Transport of thermospheric NO to the upper stratosphere?

The rate of production of NO in the thermosphere is expected to vary greatly over the course of an 11-year solar cycle because the fluxes of both extreme ultraviolet radiation and auroral particles are known to increase substantially from solar minimum to solar maximum. In the stratosphere, NO participates in a catalytic cycle which constitutes the dominant photochemical destruction mechanism for stratospheric ozone. If appreciable long range transport of NO from the thermosphere to the upper stratosphere occurs, its effects should therefore be manifested in upper atmospheric ozone density variations over the 11-year solar cycle. In this paper, model predictions of the seasonal and latitudinal variations in upper stratospheric O₃ associated with NO transport for different levels of solar activity are compared to satellite observations of upper stratospheric ozone abundances.     

The north-south asymmetry of polarization of Jupiter: The causes of seasonal variations

We present new results obtained from the analysis of the seasonal variations in the asymmetry of polarization of light reflected by Jupiter. From the 23-year set of observations, the anticorrelation between the asymmetries of polarization and insolation has been revealed. The mechanism explaining the observed seasonal variations of polarization has been proposed. The core of this mechanism is the effect of temperature changes in the planetary stratosphere on the processes of the stratospheric aerosol haze formation. Additional irregular factors that may influence the observed polarization asymmetry are considered.     

A Saturnian stratospheric seasonal climate model

Motivated by recent observational evidence that seasonal processes occur within Saturn's stratosphere, we have constructed a seasonal stratospheric climate model. This model predicts stratospheric temperatures, above the P = 0.1-atm level, as a function of time throughout the Saturnian year. Specific results are presented for South-polar and equatorial temperatures. The model predicts that substantial seasonal phase lags exist; maximum stratospheric temperatures at the South pole occur at the Southern Hemisphere's autumnal equinox. Brightness temperature observations at 17.8 μm, taken during 1977/1978, indicate that stratospheric temperatures are greater at the South pole than at the equator. The model is consistent with these observations, predicting enhanced South-polar temperatures, relative to the equator, from 1975 to 1983.     

Temporal variations of polar cap 0I 5577-Å airglow

Limb observations of the E-region 0I 5577-Å airglow in the polar caps were obtained during 1971 and 1972 from the ISIS-2 satellite. In the southern polar cap the emission rate decreased to a broad minimum of 100 R near solstice, then increased later in the winter. In the northern polar cap a maximum was observed in November. In addition to large daily variations, there were enhancements that lasted several weeks. From a correlation analysis using both satellite data supplemented by the more extensive data base of Mullen et al. (1977,Planet. Space Sci.25, 23) and stratospheric temperatures, it is clear that stratospheric warmings result in polar cap airglow enhancements. The most plausible cause of these airglow enhancements appears to be increased meridional transport of atomic oxygen into the polar cap.     

Bolide Energy Estimates from Infrasonic Measurements

The acoustic amplitude-yield relationships, including formal errors, for a population of energetic (>0.05 kt) and well-observed bolide events have been investigated. Using various infrasonic signal measurements as a function of range, these data have been calibrated against optical yield estimates from satellite measurements. Correction for the presence of stratospheric winds has also been applied to the observations and is found to be small, suggesting that either scatter is dominated by other variations amongst the fireball population such as differing burst altitudes and greater or lesser amounts of fragmentation or the magnitude of the variability in the stratospheric winds, which can be comparable to or even exceed the strength of the winds themselves. Comparison to similar point source, ground-level nuclear and high explosive airwave data shows that bolide infrasound is consistently lower in amplitude. This downward shift relative to nuclear and HE data is interpreted as due in part to increased weak non-linearity during signal propagation from higher altitudes. This is a likely explanation, since mean estimates of the altitude of maximum ene0rgy deposition along the bolide trajectory was found to be between 20 and 30 km altitude for this fireball population.     

Thermal structure of Uranus' atmosphere.

Application of a radiative-convective equilibrium model to the thermal structure of Uranus' atmosphere evaluates the role of hazes in the planet's stratospheric energy budget and places a lower limit on the internal energy flux. The model is constrained by Voyager and post-Voyager observations of the vertical aerosol and radiative active gas profiles. Our baseline model generally reproduces the observed tropospheric and stratospheric temperature profile. However, as in past studies, the model stratosphere from about 10(-3) to 10(-1) bar is too cold. We find that the observed stratospheric hazes do not warm this region appreciably and that any postulated hazes capable of warming the stratosphere sufficiently are inconsistent with Voyager and ground-based constraints. We explore the roles played by the stratospheric methane abundance, the H2 pressure-induced opacity, photochemical hazes, and C2H2, and C2H6 in controlling the temperature structure in this region. Assuming a vertical methane abundance profile consistent with that found by the Voyager UVS occultation observations, the model upper stratosphere, from 10 to 100 microbar, is also too cold. Radiation in the 7.8-micrometers band from a small abundance of hot methane in the lower thermosphere absorbed in this region can warm the atmosphere and bring models into closer agreement with observations. Finally, we find that internal heat fluxes < or approximately 60 erg cm-2 sec-1 are inconsistent with the observed tropospheric temperature profile.     

Global and temporal variations in hydrocarbons and nitriles in Titan's stratosphere for northern winter observed by Cassini/CIRS

Mid-infrared spectra measured by Cassini's Composite InfraRed Spectrometer (CIRS) between July 2004 and January 2007 (Ls=293°-328°) have been used to determine stratospheric temperature and abundances of C₂H₂, C₃H₄, C₄H₂, HCN, and HC₃N. Over 65,000 nadir spectra with spectral resolutions of 0.5 and 2.5 cm⁻¹ were used to probe spatial and temporal composition variations in Titan's stratosphere. Cassini's 180° orbital transfer in mid-2006 allowed low emission angle observations of the north polar region for the first time in the mission and allowed us to probe the full latitude range. We present the first measurements of composition variations within the polar vortex, which display increasing abundances right up to 90° N. The lack of a homogeneous abundance-latitude variation within the vortex indicates limited horizontal mixing and suggests that subsidence is greatest at the vortex core. Contrary to numerical model predictions and tropospheric cloud observations, we do not see any evidence for a secondary circulation cell near the south pole, which suggests a single Hadley-type circulation in the stratosphere at this epoch. This difference can be reconciled if the secondary cell is restricted to altitudes below 100 km, where there is no sensitivity in our data. Temporal variations in composition were observed in the south, with volatile species becoming less abundant as the season progressed. The observed variations are compared to numerical model predictions and observations from Voyager.     

Spectrophotometry of Jupiter in the Wavelength Range 320–1100 nm: Long-Term Observations of Variations over the Disk

Based on long-term spectrophotometric observations of Jupiter in the wavelength range 320–1100 nm, we investigate the variations of aerosol extinction (at 320–600 nm) and methane–ammonia absorption (at 600–1100 nm) over Jupiter's disk. We give estimates of the optical parameters for the upper cloud layer of the planet, the overlying stratospheric haze, and a Rayleigh atmosphere.     

Discussion of the 60 year total ozone record at Arosa based on measurements of the vertical distribution and a meteorological parameter

On G. M. B. Dobson's initiative, ozone measurements were started by Götz at Arosa, Switzerland, in 1926, which led to the longest total ozone record in the world over 60 years. Later these measurements were supplemented by Umkehr observations, also at Arosa, and by ozone soundings at Payerne, Switzerland, yielding the concurrent vertical distribution which allows among other things to distinguish between regional and hemispheric scale processes influencing total ozone. Using a meteorogical parameter a method is developed which allows the extension of this distinction to the early period without measurements of the vertical distribution, although with somewhat larger uncertainty. On this basis the ozone variations over Arosa during the past 60 years are discussed.

The ozone loss around the level of the ozone maximum contributed most to the strong decline in the total amount observed between 1970 and 1988. High loss rates were further detected in the upper stratosphere, extending down into the middle stratosphere. While the upper stratospheric decrease is very probably largely a consequence of the CFC input into the atmosphere the loss at the lower level seems to be only partly due to that reason, but in its main contribution to be produced by circulation changes. About one-third of the stratospheric ozone decline is compensated by rapidly rising concentrations in the troposphere caused by increasing air pollution.     

Parameters of Acoustic Signals Generated by the Atmospheric Meteoroid Explosion over Romania on January 7, 2015

System spectral analysis of temporal variations in the level of acoustic signals recorded at a number of European infrasound stations is carried out. The prevailing periods that varied within 3–5 s are found. Initial kinetic and acoustic energies of the Romanian meteoroid and infrasound parameters are calculated: celerity (280 m/s), acoustic efficiency, and stratospheric wind velocity (about 20 m/s). Parameters of cylindrical and explosive shock waves are found: duration, characteristic size, and amplitude. The dependence of the attenuation of infrasonic waves on distance is estimated. The results of the estimates are in good agreement with the results of the observations.     

Stratospheric H2O

The present state of our knowledge and understanding of H₂O in the stratosphere is reviewed. This reveals continuing discrepancies between observations and expectations following from the Brewer-Dobson hypothesis of stratospheric circulation. In particular, available observations indicate unexplained upward and poleward directed H₂O gradients immediately downstream from the tropical tropopause and variable vertical gradients above 20 km which generally disagree with those expected from oxidation of CH₄.     

The CH4 Density in the Upper Atmosphere of Titan

Previous modeling by Banaszkiewicz et al. (2000a,b) showed that the CH₄ thermospheric mixing ratio on Titan could vary as much as 35-40% due to ion-neutral chemical reactions. A new vertical methane profile has been computed by simultaneously modifying the stratospheric methane mixing ratio and the K(z) previously considered by Lara et al. (1996) and Banaszkiewicz et al. (2000a,b). A satisfactory fit of the methane thermospheric abundance and stratospheric mixing ratio of other minor constituents is achieved by placing the homopause at ∼1000 km and increasing the methane stratospheric mixing ratio (q_CH4) up to 3.8%. The new proposed eddy diffusion coefficient steadily rises from 1×10⁷ cm² s⁻¹ at 700 km to 1×10¹⁰ cm² s⁻¹ at 1500 km, whereas the stratospheric values are in the range (4-20)×10³ cm² s⁻¹. Other likely ionization sources that can influence the methane distribution are (i) a metallic ion layer produced by micrometeoroid infall and (ii) frequent X-rays solar flares. Analysis of the effects of these ionization sources on the methane distribution indicates that, unlike previously assumed, CH₄ can suffer considerable variations. These variations, although proved in this work, must be cautiously regarded since several assumptions have to be made on the rate of N₂ and CH₄ ionization by the processes previously mentioned. Hence, these results are only indicative of methane sensitivity to ionospheric chemistry.     

Temporal variability of ultraviolet cloud features in the Venus stratosphere

Statistics on the temporal variability of uv cloud features on Venus during 66 days of nominal mission imaging by the Pioneer Venus Orbiter Cloud Photopolarimeter reveal at least five types of systematic variability on large scales: (1) a low-latitude global-scale wave of period 3.94 ± 0.1 days corresponding to longitudinal motion of the dark equatorial band and propagating westward relative to the mean flow; (2) a midlatitude wave of period 5.20 ± 0.2 days corresponding to wavenumber 1 oscillations of the latitude of the bright polar bands and propagating eastward relative to the mean flow; (3) ～2- to 3-week fluctuations in the slope of longitudinal cloud brightness power spectra at intermediate wavenumbers manifested by variations in the intensity of large bow-shaped features; (4) ～2-month variations in polar region brightness consistent with polar brightening episodes observed from Earth; and (5) a monotonic decrease in the disk-integrated brightness of Venus during the nominal mission which may be either a true time variation or a solar-locked longitudinal dependence of brightness. Small-scale features appear to correlate with large-scale albedo patterns. Specifically, cellular features exist primarily where large-scale dark material is present, while the orientation of streak features with respect to latitude circles oscillates with the same ～4-day period as the large-scale features at low latitudes. The wide range of time scales present in the data suggests the complexity of Venus stratospheric dynamics. Extended observations over many years may be becessary to define the general circulation.     

Ozone and temperature fluctuations in the strato-mesosphere with solar activity

The response of the stratosphere and lower mesosphere to quasi-eleven-year solar activity cycle (indicated by sunspot variations) is studied by using temperature data obtained from rockets which are mostly based on datasonde system throughout the decade 1969–1978. It is suggested that the solar trace is evident at wintertime in the strato-mesosphere over low and middle latitudes. At summertime in the lower mesosphere over high latitudes the solar trace is absent. During springtime the solar signal appears over low latitudes and diminishes to the middle and high latitudes. The reverse occurs at falltime. The observed stratospheric temperature and ozone variations during the solar activity cycle are possibly within model calculations of UV and solar particle enhancements at solar maximum.     

The spectra of Uranus and Neptune at 8–14 and 17–23 μm

An array spectrometer was used on the nights of 1985 May 30–June 1 to observe the disks of Uranus and Neptune in the spectral regions 7–14 and 17–23 μm with effective resolution elements ranging from 0.23 to 0.87 μm. In the long-wavelength region, the spectra are relatively smooth with the broad S(1) H₂ collision-induced rotation line showing strong emission for Neptune. In the short-wavelength spectrum of Uranus, an emission feature attributable to C₂H₂ with a maximum stratospheric mixing ratio of 9 × 10⁻⁹ is apparent. An upper limit of 2 × 10⁻⁸ is placed on the maximum stratospheric mixing ratio of C₂H₆. The spectrum of Uranus is otherwise smooth and quantitatively consistent with the opacity provided by H₂ collision-induced absorption and spectrally continuous stratospheric emission, as would be produced by aerosols. Upper limits to detecting the planet near 8 μm indicate a CH₄ stratospheric mixing ratio of 1 × 10⁻⁵ or less, below a value consistent with saturation equilibrium at the temperature minimum. In the short-wavelength spectrum of Neptune, strong emission features of CH₄ and C₂H₆ are evident and are consistent with local saturation equilibrium with maximum stratospheric mixing ratios of 0.02 and 6 × 10⁻⁶, respectively. Emission at 8–10 μm is most consistent with a [CH₃D]/[CH₄] volume abundance ratio of 5 × 10⁻⁵. The spectrum of Neptune near 13.5 μm is consistent with emission by stratospheric C₂H₂ in local saturation equilibrium and a maximum mixing ratio of 9 × 10⁻⁷. Radiance detected near 10.5 μm could be attributed to stratospheric C₂H₄ emission for a maximum mixing ratio of approximately 3 × 10⁻⁹. Quantitative results are considered preliminary, as some absolute radiance differences are noted with respect to earlier observations with discrete filters.     

Seasonal change on Saturn from Cassini/CIRS observations, 2004-2009

Five years of thermal infrared spectra from the Cassini Composite Infrared Spectrometer (CIRS) are analyzed to determine the response of Saturn’s atmosphere to seasonal changes in insolation. Hemispheric mapping sequences at 15.0 cm⁻¹ spectral resolution are used to retrieve the variation in the zonal mean temperatures in the stratosphere (0.5-5.0 mbar) and upper troposphere (75-800 mbar) between October 2004 (shortly after the summer solstice in the southern hemisphere) and July 2009 (shortly before the autumnal equinox).Saturn’s northern mid-latitudes show signs of dramatic warming in the stratosphere (by 6-10 K) as they emerge from ring-shadow into springtime conditions, whereas southern mid-latitudes show evidence for cooling (4-6 K). The 40-K asymmetry in stratospheric temperatures between northern and southern hemispheres (at 1 mbar) slowly decreased during the timespan of the observations. Tropospheric temperatures also show temporal variations but with a smaller range, consistent with the increasing radiative time constant of the atmospheric response with increasing pressure. The tropospheric response to the insolation changes shows the largest magnitude at the locations of the broad retrograde jets. Saturn’s warm south-polar stratospheric hood has cooled over the course of the mission, but remains present.Stratospheric temperatures are compared to a radiative climate model which accounts for the spatial distribution of the stratospheric coolants. The model successfully predicts the magnitude and morphology of the observed changes at most latitudes. However, the model fails at locations where strong dynamical perturbations dominate the temporal changes in the thermal field, such as the hot polar vortices and the equatorial semi-annual oscillation (Orton, G., and 27 colleagues [2008]. Nature 453, 196-198). Furthermore, observed temperatures in Saturn’s ring-shadowed regions are larger than predicted by all radiative-climate models to date due to the incomplete characterization of the dynamical response to the shadow. Finally, far-infrared CIRS spectra are used to demonstrate variability of the para-hydrogen distribution over the 5-year span of the dataset, which may be related to observed changes in Saturn’s tropospheric haze in the spring hemisphere.     

On some properties of the photospheric structure

New observations made on board the stratospheric solar observatory (SSO) in 1973 confirm the conclusion of the previous paper (Krat, 1972) showing a more rough structure of the chromosphere in comparison with the photosphere.     

Impact of the seasonal variations of composition on the temperature field of Titan’s stratosphere

We investigate the role of seasonal variations of Titan’s stratospheric composition on the temperature. We use a general circulation model coupled with idealized chemical tracers that reproduce variations of ethane (C₂H₆), acetylene (C₂H₂), and hydrogen cyanide (HCN). Enhancement of the mole fractions of these compounds, at high latitudes in the winter hemisphere relative to their equatorial values, induces a relative decrease in temperature above approximately 0.2 mbar, with a peak amplitude around −20 K, and a relative increase in temperature below, around 1 mbar, with a peak amplitude around +7 K. These thermal effects are mainly due to the variations of the cooling to space induced by the varying distributions. The ethane, acetylene, and hydrogen cyanide variations affect the cooling rates in a similar way, with the dominant effect being due to ethane, though its latitudinal variations are small.     

Titan’s 5-μm window: observations with the Very Large Telescope

We report on mid-resolution (R∼2000) spectroscopic observations of Titan, acquired in November 2000 with the Very Large Telescope and covering the range 4.75-5.07 μm. These observations provide a detailed characterization of the CO (1-0) vibrational band, clearly separating for the first time individual CO lines (P10 to P19 lines of ¹³CO). They indicate that the CO/N₂ mixing ratio in Titan’s troposphere is 32±10 ppm. Comparison with photochemical models indicates that CO is not in a steady state in Titan’s atmosphere. The observations confirm that Titan’s 5-μm continuum geometric albedo is ∼0.06, and further indicates a ∼20% albedo decrease over 4.98-5.07 μm. Nonzero flux is detected at the 0.01 geometric albedo level in the saturated core of the ¹²CO (1-0) band, at 4.75-4.85 μm, providing evidence for backscattering on the stratospheric haze. Finally, emission lines are detected at 4.75-4.835 μm, coinciding in position with lines from the CO(1-0) and/or CO(2-1) bands. Matching them by thermal emission would require Titan’s stratosphere to be much warmer (by ∼ 25 K at 0.1 mbar) than indicated by the methane 7.7-μm emission and the Voyager radio-occultation. We show instead that a nonthermal mechanism, namely solar-excited fluorescence, is a more plausible source for these emissions. Improved observations and laboratory measurements on the vibrational-translational relaxation of CO are needed for further interpretation of these emissions in terms of a CO stratospheric mixing ratio.     

Meridional variations in stratospheric acetylene and ethane in the southern hemisphere of the saturnian atmosphere as determined from Cassini/CIRS measurements

These are the first results from nadir studies of meridional variations in the abundance of stratospheric acetylene and ethane from Cassini/CIRS data in the southern hemisphere of Saturn. High resolution, 0.5 cm⁻¹, CIRS data was used from three data sets taken in June-November 2004 and binned into 2° wide latitudinal strips to increase the signal-to-noise ratio. Tropospheric and stratospheric temperatures were initially retrieved to determine the temperature profile for each latitude bin. The stratospheric temperature at 2 mbar increased by 14 K from 9° to 68° S, including a steep 4 K rise between 60° and 68° S. The tropospheric temperatures showed significantly more meridional variation than the stratospheric ones, the locations of which are strongly correlated to that of the zonal jets. Stratospheric acetylene abundance decreases steadily from 30 to 68° S, by a factor of 1.8 at 2.0 mbar. Between 18° and 30° S the acetylene abundance increases at 2.0 mbar. Global values for acetylene have been calculated as (1.9±0.19)×¹⁰⁻⁷ at 2.0 mbar, (2.6±0.27)×¹⁰⁻⁷ at 1.6 mbar and (3.1±0.32)×¹⁰⁻⁷ at 1.4 mbar. Global values for ethane are also determined and found to be (1.6±0.25)×¹⁰⁻⁵ at 0.5 mbar and (1.4±0.19)×¹⁰⁻⁵ at 1.0 mbar. Ethane abundance in the stratosphere increases towards the south pole by a factor of 2.5 at 2.0 mbar. The increase in stratospheric ethane is especially pronounced polewards of 60° S at 2.0 mbar. The increase of stratospheric ethane towards the south pole supports the presence of a meridional wind system in the stratosphere of Saturn.