock or by a lack of correlation with local solar wind properties respectively. Any confusion of solar derived waves with exospherically derived ion pickup waves is not an issue at Mars because the solar-produced waves are generally at much higher frequencies than the local pickup waves and the solar waves should be mostly absorbed when convected to Mars distance as the proton cyclotron frequency in the plasma frame approaches the frequency of the solar-produced waves. In the Earth’s polar cusp, the wave properties of ion cyclotron waves are quite variable. Spatial gradients in the magnetic field may cause this variation as the background field changes between the regions in which the fast neutrals are produced and where they are re-ionized and picked up. While these waves were discovered early in the magnetospheric exploration, their generation was not understood until after we had observed similar waves in the exospheres of Mars and Venus.     

Comments on The Jupiter Effect

Several statements, on which the recent book The Jupiter Effect is based, are invalid: The planets will not be “aligned” in 1982, and such an alignment has no effect on solar activity; planetary tides on the Sun are negligible; tides raised on the Sun by Venus, Earth, and Jupiter have a period of 4 mo, not 11 yr, and Wood's curve has no physical justification; there are not more sunspots visible at the eastern limb of the Sun than at the western one; the mean number of sunspots is the same at Venus' inferior and superior conjunctions; the influence of solar flares on sudden changes in the Earth's rotation and on earthquakes is not proved. This leads to the conclusion that there is no evidence for a correlation between planetary positions and earthquakes. The “Jupiter effect” does not exist.     

Tropospheric effects of variable solar activity

Within 12 hr after strong solar flares at middle to high latitudes a cooling at tropopause level is observed along with changes in temperature and height of isobaric levels in the troposphere. Delayed tropospheric effects are reported to occur at 2–4 days after a flare. It is suggested that the early effect through changing the baroclinic instability conditions of the troposphere is responsible for the occurrence of the late effects. Computations show that the observed early effect may amplify the growth rate of the most unstable wave by at least 20% and perhaps by a factor of 1.5 to 2.Proceedings of the 14th ESLAB Symposium on Physics of Solar Variations, 16–19 September 1980, Scheveningen, The Netherlands.     

Ion cyclotron waves,instabilities and solar wind heating

The effect of alpha particles on the dispersion relation of ion cyclotron waves and its influence on the heating of the solar wind plasma are investigated. The presence of alpha particles can dramatically change the dispersion relation of ion cyclotron waves, and significantly influence the way that ion cyclotron waves heat the solar wind plasma. We find that a spectrum of ion cyclotron waves affects the thermal anisotropy of the solar wind protons and other ions differently in interplanetary space: When alpha particles have a speed u _α>0.5v _A, and both protons and alpha particles have a thermal anisotropy T _⊥/T _∥>1, ion cyclotron waves heat protons in the direction perpendicular to the magnetic field, cool them in the parallel direction, and exert the opposite effect on alpha particles.     

Solar and terrestrial parameterizations for radiative-convective models

We present a radiative-convective modelling technique with parameterizations, for both solar and terrestrial radiation transfer, which allow the rapid computation of the mean vertical temperature profile from the ground to the thermosphere. Our method has been specifically designed for modelling the evolution of the Earth's mean vertical temperature structure due to changes in atmospheric composition, variations in the solar flux, surface albedo, cloud cover, water vapour and lapse rate, and changes in the temperature of the thermosphere which is associated with solar activity.     

Coupling of acoustic waves to clouds in the jovian troposphere

Seismology is the best tool for investigating the interior structure of stars and giant planets. This paper deals with a photometric study of jovian global oscillations. The propagation of acoustic waves in the jovian troposphere is revisited in order to estimate their effects on the planetary albedo. According to the standard model of the jovian cloud structure there are three major ice cloud layers (e.g., [Atreya et al., 1999. A comparison of the atmospheres of Jupiter and Saturn: Deep atmospheric composition, cloud structure, vertical mixing, and origin. Planet Space Sci. 47, 1243-1262]). We consider only the highest layers, composed of ammonia ice, in the region where acoustic waves are trapped in Jupiter's atmosphere. For a vertical wave propagating in a plane parallel atmosphere with an ammonia ice cloud layer, we calculate first the relative variations of the reflected solar flux due to the smooth oscillations at about the ppm level. We then determine the phase transitions induced by the seismic waves in the clouds. These phase changes, linked to ice particle growth, are limited by kinetics. A Mie model [Mishchenko et al., 2002. Scattering, Absorption, and Emission of Light by Small Particles. Cambridge Univ. Press, Cambridge, pp. 158-190] coupled with a simple radiation transfer model allows us to estimate that the albedo fluctuations of the cloud perturbed by a seismic wave reach relative variations of 70 ppm for a 3-mHz wave. This albedo fluctuation is amplified by a factor of ∼70 relative to the previously published estimates that exclude the effect of the wave on cloud properties. Our computed amplifications imply that jovian oscillations can be detected with very precise photometry, as proposed by the microsatellite JOVIS project, which is dedicated to photometric seismology [Mosser et al., 2004. JOVIS: A microsatellite dedicated to the seismic analysis of Jupiter. In: Combes, F., Barret, D., Contini, T., Meynadier, F., Pagani, L. (Eds.), SF2A-2004, Semaine de l'Astrophysique Francaise, Les Ulis. In: EdP-Sciences Conference Series, pp. 257-258].