Stratospheric trace gas distributions observed in different seasons

A newly developed balloon-borne cryogenic sampler has been used to collect large air samples in the midlatitude stratosphere (44° N). The samples were analysed for their content of several longlived trace gases. The vertical profiles of N₂O, CH₄, and CF₂Cl₂ derived from two balloon flights in winter 1982 and, as part of the MAP Globus Project, in fall 1983 indicate variations that are caused by large scale dynamic processes. Significant features of the profiles are discussed and compared with averaged profiles that were derived from a series of balloon sampling flights performed previously over the same location during the summer season. The temporal variation of the individual profiles is more detailed than predicted by model calculations.     

Vertical profiles of halocarbons in the stratosphere

Stratospheric air samples collected between 10 and 35 km altitude my means of a cryogenic sampler were analyzed by gaschromatography. Thus vertical profiles of source gases for halogen radicals were derived, such as CCl₄, CCl₃F, CCl₂F₂, CClF₃, CF₄, C₂F₃Cl₃, C₂F₄Cl₂, C₂F₅Cl, C₂F₆, CH₃Cl, CH₃CCl₃, CHF₂Cl, CH₃Br, CBrF₃, and CBrCl₂F. Systematic discrepancies between measured and modelled halocarbon profiles point to deficiencies of present one- and two-dimensional models. Measurements of fully halogenated hydrocarbons provide a tool for systematically studying these deficiencies and thus improving the models.     

Composition of the Venus atmosphere below 100 km altitude

Our current knowledge on the composition of the Venus atmosphere in the altitude range from the surface to 100 km is compiled. Gases that have been measured, and whose mixing ratios are assumed to be constant with altitude, are CO₂, N₂, He, Ne, Ar, and Kr. Gases that have been identified in the lower and/or middle atmosphere, but whose mixing ratios may depend on altitude, latitude and/or local time, are CO, H₂O, HCl, HF, and SO₂. Conflicting data or only upper limits exist on some important trace gases, such as O₂, H₂, and Cl₂. The latter two are key constituents in the photochemistry of the middle atmosphere of Venus. The chapter concludes with a listing of the isotopic abundances of elements measured in the Venus atmosphere.     

The infrared synthetic spectrum of comet Halley

In order to prepare infrared sounding of comet Halley from the flyby VEGA probes, we have computed the synthetic spectrum between 2.5 and 15 μ of a typical comet at a heliocentric distance of ～ 0.8 AU. The present paper is particularly devoted to the contribution from the cometary gases. For a selection of 20 possible parent molecules, the most efficient excitation process is resonant fluorescence by the solar radiation field. The H₂O, CO, CO₂, CH₄, NH₃ and H₂CO molecules are the best candidates for detection by the IKS infrared spectrometers aboard the VEGA probes. For the water molecule, collisions are too rare to ensure thermal equilibrium in the whole coma ; therefore a limited number of fluorescence lines are expected to be present in the H₂O vibrational bands.     

Trace constituents measurements deduced from spectrometric observations on-board spacelab

The observation of infrared absorption lines by means of a grille spectrometer on board Spacelab 1 allows the determination of Co₂ and CO in the low thermosphere and in the middle atmosphere. Equal abundances of CO and CO₂ are found at 115 ± 5 km altitude. CO₂ is observed to depart from its homospheric volume mixing ratio near 100 km, dropping by a factor of 10,15 km higher. The CO largest number density is observed near 70 km altitude, close to the H Lyman alpha photoproduction peak.The analysis of one run dedicated to the observation of water vapor shows a middle atmospheric mixing ratio of this species within the limits : 3 to 8 ppmv up to 70 km altitude, with the indication of an increase from 30 to 50 km altitude. The H₂O mixing ratio drops very rapidly above 70 km.The comparison of the results from strong and weak H₂O and CO₂ lines shows the need to refine the line profile model.     

Mass spectrometry in the stratosphere

During the last few years a gas expansion system, combined with a mass spectrometer has been developed and successfully flown in the stratosphere. Neutral gas particles are formed into a molecular beam which traverses the ion source of the mass spectrometer without wall interactions. Vertical profiles of constituents such as H₂O, CO₂ and O₃ have been measured in the altitude range of 20 to 40 km during balloon descents. Isotopes of major atmospheric gases (N₂, O₂, Ar) provided in-flight calibration standards.Before each flight the mass spectrometer system was calibrated in the laboratory for many gases of interest, including ozone. Mixing ratios of ozone determined from recent flights have accuracies of better than 5%. The sensitivity of the system was sufficiently high to detect, in addition, the heavy isotope of ozone at mass 50. A pronounced enhancement of heavy ozone in the upper stratosphere has been found. The mass spectrometer system provides the unique opportunity to perform in the stratospherein-situ measurements combined with isotopic studies.     

Positive ion composition and electron density in a combined auroral and NLC event

The positive ion composition and electron density were measured in the lower ionosphere above Kiruna in salvo A of CAMP (Cold Arctic Mesopause Project). The CAMP/P (S37/P) payload carrying a magnetic ion spectrometer, positive ion and electron probes, and propagation experiments was launched on 3 August 1982 2332 UT during extended Noctilucent Clouds (NLC) and auroral activities over Kiruna. The measured electron density was 5×10³cm^?3 at 80 km and 2.5×10⁵cm^?3 at 90 km. The increase of ion and electron densities in the D- and E-region during twilight was caused by precipitating auroral particles. The height distribution of the positive ions measured by the mass spectrometer in the mass range 19–280 amu is different from a winter flight with similar auroral conditions. Below 85.5 km proton hydrates H⁺(H₂O)₃ ? H⁺(H₂O)₈ were the dominant ions. The heaviest proton hydrates H⁺(H₂O)₇ and H⁺(H₂O)₈ were most abundant at 82–85.5 km, the altitude of visible NLC. Above 85.5 km O₂⁺ and NO⁺ became dominant. A small metal ion layer was observed between 90.5–93 km with a maximum ion density of 10% of the total positive ion density at 91 km altitude. The metal ion density disappeared within about a km below 90.5 km.     

Origin and stability of lunar polar volatiles

Temperature regime at the LCROSS impact site is studied. All detected species in the Cabeus crater as well as CH₄ and CO clathrate hydrates except H₂, CO, and CH₄ are stable against evaporation at the LCROSS impact site. CO and CH₄ can be chemisorbed at the surface of the regolith particles and exist in the form of clathrate hydrates in the lunar cold traps. Flux rates of delivery of volatile species by asteroids, micrometeoroids, O-rich, C-rich, and low-speed comets into the permanently shadowed regions are estimated. Significant amounts of H₂O, CO, H₂, H₂S, SO₂, and CO₂ can be impact-produced during collisions between asteroids and O-rich comets with the Moon while CH₃OH, NH₃ and complex organic species survive during low-speed comet impacts as products of disequilibrium processes. C-rich comets are main sources of CH₄, and C₂H₄.     

Mass spectrometric measurements of stratospheric ions

Recent in situ measurements with balloon borne quadrupole mass spectrometers, between 20 and 45 km altitude, are reviewed and discussed.The major stratospheric positive ions observed are proton hydrates [H⁺(H₂O)_n] and non proton hydrates of the form H⁺X_m(H₂O)₂. The data analysis allows a derivation of the vertical mixing ratio profile of X (most probably CH₃CN), which is compared with recent model calculations. From negative ion composition data, showing the presence of NO₃^? and HSO₄^? cluster ions, the density of sulfuric acid in the stratosphere is deduced. The implications of these findings on our understanding of the sulfur chemistry is briefly treated.Finally some other aspects such as contamination, cluster break up and the use of stratospheric ion mass spectra for determination of thermochemical data and other minor constituents are discussed.     

Global comparison of the model results of GSM TIP with IRI for summer conditions

This paper presents the results of the numerical calculations thermosphere/ionosphere parameters which were executed with using of the Global Self-consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP)and comparison of these results with empirically-based model IRI-2001. Model GSM TIP was developed in West Department of IZMIRAN and solves self-consistently the time-dependent, 3-D coupled equations of the momentum, energy and continuity for neutral particles (O₂, N₂, O), ions (O⁺, H⁺), molecular ions (M⁺) and electrons and largescale eletric field of the dynamo and magnetospheric origin in the range of height from 80 km to 15 Earth’s radii. The empirically derived IRI model describes the E and F regions of the ionosphere in terms of location, time, solar activity and season. Its output provides a global specification not only of N_e but also on the ion and electron temperatures and the ion composition. These two models represent a unique set of capabilities that reflect major differences in along with a substantial approaches of the first-principles model and global database model for the mapping ionosphere parameters. We focus on global distribution of the N_e, T_i, T_e and TEC for the one moment UT and fixed altitudes: 110 km, h_mF2, 300 km and 1000 km. The calculations were executed with using of GSM TIP and IRI models for August 1999, moderate solar activity and quiet geomagnetic conditions. Results present as the global differences between the IRI and GSM TIP models predictions. The discrepancies between model results are discussed.     

Statistical global and regional atmospheric models of temperature and gas components over the northern hemisphere

Statistical mid-latitude models of altitude distribution of temperature, water vapor, ozone, carbon dioxide and trace gases (CO, CH₄, N₂O, NO, NO₂) are considered. The mean characteristics of altitude profiles of these parameters, as well as their time and space variability, have been taken into account. The statistical regional models were constructed using a temperature-humidy complex. The considered statistical mid-latitude models have been constructed as applied to solutions of the problems on remote sounding of the atmosphere and underlying surface from outer space.     

Greenhouse gases and recovery of the Earth’s ozone layer

A numerical 2-D zonally averaged dynamical radiative-photochemical model of the ozonosphere including aerosol physics is used to examine the role of the greenhouse gases CO₂, CH₄, and N₂O in the recovery of the Earth’s ozone layer after reduction of anthropogenic discharges of chlorine and bromine compounds into the atmosphere. A weakness in efficiencies of all catalytic cycles of the ozone destruction due to cooling of the stratosphere caused by greenhouse gases is shown to be a dominant mechanism of the impact of the greenhouse gases on the ozone layer. Numerical experiments show that the total ozone changes caused by greenhouse gases will be comparable in absolute value with the changes due to chlorine and bromine species in the middle of the 21st century. Continuous anthropogenic growth of CO₂ will lead to a significantly faster recovery of the ozone layer. In this case, the global total ozone in the latitude range from 60°S to 60°N will reach its undisturbed level of 1980 by about 2040. If the CO₂ growth stops, the global total ozone will reach this level only by the end of the century.     

Models of Venus neutral upper atmosphere: Structure and composition

Models of the Venus neutral upper atmosphere, based on both in-situ and remote sensing measurements, are provided for the height interval from 100 to 3,500 km. The general approach in model formulation was to divide the atmosphere into three regions: 100 to 150 km, 150 to 250 km, and 250 to 3,500 km. Boundary conditions at 150 km are consistent with both drag and mass spectrometer measurements. A paramount consideration was to keep the models simple enough to be used conveniently. Available observations are reviewed. Tables are provided for density, temperature, composition (CO₂, O, CO, He, N, N₂, and H), derived quantities, and day-to-day variability as a function of solar zenith angle on the day- and nightsides.Estimates are made of other species, including O₂ and D. Other tables provide corrections for solar activity effects on temperature, composition, and density. For the exosphere, information is provided on the vertical distribution of normal thermal components (H, O, C, and He) as well as the hot components (H, N, C, O) on the day- and nightsides.     

Ground-based millimeter-wave observations of water vapor emission (183 GHz) at Atacama,Chile

We report the first results of ground-based millimeter-wave measurements of 183 GHz atmospheric water vapor spectra from Atacama highland (4800 m alt.), Chile. The measurements were carried out in December 2005 by using a spectroscopic radiometer equipped with a superconductive heterodyne receiver. A conspicuous H₂O spectrum at 183 GHz was detected with an integration time of only 1.5 min, and this is the first high frequency-resolution H₂O spectrum at 183 GHz obtained in the southern subtropical region. The vertical profile of H₂O volume mixing ratio between 40 and 64 km were retrieved from the spectrum by using the modified optimal estimation method.     

Gravity wave mixing effects on the OH*-layer

Based on an advanced numerical model for excited hydroxyl (OH*) we simulate the effects of gravity waves (GWs) on the OH*-layer in the upper mesosphere. The OH* model takes into account (1) production by the reaction of atomic hydrogen (H) with ozone (O₃), (2) deactivation by atomic oxygen (O), molecular oxygen (O₂), and molecular nitrogen (N₂), (3) spontaneous emission, and (4) loss due to chemical reaction with O. This OH* model is part of a chemistry-transport model (CTM) which is driven by the high-resolution dynamics from the KMCM (Kühlungsborn Mechanistic general Circulation Model) which simulates mid-frequency GWs and their effects on the mean flow in the MLT explicitly. We find that the maximum number density and the height of the OH*-layer peak are strongly determined by the distribution of atomic oxygen and by the temperature. As a results, there are two ways how GWs influence the OH*-layer: (1) through the instantaneous modulation by O and T on short time scales (a few hours), and (2) through vertical mixing of O (days to weeks). The instantaneous variations of the OH*-layer peak altitude due to GWs amount to 5–10 km. Such variations would introduce significant biases in the GW parameters derived from airglow when assuming a constant pressure level of the emission height. Performing a sensitivity experiment we find that on average, the vertical mixing by GWs moves the OH*-layer down by ~2 to 7 km and increases its number density by more than 50%. This effect is strongest at middle and high latitudes during winter where secondary GWs generated in the stratopause region account for large GW amplitudes.     

Mesospheric H2O and H2O2 densities inferred from in situ positive ion composition measurement

The measurements of positive ion composition in the high latitude D-region have revealed an excess of 34⁺ under distrubed conditions which has been interpreted as H₂O₂⁺. At the same altitude range near the transition height oxonium ions were measured as well. This paper presents a new model for the production and loss of oxonium ions with their production from H₂O₂⁺ + H₂O → H₃O⁺ + HO₂ and their loss by attachment of N₂ and/or CO₂. A reaction constant of 8.5×10^?28 (300/T)⁴ cm⁶s^?1 has been obtained for the three body attachment H₃O⁺ + CO₂ + M → H₃O⁺.CO₂ + M from the measured density profile of 63⁺ in flight 18.1020. Mesospheric H₂O and H₂O₂ densities are inferred from measurements of four high latitude ion compositions based on the oxonium model. The mixing ratios of hydrogen peroxide are up to two orders of magnitude higher compared to previous model calculations. In order to explain the missing production of odd hydrogen, we consider larger O(¹D) densities, surface reactions of O(³P) on particles, and cathalytic photodissociation of water vapor on aerosol particles.     

Satellite measurements of atmospheric composition: Three years' observations of CH4 and N2O

The stratospheric and mesospheric sounder (SAMS) was launched in October 1978 on the NIMBUS 7 satellite. Between then and its eventual failure in June 1983 the instrument was used to collect over four years of radiance data from which atmospheric temperature and the abundances of a number of minor constituents have been derived. The paper will present fields of CH₄ and N₂O between 50S and 70N derived from SAMS data for the period 1979–1981. Global distributions of CH₄ and N₂O will be presented in various forms and the observed seasonal changes and interannual variability will be described. The paper will compare the SAMS CH₄ and N₂O data with model predictions and will comment upon some other areas of interest.     

The variability of stratospheric nitrogen compounds observed by LIMS in the winter of 1978–1979

The LIMS experiment was launched on the Nimbus 7 satellite for the purpose of sounding the vertical structure of temperature and key upper atmosphere trace gases on a global scale. The technique of thermal infrared limb sounding was used to obtain measurements of O₃, H₂O, NO₂, and HNO₃. LIMS collected data almost continuously from late October to late May over the latitude range from 64°S to 84°N. Two of the gases, NO₂ and HNO₃, are important elements in the NO_x chain of chemical reactions leading to ozone destruction. We will describe results for these gases in terms of zonal mean profiles and latitudinal distributions. The period selected for study is January–May 1979, when a major stratospheric warming occurred.     

Comparison of topside ionosphere scale height modeled by the Topside Sounder Model and incoherent scatter radar ionospheric model

The topside ionosphere scale height extracted from two empirical models are compared in the paper. The Topside Sounder Model (TSM) provides directly the scale height (H_T), while the incoherent scatter radar ionospheric model (ISRIM) provides electron density profiles and its scale height (H_R) is determined by the lowest gradient in the topside part of the profile. H_T and H_R are presented for 7 ISR locations along with their dependences on season, local time, solar flux F10.7, and geomagnetic index ap. Comparison reveals that H_T values are systematically lower than respective H_R values as the average offset for all 7 stations is 55 km. For the midlatitude stations Arecibo, Shigaraki, and Millstone Hill this difference is reduced to 43 km. The range of variations of H_R is much larger than that of H_T, as the H_T range overlaps the lower part of the H_R range. Dependences on ap, DoY and LT are much stronger in the ISRIM than in TSM. This results in much larger values of H_R at higher ap. Diurnal amplitude of H_R is much larger than that of H_T, with large maximum of H_R at night. The present comparison yields the conclusion that the ISR measurements provide steeper topside Ne profiles than that provided by the topside sounders.