Aerosol in the upper layer of earth’s atmosphere

The upper atmospheric layer of Venus, Mars, Jupiter, Saturn, and earth contains an aerosol layer. The meteorites, rings, and removal of small planetary particles may be responsible for its appearance. The observations from 1979–1992 have shown that the optical aerosol thickness over the earth’s polar regions varies from τ ≈ 0.0002 to 0.1 to λ = 1 μm. The highest τ value was in 1984 and 1992 and was preceded by intense activity of the El Chichon (1982) and Pinatubo (1991) volcanoes. We have shown that increase in τ of the stratospheric aerosol may lead to decrease in ozone layer registered in the 1970s. The nature of the stratospheric aerosol (a real part of the refraction index), effective size particles r, and latitudinal variation τ remain unknown. The analysis of phase dependence of the degree of polarization is effective among the distal methods of determination of n _r and r. The observation value of intensity and degree of polarization in the visible light are caused by the optical surface properties and optical atmospheric thickness, whose values varied with latitude, longitude, and in time. Thus, it is impossible to correctly distinguish the contribution of the stratospheric aerosol. In UV-rays (λ < 300 nm), the ozone layer stops the influence of the surface and earth’s atmosphere up to height of 20–25 km. In this spectrum area, the negative factors are emission of various depolarizating gases, horizontal heterogeneity of the effective optical height of the ozone layer, and oriented particles indicated by variation of the polarization plane.     

Aerosol Component of the Atmosphere of Saturn: Comparison of the Vertical Structure Characteristics in Latitudinal Belts

The altitude dependences of the aerosol and gas scattering components of the effective optical depth in the latitudinal belts of Saturn’s Northern Hemisphere have been obtained from the reflectance spectra in the methane absorption bands at λ = 727 and 619 nm measured in 2015. Zonal characteristics of the vertical structure of the cloud cover of Saturn have been estimated. In the latitudinal belts, the aerosol, the relative concentration of which monotonically decreases with depth in the atmosphere, was found, and no signs of substantial cloud clusterings and rarefactions were observed. The largest and smallest aerosol amounts were determined at the latitudes of 49° N and 80° N, respectively. The altitude levels where the sizes of aerosol particles or their nature may change were revealed. We failed to determine the atmospheric level where the relative concentration of aerosol particles is largest; however, the character of the obtained dependences suggests that such a level is probably in the higher layers of the atmosphere of the giant planet.     

Abnormal Stokes Profiles of the Photospheric Lines in the Region of Chromospheric Dual Flows in the Surroundings of a Solar Pore: 1. Observations

The results of the analysis of the full Stokes profiles of the photospheric lines Fe I λ 630.15 nm and Fe I λ 630.25 nm in a region of chromospheric dual flows appearance in the vicinity of a small pore are presented. The analysis is based on the spectropolarimetric observations of the active region NOAA 11024 with the THEMIS French–Italian telescope (Tenerife Island, Spain). The temporal variations in the high-resolution Stokes parameters I, Q, U, and V were considered for each pixel. It was found that the dual chromospheric flows appeared in the region of the abnormal Stokes profiles of the photospheric lines. Most of the Stokes profiles Q, U, and V have a complex shape and vary greatly from pixel to pixel, which indicates strong inhomogeneities in the structure of the magnetic field in that region. The amplitude and shape of the Stokes profiles were rapidly changing during the observations. A change in the polarity of the photospheric magnetic field took place during the observations in the region of a bright chromospheric point. The evidence of the emergence of a new small-scale magnetic flux of the opposite polarity is obtained; this could lead to magnetic reconnections, appearance of dual chromospheric flows, and occurrence of a microflare.     

On Determining the Vertical Structure of the Aerosol Component in the Atmosphere of Saturn

Relying upon the values of the geometric albedo of Saturn obtained in the methane absorption bands at λ = 887, 864, 842, 727, and 619 nm in 1993, how the aerosol and gaseous scattering components of the effective optical depth change with depth in the atmosphere of the planet are analyzed. The model of homogeneous spherical aerosol particles is used. For the altitude levels in the pressure range from 0.18 to 1.5 bar, that the parameters of aerosol particles used in the analysis are close to their actual values is confirmed. Above the level of 0.054 bar, the presence of stratospheric aerosol was detected. At least seven peculiarities were found in the vertical structure of the cloud cover of the upper atmosphere of Saturn. The altitude position of the maximum relative concentration of aerosol was estimated at approximately a level of 0.3 or 0.12 bar given the relative concentration of methane as 0.0021 or 0.0533, respectively. In the atmospheric layers of Saturn, where the pressure is larger than 0.44 bar, the cloud extended in altitude and containing no distinguishable aerosol layers was found. In the layers deeper than 1.5 bar, indications of probable changes in the parameters of aerosol particles were detected.     

Description of the Martian polar cap breeze

The surface temperature of the Martian polar caps is about 148 K (frost point temperature of CO₂ at a surface pressure of about 6 hPa), with the “desert” (frost-free) areas adjacent to the polar caps having much greater surface temperatures. The existence of this steep meridional gradient of temperature between the polar caps and the adjacent “desert” areas may produce in the atmosphere a baroclinic instability which generates an atmospheric circulation system similar in some aspects to the terrestrial sea breeze. We have called this circulation system the Martian polar cap breeze. In this paper, the phenomenology of the Martian polar cap breeze is developed on the basis of the indirect observational evidence. Along with friction and the Coriolis force, other factors influence the polar cap breeze: the prevailing wind, topography, irregularity of the polar cap-edge, and stability of the atmosphere. These factors are studied in a qualitative form, as well as the seasonal variations. In addition, the large-scale polar cap wind is presented as a different Martian atmospheric circulation system.     

Diagnostics of horizontal velocity field in the solar atmosphere: Line Ba II λ 455.403 nm

We proposed a method for diagnostics of the horizontal velocity field based on 2D observations at the center of the solar disk with high spatial and temporal resolution. The method consists in semiempirical modeling of the solar atmosphere by solving the inverse radiative transfer problem and subsequent obtaining horizontal velocities by solution of the corresponding hydrodynamic equations. We investigated the diagnostic capabilities of the line Ba II λ 455.403 nm (considering hyperfine structure and isotope splitting) for studying the horizontal velocity field of the nonhomogeneous solar atmosphere.     

Complex Refractive Index of Titan's Aerosol Analogues in the 200-900 nm Domain

The main gas-phase constituents of Titan's upper atmosphere, N₂ and CH₄, are photolyzed and radiolyzed by solar photons and magnetospheric electrons, respectively. The primary products of these chemical interactions evolve to heavier organic compounds that are likely to associate into the particles of haze layers that hide Titan's surface. The different theories and models that have been put forward to explain the characteristics and properties of the haze composites require a knowledge of their optical properties, which are determined by the complex refractive index. We present a new set of values for refractive index n and extinction coefficient k calculated directly from the transmittance and reflectance curves exhibited by a laboratory analogue of Titan's aerosols in the 200-900 nm range. Improvements in the aerosol analogue quality have been made. The effects of variables such as the uncertainty in sample thickness, aerosol porosity, and amount of scattered light on the final n and k values are assessed and discussed. Within the studied wavelength domain, n varies from 1.53 to 1.68 and k varies from 2.62×10⁻⁴ to 2.87×10⁻². These final n and k values should be considered as a new reference to modelers who compute the properties of Titan's aerosols in trying to explain the atmospheric dynamics and surface characteristics.     

Time variations of aerosol properties in the atmosphere of uranus

In the present paper, variations in the vertical structure of the cloud layer of the atmosphere of Uranus in 1981, 1993, and 1995 were analyzed from the data on the geometric albedo of Uranus in the profiles of the absorption bands of methane at λ = 543, 619, 702, 727, 842, 864, 887 nm (Neff, et al., 1984; Karkoschka, 1994; 1998). We used Morozhenko’s method that allows us to identify how much the vertical structure of the atmosphere diverges from the conditions of homogeneity. This method is based on the estimation of the optical depths of the layers which form the intensity in the optically-thick vertically homogeneous gasaerosol atmosphere, i.e., the effective optical depths. It has been shown that, at the depths of formation of these absorption bands, there are two extensive cloud layers, the strength of which was maximum in 1981 and minimum in 1995. They are approximately positioned at the levels that correspond to the pressure intervals from 1.4 to 2 bar and from 3.5 to 5.8 bar.     

The study of atmospheric optical parameters according to multiyear photometric observations of the sun in crimea

We describe the construction of an SF-1 automatic sun photometer designed for determining the atmospheric optical parameters in the region of 372–1005 nm during year-round observations (monitoring), as well as an improved method of automatic data processing. Observations in Crimea (in Simferopol with an SF-1 photometer since 2001 and in Karadag with an M-83 standard sun photometer since 1972) are presented. Observation data are analyzed to demonstrate the intra-annual and interannual time dependences of the aerosol optical depths and Angstrom exponents for the atmosphere over Simferopol and Karadag. The considerable decrease in the aerosol optical depth (i.e., an increase in atmospheric transparency over Crimea) since 1993 due to an abrupt decrease in the anthropogenic load on the atmosphere as a result of the suspension of main industrial plants is an important finding.     

Some aspects of a global thermospheric density model deduced from the analysis of the orbit of Intercosmos 13 rocket (1975-22B)

An empirical density formula is explored as a practical model for atmospheric variations and satellite drag analyses. Expanding neutral air density as a series of spherical harmonics and normalizing to a fixed height, an analytical expression for the rate of change of the mean motion is developed for an oblate atmosphere with density scale height varying linearly with altitude. A subset of the coefficients in the density expansion is determined by least-squares adjustment to the observed orbital decay rate of Intercosmos 13 rocket (1975-22B) for the period May 1975–December 1979. Comparisons against four thermospheric models are undertaken for the solar activity effect and the diurnal and semi-annual variations. Given the even spread of data and the increase in solar activity from low to moderate, the air density variation with solar activity is particularly well determined. The results support the “J77” model revealing a greater increase in density with the daily solar index than either the “MSIS” or “DTM” thermospheric models near the solar minimum. Analyses of the diurnal and semi-annual variations are less exact.     

Actinium Abundance in the Atmospheres of Three Red Supergiants in the Magellanic Clouds

The actinium abundance in the atmospheres of red supergiants PMMR23 and PMMR144 in the Small Magellanic Cloud and RM_1-667 in the Large Magellanic Cloud was estimated. The results of spectral observations with the ESO 3.6-m telescope with resolving power R = 30000 were used. Since actinium was not found in the atmospheres of PMMR23 and PMMR144, only the upper limits were set on its abundance: logN(Ac/H) <–15.1 and–15.0, respectively. The estimated abundance of actinium in the atmosphere of RM_1-667 varied with parameters of the atmospheric model from–14.1 to–13.3. The lines of ionized actinium λ 616.475 nm and λ 581.085 nm were used in this analysis.     

Radio science investigations by VeRa onboard the Venus Express spacecraft

The Venus Express Radio Science Experiment (VeRa) uses radio signals at wavelengths of 3.6 and 13 cm (“X”- and “S”-band, respectively) to investigate the Venus surface, neutral atmosphere, ionosphere, and gravity field, as well as the interplanetary medium. An ultrastable oscillator (USO) provides a high quality onboard reference frequency source; instrumentation on Earth is used to record amplitude, phase, propagation time, and polarization of the received signals. Simultaneous, coherent measurements at the two wavelengths allow separation of dispersive media effects from classical Doppler shift.VeRa science objectives include the following:

• (1)Determination of neutral atmospheric structure from the cloud deck (approximately 40 km altitude) to 100 km altitude from vertical profiles of neutral mass density, temperature, and pressure as a function of local time and season. Within the atmospheric structure, search for, and if detected, study of the vertical structure of localized buoyancy waves, and the presence and properties of planetary waves.
• (2)Study of the H₂SO₄ vapor absorbing layer in the atmosphere by variations in signal intensity and application of this information to tracing atmospheric motions. Scintillation effects caused by radio wave diffraction within the atmosphere can also provide information on small-scale atmospheric turbulence.
• (3)Investigation of ionospheric structure from approximately 80 km to the ionopause (<600 km), allowing study of the interaction between solar wind plasma and the Venus atmosphere.
• (4)Observation of forward-scattered surface echoes obliquely reflected from selected high-elevation targets with anomalous radar properties (such as Maxwell Montes). More generally, such bistatic radar measurements provide information on the roughness and density of the surface material on scales of centimeters to meters.
• (5)Detection of gravity anomalies, thereby providing insight into the properties of the Venus crust and lithosphere.
• (6)Measurement of the Doppler shift, propagation time, and frequency fluctuations along the interplanetary ray path, especially during periods of superior conjunction, thus enabling investigation of dynamical processes in the solar corona.

     

Corrected spectral dependence of the imaginary part of the refractive index of aerosol in Jupiter’s atmosphere in the short-wavelength spectral range

To correctly determine the relative contribution of aerosol to the scattering properties of a gas–aerosol medium in the continuum, we propose a method that allows more reliable values of the imaginary part of the refractive index n _i to be obtained for Jupiter’s atmosphere in the short-wavelength spectral range. We considered the measurement data on the spectral values of the geometric albedo of Jupiter acquired in 1993 and used the model of homogeneous spherical aerosol particles. The obtained values of n _i are 0.00378, 0.00309, 0.00254, 0.00175, 0.00123, 0.00084, 0.00064, 0.00045, 0.00031, 0.00033, 0.00013, and 0.00008 at wavelengths λ = 320, 350, 375, 400, 420, 450, 470, 500, 520, 550, 606, and 631 nm, respectively.     

A physical model of Titan's clouds

We have constructed a model of the physical processes controlling Titan's clouds. Our model produces clouds that qualitatively match the present observational constraints in a wide variety of model atmospheres, including those with low atmospheric pressures (25 mbar) and high atmospheric pressures. We find the following: (1) high atmospheric temperatures (160°K) are important so that there is a large scale height in the first few optical depths of cloud; (2) the aerosol mass production occurs at very low aerosol optical depth so that the cloud particles do not directly affect the photochemistry producing them; (3) the production rate of aerosol mass by chemical processes is probably greater than 3.5 × 10^?14 g cm^?2 sec^?1; (4) and the eddy diffusion coefficient is less than 5 × 10⁶ cm² sec^?1 except perhaps in the top optical depth of the cloud. Our model is not extremely sensitive to particle shape, but it is sensitive to particle density. Higher particle densities require larger aerosol mass production rates to produce satisfactory clouds. Particle densities of unity require a mass production rate on the order of 3.5 × 10^?13 g cm^?2 sec^?1. We also show that an increase in mass input causes a decrease in the mean particle size, as required by J. B. Pollack et al. (1980, Geophys. Res. Lett. 7, 829–832), to explain the observed correlation between the solar cycle and Titan's albedo; that coagulation need not be extremely inefficient in order to obtain realistic clouds as proposed by M. Podolak and E. Podolak (1980, Icarus43, 73–83); that coagulation could be inefficient due to photoelectric charging of the particles; and, that the lifetime of particles near the altitude of unit optical depth is a few months, as required to explain the temporal variability observed by S. T. Suess and G. W. Lockwood and D. P. Cruikshank and J. S. Morgan (1979, Bull. Amer. Astron. Soc.11, 564). Although Titan's aerosols are ottically thick in the vertical direction, the atmosphere is so extended that the horizontal visibility is greater than that found anywhere at Earth's surface.     

Atmospheric effect on the upwelling radiation at the top of the atmosphere over a stream

A new version is adopted for the evaluation of the upwelling radiation from atmosphere bounded by the surface, where the surface is composed of two half semi-infinite Lambert surfaces and a stream is inserted between them. The contrast of the stream is discussed with respect to the atmospheric effect. The width of the stream is considered to be 0.5, 1, and 3km; The solar and observational direction is located in the normal plane to the stream. The observational site is located at altitude 30km. The horizontal distance of observational site to the stream is fixed to 6.28 . The atmosphere is assumed to be homogeneous, which is composed of aerosol and molecules, where the model aerosol is of the oceanic type.In the computational procedure, a probability of radiation interacting with respective half surfaces and the stream are calculated based on the assumption of single scattering in the atmosphere, where isotropic scattering is undertaken. By use of this probability, the emergent radiation at the top of the atmosphere is calculated approximately by considering the radiative interactions between atmosphere and surfaces up to twice. The numerical simulation exhibits the extraordinary effect near the stream. The contrast of the stream depends upon the albedo of the surrounding surfaces. It increases with the increase of the stream width and decreases with the optical thickness.     

Saturn's vertical and latitudinal cloud structure 1991-2004 from HST imaging in 30 filters

We analyzed 134 images of Saturn taken by the Hubble Space Telescope between 1991 and 2004. The images cover wavelengths between 231 and 2370 nm in 30 filters. We combined some 10 million calibrated reflectivity measurements into 18,000 center-to-limb curves. We used the method of principal component analysis to find the main latitudinal and temporal variations in Saturn's atmosphere and their spectral characteristics. The first principal variation is a strong latitudinal variation of the aerosol optical depth in the upper troposphere. This structure shifts with Saturn's seasons, but the structure on small scales of latitude stays constant. The second principal variation is a variable optical depth of stratospheric aerosols. The optical depth is large at the poles and small at mid- and low latitudes with a steep gradient in-between. This structure remains essentially constant in time. The third principal variation is a variation in the tropospheric aerosol size, which has only shallow gradients with latitude, but large seasonal variations. Thus, aerosol sizes and their phase functions inferred at a particular season are not representative of Saturn's atmosphere at other seasons. Aerosols are largest in the summer and smallest in the winter. The fourth principal variation is a feature of the tropospheric aerosols with irregular latitudinal structure and fast variability, on the time scale of months. Spherical aerosols do not display the spectral characteristic of that feature. We suspect that variations in the shape of aerosols may play a role. We found a spectral feature of the imaginary index of aerosols, which darkens them near 400 nm wavelength. While we can describe Saturn's variations quite accurately, our presented model of Saturn's average atmosphere is still uncertain due to possible systematic offsets in methane absorption data and limitations of the knowledge about the shape of aerosols. In order to compare our results with those from comparable investigations, which used less than 30 filters, we fit models to spectral subsets of our data. We found very different best-fitting models, depending on the subset of filters, indicating a high sensitivity of results on the spectral sampling.     

Impact of aerosols and adverse atmospheric conditions on the data quality for spectral analysis of the H.E.S.S. telescopes

The Earth’s atmosphere is an integral part of the detector in ground-based imaging atmospheric Cherenkov telescope (IACT) experiments and has to be taken into account in the calibration. Atmospheric and hardware-related deviations from simulated conditions can result in the mis-reconstruction of primary particle energies and therefore of source spectra. During the eight years of observations with the High Energy Stereoscopic System (H.E.S.S.) in Namibia, the overall yield in Cherenkov photons has varied strongly with time due to gradual hardware aging, together with adjustments of the hardware components, and natural, as well as anthropogenic, variations of the atmospheric transparency. Here we present robust data selection criteria that minimize these effects over the full data set of the H.E.S.S. experiment and introduce the Cherenkov transparency coefficient as a new atmospheric monitoring quantity. The influence of atmospheric transparency, as quantified by this coefficient, on energy reconstruction and spectral parameters is examined and its correlation with the aerosol optical depth (AOD) of independent MISR satellite measurements and local measurements of atmospheric clarity is investigated.     

Optical and chemical properties of atmospheric organic aerosols

In the light of recent field and laboratory measurements we developed a structural and chemical model for organic atmospheric aerosols. The model organic aerosol consists of an aqueous core surrounded by a hydrophobic organic layer of biological origin. The role of organic aerosols is to concentrate organic materials at the surface and transport these organic molecules in the atmosphere. The nascent hydrophobic organic aerosol is not expected to nucleate clouds efficiently. Processing by atmospheric radicals creates hydrophilic sites on the surface. The processed, aged organic aerosol is expected to accommodate water and form cloud condensation nuclei. Processing of organic atmospheric aerosols implicates them in atmospheric radiative transfer.     

Mid-infrared detection of large longitudinal asymmetries in Io's SO2 atmosphere

We have observed about 16 absorption lines of the ν₂ SO₂ vibrational band on Io, in disk-integrated 19-μm spectra taken with the TEXES high spectral resolution mid-infrared spectrograph at the NASA Infrared Telescope Facility in November 2001, December 2002, and January 2004. These are the first ground-based infrared observations of Io's sunlit atmosphere, and provide a new window on the atmosphere that allows better longitudinal and temporal monitoring than previous techniques. Dramatic variations in band strength with longitude are seen that are stable over at least a 2 year period. The depth of the strongest feature, a blend of lines centered at 530.42 cm⁻¹, varies from about 7% near longitude 180° to about 1% near longitude 315° W, as measured at a spectral resolution of 57,000. Interpretation of the spectra requires modeling of surface temperatures and atmospheric density across Io's disk, and the variation in non-LTE ν₂ vibrational temperature with altitude, and depends on the assumed atmospheric and surface temperature structure. About half of Io's 19-μm radiation comes from the Sun-heated surface, and half from volcanic hot spots with temperatures primarily between 150 and 200 K, which occupy about 8% of the surface. The observations are thus weighted towards the atmosphere over these low-temperature hot spots. If we assume that the atmosphere over the hot spots is representative of the atmosphere elsewhere, and that the atmospheric density is a function of latitude, the most plausible interpretation of the data is that the equatorial atmospheric column density varies from about 1.5×¹⁰¹⁷ cm⁻² near longitude 180° W to about 1.5×¹⁰¹⁶ cm⁻² near longitude 300° W, roughly consistent with HST UV spectroscopy and Lyman-α imaging. The inferred atmospheric kinetic temperature is less than about 150 K, at least on the anti-Jupiter hemisphere where the bands are strongest, somewhat colder than inferred from HST UV spectroscopy and millimeter-wavelength spectroscopy. This longitudinal variability in atmospheric density correlates with the longitudinal variability in the abundance of optically thick, near-UV bright SO₂ frost. However it is not clear whether the correlation results from volcanic control (regions of large frost abundance result from greater condensation of atmospheric gases supported by more vigorous volcanic activity in these regions) or sublimation control (regions of large frost abundance produce a more extensive atmosphere due to more extensive sublimation). Comparison of data taken in 2001, 2002, and 2004 shows that with the possible exception of longitudes near 180° W between 2001 and 2002, Io's atmospheric density does not appear to decrease as Io recedes from the Sun, as would be expected if the atmosphere were supported by the sublimation of surface frost, suggesting that the atmosphere is dominantly supported by direct volcanic supply rather than by frost sublimation. However, other evidence such as the smooth variation in atmospheric abundance with latitude, and atmospheric changes during eclipse, suggest that sublimation support is more important than volcanic support, leaving the question of the dominant atmospheric support mechanism still unresolved.