Gravitational tidal waves in Titan's upper atmosphere

Tidal waves driven by Titan's orbital eccentricity through the time-dependent component of Saturn's gravitational potential attain nonlinear, saturation amplitudes (|T^′|>10 K, , and ) in the upper atmosphere (?500 km) due to the approximate exponential growth as the inverse square root of pressure. The gravitational tides, with vertical wavelengths of ∼100-150 km above 500 km altitude, carry energy fluxes sufficient in magnitude to affect the energy balance of the upper atmosphere with heating rates in the altitude range of 500-900 km.     

Joule heating and temperature in the upper atmosphere

Joule heating has been shown to be very effective in increasing electronic temperature in the upper atmosphere. It is found theoretically that the electronic temperature can rise up to several thousands °K soon after certain ionospheric current disturbances occur, while the temperature of neutral particles increases only very slowly. Temperatures in various conditions have been computed and are found to be compatible with observation. It is also possible that the high electronic temperatures may explain the excitation of certain auroral glows.     

Transient heating of the upper atmosphere by auroral electric field

Magnetohydrodynamic formulation has been used to deduce the velocity distribution of the upper atmospheric movement caused by the auroral electric field at the thermospheric height. The expressions for Joule heating and viscous heating are obtained. Numerical analysis has been made to estimate their magnitudes as well as the rate of their variations with time. The results are presented graphically.     

Estimated energy balance in the jovian upper atmosphere during an auroral heating event

We present an analysis of a series of observations of the auroral/polar regions of Jupiter, carried out between September 8 and 11, 1998, making use of the high-resolution spectrometer, CSHELL, on the NASA InfraRed Telescope Facility (IRTF), Mauna Kea, Hawaii; these observations spanned an “auroral heating event.” This analysis combines the measured line intensities and ion velocities with a one-dimensional model vertical profile of the jovian thermosphere/ionosphere. We compute the model line intensities both assuming local thermodynamic equilibrium (LTE) and, relaxing this condition (non-LTE), through detailed balance calculations, in order to compare with the observations. Taking the model parameters derived, we calculate the changes in heating rate required to account for the modelled temperature profiles that are consistent with the measured line intensities. We compute the electron precipitation rates required to give the modelled ion densities that are consistent with the measured line intensities, and derive the corresponding Pedersen conductivities. We compute the changes in heating due to Joule heating and ion drag derived from the measured ion velocities, and modelled conductivities, making use of ion-neutral coupling coefficients derived from a 3-D global circulation model. Finally, we compute the cooling due to the downward conduction of heat and the radiation-to-space from the molecular ion and hydrocarbons. Comparison of the various heating and cooling terms enables us to investigate the balance of energy inputs into the auroral/polar atmosphere. Increases in Joule heating and ion drag are sufficient to explain the observed heating of the atmosphere; increased particle precipitation makes only a minor heating contribution. But local cooling effects—predominantly radiation-to-space—are shown to be too inefficient to allow the atmosphere to relax back to pre-event thermal conditions. Thus we conclude that this event provides observational, i.e. empirical, evidence that heat must be transported away from the auroral/polar regions by thermally or mechanically driven winds.     

Solar heating of the Martian dusty atmosphere

This paper examines the solar heating of the Martian atmosphere during the 1971 global dust storm observed by Mariner 9. Radiative scattering as well as absorption is included by utilizing the delta-Eddington approximation to the full radiative transfer equation. The necessary optical parameters are generated by a Mie program which uses a size distribution and a complex refractive index inferred from a number of sources, particularly from recent analyces of Mariner 9 UVS and TV observations. Assuming uniform mixing of the dust, the solar heating per unit mass during a Martian global dust storm is remarkably uniform with height for small solar zenith angles. Heating rates may reach 80°K day^? for overhead sunlight. Overall, 20% of the direct insolation is absorbed by the dust-laden atmosphere. Even optically thin widespread dust hazes may produce heating rates of several degrees Kelvin per day.     

Density models for the upper atmosphere

Modeling the effects of atmospheric drag is one of the more important problems associated with the determination of the orbit of a near-earth satellite. Errors in the drag model can lead to significant errors in the determination and prediction of the satellite motion. The uncertainty in the drag acceleration can be attributed to three separate effects: (a) errors in the atmospheric density model, (b) errors in the ballistic coefficient, and (c) errors in the satellite relative velocity. In a number of contemporary satellite missions, the requirements for performing the orbit determination and predictions in near real-time has placed an emphasis on density model computation time as well as the model accuracy. In this investigation, a comparison is made of three contemporary atmospheric density models which are candidates for meeting the current orbit computation requirements. The models considered are the analytic Jacchia-Roberts model, the modified Harris-Priester model, and the USSR Cosmos satellite derived density model. The computational characteristics of each of the models are compared and a modification to the modified Harris-Priester model is proposed which improves its ability to represent the diurnal variation in the atmospheric density.This investigation was supported by the NASA Goddard Spaceflight Center under contract NAS5-20946 and Contract NSG 5154.     

Infrared heating of Comet Halleys atmosphere

The warm circumnuclear dust in the inner cometary coma reradiates in the IR in the wavelength range of the ground state rotational band of the dominant atmospheric molecule, H₂O. However, the interaction of this radiation with H₂O has hitherto not been taken into account in cometary atmospheric models. Here we have extended our earlier two-phase, multifluid model of the dusty atmosphere by including this effect. Although this IR radiation initially pumps the rotational levels of H₂O, frequent intermolecular collisions in the inner coma transfer this energy from rotational modes to translational modes. As a result the temperature in the innermost coma no longer decreases to about 10 K, as predicted by the earlier models, but reaches a minimum of only about 120 K.     

Auroral heating and the composition of the neutral atmosphere

Heating of the neutral atmosphere by auroral particle fluxes and by orthogonal electric fields is responsible for large changes in the thermospheric composition that have been observed by satellite mass spectrometers. Vertical winds of a few meters per second are produced in the region subject to auroral heating; this vertical upwelling drives circulation cells that extend the effects of heating in the auroral region on a global scale. Our analysis focuses on the initial phase of a magnetic storm within the auroral region.     

NO infrared radiation in the upper atmosphere

A kinetic model is developed for the prediction of upper atmospheric i.r. radiation from the vibrational bands of NO. The model is appropriate to both the quiescent and aurorally excited nighttime atmosphere and has been exercised to examine the variation in NO radiation levels which can result from both natural atmospheric variability and uncertainties in kinetic parameters. Comparisons between model predictions and i.r. radiance data are presented.     

The aeronomy of the upper atmosphere of Venus

Density profiles for CO, O, and O₂ in the Cytherean atmosphere above 90 km are plotted with eddy diffusion coefficient (K) as a parameter, subject to the constraint that the mixing ratios of CO and O₂ approach their observed value or values under the observed upper limit at the lower boundary. It is then shown that the value of K puts upper limits on the amount of hydrogen (in the form of H₂O, HCl, and H₂) the atmosphere near 90km can contain. This value is a function of the density and temperature of hydrogen at the critical level and the magnitude of the total escape flux, where unspecified flux mechanisms other than thermal are postulated ad hoc. In general these constraints call for large values of K to accomodate the atomic hydrogen produced by measured mixing ratios of HCl and H₂O. Hence they constrain thee amount of O in the upper atmosphere to values well under 1% at 130 km unless there are very large hydrogen escape fluxes, 10⁷ cm^?2sec^?1 or larger. The freedom to assume arbitrary amounts of H₂ in the atmosphere is also restricted. We suggest either very effective escape mechanisms—despite low exospheric hydrogen densities—or novel excitation mechanisms for O(3³S) and O(3⁵S) in the upper atmosphere.     

Transverse motions and wave heating of the solar atmosphere

Periodic shaking or buffeting of magnetic flux tubes could generate magnetohydrodynamic waves which propagate along the flux tubes and dissipate energy in the chromosphere and/or corona. If we make an assumption that the G-band bright points represent flux tubes, then there should exist a relationship between the transverse motions and the brightening of these bright points. We tracked a total of 56 bright points, obtained their velocity and intensity power spectrum. We also estimated the r.m.s. velocity, average velocity, r.m.s. intensity and average intensity of these bright points. We do not see any clear evidence for a relationship between these estimated quantities.     

Hydrocarbon photochemistry in the upper atmosphere of Jupiter

The hydrocarbon photochemistry in the upper atmosphere of Jupiter is investigated using a one-dimensional, photochemical-diffusive, and diurnally averaged model. The important chemical cycles and pathways among the major species are outlined and a standard model for the North Equatorial Belt region is examined in detail. It is found that several traditionally dominant chemical pathways among the C and C2 species are replaced in importance by cycles involving C-C4 species. The pressure and altitude profiles of mixing ratios for several observable hydrocarbon species are compared with available ultraviolet- and infrared-derived abundances. The results of sensitivity studies on the standard model with respect to variations in eddy diffusion profile, solar flux, atomic hydrogen influx, latitude, temperature, and important chemical reaction rates are presented. Measured and calculated airglow emissions of He at 584 angstroms and H at 1216 angstroms are also used to provide some constraints on the range of model parameters. The relevance of the model results to the upcoming Galileo mission is briefly discussed. The model is subject to considerable improvement; there is a great need for laboratory measurements of basic reaction rates and photodissociation quantum yields, even for such simple species as methylacetylene and allene. Until such laboratory measurements exist there will be considerable uncertainty in the understanding of the C3 and higher hydrocarbons in the atmospheres of the jovian planets.     

Effects of solar variations on the upper atmosphere

Several semi-empirical models of the terrestrial upper atmosphere are presently available. These models take into account solar activity effects by using the solar decimetric flux as an index. Such a procedure is a consequence of the lack of continuous determinations of the solar spectrum directly responsible for the physical structure of the upper atmosphere. Variations of the thermopause temperature are discussed. Using five sets of solar irradiances measured in the ultraviolet and in the extreme ultraviolet, the penetration of solar radiation is analyzed as a function of solar activity. Several examples of absorption profiles and ion production rates are discussed for variable conditions. Various energetic effects are also described. All computations are made for physical conditions above Scheveningen (52.08° N) where the 14th ESLAB symposium was held.Proceedings of the 14th ESLAB Symposium on Physics of Solar Variations, 16–19 September 1980, Scheveningen, The Netherlands.     

Bulk mineralogical changes of hydrous micrometeorites during heating in the upper atmosphere at temperatures below 1000 °C

Abstract— Small particles 200 μm in diameter from the hydrous carbonaceous chondrites Orgueil CI, Murchison CM2, and Tagish Lake were experimentally heated for short durations at subsolidus temperatures under controlled ambient pressures in order to examine the bulk mineralogical changes of hydrous micrometeorites during atmospheric entry. The three primitive meteorites consist mainly of various phyllosilicates and carbonates that are subject to decomposition at low temperatures, and thus the brief heating up to 1000 °C drastically changed the mineralogy. Changes included shrinkage of interlayer spacing of saponite due to loss of molecular water at 400–600 °C, serpentine and saponite decomposition to amorphous phases at 600 and 700 °C, respectively, decomposition of Mg‐Fe carbonate at 600 °C, recrystallization of secondary olivine and Fe oxide or metal at 700–800 °C, and recrystallization of secondary low‐Ca pyroxene at 800 °C. The ambient atmospheric pressures controlled species of secondary Fe phase: taenite at pressures lower than 10^?2 torr, magnesiowüstite from 10^?3 to 10^?1 torr, and magnetite from 10^?2 to 1 torr. The abundance of secondary low‐Ca pyroxene increases in the order of Murchison, Orgueil, and Tagish Lake, and the order corresponds to saponite abundance in samples prior to heating. Mineralogy of the three unmelted micrometeorites F96CI024, kw740052, and kw740054 were investigated in detail in order to estimate heating conditions. The results showed that they might have come from different parental objects, carbonaterich Tagish Lake type, carbonate‐poor Tagish Lake or CI type, and CM type, respectively, and experienced different peak temperatures, 600, 700, and 800?900 °C, respectively, at 60–80 km altitude upon atmospheric entry.     

Photon heating of the atmosphere at F-region heights

The transfer of energy from an ionizing photon to the atoms and molecules of the neutral gas in the F-region of the atmosphere is investigated. It is found that photoionization heating should be divided into two parts: (1) photoelectron heating associated with the slowing down of the fast photoelectrons formed by photoionization; and (2) reaction heating associated with the chemical reactions undergone by the ions formed in the photoionization process. The photoelectron heating will take place near the time and place of photoionization while the reaction heating will occur at the time and place of the ionic reactions.

Photoelectron and reaction heating rates per unit column are computed for the daytime, and reaction heating rates per unit column are computed for the nighttime. It is concluded that: (1) chemical reactions at night lead to a small but significant amount of F-region heating; and (2) reaction heating during the day is nearly proportional to the cosine of the solar zenith angle except near sunrise and sunset.     

I.R. Radiation of the upper atmosphere

A theory of the i.r. radiation (2–20 μ) of the upper atmosphere (90–250 km height) has been developed. It includes the calculation of concentrations and temperatures as well as the analysis of atomic and molecular level population kinetics. Various excitation and quenching processes are analysed. Results are given for the following bands: NO (5.3μ), NO⁺(4.3μ.), CO (4.7 μ), N¹⁴N¹⁵ (4.4 μ), CO₂(4.3 and 15 μ), H₂O(2.7 and 6.3 μ), N₂O(4.5; 7.8 and 17μ), O₃(9.6 and 14.4 μ). The energy aspect of the problem is discussed. It is found that at a height of 120 km intensity in the region of 2 to 20 μ 3 to 10 is that of the 63 μ line of atomic oxygen. The comparison of theory with the experiment was carried out and satisfactory agreement obtained. The correlations of intensities in i.r. bands and emissions in visible and u.v. spectra were considered.     

A revaluation of the rotational speed of the upper atmosphere

In this paper the rotational speed of the upper atmosphere, mainly at heights of 200–300 km, is evaluated from the changes in the orbital inclinations of thirteen satellites. The values obtained represent the mean rotational speed over the latitudes covered by the satellites, at dates between late 1962 and early 1966, i.e. when solar activity was low.

If the angular velocity of the atmosphere is taken as Λ times that of the Earth, the values of Λ found are mostly between 1.0 and 1.6 with estimated S.D. between 0.1 and 0.25. If we exclude two values at heights above 300 km and one anomalous value, the mean of the remaining ten values of Λ obtained is 1.27, with r.m.s. scatter 0.18: this would correspond to an average west-to-east wind of about 100 m/sec in mid-latitudes.     

On the presence of cosmic dust in the upper atmosphere

The activity of Librids on 4 April 1973 was detected by the rise of the twilight luminosity. The ratio of circumzenithal luminosity in the antisolar to solar azimuth also increases in the presence of cosmic dust in the upper atmosphere.