Atmosphere Removal Research Articles

Atmosphere loss in oblique Super-Earth collisions

ABSTRACT Using smoothed particle hydrodynamics we model giant impacts of Super-Earth mass rocky planets between an atmosphere-less projectile and an atmosphere-rich target. In this work, we present results from head-on to grazing collisions. The results of the simulations fall into two broad categories: (1) one main post-collision remnant containing material from target and projectile; (2) two main post-collision remnants resulting from ‘erosive hit-and-run’ collisions. All collisions removed at least some of the target atmosphere, in contrast to the idealized hit-and-run definition in which the target mass is unchanged. We find that the boundary between ‘hit-and-run’ collisions and collisions that result in the projectile and target accreting/merging to be strongly correlated with the mutual escape velocity at the predicted point of closest approach. Our work shows that it is very unlikely for a single giant impact to remove all of the atmosphere. For all the atmosphere to be removed, head-on impacts require roughly the energy of catastrophic disruption (i.e. permanent ejection of half the total system mass) and result in significant erosion of the mantle. We show that higher impact angle collisions, which are more common, are less efficient at atmosphere removal than head-on collisions. Therefore, single collisions that remove all the atmosphere without substantially disrupting the planet are not expected during planet formation.

HATCH: results from simulated radiances, AVIRIS and hyperion

The atmospheric correction program High-accuracy Atmospheric Correction for Hyperspectral data (HATCH) has been developed specifically to convert radiance from imaging spectrometer sensors to reflectance on a pixel-by-pixel basis. HATCH was developed to update the previously available model, the Atmosphere Removal model (ATREM). In this paper, we test the HATCH model against model data using MODTRAN 4 as well as with Airborne Visible/Infrared Imaging Spectroradiomter and Hyperion data for which simultaneous ground reflectances were acquired. We also compare HATCH to the commercially available ACORN model. Results show that HATCH produces smoother-looking spectra than its predecessor ATREM and is less influenced by liquid water in vegetation. Comparisons with MODTRAN were made by calculating above-atmosphere radiances from a hypothetical target with a 0.5 reflectance at all wavelengths between 400 and 2500 nm and retrieving them with HATCH. The results show a maximum deviation of 10% at several wavelengths, highlighting the differences between the models. Hyperion images contain striping artifacts. We show that optimum removal is obtained by normalizing the means and standard deviations of each column after converting radiance to reflectance with an atmospheric model. HATCH produces water vapor corrections virtually unaffected by vegetation liquid water if the water vapor band at 940 nm is used in the calculation. Retrievals using the 1140-nm band are subject to errors associated with liquid water in vegetation. Retrievals of reflectance from Hyperion radiances require use of the 1140-nm band because the 940-nm band falls in the detector crossover region.

The high accuracy atmospheric correction for hyperspectral data (hatch) model

The High-accuracy Atmospheric Correction for Hyperspectral Data (HATCH) model was developed for deriving high-quality surface reflectance spectra from remotely sensed hyperspectral imaging data. This paper presents the novel techniques applied in HATCH. An innovative technique, a smoothness test for water vapor amount retrieval and for automatic spectral calibration, is developed for HATCH. HATCH also includes an original fast radiative transfer equation solver and a correlated-k gaseous absorption model based on HITRAN 2000 database. Spectral regions with overlapping absorptions by different gases are handled by precomputing a correlated-k lookup table for various gas mixing ratios. The interaction between multiple scattering and absorption is explicitly handled through the use of the correlated-k method for gaseous absorption. Finally, some results are presented for HATCH applied to Airborne Visible Infrared Imaging Spectoradiometer data and together with comparison of the results between HATCH and the Atmosphere Removal program. The limitations in HATCH include that the HATCH assumes a Lambertian surface, and adjacent effect is not considered. HATCH assumes aerosols to be spatially homogeneous in a scene.

Temperature dependence of the collisional removal of O2(b 1Σg+, v=1 and 2) at 110–260 K, and atmospheric applications

The temperature dependence of the collisional removal of O2 in the v=1 and 2 vibrational levels of the b 1Σg+ state by O2, N2, and CO2 has been investigated over the 110–260 K temperature range. For the v=1 level, O2 removes energy more effectively than N2 or CO2 at all measured temperatures. For v=2, the difference in effectiveness between colliders is not as great, and the removal by O2 exhibits a substantial positive activation energy; at 125 K O2 in the v=2 level is removed about 40 times more slowly than v=1. Even with this large difference, in the terrestrial atmosphere removal via collisions with O2 controls the lifetime of the vibrationally excited species. Recent atmospheric nightglow measurements performed at the W. M. Keck telescope on Mauna Kea, Hawaii, confirm the presence of O2 in these and higher levels through observation of the naturally occurring b 1Σg+–X 3Σg− emission.

Intercellular Deformation in Compressed Organs

Intercellular deformations, caused by increasing levels of compression applied by a pressure chamber to an organ covered with a plastic sealant and evaluated according to the internal atmosphere removal rate, were observed in carrots ( Daucus carota L. sativa), potatoes ( Solanum tuberosum L.) and sweet-potatoes ( Ipomea batatas L. Lam). The maximum internal gas volume removed in these kinetic assays was close to the intercellular air volume ( V g ) measured by the pycnometric method. Presumably a compression larger than the average organ turgor was required to remove all V g and above this point the cells should become completely flattened against each other. The intercellular deformation caused by a compressing load, observed by constant pressure volumetry, induced a reduction in the endogenous O 2 concentration at the stressed area, according to polarographic measurements. Cellular deformations and eventual V g flooding caused by water movement from the symplasm to the apoplasm of externally compressed organs were distinct from the usual pressure chamber assays, where all cells are exposed to homogeneous gas pressurization, without the development of forces to cause large cellular deformation and intercellular flooding. These gas transport restrictions were suggested as potential causes for post harvest deterioration in fragile commodities subjected to compression.

Design and Commissioning of a Continuous Transferred ARC Plasma Melter for the Vitrification of Nuclear Waste

ABSTRACTA 40-kW transferred arc plasma melter has been designed and constructed to test the potential of this type of system for the vitrification of high level nuclear waste. Present technology relies on joule or induction heaters which are limited in operating temperature and are characterized by large liquid holdup and long residence times. The use of a plasma melter will allow the production of higher melting glasses and glass ceramics which are more durable and leach resistant in underground storage. The use of a plasma greatly decreases residence times in the heater and may even reduce the loss of volatiles by control of the melting atmosphere and continuous removal of the product as a solid ingot. Standard borosilicate glass has been melted with continuous withdrawal of product in a series of commissioning runs.

First-order removal of particulate aluminium in oceanic surface layers

Little is known about processes which remove particles with radii of <5 µm from surface layers of the oceans although they influence the geochemical cycling of many substances. Agglomeration resulting from particle–particle interactions and/or incorporation into faecal pellets by organisms may accelerate the settling rate of such particles1,2. We report here the vertical distribution of particulate aluminium in the Gulf Stream which is consistent with that expected if primary input were from the atmosphere and first-order removal occurred in the upper 100 m of the water column. We hypothesize that filter feeding, particularly by salps, may be responsible for calculated removal rates.

Critique of ‘Cometary impact and the origin of tektites’

Lin [1966] recently outlined two mechanisms by which he suggests that it is dynamically possible for the Australasian tektites to have originated from an impact on earth by some gigantic cosmic body. He calculates that the energy of such an event, in order to remove the earth's atmosphere, would excavate a crater over 300 km in diameter. It is the purpose of this critique to indicate, quite apart from pointing out that 300-km craters associated with the possibility of terrestrial tektite origin are undiscovered, that both mechanisms suggested by Lin are contradicted by present aerodynamic and petrographic data on Australasian tektites. Also, we emphasize here a conclusion inherent in Lin's analysis, but not explicitly stated by him: namely, that, in comparison to the magnitude of atmosphere-removing events, such relatively insignificant earth cavities as the Ries and Bosumtwi craters (thought by some, from age considerations, to be sources of tektites) are far too small to be associated energetically with atmosphere removal.