Author
Gordon L. Bjoraker
Bio: Gordon L. Bjoraker is an academic researcher from Goddard Space Flight Center. The author has contributed to research in topics: Stratosphere & Jupiter. The author has an hindex of 38, co-authored 144 publications receiving 5133 citations.
Topics: Stratosphere, Jupiter, Titan (rocket family), Atmosphere, Saturn
Papers published on a yearly basis
Papers
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TL;DR: In this paper, the authors analyzed data recorded by the Composite Infrared Spectrometer (CIRS) aboard the Cassini spacecraft during the Titan flybys T0-T10 (July 2004-January 2006).
388 citations
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Goddard Space Flight Center1, Cornell University2, University of Maryland, College Park3, Janssen Pharmaceutica4, University of Oxford5, Johns Hopkins University6, Jet Propulsion Laboratory7, University of Hawaii8, Southwest Research Institute9, Search for extraterrestrial intelligence10, Marshall Space Flight Center11, University of Paris12, Cardiff University13, Lawrence Livermore National Laboratory14
TL;DR: Early Cassini infrared observations of Titan show a stratopause at an altitude of 310 kilometers (and 186 kelvin at 15°S), and the concentrations of several stratospheric organic compounds are enhanced at mid- and high northern latitudes, and the strong zonal winds may inhibit mixing between these latitudes and the rest of Titan.
Abstract: Temperatures obtained from early Cassini infrared observations of Titan show a stratopause at an altitude of 310 kilometers (and 186 kelvin at 15°S). Stratospheric temperatures are coldest in the winter northern hemisphere, with zonal winds reaching 160 meters per second. The concentrations of several stratospheric organic compounds are enhanced at mid- and high northern latitudes, and the strong zonal winds may inhibit mixing between these latitudes and the rest of Titan. Above the south pole, temperatures in the stratosphere are 4 to 5 kelvin cooler than at the equator. The stratospheric mole fractions of methane and carbon monoxide are (1.6 ± 0.5) × 10-2 and (4.5 ± 1.5) × 10-5, respectively.
346 citations
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Goddard Space Flight Center1, University of Maryland, College Park2, Marshall Space Flight Center3, Cardiff University4, University of Oxford5, European Southern Observatory6, Cornell University7, Jet Propulsion Laboratory8, University of Hawaii9, University of Paris10, Stanford University11, Southwest Research Institute12
TL;DR: The Composite Infrared Spectrometer (CIRS) is a remote-sensing Fourier transform spectrometer on the Cassini orbiter that measures thermal radiation over two decades in wavenumber, with a spectral resolution that can be set from 0.5 to 15.5 cm− 1.
Abstract: The Composite Infrared Spectrometer (CIRS) is a remote-sensing Fourier Transform Spectrometer (FTS) on the Cassini orbiter that measures thermal radiation over two decades in wavenumber, from 10 to 1400 cm− 1 (1 mm to 7μ m), with a spectral resolution that can be set from 0.5 to 15.5 cm− 1. The far infrared portion of the spectrum (10–600 cm− 1) is measured with a polarizing interferometer having thermopile detectors with a common 4-mrad field of view (FOV). The middle infrared portion is measured with a traditional Michelson interferometer having two focal planes (600–1100 cm− 1, 1100–1400 cm− 1). Each focal plane is composed of a 1× 10 array of HgCdTe detectors, each detector having a 0.3-mrad FOV. CIRS observations will provide three-dimensional maps of temperature, gas composition, and aerosols/condensates of the atmospheres of Titan and Saturn with good vertical and horizontal resolution, from deep in their tropospheres to high in their mesospheres. CIRS’s ability to observe atmospheres in the limb-viewing mode (in addition to nadir) offers the opportunity to provide accurate and highly resolved vertical profiles of these atmospheric variables. The ability to observe with high-spectral resolution should facilitate the identification of new constituents. CIRS will also map the thermal and compositional properties of the surfaces of Saturn’s icy satellites. It will similarly map Saturn’s rings, characterizing their dynamical and spatial structure and constraining theories of their formation and evolution. The combination of broad spectral range, programmable spectral resolution, the small detector fields of view, and an orbiting spacecraft platform will allow CIRS to observe the Saturnian system in the thermal infrared at a level of detail not previously achieved.
326 citations
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École Polytechnique1, University of Paris-Sud2, Rutherford Appleton Laboratory3, Centre national de la recherche scientifique4, Goddard Space Flight Center5, California Institute of Technology6, Pierre-and-Marie-Curie University7, University of Burgundy8, Université libre de Bruxelles9, University of Strathclyde10, Université catholique de Louvain11, University of Massachusetts Lowell12, University of Denver13, Stony Brook University14, University of Bremen15, Langley Research Center16, École Centrale Paris17, Technische Universität München18, University of Alabama19
TL;DR: The current version of the GEISA-97 database is described in this paper, which contains 1,346,266 entries and includes a catalog of absorption cross-sections of molecules such as chlorofluorocarbons which exhibit unresolvable spectra.
Abstract: The current version GEISA-97 of the computer-accessible database system GEISA (Gestion et Etude des Informations Spectroscopiques Atmospheriques: Management and Study of Atmospheric Spectroscopic Information) is described. This catalogue contains 1,346,266 entries. These are spectroscopic parameters required to describe adequately the individual spectral lines belonging to 42 molecules (96 isotopic species) and located between 0 and 22,656 cm-1. The featured molecules are of interest in studies of the terrestrial as well as the other planetary atmospheres, especially those of the Giant Planets. GEISA-97 contains also a catalog of absorption cross-sections of molecules such as chlorofluorocarbons which exhibit unresolvable spectra. The modifications and improvements made to the earlier edition (GEISA-92) and the data management software are described. GEISA-97 and the associated management software are accessible from the ARA/LMD (Laboratoire de Meteorologie Dynamique du CNRS, France) web site: http://ara01.polytechnique.fr/registration.
288 citations
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Goddard Space Flight Center1, Cornell University2, University of Maryland, College Park3, Janssen Pharmaceutica4, Jet Propulsion Laboratory5, Southwest Research Institute6, University of Oxford7, University of Hawaii8, Ames Research Center9, Johns Hopkins University10, Marshall Space Flight Center11, University of Paris12, Cardiff University13, Lawrence Livermore National Laboratory14
TL;DR: Diurnal surface temperature variations on Phoebe suggest a more porous regolith than on the jovian satellites, and Saturn's ring temperatures have radial variations down to the smallest scale resolved (100 kilometers).
Abstract: Stratospheric temperatures on Saturn imply a strong decay of the equatorial winds with altitude If the decrease in winds reported from recent Hubble Space Telescope images is not a temporal change, then the features tracked must have been at least 130 kilometers higher than in earlier studies Saturn's south polar stratosphere is warmer than predicted from simple radiative models The C/H ratio on Saturn is seven times solar, twice Jupiter's Saturn's ring temperatures have radial variations down to the smallest scale resolved (100 kilometers) Diurnal surface temperature variations on Phoebe suggest a more porous regolith than on the jovian satellites
185 citations
Cited by
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Harvard University1, University of Reims Champagne-Ardenne2, College of William & Mary3, Old Dominion University4, University of Lisbon5, University of Burgundy6, California Institute of Technology7, Centre national de la recherche scientifique8, Université catholique de Louvain9, University of York10, University College London11, National Institute of Standards and Technology12, University of Waterloo13, National Center for Atmospheric Research14, University of Cologne15, Karlsruhe Institute of Technology16, Langley Research Center17
TL;DR: The new HITRAN is greatly extended in terms of accuracy, spectral coverage, additional absorption phenomena, added line-shape formalisms, and validity, and molecules, isotopologues, and perturbing gases have been added that address the issues of atmospheres beyond the Earth.
Abstract: This paper describes the contents of the 2016 edition of the HITRAN molecular spectroscopic compilation. The new edition replaces the previous HITRAN edition of 2012 and its updates during the intervening years. The HITRAN molecular absorption compilation is composed of five major components: the traditional line-by-line spectroscopic parameters required for high-resolution radiative-transfer codes, infrared absorption cross-sections for molecules not yet amenable to representation in a line-by-line form, collision-induced absorption data, aerosol indices of refraction, and general tables such as partition sums that apply globally to the data. The new HITRAN is greatly extended in terms of accuracy, spectral coverage, additional absorption phenomena, added line-shape formalisms, and validity. Moreover, molecules, isotopologues, and perturbing gases have been added that address the issues of atmospheres beyond the Earth. Of considerable note, experimental IR cross-sections for almost 300 additional molecules important in different areas of atmospheric science have been added to the database. The compilation can be accessed through www.hitran.org. Most of the HITRAN data have now been cast into an underlying relational database structure that offers many advantages over the long-standing sequential text-based structure. The new structure empowers the user in many ways. It enables the incorporation of an extended set of fundamental parameters per transition, sophisticated line-shape formalisms, easy user-defined output formats, and very convenient searching, filtering, and plotting of data. A powerful application programming interface making use of structured query language (SQL) features for higher-level applications of HITRAN is also provided.
7,638 citations
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TL;DR: The authors reviewed the current understanding of mechanisms that are, or may be, acting to cause climate change over the past century, with an emphasis on those due to human activity, and discussed the general level of confidence in these estimates and areas of remaining uncertainty.
Abstract: Our current understanding of mechanisms that are, or may be, acting to cause climate change over the past century is briefly reviewed, with an emphasis on those due to human activity. The paper discusses the general level of confidence in these estimates and areas of remaining uncertainty. The effects of increases in the so-called well-mixed greenhouse gases, and in particular carbon dioxide, appear to be the dominant mechanism. However, there are considerable uncertainties in our estimates of many other forcing mechanisms; those associated with the so-called indirect aerosol forcing (whereby changes in aerosols can impact on cloud properties) may be the most serious, as its climatic effect may be of a similar size as, but opposite sign to, that due to carbon dioxide. The possible role of volcanic eruptions as a natural climate change mechanism is also highlighted.
1,403 citations
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TL;DR: In this paper, high-precision spectrophotometric observations of four planetary transits of HD 209458, in the region of the sodium resonance doublet at 589.3 nm, were reported.
Abstract: We report high-precision spectrophotometric observations of four planetary transits of HD 209458, in the region of the sodium resonance doublet at 589.3 nm. We find that the photometric dimming during transit in a bandpass centered on the sodium feature is deeper by (2.32 ± 0.57) × 10-4 relative to simultaneous observations of the transit in adjacent bands. We interpret this additional dimming as absorption from sodium in the planetary atmosphere, as recently predicted from several theoretical modeling efforts. Our model for a cloudless planetary atmosphere with a solar abundance of sodium in atomic form predicts more sodium absorption than we observe. There are several possibilities that may account for this reduced amplitude, including reaction of atomic sodium into molecular gases and/or condensates, photoionization of sodium by the stellar flux, a low primordial abundance of sodium, and the presence of clouds high in the atmosphere.
1,300 citations
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TL;DR: Direct atmospheric measurements from the Gas Chromatograph Mass Spectrometer (GCMS), including altitude profiles of the constituents, isotopic ratios and trace species (including organic compounds), were reported, confirming the primary constituents were confirmed to be nitrogen and methane.
Abstract: Saturn's largest moon, Titan, remains an enigma, explored only by remote sensing from Earth, and by the Voyager and Cassini spacecraft. The most puzzling aspects include the origin of the molecular nitrogen and methane in its atmosphere, and the mechanism(s) by which methane is maintained in the face of rapid destruction by photolysis. The Huygens probe, launched from the Cassini spacecraft, has made the first direct observations of the satellite's surface and lower atmosphere. Here we report direct atmospheric measurements from the Gas Chromatograph Mass Spectrometer (GCMS), including altitude profiles of the constituents, isotopic ratios and trace species (including organic compounds). The primary constituents were confirmed to be nitrogen and methane. Noble gases other than argon were not detected. The argon includes primordial 36Ar, and the radiogenic isotope 40Ar, providing an important constraint on the outgassing history of Titan. Trace organic species, including cyanogen and ethane, were found in surface measurements.
914 citations
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TL;DR: A detailed survey of more than 100 comets has been carried out by as mentioned in this paper, which enabled taxonomic groupings based on free radical species and on crystallinity of rocky grains.
Abstract: Cometary nuclei contain the least modified material from the formative epoch of our planetary system, and their compositions reflect a range of processes experienced by material prior to its incorporation in the cometary nucleus. Dynamical models suggest that icy bodies in the main cometary reservoirs (Kuiper Belt, Oort Cloud) formed in a range of environments in the protoplanetary disk, and (for the Oort Cloud) even in disks surrounding neighboring stars of the Sun's birth cluster. Photometric and spectroscopic surveys of more than 100 comets have enabled taxonomic groupings based on free radical species and on crystallinity of rocky grains. Since 1985, new surveys have provided emerging taxonomies based on the abundance ratios of primary volatiles. More than 20 primary chemical species are now detected in bright comets. Measurements of nuclear spin ratios (in water, ammonia, and methane) and of isotopic ratios (D/H in water and HCN; 14N/15N in CN and HCN) have provided critical insights on factors affec...
849 citations