Photochemical growing of complex organics in planetary atmospheres

UV induced syntheses of organic compounds from the main atmospheric constituents can be a very important source of organics in a given planetary environment provided the atmosphere is in a reduced state. The evolution of a CO₂ rich medium only produces very low yields of formaldehyde and related oxygenated compounds. Considering a CO rich atmosphere, the photochemical yield of O-organics formation is much higher, when the synthesis of N-organics remains difficult. The most favourable atmosphere as far as photochemical organic synthesis is concerned is a CH₄ rich milieu.. The photochemical evolution of such a CH₄ atmosphere under UV irradiation leads to a chain of various organics, the complexity of which increases together with the number of pathways involved in their formation. Their complexity also closely correlates with their UV photoabsorption spectrum: the more complex they are, the more shifted is their UV spectrum toward the visible range. Direct photodissociation of methane requires UV photon of wavelengths shorter than about 145 nm. It mainly produces ethane which absorbs UV at wavelengths shorter than about 160 nm, and acetylene, that presents an absorption spectrum extending up to 200 nm. This shift still continuously increases with further increase in number of C atoms. Unsaturated hydrocarbons with 4 and more C atoms have UV absorption characteristics including noticeable band structures in the 250–300 nm range. This trend has very important implication in the photochemical behaviour of a CH₄-rich planetary atmosphere, as it induces many catalytic processes. The occurrence of such processes is closely related to vertical atmospheric and energy deposition profiles. Titan provides a very good example of such a UV-directed organic atmospheric chemistry.     

Dynamics of the low altitude secondary proton radiation belt

At the interface between the upper atmosphere and the radiation belt region, there exists a secondary radiation belt consisting mainly of energetic ions that have become neutralized in the ring current and the main radiation belt and then re-ionized by collisions in the inner exosphere. The time history of the proton fluxes in the 0.64 – 35 MeV energy range was traced in the equatorial region beneath the main radiation belts during the three year period from 21 February 1984 to 26 March 1987 using data obtained with the HEP experiment on board the Japanese OHZORA satellite. During most of this period a fairly small proton flux of −1.2 cm⁻² s⁻¹ sr⁻¹ was detected on geomagnetic field lines in the range 1.05 < L < 1.15. We report a few surprisingly deep and rapid flux decreases (flux reduction by typically two orders of magnitude). These flux decreases were also long in duration (lasting up to three months). We also registered abrupt flux increases where the magnitude of the proton flux enhancements could reach three orders of magnitude with an enhancement duration of 1–3 days. Possible reasons for these unexpected phenomena are discussed.     

The dynamics of the object potential during electron beam injection and the possibility to control it

This review of the rocket and satellite experiments on electron beam injection in the height range of the ionosphere-magnetosphere shows a variety of manifestations of the positive charge potential on the body of the injector unit or in the space charge zone.

The possibilities of compensation are considered on the basis of theoretical models taking into account the beam-plasma collective interactions. The examples of numerical modeling of the charge-discharge dynamics are provided for the APEX conditions. It is shown that changing the pulse form and rise rate (dI/dt) one can change the structure of the space charge zone i.e. try to create the strong disturbance or resonance conditions in the time interval of πω_p≤ t ≤ t_ion. From these positions, we consider the APEX facilities used to control the inflow current, the spectrum of energetic particles, the high-frequency oscillations and the spatial distribution of optical emissions in the injector vicinity with high time resolution.     

Intensity profiles of the multiple scattering light near the cometary nucleus

The multiple scattering of solar radiation in the cometary atmosphere is treated with the method of successive scattering. Referring to in situ measurements of comet Halley about the size and spatial distributions of dust, the optical thickness τ₁ of dust has been estimated, i.e. τ₁=0.03 at wavelength λ=0.62μm in a quiet time, but τ₁=0.3 when the outbursts/jets occur. In the derivation of τ₁, optical properties of dust including a mixing ratio of absorbing to silicate grains, are determined based on the polarimetry of P/Halley at λ=0.62μm observed during the phase angles over Nov. 1985 to May 1986 at the Dodaira Station of Tokyo Astronomical Observatory.

It is found that a temporary enhancement of τ₁ leads an increase of the upward reflected intensity when the surface albedo A of the nucleus is less than 0.04, but the reverse is true when A>0.04. On the other hand, the intensity of the downward radiation at the surface of the nucleus always decreases as an increase of τ₁.     

Solar heavy ion Heinrich fluence spectrum at low earth orbit

Solar heavy ions from the JPL Solar Heavy Ion Model have been transported into low earth orbit using the Schulz cutoff criterion for L-shell access by ions of a specific charge to mass ratio. The NASA Brouwer orbit generator was used to get L values along the orbit at 60 second time intervals. Heavy ion fluences of ions 2≤Z≤92 have been determined for the LET range 1 to 130 MeV-cm²/mg by 60, 120 or 250 mils of aluminum over a period of 24 hours in a 425 km circular orbit inclined 51°. The ion fluence is time dependent in the sense that the position of the spacecraft in the orbit at the flare onset time fixes the relationship between particle flux and spacecraft passage through high L-values where particles have access to the spacecraft.     

Modeling of artificial plasma “bubble” in ionosphere

Results of a combination of radio-crossing and in situ measurements of plasma density in an artificial plasma “bubble” in the ionosphere are presented. Shaped — charge barium injection was made at short distance (≤50 m) to plasma diagnostics on the rocket. After injection the rocket passed through expanding plasma shell. Plasma density depletion inside was more than one order and plasma enhancements on the boundary about 3–5 times that of background. When the rocket passed the shell and went away by 2.1 km an abrupt drop of telemetry signal level (≤ 65 dB) was registered though plasma density was not more than 3×10³sm⁻³. An estimation of high frequency signal refraction on the plasma shell is in good accordance with refraction data of geostationary satellite signals on equatorial bubbles.     

The search for nitrogen compounds on the surface of Mars

Nitrogen is an essential element for life. Specifically, “fixed nitrogen” (i.e., NH₃, NH₄⁺, NO_x, or N that is chemically bound to either inorganic or organic molecules and is releasable by hydrolysis to NH₃ or NH₄⁺) is the form of nitrogen useful to living organisms. To date no direct analysis of Martian soil nitrogen content, or content of fixed nitrogen compounds has been done. Consequently, the planet's total inventory of nitrogen is unknown. What is known is that the N₂ content of the present-day Martian atmosphere is 0.2 mbar. It has been hypothesized that early in Mars' history (3 to 4 billion years ago) the Martian atmosphere contained much more N₂ than it does today. The values of N₂ proposed for this early Martian atmosphere, however, are not well constrained and range from 3 to 300 mbar of N₂. If the early atmosphere of Mars did contain much more N₂ than it does today the question to be answered is, Where did it go? The two main processes that could have removed it rapidly from the atmosphere include: 1) nonthermal escape of N-atoms to space; and 2) burial within the regolith as nitrates and nitrites. Nitrate will be stable in the highly oxidized surface soil of Mars, and will tend to accumulate in the soil. Such accumulations are observed in certain desert environments on Earth. Some NH₄⁺---N may also be fixed and stabilized in the soil by inclusion as a structural cation in the crystal lattices of certain phyllosilicates replacing K. Analysis of the Martian soil for traces of NO₃⁻ and NH₄⁺ during future missions will supply important information regarding the nitrogen abundance on Mars, its past climate as well as its potential for the evolution of life.     

Variability in the solar constant from irradiances shortward of Lyman-Alpha

The variation in the solar constant, S(t), is reproduced by the SOLAR2000 Research Grade v1.05 empirical solar irradiance model and is described for 5 solar cycles between cycles 18 and 23 (February 14, 1947 through May 31, 2000). This solar constant variation is dependent upon the derivation data sets and the formulation of SOLAR2000 which are described in more detail. The S(t) temporal variability in SOLAR2000 is shown for the solar spectrum between 1–122 nm. The variability is consistent with previous discussions in the literature and a new result is shown where the 1–122 nm wavelength range accounts for about 5–14% of the standard deviation reported in the ASTM E-490 standard. The minimum-maximum range of S(t) variation due to 1–122 nm variability is between 1367.2768 Wm⁻² on 1986-152 and 1367.2877 Wm⁻² on 1957-340. The mean S(t) in these data is 1367.2796 Wm⁻².     

Controllable passive detectors for study of the radiation environment in space and the atmosphere

We propose to study the radiation environment on board different flight vehicles: cosmos-type satellites, orbital stations, Space Shuttles and civil (sonic and supersonic) aircraft. These investigations will be carried out with single type of passive detector, namely, nuclear photoemulsions (NPE) with adjustable threshold of particle detection within broad range of linear energy transfer (LET) that is done by means of the technique of selective development of NPE exposed in space.

These investigations will allow one to determine:

• integral spectra of LET of charged particles of cosmic ray (CR) over a wide range from 2.0 to 5×10⁴ MeV/cm in biological tissue;

• differential energy spectra of fast neutrons (1–20 MeV);

• estimation of absorbed and equivalent doses from charged and neutral component CR;

• charge and energy spectra of low energy nuclei (E≤100 MeV) with Z≥2 having in view the extreme hazard radiation to biological objects and microelectronic schemes taken on board inside and outside of these different flight vehicles with exposures from several days to several months.

The investigation of radiation environment on board the airplanes depending on the flight parameters will be conducted using emulsions of different sensitivity without any controlling of threshold sensitivity (Akopova et al., 1996). The proposed detector can be used in the joint experiments on the new International Cosmic Station “Alpha”.     

Modeling the (upper) solar atmosphere including the magnetic field

The atmosphere of the Sun is highly structured and dynamic in nature. From the photosphere and chromosphere into the transition region and the corona plasma-β changes from above to below one, i.e., while in the lower atmosphere the energy density of the plasma dominates, in the upper atmosphere the magnetic field plays the governing role – one might speak of a “magnetic transition”. Therefore the dynamics of the overshooting convection in the photosphere, the granulation, is shuffling the magnetic field around in the photosphere. This leads not only to a (re-)structuring of the magnetic field in the upper atmosphere, but induces also the dynamic reaction of the coronal plasma, e.g., due to reconnection events. Therefore the (complex) structure and the interaction of various magnetic patches is crucial to understand the structure, dynamics and heating of coronal plasma as well as its acceleration into the solar wind.

The present article will emphasize the need for three-dimensional modeling accounting for the complexity of the solar atmosphere to understand these processes. Some advances on 3D modeling of the upper solar atmosphere in magnetically closed as well as open regions will be presented together with diagnostic tools to compare these models to observations. This highlights the recent success of these models which in many respects closely match the observations.     

EUVITA — An extreme UV imaging telescope array with spectral capability

EUVITA is a set of 8 extreme UV normal incidence imaging telescopes, each of them sensitive in a narrow band (λ/Δλ = 15 to 80), centered at wavelengths between 50 and 175 Å. Each telescope has an effective area of a few cm²; a field of view of 1.2° and a spatial resolution of 10 arcsec.

EUVITA will be flown on the Russian mission SPECTRUM X-G. This satellite will be launched in a highly eccentric orbit with a period of 4 days, allowing long, uninterrupted observations (e.g. 10⁵ seconds). EUVITA's narrow spectral bands allow the measurement of source parameters such as temperature or power law index as well as interstellar absorption, and will resolve groups of strong lines emitted by optically thin hot plasmas.     

Remote infrared observations of parent volatiles in comets: A window on the early solar system

Organic volatiles and water in Oort Cloud comets were investigated at infrared wavelengths. The detected species include H₂O, CO, CH₃OH, CH₄, C₂H₂, C₂H₆, OCS, HCN, NH₃, and H₂CO. Several daughter fragments (CN, OH, NH₂, etc.) are also measured, and OH prompt emission provides a proxy for water. Long-slit spectra are taken at high spectral dispersion and high spatial resolution, eliminating several sources of systematic error. The resulting parent volatile production rates are highly robust, permitting a sensitive search for compositional diversity among comets. Here, seven OC comets are compared. Six (including Halley) exhibit similar compositions (excepting CO and CH₄). Their low formation temperatures (30 K) suggest this group probably formed beyond 30 AU from the young sun. However, C/1999 S4 is severely depleted in hypervolatiles and also in methanol, and it likely formed near 5–10 AU. C/2001 A2 is discussed briefly to illustrate future prospects.     

Simultaneous determination of aerosol- and surface characteristics from top-of-atmosphere reflectance using MERIS on board of ENVISAT

The determination of aerosol optical thickness (AOT) from nadir scanning multi-spectral radiometers, like SeaWiFS, MERIS or MODIS, requires the separation of spectral atmospheric and surface properties. Since SeaWiFS and MERIS do not provide information at 2.1 μm, like MODIS, the estimation of the surface reflectance cannot be made by the cross correlation approach described by Kaufman et al., 1997. The BAER approach (Bremen AErosol Retrieval), von Hoyningen-Huene et al., 2003, uses a linear mixing model of spectra for ‘green vegetation’ and ‘bare soil’, tuned by the NDVI, determining an apparent surface to enable this separation of aerosol and surface properties from VIS and NIR channels. Thus AOT can be derived over a wide range of land surfaces for wavelengths <0.67 μm. Using MERIS L1 data over Europe, the AOT retrieved is comparable with ground-based observations, provided by AERONET. Regional variation of AOT can be observed, showing the atmospheric variability for clear sky conditions by: large scale variation of aerosol turbidity, regional pollution, urban regions, effects of contrails and cases of aerosol-cloud interaction. Simultaneously with the spectral AOT also spectral surface reflectance is obtained, where all atmospheric influences have been considered (molecules, aerosols and absorbing gases (O₃)) for channels with wavelengths <0.67 μm. The AOT is extrapolated by Angström power law to NIR channels and the atmospheric correction for land surface properties is performed, enabling the further investigation of land use and spectral land properties.     

Fe XVII X-ray lines in solar coronal plasmas

Calculated intensities of the Fe X-ray lines due to transitions 2p⁶ − 2p⁵3d lines (near 15 Å) and 2p⁶ − 2p⁵3s lines (near 17 Å) are compared with measured line intensities in solar and tokamak spectra. For the solar spectra, temperature T_e is obtained from the ratio of the Fe 16.776 Å line to a nearby Fe line. We find excellent agreement for all the major Fe line features in the 15–17 Å region except the Fe 15.015 Å line, the observed flux of which is less than the theoretical by a factor f. We find that f strongly depends on the heliocentric angle θ of the emitting region, being smallest (0.2) when the region is nearest Sun centre, but nearly 1 near the limb. Attributing this to resonance scattering, we are able to deduce the path length and electron density from the observations. Possible application to stellar active regions is given.     

Direct radiative forcing from black carbon aerosols over urban environment

There is growing evidence that the earth’s climate is changing and will likely continue to change in the future. It is still debated whether these changes are due to natural variability of the climate system or a result of increases in the concentration of greenhouse gases in the atmosphere. Black carbon (BC) has become the subject of interest for a variety of reasons. BC aerosol may cause environmental as well as harmful health effects in densely inhabited regions. BC is a strong absorber of radiation in the visible and near-infrared part of the spectrum, where most of the solar energy is distributed. Black carbon is emitted into the atmosphere as a byproduct of all combustion processes, viz., vegetation burning, industrial effluents and motor vehicle exhausts, etc. In this paper, we present results from our measurements on black carbon aerosols, total aerosol mass concentration and aerosol optical depth over an urban environment namely Hyderabad during January to May, 2003. Diurnal variations of BC indicate high BC concentrations during 6:00–9:00 and 19:00–23:00 h. Weekday variations of BC concentrations increase gradually from Monday to Wednesday and gradually decrease from Thursday to Sunday. Analysis of traffic density along with meteorological parameters suggests that the primary determinant for BC concentration levels and patterns is traffic density. Seasonal variations of BC suggest that the BC concentrations are high during dry season compared to rainy season due to the scavenging by air. The fraction of BC to total mass concentration has been observed to be 7% during January to May. BC showed positive correlation with total mass concentration and aerosol optical depth at 500 nm. Radiative transfer calculations suggests that during January to May, diurnal averaged aerosol forcing at the surface is −33 Wm² and at the top of the atmosphere (TOA) above 100 km it is observed to be +9 Wm⁻². The results have been discussed in detail in the paper.     

Quiet sun XUV and EUV spectroscopy

The two XUV–EUV spectrometers on SOHO have collected a large amount of data in the 6000–10⁶ K solar plasma temperature range. These data have allowed us to greatly enhance our knowledge of the processes acting in the solar atmosphere, from the chromosphere to the corona. Some results on the quiet Sun structure (network, quiet Sun versus coronal hole), on the dynamics (velocities, waves, transient events), and the main characteristics of the quiet Sun atmosphere are presented and discussed.     

Diurnal variations of ion flux intensity on a synchronous orbit

The data from the synchronous-orbit satellites of the Gorizont series are used to study the dependences of the ion flux variation amplitudes in the synchronous altitude region (the diurnal behaviour) on particle energies and on the form and rigidity of the particle energy spectrum. The proton fluxes were measured in the energy range E 60–120 keV, and the [N,0]²⁺ and [C,N,0]⁴⁺ ion fluxes in the energy range E 60–70 keV/e.

The ratio of the diurnal variation amplitudes of the studied ions is shown to correspond to the similarity of their energy spectra in the E/Q representation. The magnetically-quiet time gradient of the distribution function F(μ,J,L) in the synchronous-orbit region is shown to be (∂F/∂L)=0 for the H⁺ and [N,0]²⁺ ions and (∂F/∂L) > 0 for the [C,N,0]⁴⁺ ions (at the values of μ corresponding to the examined energy ranges). During magnetically-disturbed periods the inner boundary of the (∂F/∂L)=0 region shifts to lower L and (∂ F/∂L) = O in the synchronous altitude region must be also for the [C,N,O]⁴⁺ ions.     

Global N2O cycles — Terrestrial emissions, atmospheric accumulation and biospheric effects

Tropospheric nitrous oxide concentration has increased by 0.2 – 0.4% per year over the period 1975 to 1982, amounting to net addition to the atmosphere of 2.8 – 5.6 Tg N₂O-N per year. This perturbation, if continued into the future, will affect stratospheric chemical cycles, and the thermal balance of the Earth. In turn it will have direct and indirect global effects on the biosphere. Though the budget and cycles of N₂O on Earth are not yet fully resolved, accumulating information and recent modelling efforts enable a more complete evaluation and better definition of gaps in our knowledge.     

Near infrared observations of comet Halley from Vega 2

Spatial distribution of the continuum radiation in the range of 0.95–1.9 μm presumes total dust production rate of the comet of 10ρ tonne s⁻¹ (ρ is the dust material density) and its angular distribution proportional cos . Observations of the water vapor band at 1.38 μ m reveal strong jets, their time shift from the dust jet measured in situ is consistent with gas velocity of 0.82±0.1 km s⁻¹ and dust velocity of 0.55±0.08 km s⁻¹. The OH vibrational-rotational bands observed are excided directly via photolysis of water vapor. Water vapor production rate deduced from the H₂O band and OH band intensities is 8×10²⁹ s⁻¹. Intensity of the CN(0,0) band result in the CN column density of 9×10¹² cm⁻², i.e. larger by a factor of 3 than given by the violet band.