Oxygen Column Density Research Articles

A survey of large‐scale variations in thermospheric oxygen column density with magnetic activity as inferred from observations of the FUV dayglow

Brightness of the terrestrial far‐ultraviolet (FUV) dayglow is dominated by the 130.4‐nm emission of neutral atomic oxygen, O I, and variations in the brightness observed from altitudes high above the emitting region reflect variations in thermospheric oxygen density. This paper summarizes the results of an initial survey of the Dynamics Explorer 1 observations of the FUV dayglow through a presentation of 13 representative events selected to demonstrate the spatial extent and short‐term temporal stability of the brightness perturbations. The emphasis here is on the morning sector of local time and the polar cap for observations obtained in the time interval from September 23, 1981, through January 19, 1982. An analytic expression is derived for the average response of the FUV photometer to the dayglow during periods of high‐latitude magnetic quiescence. The remaining observations in this time interval are then analyzed for their deviations from the established quiet time values. Deviations of −40% to +30% are found following intervals of increased magnetic activity. The most significant decreases (−30% to −40%) are observed equatorward of the instantaneous auroral oval only after sustained periods (∼6 hours) of intense magnetic activity (average AE greater than ∼700 nT). Decreases extend equatorward from the aurora to geographic latitudes as low as ∼30° N. Decreases of lesser magnitude that do not extend as far equatorward are associated with sustained periods of more moderate activity in which the average value of AE is smaller (∼300–400 nT). Also, the spatial extent and magnitude of the decreases in the morning sector appear greater when the IMF By component is positive. In both cases, decreases are readily observed within the polar cap. Localized enhancements of +20% to +30% occur much less frequently and are detected at the middle latitudes, well equatorward of the auroral oval.

Satellite remote sensing of thermospheric O/N2 and Solar EUV: 2. Data analysis

The companion paper by Strickland et al. (this issue) describes a technique for deriving QEUV and O/N2 from disk observations of OI 135.6‐nm and N2 LBH dayglow emission. QEUV refers to the integrated solar EUV energy flux below 45 nm and is derived from knowledge of the 135.6/LBH ratio or O/N2 in conjunction with either the 135.6 nm or LBH intensity. O/N2 refers to the ratio of the atomic oxygen (O) column density to the molecular nitrogen (N2) column density at a given value of the N2 column density. Strickland et al. show that the least uncertainty in derived values O/N2 occurs in the vicinity of an N2 depth of 1017 cm−2. The O/N2 values presented in this paper are referenced to this depth. While QEUV is obtained from the intensity of either 135.6 nm or LBH, O/N2 is obtained from the intensity ratio designated by 135.6/LBH. The technique has been used to derive O/N2 and QEUV values from nadir‐viewing far ultraviolet dayglow data obtained by the auroral and ionospheric remote sensor instrument on board the Polar BEAR satellite. Data are considered from single passes on July 15, 16, and 21, 1987, spanning a latitude range from 25° to 55°N. The 3‐hour ap index was between 20 and 30 for the first two passes and only about 5 for the third pass. The 135.6‐nm and LBH signals were obtained from spectra recorded at a resolution of 3.6 nm from which a background was subtracted followed by integration over the intervals from 134.5 to 139.0 nm and 155.0 to 170.0 nm. Uncertainties were assigned to the signals and their ratios that took into account statistical uncertainties in the true signal and in the subtracted background signal. Profiles of derived O/N2 with uncertainties reflecting the data uncertainties are shown along with mass spectrometer/incoherent scatter (MSIS) O/N2 profiles over 25°–55°N. More structure is seen in the profiles on July 15 and 16, which are more disturbed days than July 21. In all cases, O/N2 increases from high to low latitudes. MSIS also shows such an increase but is much less structured. The results are shown to agree qualitatively with O/N2 values obtained from a general circulation model. Derived QEUV values are in the range from 1.1 to 1.4 ergs cm−2 s−1 and are in good agreement with values derived from the Hinteregger spectrum for the F10.7 values appropriate to the observations. The results illustrate the potential of the technique for monitoring thermospheric dynamics through latitudinal and temporal variations in O/N2 which are signatures of ascending and descending motion in the thermosphere.

Search for molecular oxygen in VII ZW 31

view Abstract Citations (21) References (18) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Search for Molecular Oxygen in VII ZW 31 Goldsmith, Paul F. ; Young, Judith S. Abstract We have carried out a search for emission from the 1(1)1(0) transition of molecular oxygen from the infrared- and CO-luminous galaxy VII Zw 31. Its redshift (cz = 16,280 km s^-1^) results in the line being shifted from a rest frequency near 118.8 GHz, which is entirely blocked by O_2_ in the terrestrial atmosphere, to a frequency of 112.6 GHz, where atmospheric effects are quite small. The 1 σ upper limit to the integrated intensity in a 250 km s^-1^ interval is 0.16 K km s^-1^, which is 0.024 times the integrated intensity of the J = 1-0 CO transition. The resulting upper limit to the molecular oxygen column density is 8.4 x 10^15^ cm^-2^, implying a 1 σ upper limit to fractional abundance of O_2_ relative to H_2_ of 4 x 10^-6^. This is the most stringent upper limit on the molecular oxygen abundance obtained to date, and to the extent that the interstellar medium of VII Zw 31 is similar to that of our Galaxy, significantly constrains the chemical models of the interstellar medium. Publication: The Astrophysical Journal Pub Date: June 1989 DOI: 10.1086/167530 Bibcode: 1989ApJ...341..718G Keywords: Galaxies; Infrared Sources (Astronomy); Interstellar Matter; Molecular Clouds; Oxygen Spectra; Abundance; Line Spectra; Luminosity; Molecular Spectra; Astrophysics; GALAXIES: ABUNDANCES; GALAXIES: INTERSTELLAR MATTER; INTERSTELLAR: MOLECULES full text sources ADS | data products SIMBAD (4) NED (4)

High-resolution X-ray spectroscopy of the Crab Nebula and the oxygen abundance of the interstellar medium

The measurement and analysis of a high-resolution soft X-ray spectrum of the Crab Nebula obtained with the Focal Plane Crystal Spectrometer on the Einstein Observatory are reported. A hydrogen column density of 3.45 + or - 0.42 x 10 to the 21st/sq cm and an oxygen column density of 2.78 + or - 0.55 x 10 to the 18th/sq cm, corresponding to an oxygen abundance of 1.1 + or - 0.3 times solar, were obtained. The absence of any evident oxygen depletion effects suggests that most interstellar grains are reasonably transparent to soft X-rays, implying sizes of less than 0.4 micron. The detailed spectrum in the vicinity of the oxygen edge gives marginal evidence for a resonant absorption line and suggests an edge from singly ionized oxygen.

Interstellar abundances of oxygen and nitrogen

Neutral nitrogen and oxygen column densities or limits are derived for 53 path lengths through the diffuse interstellar medium and compared with column densities of neutral hydrogen. For neither N nor O is a systematic increase of depletion found as reddening increases. The value found for forbidden O/N is 8, and the abundances of N and O are both between 40% and 70% of the solar values. Implications of these results for models of interstellar grains are briefly discussed.

The prebiological paleoatmosphere: stability and composition.

In the past, it was generally assumed that the early atmosphere of the Earth contained appreciable quantities of methane (CH4) and ammonia (NH3). This was the type of atmosphere believed to be the most suitable environment for chemical evolution, the nonbiological formation of complex organic molecules, the precursors of living systems. Photochemical considerations suggest that a CH4-NH3 dominated early atmosphere was probably very short-lived, if it ever existed at all. Instead, an early atmosphere of carbon dioxide (CO2) and nitrogen (N2) is favored by photochemical as well as geological and geochemical considerations. Photochemical calculations also indicate that the total oxygen column density of the prebiological paleoatmosphere did not exceed 10(-7) of the present atmospheric level.

Measurements of spectrally integrated atmospheric transmittance in the O2 Schumann‐Runge bands and derived oxygen column densities: 76–102 km

Atmospheric transmittances integrated over wavelength intervals corresponding approximately to the (15–0) through (4–0) Schumann‐Runge bands of O2 have been determined from EUV solar spectra (1768 Å <λ <1948 Å) photographed at seven altitudes between 102 and 76 km with a rocket‐borne spectrograph having a resolution of 0.07 Å. The observed transmittances are compared with atmospheric transmittances predicted from three models of the O2 absorption cross section. The predicted transmittances have also been used to derive column densities of atmospheric O2 from the observations. The results are compared with values calculated from the U.S. Standard Atmosphere (1976) and with oxygen column densities determined by Prinz and Brueckner (1977) from EUV solar spectra of the Schumann‐Runge continuum (λ <1750 Å) and of the H‐Lyman alpha line (1216 Å) recorded on the same films used in the present research. The comparisons test the utility of the models for studies of atmospheric photochemistry, suggest which models may be best for this purpose, and indicate how the models can be improved.

Europa - Ultraviolet emissions and the possibility of atomic oxygen and hydrogen clouds

Emission signals from Europa with wavelength below 800 A were detected by the Pioneer 10 ultraviolet photometer. In the present paper, improved procedures for data reduction are used to determine the spatial region as well as the intensity of the suggested emission sources. The observations indicate a cloud with a radius of about 1.5 Jupiter radii and an apparent brightness of approximately 10 rayleighs for a wavelength of 500 A. It is argued that neutral oxygen atoms, along with neutral hydrogen, are produced through dissociation of water ice on the surface of Europa by particle impact. Electron impact ionization excitation of oxygen atoms in the resulting cloud then gives rise to the observed emission. The present source brightness and cloud radius results are used to estimate an oxygen column density of the order of 10 trillion per sq cm, while the density of atomic hydrogen is at most 100 billion per sq cm and 1 trillion per sq cm for molecular hydrogen.

Global atomic oxygen density derived from OGO-6 1304 Å airglow measurements

The OGO-6 UV photometer experiment measured the atomic oxygen OI 1304 Å triplet in the Earth's dayglow between 400 and 1100 km. We have analyzed the data for the period 15 September–25 October 1969 by obtaining best-fit models in which the 1304 Å emission is excited by solar resonance scattering and photoelectron excitation. Provided the excitation processes are specified, we find a unique relationship between the vertical column density of atomic oxygen and the zenith 1304 Å intensity. This is essentially independent of the atmospheric temperature. Because of the large numerical uncertainties, the excitation sources are determined from the 1304 Å data and quiet-time in situ measurements of atomic oxygen density. They are found to be in good agreement with recent solar measurements of the 1304 Å lines and with calculations of the photoelectron excitation source. The deduced variations of atomic oxygen column densities over the daytime atmosphere are found to agree well with the Jacchia 1971 models. During the geomagnetic storm, the column density generally increased above a fixed altitude. However, the latitudinal dependence is complex. Following the strong geomagnetic activity between 15 September and 1 October, depletions in atomic oxygen are observed. At times, there is evidence of high-altitude transport of atomic oxygen from high latitude to low latitude.