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NASA NTRS1982

Deducing the age of the dense Venus atmosphere

It is shown how crater size-density counts may be used to help constrain the history of the Venus atmosphere, based on the predictions of simple but reasonable models for crater production, surface erosion, and the effects of atmospheric drag and breakup on incident meteors in the Venus atmosphere. In particular, if the atmosphere is young, the old (uneroded) surfaces will have crater densities upward of 0.0001/sq km and a ratio of small (4 km) craters to large (128 km) craters near 1000. If the atmosphere is old and the breakup mechanism is dominant, absolute crater densities on Venus surfaces will be diminished by several orders of magnitude relative to the young atmosphere case. If atmospheric drag is dominant, the absolute crater density will be lowered by perhaps an order of magnitude relative to the young atmosphere case, and the ratio of small to large craters will be reduced to a value near 10 to the 1.5 power. Once a large fraction of Venus surface has been imaged at kilometer resolution, as the VOIR project promises to do, it could be possible to make an early determination of the age of the Venus atmosphere.

Kahn, R.↗

NASA NTRS1989

Deducing the age of the dense Venus atmosphere

It is shown how crater size-density counts may be used to help constrain the history of the Venus atmosphere, based on the predictions of simple but reasonable models for crater production, surface erosion, and the effects of atmospheric drag and breakup on incident meteors in the Venus atmosphere. In particular, if the atmosphere is young, the old (uneroded) surfaces will have crater densities upward of 0.0001/sq km and a ratio of small (4 km) craters to large (128 km) craters near 1000. If the atmosphere is old and the breakup mechanism is dominant, absolute crater densities on Venus surfaces will be diminished by several orders of magnitude relative to the young atmosphere case. If atmospheric drag is dominant, the absolute crater density will be lowered by perhaps an order of magnitude relative to the young atmosphere case, and the ratio of small to large craters will be reduced to a value near 10 to the 1.5 power. Once a large fraction of Venus surface has been imaged at kilometer resolution, as the Venus Orbiting Imaging Radar project promises to do, it could be possible to make an early determination of the age of the Venus atmosphere.

Kahn, R.↗

NASA NTRS1992

Regional climatic effects of atmospheric SO2 on Mars

The conditions under which the valley networks on Mars may have formed remains controversial. The magnitude of an atmospheric greenhouse effect by an early massive CO2 atmosphere has recently been questioned by Kasting. Recent calculations indicate that if solar luminosity were less than about 86 percent of its current value, formation of CO2 clouds in the Martian atmosphere would depress the atmospheric lapse rate and reduce the magnitude of surface warming. In light of recent revisions of magma generation on Mars during each Martian epoch, and the suggestions by Wanke et al. that the role of liquid SO2 should be more carefully explored, we have recalculated the potential greenhouse warming by atmospheric SO2 on Mars, with an emphasis on more localized effects. In the vicinity of an active eruption, the concentration of atmospheric SO2 will be higher than if it is assumed that the erupted SO2 is instantaneously globally distributed. The local steady-state concentration of SO2 is a function of the rate at which it is released, its atmospheric lifetime, and the rate at which local winds act to disperse the SO2. We have made estimates of eruption rates, length of eruption, and dispersion rates of volcanically released SO2, for a variety of atmospheric conditions and atmospheric lifetimes of SO2 to explore the maximum regional climatic effect of SO2.

Postawko, S. E.↗

NASA NTRS1992

How Mars lost its atmosphere

There is a widespread suspicion that Mars thin atmosphere is in some way attributable to the planet's size. Another possibility is that the atmosphere was never degassed or outgassed in the first place. I prefer escape. Hydrodynamic escape (vigorous thermal escape) and impact erosion (expulsion of atmosphere by impacts) are two processes that should have been operative early. Although in principle hydrodynamic escape could have shrunk Mars atmosphere a hundredfold while leaving the composition of the remnant atmosphere nearly unaltered, very high escape fluxes are required. The implicated escape mechanism must have been efficient, nearly non-fractionating, and vastly more potent for Mars than for Earth or Venus. Impact erosion is an appealing candidate. Noble gases are the obvious first test. Noble gases are the most volatile elements and so are the most likely to have been affected by impact erosion and the easiest to address quantitatively. Xenon in particular imposes three constraints on how Mars lost its atmosphere: (1) the very low abundance of nonradiogenic Xe abundance of nonradiogenic Xe compared to Earth, Venus, and likely meteoritic sources; (2) its nonradiogenic isotopes distinct from likely meteoritic sources; and (3) the relatively high absolute abundance of radiogenic daughter of the extinct radionuclide I-129 (half-life 17 Myr). In impact erosion, the first two become constraints on the composition, mass distribution, and orbital elements of the impactors. The third requires that Mars lost its nonradiogenic Xe early, probably before it was 100 Myr old. Impact erosion can explain Mars by any of three stories. (1) Mars in unlikely. In a sort of planetary brinkmanship, impact erosion almost removed the entire atmosphere but was arrested just in time. (2) Martian noble gases are cometary and cometary Xe is as isotopically mass fractionated as Martian and terrestrial Xe. This is most easily accomplished if a relatively thick geochemically controlled CO2 atmosphere protected trace atmophiles against escape. (3) Mars was indeed stripped of its early atmosphere but a small remnant was safely stored in the regolith, later released as a byproduct of water mobilization.

Zahnle, Kevin↗

NASA NTRS1992

Some issues on modeling atmospheric turbulence experienced by helicopter rotor blades

The atmospheric turbulence velocities seen by nonrotating aircraft components and rotating blades can be substantially different. The differences are due to the spatial motion of the rotor blades, which move fore and aft through the gust waves. Body-fixed atmospheric turbulence refers to the actual atmospheric turbulence experienced by a point fixed on a nonrotating aircraft component such as the aircraft's center of gravity or the rotor hub, while blade-fixed atmospheric turbulence refers to the atmospheric turbulence experienced by an element of the rotating rotor blade. An example is presented, which, though overly simplified, shows important differences between blade- and body-fixed rotorcraft atmospheric turbulence models. All of the information necessary to develop the dynamic equations describing the atmospheric turbulence velocity field experienced by an aircraft is contained in the atmospheric turbulence velocity correlation matrix. It is for this reason that a generalized formulation of the correlation matrix describing atmospheric turbulence that a rotating blade encounters is developed. From this correlation matrix, earlier treated cases restricted to a rotor flying straight and level directly into the mean wind can be recovered as special cases.

Costello, Mark↗

NASA NTRS1992

Long-term variations in abundance and distribution of sulfuric acid vapor in the Venus atmosphere inferred from Pioneer Venus and Magellan radio occultation studies

Radio occultation experiments have been used to study various properties of planetary atmospheres, including pressure and temperature profiles, and the abundance profiles of absorbing constituents in those planetary atmospheres. However, the reduction of amplitude data from such experiments to determine abundance profiles requires the application of the inverse Abel transform (IAT) and numerical differentiation of experimental data. These two operations preferentially amplify measurement errors above the true signal underlying the data. A new technique for processing radio occultation data has been developed that greatly reduces the errors in the derived absorptivity and abundance profiles. This technique has been applied to datasets acquired from Pioneer Venus Orbiter radio occultation studies and more recently to experiments conducted with the Magellan spacecraft. While primarily designed for radar studies of the Venus surface, the high radiated power (EIRP) from the Magellan spacecraft makes it an ideal transmitter for measuring the refractivity and absorptivity of the Venus atmosphere by such experiments. The longevity of the Pioneer Venus Orbiter has made it possible to study long-term changes in the abundance and distribution of sulfuric acid vapor, H2SO4(g), in the Venus atmosphere between 1979 and 1992. The abundance of H2SO4(g) can be inferred from vertical profiles of 13-cm absorptivity profiles retrieved from radio occultation experiments. Data from 1979 and 1986-87 suggest that the abundance of H2SO4(g) at latitudes northward of 70 deg decreased over this time period. This change may be due to a period of active volcanism in the late 1970s followed by a relative quiescent period, or some other dynamic process in the Venus atmosphere. While the cause is not certain, such changes must be incorporated into dynamic models of the Venus atmosphere. Potentially, the Magellan spacecraft will extend the results of Pioneer Venus Orbiter and allow the continued monitoring of the abundance of distribution of H2SO4(g) in the Venus atmosphere, as well as other interesting atmospheric properties. Without such measurements it will be difficult to address other issues such as the short-term spatial variability of the abundance of H2SO4(g) at similar latitudes in Venus atmosphere, and the identities of particles responsible for large-scale variations observed in NIR images.

Jenkins, J. M.↗

NASA NTRS1993

Numerical modeling of impact erosion of atmospheres: Preliminary results

It is clear from the great diversity of atmospheres among the terrestrial planets that their formation and evolution must have depended on a balance among a number of different processes. One of these processes is atmospheric erosion by impacts, which may have been particularly effective on Mars. The reason is that geomorphic evidence on Mars suggests that this planet had, early in its history, dense enough atmosphere to sustain active precipitation over geologically significant periods of time. Analytic calculations indicate that neither the projectile entering the atmosphere nor the main crater ejecta can cause the lose of significant amounts of atmosphere. The vapor plume that is formed, however, expands rapidly as its internal energy is converted into kinetic energy, and may blow off the overlying atmosphere. A model of this part of the impact/atmosphere interaction predicts Mars could have lost a substantial early atmosphere by impact erosion alone. Although our more detailed calculations, which took into account the anisotropy of the atmosphere with respect to zenith angle, show that the process isn't quite as effective, they still indicate the probability of substantial atmospheric loss from Mars. The first results from 2-D hydrocode runs are discussed. These include two runs which make most of the same simplifying approximations as the analytic models, in order to compare the analytic and numerical results directly, and one run (as yet incomplete) that models the full impact.

Vickery, A. M.↗

NASA NTRS1994

Mars atmospheric loss and isotopic fractionation by pick-up-ion sputtering and photochemical escape

We examine the effects of loss of constituents of the Martian atmosphere due to sputtering by solar-wind pick-up ions and photochemical escape during the last 3.8 billion years. Sputtering is capable of efficiently removing species from the upper atmosphere to space, including the light noble gases; nitrogen and oxygen are removed by both sputtering ad photochemical processes. Due to diffusive separation (by mass) above the homopause, removal from the top of the atmosphere will fractionate the isotopes of each species, with the lighter isotope being preferentially lost. This allows current measurements of the isotopic ratios to be used as a measure of the atmospheric evolution as integrated over geologic time. For carbon and oxygen, isotopic fractionation is buffered by exchange of atmospheric species with non-atmospheric reservoirs of CO2 and H2O. This allows us to determine the size of the non-atmospheric reservoirs which are capable of mixing with the atmosphere; these reservoirs can be CO2 absorbed in the regolith and/or H2O in the polar ice caps. Such an exchangeable reservoir is required in order to keep the fractionation of the atmospheric gases as low as is observed.

Jakosky, B. M.↗

NASA NTRS1998

Stellar Occultation Probe of Triton's Atmosphere

The goals of this research were (i) to better characterize Triton's atmospheric structure by probing a region not well investigated by Voyager and (ii) to begin acquiring baseline data for an investigation of the time evolution of the atmosphere which will set limits on the thermal conductivity of the surface and the total mass of N2 in the atmosphere. Our approach was to use observations (with the Kuiper Airborne Observatory) of a stellar occultation by Triton that was predicted to occur on 1993 July 10. As described in the attached reprint, we achieved these objectives through observation of this occultation and a subsequent one with the KAO in 1995. We found new results about Triton's atmospheric structure from the analysis of the two occultations observed with the KAO and ground-based data. These stellar occultation observations made both in the visible and infrared, have good spatial coverage of Triton including the first Triton central-flash observations, and are the first data to probe the 20-100 km altitude level on Triton. The small-planet light curve model of Elliot and Young (AJ 103, 991-1015) was generalized to include stellar flux refracted by the far limb, and then fitted to the data. Values of the pressure, derived from separate immersion and emersion chords, show no significant trends with latitude indicating that Triton's atmosphere is spherically symmetric at approximately 50 km altitude to within the error of the measurements. However, asymmetry observed in the central flash indicates the atmosphere is not homogeneous at the lowest levels probed (approximately 20 km altitude). From the average of the 1995 occultation data, the equivalent-isothermal temperature of the atmosphere is 47 +/- 1 K and the atmospheric pressure at 1400 km radius (approximately 50 km altitude) is 1.4 +/- 0.1 microbar. Both of these are not consistent with a model based on Voyager UVS and RSS observations in 1989 (Strobel et al, Icarus 120, 266-289). The atmospheric temperature from the occultation is 5 K colder than that predicted by the model and the observed pressure is a factor of 1.8 greater than the model.

Elliot, James L.↗

NASA NTRS1999

Coupled Land Atmosphere Predictability

We have designed and executed a set of predictability experiments, designed around the driest and wettest June soil moisture anomalies from a CCM3 simulation forced by observed SST for the period from 1958 through 1998. Each set contains an ensemble of five runs, all begun on June I radiation date. One set of these experiments helps to assess the extent to which the wet or dry conditions depend solely on the initial state of the atmosphere. The other set of experiments helps to assess the extent to which the wet or dry conditions depend sole on the initial state of the land surface. Preliminary analysis of these experiments suggests that the initial atmospheric state is more important than the initial state of the surface soil moisture in predicting the occurrence of wet or dry periods. These results suggest that when the atmosphere is inclined to generate dry surface conditions (through reduced moisture availability and increased evaporation) it matters little what initial levels of soil water are at; the soil will rapidly dry out. The ensemble forcing the ensembles with dry soil conditions, but utilizing 'normal' atmospheric conditions show little if any indication of the sharp reduction in soil moisture experienced in the control, indicating that the 'normal' atmospheric state is more important than the initial state of the soil moisture in predicting the occurrence of drought. Our work to date has documented the response of surface hydrologic variability, particularly over North America, to atmospheric forcing. While we have seen some suggestion that pre-existing surface anomalies can affect atmospheric circulation over this region, by far the strongest signal is the atmospheric anomalies leading those of soil moisture and surface energy balance changes. This is not an unexpected result since wintertime NA precipitation links to remote atmospheric forcing by ENSO are known to be statistically significant. While warm season links to remote forcing are more tenuous and not well explored, the present results encourage us to examine in more detail the SST forcing from the tropical and North Pacific.

Roads, John↗

NASA NTRS2000

Understanding Microbial Contributions to Planetary Atmosphere

Should our search of distant, extrasolar planetary atmospheres encounter evidence of life, that evidence will most likely be the gaseous products of microorganisms. Our biosphere was exclusively microbial for over 80 percent of its history and, even today, microbes strongly influence atmospheric composition. Life's greatest environmental impact arises from its capacity for harvesting energy and creating organic matter. Microorganisms catalyze the equilibration of C, S and transition metal species at temperatures where such reactions can be very slow in the absence of life. Sunlight has been harvested through photosynthesis to create enormous energy reservoirs that exist in the form of coexisting reservoirs of reduced, organic C and S stored in Earth's crust, and highly oxidized species (oxygen, sulfate and ferric iron) stored in the crust, oceans and atmosphere. Our civilization taps that storehouse of energy by burning fossil fuels. As astrobiologists, we identify the chemical consequences of distant biospheres as expressed in the atmospheres of their planets. Our approach must recognize that planets, biospheres and atmospheres evolve and change. For example, a tectonically more active early Earth hosted a thermophilic, non-photosynthetic biosphere and a mildly reducing, carbon dioxide-rich and oxygen-poor atmosphere. Microorganisms acquired energy by consuming hydrogen and sulfide and producing a broad array of reduced C and S gases, most notably, methane. Later, diverse types of bacterial photosynthesis developed that enhanced productivity but were incapable of splitting water to produce oxygen. Later, but still prior to 2.6 billion years ago, oxygenic photosynthesis developed. We can expect to encounter distant biospheres that represent various stages of evolution and that coexist with atmospheres ranging from mildly reducing to oxidizing compositions. Accordinaly, we must be prepared to interpret a broad range of atmospheric compositions, all containing signatures of life. Remarkably little is known about the composition of our own earlier atmosphere, particularly prior to the rise of oxygen levels some 2.0 to 2.2 billion years ago. Thus, field and laboratory observations and theoretical simulations should be conducted to examine the relationships between the structure and function of microbial ecosystems and their gaseous products. Ecosystems that are analogs of our ancient biosphere (e.g., based upon chemosynthesis or non-oxygenic photosynthesis, thermophilic and subsurface communities, etc.) should be included. Because key environmental parameters such as temperature and levels of hydrogen, carbon dioxide and oxygen varied during planetary evolution, their consequences for microbial ecosystems should be explored.

DesMarais, David J.↗

NASA NTRS2001

Atmospheric Constraints on Landing Site Selection

The Martian atmosphere is a significant part of the environment that the Mars Exploration Rovers (MER) will encounter. As such, it imposes important constraints on where the rovers can and cannot land. Unfortunately, as there are no meteorological instruments on the rovers, there is little atmospheric science that can be accomplished, and no scientific preference for landing sites. The atmosphere constrains landing site selection in two main areas, the entry descent and landing (EDL) process and the survivability of the rovers on the surface. EDL is influenced by the density profile and boundary layer winds (up to altitudes of 5 to 10 km). Surface survivability involves atmospheric dust, temperatures and winds. During EDL, the atmosphere is used to slow the lander down, both ballistically and on the parachute. This limits the maximum elevation of the landing site to -1.3 km below the MOLA reference aeroid. The landers need to encounter a sufficiently dense atmosphere to be able to stop, and the deeper the landing site, the more column integrated atmosphere the lander can pass through before reaching the surface. The current limit was determined both by a desire to be able to reach the hematite region and by a set of atmosphere models we developed for EDL simulations. These are based on Thermal Emission Spectrometer (TES) atmospheric profile measurements, Ames Mars General Circulation Model (MGCM) results, and the 1-D Ames GCM radiative/convective model by J. Murphy. The latter is used for the near surface diurnal cycle. The current version of our model encompasses representative latitude bands, but we intend to make specific models for the final candidate landing sites to insure that they fall within the general envelope. The second constraint imposed on potential landing sites through the EDL process is the near surface wind. The wind in the lower approximately 5 km determines the horizontal velocity that the landers have when they land. Due to the mechanics of the landing process, the total velocity (including both the horizontal and vertical components) determines whether or not the landers are successful. Unfortunately, the landing system has no easy way to nullify any horizontal velocity imparted by the wind, so the landing sites selected need to have as little wind as possible. In addition to the mean wind velocity, the landing system is sensitive to vertical wind shear in the lowest kilometer or so. Wind shear can deflect the retro rockets (RADs) from their nominal vertical orientation producing unwanted horizontal spacecraft velocities. Both mean velocity and wind shear are dominated by the the local topography and other surface properties (in particular albedo and thermal inertia which control the surface temperature). This is seen even in simplified 2-D mesoscale models. The effects in a fully 3-D model are expected to he even more topographically dependent. In particular there is potential for wind channeling in canyons and other terrain features. Boundary layer winds and wind shear are currently being modeled based on terrestrial data and boundary layer scaling laws modified for Martian conditions. We hope to supplement this with mesoscale model results (from several sources) once the number of landing sites is reduced to a manageable number.

Kass, David M.↗

NASA NTRS2010

Composition Changes After the "Halloween" Solar Proton Event: The High-Energy Particle Precipitation in the Atmosphere (HEPPA) Model Versus MIPAS Data Intercomparison Study

We have compared composition changes of NO, NO2, H2O2,O3, N2O, HNO3 , N2O5, HNO4, ClO, HOCl, and ClONO2 as observed by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on Envisat in the aftermath of the "Halloween" solar proton event (SPE) in October/November 2003 at 25-0.01 hPa in the Northern hemisphere (40-90 N) and simulations performed by the following atmospheric models: the Bremen 2D model (B2dM) and Bremen 3D Chemical Transport Model (B3dCTM), the Central Aerological Observatory (CAO) model, FinROSE, the Hamburg Model of the Neutral and Ionized Atmosphere (HAMMONIA), the Karlsruhe Simulation Model of the Middle Atmosphere (KASIMA), the ECHAM5/MESSY Atmospheric Chemistry (EMAC) model, the modeling tool for SO1ar Climate Ozone Links studies (SOCOL and SOCOLi), and the Whole Atmosphere Community Climate Model (WACCM4). The large number of participating models allowed for an evaluation of the overall ability of atmospheric models to reproduce observed atmospheric perturbations generated by SPEs, particularly with respect to NOS, and ozone changes. We have further assessed the meteorological conditions and their implications on the chemical response to the SPE in both the models and observations by comparing temperature and tracer (CH4 and CO) fields. Simulated SPE-induced ozone losses agree on average within 5% with the observations. Simulated NO(y) enhancements around 1 hPa, however, are typically 30% higher than indicated by the observations which can be partly attributed to an overestimation of simulated electron-induced ionization. The analysis of the observed and modeled NO(y) partitioning in the aftermath of the SPE has demonstrated the need to implement additional ion chemistry (HNO3 formation via ion-ion recombination and water cluster ions) into the chemical schemes. An overestimation of observed H2O2 enhancements by all models hints at an underestimation of the OH/HO2 ratio in the upper polar stratosphere during the SPE. The analysis of chlorine species perturbations has shown that the encountered differences between models and observations, particularly the underestimation of observed ClONO2 enhancements, are related to a smaller availability of ClO in the polar night region already before the SPE. In general, the intercomparison has demonstrated that differences in the meteorology and/or initial state of the atmosphere in the simulations causes a relevant variability of the model results, even on a short timescale of only a few days.

Funke, B.↗

NASA NTRS2011

Direct EPP Affects on the Middle Atmosphere

Energetic precipitating particles (EPPs) can cause significant direct constituent changes in the mesosphere and stratosphere (middle atmosphere) during certain periods. Both protons and electrons can influence the polar middle atmosphere through ionization and dissociation processes. EPPs can enhance HOx (H, OH, HO2) through the formation of positive ions followed by complex ion chemistry and NOx (N, NO, NO2) through the dissociation of molecular nitrogen. The HOx increases result in direct ozone destruction in the mesosphere and upper stratosphere via several catalytic loss cycles. Such middle atmospheric HOx-caused ozone loss is rather short-lived due to the relatively short lifetime (hours) of the HOx constituents. The NOx family has a considerably longer lifetime than the HOx family and can also lead to catalytic ozone destruction. EPP-caused enhancements of the NOx family can affect ozone directly, if produced in the stratosphere. Ozone decreases from the EPPs lead to a reduction in atmospheric heating and, subsequent atmospheric cooling. Conversely, EPPs can cause direct atmospheric heating through Joule heating. Measured HOx constituents OH and HO2 showed increases due to solar protons. Observed NOx constituents NO and NO2 were enhanced due to both solar protons and precipitating electrons. Other hydrogen- and nitrogen-ocntaining constituents were also measured to be directly influenced by EPPs, including N2O, HNO3, HO2NO2, N2OS, H2O2, ClONO2, HCl, and HOCl. Observed constituents ClO and CO were directly affected by EPPs as well. Many measurements indicated significant direct ozone decreases. A significant number of satellites housed instruments, which observed direct EPP-caused atmospheric effects, including Nimbus 4 (BUV), Nimbus 7 (SBUV), several NOAA platforms (SBUV/2), SME, UARS (HALOE, CLAES), SCISAT-1 (ACE-FTS), Odin (OSIRIS), Envisat-l (GOMOS, MIPAS, SCIAMACHY), and Aura (MLS). Measurements by rockets and ground-based radar also indicated EPP direct impacts. Atmospheric models have been used with some success in predicting the direct EPP impacts on the mesosphere and stratosphere. A review of the observed direct effects of EPP on the middle atmosphere will be given in this presentation.

Jackman, Charles H.↗

NASA NTRS2010

Lithosphere-Atmosphere-Ionosphere Coupling (LAIC) Model - An Unified Concept for Earthquake Precursors Validation

The paper presents a conception of complex multidisciplinary approach to the problem of clarification the nature of short-term earthquake precursors observed in atmosphere, atmospheric electricity and in ionosphere and magnetosphere. Our approach is based on the most fundamental principles of tectonics giving understanding that earthquake is an ultimate result of relative movement of tectonic plates and blocks of different sizes. Different kind of gases: methane, helium, hydrogen, and carbon dioxide leaking from the crust can serve as carrier gases for radon including underwater seismically active faults. Radon action on atmospheric gases is similar to the cosmic rays effects in upper layers of atmosphere: it is the air ionization and formation by ions the nucleus of water condensation. Condensation of water vapor is accompanied by the latent heat exhalation is the main cause for observing atmospheric thermal anomalies. Formation of large ion clusters changes the conductivity of boundary layer of atmosphere and parameters of the global electric circuit over the active tectonic faults. Variations of atmospheric electricity are the main source of ionospheric anomalies over seismically active areas. Lithosphere-Atmosphere-Ionosphere Coupling (LAIC) model can explain most of these events as a synergy between different ground surface, atmosphere and ionosphere processes and anomalous variations which are usually named as short-term earthquake precursors. A newly developed approach of Interdisciplinary Space-Terrestrial Framework (ISTF) can provide also a verification of these precursory processes in seismically active regions. The main outcome of this paper is the unified concept for systematic validation of different types of earthquake precursors united by physical basis in one common theory.

Pulinets, S.↗

NASA NTRS2011

Atmospheric Chemistry Over Southern Africa

During the southern African dry season, regional haze from mixed industrial pollution, biomass burning aerosol and gases from domestic and grassland fires, and biogenic sources from plants and soils is worsened by a semi-permanent atmosphere gyre over the subcontinent. These factors were a driver of several major international field campaigns in the 1990s and early 2000s, and attracted many scientists to the region. Some researchers were interested in understanding fundamental processes governing chemistry of the atmosphere and interaction with climate change. Others found favorable conditions for evaluating satellite-derived measurements of atmospheric properties and a changing land surface. With that background in mind a workshop on atmospheric chemistry was held in South Africa. Sponsored by the International Commission for Atmospheric Chemistry and Global Pollution (ICACGP; http://www.icacgp.org/), the workshop received generous support from the South African power utility, Eskom, and the Climatology Research Group of the University of the Witwatersrand, Johannesburg, South Africa. The purpose of the workshop was to review some earlier findings as well as more recent findings on southern African climate vulnerability, chemical changes due to urbanization, land-use modification, and how these factors interact. Originally proposed by John Burrows, president of ICACGP, the workshop was the first ICACGP regional workshop to study the interaction of air pollution with global chemical and climate change. Organized locally by the University of the Witwatersrand, the workshop attracted more than 60 delegates from South Africa, Mozambique, Botswana, Zimbabwe, France, Germany, Canada, and the United States. More than 30 presentations were given, exploring both retrospective and prospective aspects of the science. In several talks, attention was focused on southern African chemistry, atmospheric pollution monitoring, and climate processes as they were studied in the field campaigns such as Transport and Atmospheric Chemistry Near the Equator-Atlantic (TRACE-A), Southern African Fire-Atmosphere Research Initiative (SAFARI-92), and Southern African Regional Science Initiative (SAFARI 2000). Since those large international efforts, satellites have matured enough to enable quantifiable measurements of regional land surface, atmosphere, and ocean. In addition, global and chemical transport models have also been advanced to incorporate various data. Thus, the timing of the workshop was right for a full-fledged re-assessment of the chemistry, physics, and socio-economical impacts caused by pollution in the region, including a characterization of sources, deposition, and feedbacks with climate change.

Gatebe, Charles K.↗

NASA NTRS2012

Heated-Atmosphere Airship for the Titan Environment: Thermal Analysis

Future exploration of Saturn's moon Titan can be carried out by airships. Several lighter-than-atmosphere gas airships and passive drifting heated-atmosphere balloon designs have been studied, but a heated-atmosphere airship could combine the best characteristics of both. This work analyses the thermal design of such a heated-atmosphere vehicle, and compares the result with a lighter-than-atmosphere (hydrogen) airship design. A design tool was created to enable iteration through different design parameters of a heated-atmosphere airship (diameter, number of layers, and insulating gas pocket thicknesses) and evaluate the feasibility of the resulting airship. A baseline heated-atmosphere airship was designed to have a diameter of 6 m (outer diameter of 6.2 m), three-layers of material, and an insulating gas pocket thickness of 0.05 m between each layer. The heated-atmosphere airship has a mass of 161.9 kg. A similar mission making use of a hydrogen-filled airship would require a diameter of 4.3 m and a mass of about 200 kg. For a long-duration mission, the heated-atmosphere airship appears better suited. However, for a mission lifetime under 180 days, the less complex hydrogen airship would likely be a better option.

Heller, R. S.↗

NASA NTRS2015

Understanding the Atmosphere of 51 Eri b: Do Photochemical Hazes Cloud the Planets Spectrum?

The first young giant planet to be discovered by the Gemini Planet Imager was the (is) approximately 2MJ planet 51 Eri b. This approximately 20 Myr old young Jupiter is the first directly imaged planet to show unmistakable methane in H band. To constrain the planet's mass, atmospheric temperature, and composition, the GPI J and H band spectra as well as some limited photometric points were compared to the predictions of substellar atmosphere models. The best fitting models reported in the discovery paper (Macintosh et al. 2015) relied upon a combination of clear and cloudy atmospheric columns to reproduce the data. However for an object as cool as 700 K, the origin of the cloud coverage is somewhat puzzling, as the global silicate and iron clouds would be expected to have sunk well below the photosphere by this effective temperature. While strong vertical mixing in these low gravity atmospheres remains a plausible explanation, we have explored whether atmospheric photochemistry, driven by the UV flux from the primary star, may yield hazes that also influence the observed spectrum of the planet. To explore this possibility we have modeled the atmospheric photochemistry of 51 Eri b using two state-of-the-art photochemical models, both capable of predicting yields of complex hydrocarbons under various atmospheric conditions. In our presentation we will summarize the modeling approach employed to characterize 51 Eri b, explaining constraints on the planet's effective temperature, gravity, and atmospheric composition and also present results of our studies of atmospheric photochemistry. We will discuss whether photochemical hazes could indeed be responsible for the particulate opacity that apparently sculpts the spectrum of the planet.

GPI - Gemini Planet Imager↗