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  • GEOPHYSICS  (823)
  • 1985-1989  (823)
  • 1950-1954
  • 1925-1929
  • 1988  (823)
  • 1
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    A comparison of solar irradiances measured by SBUV, SME, and rockets (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: In this paper, Solar Backscatter Ultraviolet (SBUV) measurements of solar irradiance and predictions from the Mg 280-nm index are compared with each other and with coincident Solar Mesosphere Explorer (SME) and rocket measurements. The SBUV irradiances show a systematic decrease with time not seen in the rocket measurements; a correction for this decrease is introduced. The scatter and overall structure in the SME spectra is 3-5 percent, of the order of or larger than most of the changes predicted by the Mg index. The corrected SBUV ratio and the Mg index prediction for it agree to within 1 percent. Such agreement supports a common origin for variations between solar maximum and minimum and those for individual rotations: the degree to which active regions cover the visible hemisphere of the sun.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 7091-710
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  • 2
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    Effect of solar proton events in 1978 and 1979 on the odd nitrogen abundance in the middle atmosphere (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Daily average solar proton flux data for 1978 and 1979 are used in a proton energy degradation scheme to derive ion pair production rates and atomic nitrogen production rates. The latter are computed in a form suitable for inclusion in an atmopheric, two-dimensional, time-dependent photochemical model. Odd nitrogen distributions are computed from the model, including atomic nitrogen production from solar protons, and are compared with baseline distributions. The comparisons show that the average effect of the solar protons in 1978 and 1979 was to cause changes in odd nitrogen only above 10 mbar and at latitudes only above about 50 deg in both hemispheres. The influence of the solar proton-produced odd nitrogen on the local abundance of odd nitrogen depends primarily on the background odd nitrogen abundance as well as the altitude and season.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 7084-709
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  • 3
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    Non-seasonal changes in total column ozone from satellite observations, 1970-86 (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Analyses of nonseasonal changes in total column ozone from satellite observations during the period 1970-86 suggest, when combined with analyses of Dobson network data, that the largest reduction in global ozone since 1959 occurred between 1978 and 1986. The existence of an Arctic region of enhanced ozone depletion with similar but less pronounced characteristics of the Antarctic region is described. Before 1983 large rates of decrease were confined to high latitudes, subsequently regions of large rates of ozone depletion have appeared at midlatitudes.
    Keywords: GEOPHYSICS
    Type: Nature (ISSN 0028-0836); 332; 219-227
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  • 4
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    Mass extinctions, atmospheric sulphur and climatic warming at the K/T boundary (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The possible climatic effects of a drastic decrease in cloud condensation nuclei (CCN) associated with a severe reduction in the global marine phytoplankton abundance are investigated. Calculations suggest that a reduction in CCN of more than 80 percent and the resulting decrease in marine cloud albedo could have produced a rapid global warming of 6 C or more. Oxygen isotope analyses of marine sediments from many parts of the world have been interpreted as indicating a marked warming coincident with the demise of calcareous nannoplankton at the K/T boundary. Decreased marine cloud albedo and resulting high sea surface temperatures could have been a factor in the maintenance of low productivity in the 'Strangelove Ocean' period following the K/T extinctions.
    Keywords: GEOPHYSICS
    Type: Nature (ISSN 0028-0836); 332; 63-65
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  • 5
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    Extremely low N2O concentrations in the springtime stratosphere at McMurdo Station, Antarctica (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Measurements have been made of stratospheric N2O using the Stony Brook millimeter-wave remote sensing spectrometer at McMurdo Station, and NO2 mixing ratios are found that are less than 1.5 at 20 km and less than 1.10 at 25 km compared to values measured during the Antarctic summer. The observed mixing ratios are also much less than those predicted by global-scale models of stratospheric chemistry and dynamics. As the NO2 signal remained very weak when McMurdo was at the edges of the ozone hole and showed no signs of recovering during October, it is concluded that the geographical and temporal extent of the region of low NO2 is comparable to or greater than that of the ozone hole. These results argue against theories that require springtime upwelling to explain the Antarctic ozone hole. It is suggested that the air in the Antarctic lower stratosphere during late winter and early spring has been subjected to considerable downward transport.
    Keywords: GEOPHYSICS
    Type: Nature (ISSN 0028-0836); 332; 53-55
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  • 6
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    Effect of computed horizontal diffusion coefficients on two-dimensional N2O model distributions (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The effects of horizontal diffusion coefficients K(yy) and K(yz), computed directly from the residual circulation, on the N2O distribution in a photochemical model were investigated, using a modified version of the two-dimensional model of Guthrie et al. (1984). The residual circulation was computed using the NMC's temperature data and the heating rates reported by Rosenfield et al. (1987). As compared with the effect of the residual circulation alone, the use of horizontal diffusion coefficients produced substantial changes in the N2O distribution and increased the N2O's lifetime values by a few percent. It is suggested that trace gases, such as CH4, CFCl3, CF2Cl2, CH3Cl, and CCl4, which impact the NO(x), HO(x), and Cl(x) radical distributions and therefore ozone, will be influenced in a similar manner by the addition of more realistic diffusion fields.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 5213-521
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  • 7
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    VLF noises triggered by whistlers as observed in the topside ionosphere (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: ISIS-1, ISIS-2, and DE-1 VLF electric field data from Kashima station, Japan are used to investigate characteristics of whistler triggered emissions in the topside ionosphere. The occurrence rate for nonducted whistler triggered emission is shown to be distributed randomly between L = 2.0 and 4.2, while the occurrence rate of ducted whistler triggered emissions increases with latitudes between L = 1.5 and 2.9, attains a maximum at L = 2.7, and abruptly drops off at L = 3.0. The findings indicate that some whistler triggered emissions may be generated by the interaction of whistlers with magnetospheric electrons.
    Keywords: GEOPHYSICS
    Type: Radio Research Laboratory, Journal (ISSN 0033-8001); 35; 15-26
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  • 8
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    Effect of a uniform sea-level change on the earth's rotation and gravitational field (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Global water redistriburtion between the oceans, atmosphere and continents causes changes in the earth's rotation and gravitational field. To conserve water mass, the effect of the small uniform change in sea-level must be considered. Explicit formulas are provided for these sea-level corrections to the gravitational Stokes coefficients, polar motion and length of day. In two recent publications, this sea-level correction term for polar motion was given incorrectly. These errors which arose from normalization conventions with the ocean function are corrected.
    Keywords: GEOPHYSICS
    Type: Geophysical Journal (ISSN 0952-4592); 93; 191-193
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  • 9
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    Comparison of SAGE II solar extinction data with airborne measurements of atmospheric backscattering in the troposphere and lower stratosphere (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: In April 1986, during passage of the SAGE I satellite, the first simultaneous measurements of the atmospheric backscattering coefficient beta (pi, 10.6 microns) were made with an airborne CO2 lidar. Individual ratios of beta and the SAGE II extinction sigma (1.02 micron) are in reasonable accord with previously calculated values. The trend with height shows a distinctly nonlinear relation, which is probably attributable to steadily changing size distributions of aerosols.
    Keywords: GEOPHYSICS
    Type: Nature (ISSN 0028-0836); 332; 709-711
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  • 10
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    Balloon-borne measurements of middle atmosphere aerosols and trace gases in Antarctica (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: This paper reviews data on in situ balloon-borne measurements on stratospheric ozone concentrations and aerosol contents obtained prior to 1986, along with the measurements obtained in 1986 during the National Ozone Expedition. The data indicate that the phenomenon of ozone depletion appears to be shaped spatially and temporally by dynamical stratospheric phenomena. In terms of Antarctic stratospheric research, it appears that the most important problems at the moment involve delineating the springtime ozone depletion through accurate in situ measurements of temperature, trace gas, and particle size (in addition to remote sensing from space).
    Keywords: GEOPHYSICS
    Type: Reviews of Geophysics (ISSN 8755-1209); 26; 113-130
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  • 11
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    A ground-based technique for millimeter wave spectroscopic observations of stratospheric trace constituents (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Recent concern over possible long term stratospheric changes caused by the introduction of man-made compounds has increased the need for instrumentation that can accurately measure stratospheric minor constituents. The technique of radio spectroscopy at millimeter wavelengths was first used to observe rotational transitions of stratospheric ozone nearly two decades ago, but has not been highly developed until recently. A ground-based observing technique is reported which employs a millimeter-wave superheterodyne receiver and multichannel filter spectrometer for measurements of stratospheric constituents that have peak volume mixing ratios that are less than 10 to the -9th, more than 3 orders of magnitude less than that for ozone. The technique is used for an extensive program of observations of stratospheric chlorine monoxide and also for observations of other stratospheric trace gases such as (O-16)3, vibrationally excited (O-16)3, (O-18)2(O-16), N2O, HO2, and HCN. In the present paper, analysis of the observing technique is given, including the method of calibration and analysis of sources of error. The technique is found to be a reliable means of observing and monitoring important stratospheric trace constituents.
    Keywords: GEOPHYSICS
    Type: Radio Science (ISSN 0048-6604); 23; 106-118
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  • 12
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    Comment on 'A new method of forecasting geomagnetic activity and proton showers' by A. Hewish and P.J. Duffet-Smith (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: GEOPHYSICS
    Type: Planetary and Space Science (ISSN 0032-0633); 36; 205
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  • 13
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    Magnetic clouds, geomagnetic disturbances, and cosmic ray decreases (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Nineteen magnetic clouds are identified in the years from 1978 through 1982 and studied using superposed epoch analysis. The magnetic-field intensity, proton density and proton temperature are enhanced ahead of magnetic clouds that are preceded by shock, while strong magnetic-field intensity and low proton temperature are observed within the clouds. A relatively large (about 2.5 percent) decrease in cosmic-ray intensity is associated with magnetic clouds that are preceded by a shock, perhaps caused by the turbulent sheath behind an interplanetary shock ahead of the magnetic cloud, whereas only a small (0.5 percent) decrease in intensity is associated with the magnetic cloud itself. Magnetic clouds can produce geomagnetic activity with a decrease in Dst index of the order 100 gamma. The magnitude of the change in the Dst index for the case when southward fields arrive first is comparable to that for the case when northward fields arrive first, and the phase is such that geomagnetic activity is associated with southward fields.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 2511-251
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  • 14
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    Diurnal variation of nitric oxide at 32 km - Measurements and interpretation (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Balloon observations of NO and ozone near sunset and sunrise around 32 km were made on September 19 and October 4, 1985 from Aire sur l'Adour, France. The NO concentration built up rapidly after sunrise, remained fairly steady during the day, and decreased slowly near sunset. This variation is interpreted quantitatively in terms of current photochemistry in relation to ozone.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 2451-546
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  • 15
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    Effect of line mixing on atmospheric brightness temperatures near 15 microns (1988)
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    Publication Date: 2011-08-19
    Description: The effect of line mixing on the effective blackbody brightness temperature of the earth in the region of the 15-micron nu 2 Q branch of CO2 is calculated. The procedures used to compute line mixing follow those used to successfully model mixing observed in laboratory spectra of two near-infrared CO2 Q branches. The atmospheric radiances are calculated between 664 and 670/cm, a spectral region that is of interest for sounding the upper troposphere and the stratosphere. Mixing was found to lower the observed brightness temperatures by as much as 3 K for some temperature profiles. Ignoring this effect would significantly impact the ability of advanced sounders to produce temperature retrievals which meet the projected accuracy requirement of 1 K/km.
    Keywords: GEOPHYSICS
    Type: Applied Optics (ISSN 0003-6935); 27; 872-878
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  • 16
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    F region electron temperature signatures of the plasmapause based on Dynamics Explorer 1 and 2 measurements (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A large DE 1 and 2 database covering all local times is used to explore the relationship between electron temperature (Te) signatures in the F region and plamaspheric density structures. The quiet time Te signature remains in the vicinity of 60 deg invariant latitude at all local times, while the plasmapause is found to bulge to about 60 deg at 1500 LT. The plasmasphere in the bulge region is shown to exhibit an internal feature in the vicinity of 60 deg which takes the form of a sharp H(+) gradient. It is suggested that the light-ion gradient may represent a recently created sharp boundary between an old plasmasphere and a new plasmasphere. The present Te characteristics are consisent with plasmasphere depletion and refilling time constants.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 1896-190
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  • 17
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    Low-energy bouncing ions in the magnetosphere - A three-dimensional numerical study of Dynamics Explorer 1 data (1988)
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    Publication Date: 2011-08-19
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 1859-187
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  • 18
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    First Viking results - Magnetic field measurements (1988)
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    Publication Date: 2011-08-19
    Description: The magnetic field experiment on the Swedish Viking satellite consists of a triaxial fluxgate magnetometer system with the sensors mounted on a 2-m boom. Transverse magnetic field perturbations are readily observed which identify the large-scale auroral and cusp-region Birkeland current (BC) systems. A sharp gradient was observed in the dayside region near apogee and 08:40 MLT during a pass on March 25, 1986 which has been interpreted as an earthward-flowing BC of 8 micro-A/sq m. When projected to ionospheric altitudes it is estimated that the current density is 200 micro-A/sq m.
    Keywords: GEOPHYSICS
    Type: Physica Scripta (ISSN 0031-8949); 37; 3, Ma; 479-481
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  • 19
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    Trace gas emissions from a mid-latitude prescribed chaparral fire (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Smoke-plume gas samples were collected at altitudes from 35-670 m above the ground over the San Dimas Experimental Forest during a 400-acre prescribed chaparral fire. Mean emission ratios relative to CO2 for CO, H2, CH4, and total nonmethane hydrocarbons were lower than previous values obtained for large biomass-burning field experiments. Comparison of samples from vigorously flaming and mixed stages of combustion revealed little differences in CO2 normalized emission ratios for these gases (except for N2O).
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 1653-165
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  • 20
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    Measurements of odd nitrogen compounds in the stratosphere by the ATMOS experiment on Spacelab 3 (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Spacelab 3's Atmospheric Trace Molecule Spectroscopy (ATMOS) experiment has obtained 30 deg N and 48 deg S vertical profiles of reservoir gases, source gases, and other trace molecules that are important in the middle atmosphere's odd nitrogen, odd chlorine, and odd hydrogen chemical families. The abundances of individual gases and total odd nitrogen levels measured by ATMOS have been compared with prior results obtained from balloon and satellite platforms. The lower-limit profile agrees with ATMOS data to within 16 percent up to 42 km altitude.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 1718-173
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  • 21
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    Measurements of atmospheric hydrocarbons and biogenic emission fluxes in the Amazon boundary layer (1988)
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    Publication Date: 2011-08-19
    Description: Tropospheric mixing ratios of methane, C2-C10 hydrocarbons, and carbon monoxide were measured over the Amazon tropical forest near Manaus, Amazonas, Brazil, in July and August 1985. The measurements, consisting mostly of altitude profiles of these gases, were all made within the atmospheric boundary layer up to an altitude of 1000 m above ground level. Data characterize the diurnal hydrocarbon composition of the boundary layer. Biogenic emissions of isoprene control hydroxyl radical concentrations over the forest. Biogenic emission fluxes of isoprene and terpenes are estimated to be 25,000 micrograms/sq m per day and 5600 micrograms/sq m per day, respectively. This isoprene emission is equivalent to 2 percent of the net primary productivity of the tropical forest. Atmospheric oxidation of biogenic isoprene and terpenes emissions from the Amazon forest may account for daily increases of 8-13 ppb for carbon monoxide in the planetary boundary layer.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 1407-141
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  • 22
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    Nonlinear evolution of the Kelvin-Helmholtz instability in the high-latitude ionosphere (1988)
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    Publication Date: 2011-08-19
    Description: The first numerical simulations of the nonlinear evolution of the electrostatic Kelvin-Helmholtz (K-H) instability with ionospheric Perderson conductivity coupling are presented. It is found that the K-H instability develops in a distinctly different manner in the nonlinear regime with Pedersen coupling than without it. Pedersen coupling effects, in conjunction with a neutral wind and density gradient, are shown to result in an increased time scale for K-H instability wave growth, to inhibit K-H vortex formation, to lead to nonlinear structures which can be described as 'breaking waves', and to generate, in the nonlinear regime, small-scale turbulence by means of secondary instabilities growing on primary waves. The spatial power spectra of the electrostatic potential and density fluctuations are computed, and differences with and without Pedersen effects are reported.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 137-152
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  • 23
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    The role of molecular hydrogen and methane oxidation in the water vapour budget of the stratosphere (1988)
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    Publication Date: 2011-08-19
    Description: The detailed photochemistry of methane oxidation has been studied in a coupled chemical/dynamical model of the middle atmosphere. The photochemistry of formaldehyde plays an important role in determining the production of water vapor from methane oxidation. At high latitudes, the production and transport of molecular hydrogen is particularly important in determining the water vapor distribution. It is shown that the ratio of the methane vertical gradient to the water vapor vertical gradient at any particular latitude should not be expected to be precisely 2, due both to photochemical and dynamical effects. Modeled H2O profiles are compared with measurements from the Limb Infrared Monitor of the Stratosphere (LIMS) experiment at various latitudes. Molecular hydrogen is shown to be responsible for the formation of a secondary maximum displayed by the model water vapor profiles in high latitude summer, a feature also found in the LIMS data.
    Keywords: GEOPHYSICS
    Type: Royal Meteorological Society, Quarterly Journal (ISSN 0035-9009); 114; 281-295
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  • 24
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    ISEE-3 observations of the earth's radio continuum through the bow shock and magnetosheath and in the magnetosphere (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: On October 1 1983, ISEE-3 crossed the earth's bow shock several times and entered the magnetosphere while continuously recording the nonthermal continuum (NTC) radio emission which is generated inside the magnetosphere. The effects of the solar wind, the bow shock, the magnetosheath, and the magnetopause on the propagation of the NTC are studied. On that day it is found that: (1) the relative values of the NTC low frequency cut-off in the solar wind and in the magnetosheath is due to an unusually high density overshoot in the bow shock, 7 to 11 times the solar wind density; (2) refraction at the interface between the magnetosheath and the solar wind can explain most of the decrease in the source angular size when the observer travels away from the earth; (3) plasma density irregularities in the magnetosheath cause considerable scattering of the NTC, and this effect gives a large apparent size to the NTC source when observed from inside the magnetosheath; and (4) the apparent source is also relatively large inside the magnetosphere, probably due to an approach to ray isotropy caused by oblique reflections from the magnetopause.
    Keywords: GEOPHYSICS
    Type: Annales Geophysicae (ISSN 0980-8752); 6; 309-318
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  • 25
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    New evidence from the South China Sea for an abrupt termination of the last glacial period (1988)
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    Publication Date: 2011-08-19
    Description: Results demonstrating an abrupt change in the rate and character of sedimentation in the South China Sea at the close of the last glacial period are presented. Radiocarbon dating and its position in the oxygen isotope shift suggest that this change may be coincident with the abrupt change in climatic conditions seen at high latitudes in the North Atlantic and the Antarctic at 13 kyr BP. These results support the contention that a major global climatic change occurred between 14 and 13 kyr BP.
    Keywords: GEOPHYSICS
    Type: Nature (ISSN 0028-0836); 333; 156-158
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  • 26
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    Comparison of OGO 6 measured thermospheric temperatures with the MSIS-86 empirical model (1988)
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    Publication Date: 2011-08-19
    Description: The thermospheric temperatures measured by the Fabry-Perod interferometer on the OGO 6 satellite are found to be reasonably represented by the mass spectrometer/incoherent scatter 1986 (MSIS-86) empirical model except for two anomalies, one in the South Atlantic and the other near noon local time. These anomalies are likely due to measurement problems. The OGO 6 temperature data were not used in the generation the MSIS models, so this is an independent comparison of measured and model temperatures. The measurements were made primarily during daytime at mid to low latitudes and throughout the day at high latitudes. On average, the measured temperatures are 16 K below the MSIS-86 model temperatures. Latitude gradients during solstices as well as for the yearly average are well represented by the model, as are high-latitude longitudinal and magnetic activity variations.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 5965-597
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  • 27
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    Observation of an ionospheric disturbance caused by a gamma-ray burst (1988)
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    Publication Date: 2011-08-19
    Description: A first observation of an ionospheric disturbance from a gamma-ray burst is reported. The burst, GB30801, occurred at 22:14:18 UT on August 1, 1983, and was one of the strongest ever observed. The total fluence was 0.002 erg/sq cm, most of which occurred in the first 4 s of the burst. Simultaneously, a change was observed in the amplitude of a VLF radio signal from a transmitter in Rugby, England indicative of an ionospheric disturbance. Weaker disturbances were also recorded at the same receiving site on signals from VLF stations in Annapolis, Maryland and Lualualei, Hawaii. The times of the burst and the disturbances are coincident within the 10-s resolution of the VLF recording system. No similar disturbances were observed within 60 hr around the time of the burst. In the future, a network of VLF burst monitors may provide measurements of the total ionizing energy fluence from a burst, as well as some limited directional information.
    Keywords: GEOPHYSICS
    Type: Nature (ISSN 0028-0836); 331; 418-420
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  • 28
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    Gravity domains and assembly of the North American continent by collisional tectonics (1988)
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    Publication Date: 2011-08-19
    Description: A gravity trend map of North America, based on a horizontal Bouguer gravity gradient map produced from gravity data for Canada and the conterminous United States, is presented and used to define a continental mosaic of gravity trend domains akin to structural domains. Contrasting trend characteristics at gravity domain boundaries support the concept of outward growth of the continent primarily by accretionary tectonics. Gravity patterns, however, indicate a different style of tectonics dominated in the development of now-buried Proterozoic orogenic belts in the south-central United States, supporting a view that these belts formed along the leading edge of a southward-migrating Proterozoic continental margin.
    Keywords: GEOPHYSICS
    Type: Nature (ISSN 0028-0836); 331; 333
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  • 29
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    Atmospheric ozone at South Pole, Antarctica, in 1986 (1988)
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    Publication Date: 2011-08-19
    Description: Results of NOAA's measurements of the ozone vertical distributions at the South Pole and of the annual course of total ozone, conducted in 1986 with balloon-borne electrochemical concentration cell (ECC) ozonesondes and a Dobson spectrophotometer, are described. The major finding was that the stratospheric ozone decreases abruptly between September 20 and October 15, with the bulk decrease occurring between 12 and 21 km. In this period, the column ozone and ozone volume mixing ratio at 16 km (the altitude of the normal ozone maximum at South Pole) decreased by 78 percent, and column ozone between 12 and 21 km decreased by 50 percent. The results of these measurements are compared with data obtained in 1971, and the changes observed in the ozone vertical distributions and in the temporal variations of atmospheric ozone are discussed.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 5167-518
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    Simultaneous measurement of minor stratospheric constituents with emission far-infrared spectroscopy (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The vertical mixing ratio profiles of H2O, HDO, O3, heavy ozone, HF, HCl, HCN, and OH in the stratosphere are retrieved from high-resolution far-infrared emission spectra. These spectra were obtained with a balloon-borne Fourier transform spectrometer in the spring of 1979 at 32 deg N. The nonlinear least squares fit method is used in the analysis. The results are obtained relative to the O2 mixing ratio, whose emission features can be found in the same spectra. The retrieval of OH together with other species should be particularly significant for the study of upper stratospheric photochemistry, although the errors are relatively large: 28 percent for OH and 16-19 percent for other species.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 3851-386
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    Antarctic springtime ozone depletion computed from temperature observations (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: An observationally based, mechanistic dynamical model is used to simulate the decline of total ozone during September and October for the years 1979 through 1986. Vertical velocities derived from observed stratospheric temperature changes and computed radiative heating rates are used to advect an ozone mixing ratio profile during the Antarctic spring period. An early August 1982 Syowa balloonsonde ozone profile is used to initialize the computations. The model reasonably simulates the September and October changes in total ozone, considering the uncertainties in the observed data and the radiative heating. The simulated decline is found to be very sensitive to the choice of initial ozone profile and to small changes in the radiative heating. The results of this study suggest that the dynamical hypothesis of the Antarctic ozone depletion is both quantitatively credible and consistent with the observed temperature changes.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 3833-384
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  • 32
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    Resonant geomagnetic field oscillations and Birkeland currents in the morning sector (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The relationship between large-scale Birkeland currents and resonant oscillations of the geomagnetic field is investigated on the basis of Viking magnetic-field, electric-field, and particle measurements and AMPTE-CEE and IMP-8 magnetic-field measurements obtained during April 23-25, 1986. The data are presented in extensive graphs and characterized in detail. The 3-16-mHz 5-60-nT magnetic-field oscillations detected by Viking are also seen by AMPTE-CEE below L = 8.8 and extend from the lower L shells to the boundary between regions 1 and 2 of the Birkeland-current system, and this boundary is shown to be closely related to the interface between the low-latitude boundary layer and the central plasma sheet. It is suggested that the magnetospheric oscillations may be driven by several different solar-wind features, possibly depending on the direction of the IMF.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 2661-267
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  • 33
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    A few parts in 10 to the 8th geodetic baseline repeatablity in the Gulf of California using the Global Positioning System (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: GPS geodetic measurements of 350-650 km baselines across the Pacific-North America plate boundary in the Gulf of California are presented. The analysis employs a four-station U.S. fiducial network and combined carrier phase and pseudorange data. Water vapor radiometer data at the Gulf sites are used to calibrate the GPS signal for wet tropospheric path delays. Residual tropospheric delays are modeled as first-order exponentially correlated stochastic processes. The measurement precision for horizontal components is a few parts in 10 to the 8th or better.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 15; 353-356
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  • 34
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    Iridium abundance maxima in the Upper Cenomanian extinction interval (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Two iridium abundance peaks, both 0.11 ppb (whole-rock basis) over a local background of 0.017 ppb, have been found in Middle Cretaceous marine rocks near Pueblo, Colorado. They occur just below the 92-million-year-old Cenomanian-Turonian (C-T) stage boundary. No other peaks were found in 45 meters of strata (about 2.5 million years of deposition) above and below the boundary interval. The broad lower peak straddles the first in a series of extinctions of benthic and nektonic macrobiota which comprise the C-T extinction event. The sharp upper peak occurs stratigraphically about 1.2 meters above the lower peak. The excess Ir might be from meteoroid impacts.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 15; 346-349
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  • 35
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    Boundary layer ozone - An airborne survey above the Amazon Basin (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Ozone data obtained over the forest canopy of the Amazon Basin during July and August 1985 in the course of NASA's Amazon Boundary Layer Experiment 2A are discussed, and ozone profiles obtained during flights from Belem to Tabatinga, Brazil, are analyzed to determine any cross-basin effects. The analyses of ozone data indicate that the mixed layer of the Amazon Basin, for the conditions of undisturbed meteorology and in the absence of biomass burning, is a significant sink for tropospheric ozone. As the coast is approached, marine influences are noted at about 300 km inland, and a transition from a forest-controlled mixed layer to a marine-controlled mixed layer is noted.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 1452-146
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    Tropospheric nitric oxide measurements over the Amazon Basin (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Horizontal and vertical distributions of nitric oxide (NO) were measured over the Amazon Basin during NASA's Global Tropospheric Experiment (GTE) Amazon Boundary Layer Experiment mission in July-August 1985. During transit flights between the Virginia coast and Manaus, Brazil, NO mixing ratios were 12-15 pptv at 5 km altitude. Values up to 200 pptv were observed in electrically active clouds. During longitudinal surveys over the Amazon region, NO mixing ratios in the lower planetary boundary layer decreased from 25-60 pptv over the central basin to 10-12 pptv in coastal regions. In the convective cloud layer or free troposphere, NO mixing ratios averaged 13 pptv in regions not influenced by biomass burning. No longitudinal trend above the mixed layer could be detected. A steep negative gradient with increasing altitude was noted within the mixed layer before midday. Mixing ratios decreased from 60 pptv at 0.2 km to about 15 pptv at the top of the mixed layer (1 km). By midday, growth of the mixed layer height and enhanced mixing reduced the gradient, and evidence for mixing of NO into the convective cloud layer was noted.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 1396-140
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    Tropospheric ozone and aerosol distributions across the Amazon Basin (1988)
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    Publication Date: 2011-08-19
    Description: As a part of the NASA Global Tropospheric Experiment to study the Amazon boundary layer, ozone and aerosol distributions were made measured in July-August 1985 by a NASA Electra aircraft on several long-range flights spanning different areas between Tabatinga and Belem, Brazil. Both positive and negative correlations were found in PBL between aerosol concentrations and O3 mixing ratios. The negative correlations result from the downward transport of relatively clean O3-rich air from the upper troposphere into PBL (which normally has higher aerosol loading and lower O3 concentrations than troposphere); positive correlations are found in biomass-burning plumes, where the aerosols are emitted into the air and O3 is photochemically produced. It was found that, in the dry season, a significant portion of the ozone over the rain forest is a result of biomass burning and that the distribution of photochemically produced O3 is strongly affected by synoptic-scale transport from large fires to the south/southeast.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 1431-145
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  • 38
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    Structure and growth of the mixing layer over the Amazonian rain forest (1988)
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    Publication Date: 2011-08-19
    Description: The structure and growth of the atmospheric mixed layer over the Amazonian rain forest were examined using measurements obtained during the NASA Amazon Boundary Layer Experiment. Measurements of temperature, moisture, and horizontal wind were carried out in and above the mixed layer by means of a tethered balloon, rawinsonde, and aircraft; fluxes of sensible and latent heat were measured at the top of the canopy. It was found that the mixing layer grows rapidly, at 5-8 cm/sec, soon after sunrise to a mean maximum height of 1200 m by 1300 LT; during undisturbed conditions, mixed layer heights of 1000 are common between 1000 and 1600 LT. No horizontal inhomogeneities in the mixed layer structure or depth were found over large distances. A simple mixed layer model was applied to show how fluxes of species might be estimated using only quantities measured at the surface and prescribing an initial condition and boundary condition for the mixed layer.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 1361-137
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  • 39
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    Antarctic ozone - Meteoric control of HNO3 (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Atmospheric circulation leads to an accumulation of debris from meteors in the Antarctic stratosphere at the beginning of austral spring. The major component of meteoric material is alkaline, comprised predominantly of the oxides of magnesium and iron. These metals may neutralize the natural acidity of stratospheric aerosols, remove nitric acid from the gas phase, and bond it as metal nitrates in the aerosol phase. Removal of nitric acid vapor has been previously shown to be a critical link in the photochemical depletion of ozone in the Antarctic spring, by allowing for increased catalytic loss from chlorine and bromine.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 15; 1-4
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  • 40
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    Measurements of air-broadened and nitrogen-broadened Lorentz width coefficients and pressure shift coefficients in the nu4 and nu2 bands of C-12H4 (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Air-broadened and N2-broadened halfwidth and pressure shift coefficients of 294 transitions in the nu4 and nu2 bands of C-12H4 have been measured from laboratory absorption spectra recorded at room temperature with the Fourier transform spectrometer in the McMath solar telescope facility of the National Solar Observatory. Total pressures of up to 551 Torr were employed with absorption paths of 5-150 cm, CH4 volume mixing ratios of 2.6 percent or less, and resolutions of 0.005 and 0.01/cm. A nonlinear least-squares spectral fitting technique has been utilized in the analysis of the twenty-five measured spectra. Lines up to J double-prime = 18 in the nu4 band and J double-prime = 15 in the nu2 band have been analyzed.
    Keywords: GEOPHYSICS
    Type: Applied Optics (ISSN 0003-6935); 27; 631-651
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  • 41
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    On the possible role of the reaction O + HO2 - OH + O2 in OH airglow (1988)
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    Publication Date: 2011-08-19
    Description: Experimental data on the so-called 'perhydroxyl' reaction O + HO2 - OH + O2 by which vibrationally excited OH is produced in the upper atmosphere are briefly reviewed. Both isotopic labeling studies and studies on the temperature dependence of the rate constant and the possible importance of its inverse are considered. The implication of the results for analysis of OH airglow data are emphasized. Some additional results on the dynamics of reactions related to OH airglow which may affect interpretation of OH emission measurements are summarized.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 285-288
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  • 42
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    Ground-level detection of low- and medium-frequency auroral radio emissions (1988)
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    Publication Date: 2011-08-19
    Description: Natural radio emissions in the frequency range of several hundred kHz were detected at ground level in the auroral region during a ground-level observing program conducted near Fairbanks, Alaska in the spring of 1986 in an attempt to detect auroral cyclotron-maser-generated whistler modes. Most of the strongest emissions were observed in a small time interval around midnight magnetic local time, suggesting a close tie-in with auroral processes. The results support earlier reports of radio noise from the aurora at frequencies of about 100 kHz and indicate the importance of extending the upper frequency of ground-based high-latitude VLF stations to the vicinity of 1 MHz.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 277-283
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    The Antarctic ozone hole (1988)
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    Publication Date: 2011-08-19
    Description: Observations of Antarctic ozone levels and the discovery of a hole in the Antarctic region are examined. The effects of chlorofluorocarbons (CFCs) on the level of stratospheric ozone are analyzed. Three cycles explaining the cause of ozone depletion in the poles are proposed. A comparison of field data and proposed depletion cycles reveals that the chemical origin of the ozone hole is due to CFCs. The potential global effects of the Antarctic ozone hole are discussed.
    Keywords: GEOPHYSICS
    Type: Oceanus (ISSN 0029-8182); 31; 47-52
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    Tersail - A numerical model for combined analysis of vegetation canopy bidirectional reflectance and thermal emissions (1988)
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    Publication Date: 2011-08-19
    Description: A modification of the Tergra model (Soer, 1977) is presented, which incorporates the scattering from arbitrarily inclined leaves canopy reflectance model (Verhoef and Bunnik, 1981) for the calculation of albedo and canopy resistance. The combined model, known as Tersail, is capable of simulating the relationship between the bidirectional reflectance and the thermal response of a canopy. The accuracy of the model is tested using data over wheat canopies in Phoenix, Arizona, showing that the model is a good simulator of canopy temperatures under a variety of conditions.
    Keywords: GEOPHYSICS
    Type: Remote Sensing of Environment (ISSN 0034-4257); 26; 287-300
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  • 45
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    An intercomparison of results from ferrous sulphate and photolytic converter techniques for measurements of NO(x) made during the NASA GTE/CITE 1 aircraft program (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Two techniques designed for measurements of NO(x (NO + NO2) were intercompared during aircraft flights made in the spring of 1984 in the middle free troposphere over the eastern Pacific Ocean and southwestern U.S. One NO chemiluminescence instrument was equipped with a ferrous sulphate converter, another with a photolytic converter. The ferrous sulphate-equipped instrument was apparently much less specific for NO2. It registered levels about three times larger than the photolytic converter and gave NO2/NO ratios that were much larger than photochemical calculations would indicate as reasonable. Additionally, the results imply that active NO(x) was only 10-20 percent of the total odd nitrogen in the middle free troposphere.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 15803-15
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  • 46
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    Formation of the Antarctic ozone hole by the ClO dimer mechanism (1988)
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    Publication Date: 2011-08-19
    Description: New measurements of the low-altitude ClO profile, made during September 1987, are presented along with detailed observations of ozone depletion over McMurdo Station, Antarctica during the same period. The results show that both the rate and altitude range of ozone depletion can be quantitatively accounted for by a mechanism in which the ClO dimer is the important intermediary in the catalytic destruction of ozone. An alternative bromine mechanism appears capable of contributing only 5-15 percent to the ozone loss rate.
    Keywords: GEOPHYSICS
    Type: Nature (ISSN 0028-0836); 336; 455-458
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  • 47
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    NO and NO2 in the troposphere - Technique and measurements in regions of a folded tropopause (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Measurements of NO, NO2, O3, and CO were obtained for tropopause fold events encountered during two flights of the NASA global tropospheric experiment aircraft in 1984. The results suggest that NO(x) may not always be a good tracer of air of recent stratospheric origin. It is suggested that the stratospheric source of NO(x) acts to introduce NO(x) over a short period and through a large vertical region of the troposphere.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 15813-15
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    Chlorine-hydrocarbon photochemistry in the marine troposphere and lower stratosphere (1988)
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    Publication Date: 2011-08-19
    Description: The role of chlorine atoms in the oxidation of methane and nonmethane hydrocarbons (NMHCs) in the marine troposphere and lower stratosphere was investigated using a one-dimensional photochemical model that incorporated the chemistry of CH4, NMHCs, NO(x), O(x), and HO(x), as well as organic and inorganic halogens in the troposphere and lower stratosphere. The model predicted that chlorine atoms are present in the marine troposphere at the concentrations of about 1000/cu cm, mostly as a product of the reaction between OH and HCl released from sea spray. The results indicate that Cl atoms cause 20 to 40 percent of NMHC oxidation in the troposphere and 40 to 90 percent in the lower stratosphere. At 15 km, the NMHC-Cl reactions account for nearly 80 percent of the PAN produced. Where available, experimental data confirmed the model predictions.
    Keywords: GEOPHYSICS
    Type: Journal of Atmospheric Chemistry (ISSN 0167-7764); 7; 261-285
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  • 49
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    The effect of random precipitation times on the scavenging rate for tropospheric nitric acid (1988)
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    Publication Date: 2011-08-19
    Description: A model for the effective scavenging rate of a soluble species has been developed. The model takes into account the possibility of positive as well as negative correlations between departures from the mean of the scavenging rate and species concentration. The model is demonstrated for the case of late afternoon rainout of nitric acid occurring just prior to the nighttime cessation of its chemical production. The calculations give effective scavenging rates which are about a factor of 2 to 3 greater than those calculated using the models of Rodhe and Grandell (1972) and Giorgi and Chameides (1985).
    Keywords: GEOPHYSICS
    Type: Tellus, Series B - Chemical and Physical Meteorology (ISSN 0280-6509); 40B; 285-296
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  • 50
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    Changes in the earth's rate of rotation between A.D. 1672 and 1806 as deduced from solar eclipse timings (1988)
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    Publication Date: 2011-08-19
    Description: Solar eclipse timings measured between A.D. 1672 and 1806 are analyzed to study the variation of Delta T (= ET - UT) over this interval. These solar eclipse observations confirm the results of Brouwer (1952), Martin (1969), and Stephenson and Morrison (1969) which were obtained from the analysis of occultations in this period. It is believed that Goldstein's (1985) analysis inadequately represents the changes in Delta T.
    Keywords: GEOPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 200; 1-2,
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    Effect of the orbital debris environment on the high-energy Van Allen proton belt (1988)
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    Publication Date: 2011-08-19
    Description: The lifetimes of high-energy (greater than 55 MeV) protons in the Van Allen radiation belt are calculated, assuming that in time the protons will collide with and be absorbed by particulate orbiting material. The calculations are based on the NASA/DoD Civil Needs Database for orbital debris (Gaines, 1966) and moderate assumptions of future space traffic. It is found that the lifetimes of high-energy protons below 1500 km will decrease, leading to a noticeable redution in their fluxes.
    Keywords: GEOPHYSICS
    Type: Science (ISSN 0036-8075); 242; 1283-128
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    Mantle-derived fluids in diamond micro-inclusions (1988)
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    Publication Date: 2011-08-19
    Description: Microinclusions in diamonds from Zaire and Botswana differ in composition from the more common large inclusions of the peridotitic or eclogitic assemblages. These sub-micrometer inclusions resemble potassic magmas in their composition, but are enriched in H2O, CO2(3-), and K2O and depleted in MgO. This composition represents a volatile-rich fluid or melt from the upper mantle, which was trapped in the diamonds as they grew.
    Keywords: GEOPHYSICS
    Type: Nature (ISSN 0028-0836); 335; 784-789
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    Stratospheric NO2 over Antarctica as measured by the Solar Mesosphere Explorer during austral spring, 1986 (1988)
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    Publication Date: 2011-08-19
    Description: This paper presents the results of polar NO2 measurements carried out by the SME satellite during the fall and spring of 1985 and 1986 and compares the results with observations at the north pole and the results of model calculations. During the austral spring, a polar low was observed in stratospheric NO2 densities measured between 24 and 40 km, consistent with the predictions of standard photochemical theory. The geographic extent of the area of low NO2 densities was found to decrease as the hours of sunlight increased, in marked contrast to the behavior of the Antarctic ozone hole during the same period. A comparison of measurements with model calculations for NO2 imply that much of the odd nitrogen is converted to HNO3 during the polar night. Data also suggest no evidence that changes in high-altitude odd nitrogen are influencing the ozone below, or that the 'ozone hole' penetrates above 24 km to affect odd nitrogen there.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 12561-12
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    Measurement of nighttime stratospheric N2O5 from infrared emission spectra (1988)
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    Publication Date: 2011-08-19
    Description: The mixing ratio profile of N2O5 has been inferred from high-resolution emission spectra obtained with a balloon-borne Fourier spectrometer. The observations were taken for the period from midnight to predawn on September 16, 1986 at 32 deg N latitude. The inferred volume mixing ratio from nighttime average spectra has a peak of about 1.8 x 10 to the -9th in the 32-35 altitude range. The inferred mixing ratio is generally less than the theoretical predictions from a one-dimensional model.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 15; 1177-118
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  • 55
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    The diamagnetic effect during AMPTE's tail releases - Initial results (1988)
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    Publication Date: 2011-08-19
    Description: A series of four plasma injection experiments were performed by the AMPTE-IRM spacecraft in the nighttime magnetosphere between 12 and 18 earth radii geocentric distance during spring 1985. The most prominent effect of these tail releases is the creation of magnetic cavities. The lifetime of the cavities ranged from a few seconds to some minutes, depending mainly on the ion species and secondly on the ambient field strength. Due to the subsonic and sub-Alfvenic environment, the interaction between the plasma cloud and the ambient plasma flow played only a minor role in these cases (in contrast to the releases in the solar wind), and thus the diamagnetic effect could be studied extensively. The perturbation of the exterior field and fine structures in the current-carrying shell were observed. The thickness of the shell and the current distribution in this layer were deduced from the magnetic recordings each time IRM entered the cavity.
    Keywords: GEOPHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 8; 1, 19
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    Magnetic ULF fluctuations in the compressional zone of AMPTE's artificial comets (1988)
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    Publication Date: 2011-08-19
    Description: The two Ba releases in the solar wind, termed artificial comets (the first in interplanetary space, the second in the terrestrial magnetosheath), showed a number of common magnetic features. Both times a magnetic cavity was detected and a field pile-up observed with magnitudes several times the ambient field strength upstream of the cavity. The magnetic fluctuations in the compressed region are generally enhanced by a factor comparable to the amount of field pile-up. There is a peak in the spectra of both events around 0.1 Hz in the component which is perpendicular to the solar-wind velocity vector and almost field-aligned. This magnetosonic wave has been interpreted as the fundamental mode of resonance oscillations of the compression zone. For frequencies beyond 2 Hz the spectra decrease more steeply in the case of the second 'comet' than in the first. This is due to the interaction of the supersonic solar wind with the first comet. The spectra obtained during the first comet at the solar-wind/ion-cloud interface are identical to those observed during bow-shock crossings.
    Keywords: GEOPHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 8; 1, 19; 23-26
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    Trends in atmospheric ozone - Conflicts between models and SBUV data (1988)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Results obtained from simple models for the long-term change in ozone and its seasonal amplitude as a function of atmospheric pressure in the region from 3.0-0.1 mbar are compared with ozone measurements obtained with the Solar Backscatter Ultraviolet Instrument (SBUV). The SBUV data show secular trends in ozone which are negative and larger than the largest model trends by a factor of two or more. It is suggested that temperature-correlated variations in photochemistry should be included in the model.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 8431-843
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    Polar stratospheric clouds and the Antarctic ozone hole (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A theoretical model for the formation and growth of polar stratospheric clouds (PSCs) has been developed. Results for the calculated temperature dependence of optical backscattering are found to agree well with values obtained during two Arctic airborne-lidar experiments. Results for PSC formation in Antarctica show that at the 70-mbar level, about 80 percent of the HNO3 and about 30 percent of the H2O vapor available may be sequestered in relatively large PSC particles at a temperature near 189 K.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 8423-843
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    Smoke optical depths - Magnitude, variability, and wavelength dependence (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: An airborne autotracking sun-photometer has been used to measure magnitudes, temporal/spatial variabilities, and the wavelength dependence of optical depths in the near-ultraviolet to near-infrared spectrum of smoke from two forest fires and one jet fuel fire and of background air. Jet fuel smoke optical depths were found to be generally less wavelength dependent than background aerosol optical depths. Forest fire smoke optical depths, however, showed a wide range of wavelength depedences, such as incidents of wavelength-independent extinction.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 8388-840
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    Modeling surface deformations at complex strike-slip plate boundaries (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Two new versions of the physical base-traction model of Li and Rice (1987) have been developed to study the loading processes and surface deformation near plate boundaries with geometric complexities, including a shallow creeping fault segment and two subparallel faults. Predictions of surface velocity and surface slip rate for the region between the San Andreas fault and the Pacific coast at the latitude of the Parkfield-Cholame segment using model parameters based on geologic, geodetic, and seismic considerations were found to be in good agreement with contemporary geodetic field data (not used in constrainning model parameters). Also, predicted surface velocity for the Salton Sea-Coachella Valley area were fit to recently derived contemporary geodetic data and very large baseline interferometry data, althoug here the model parameters are not well constrained.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 7943-795
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    Measurements of coseismic deformation in southern California - 1972-1982 (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: This paper compares records collected in the years 1972-1982 from two classes of instruments at Pinon Flat Observatory (PFO), southern California: the long-base-length (greater than 100 m) strain meters and tiltmeters described by Berger and Lovberg(1970) and Wyatt et al. (1982), respectively; and the short-base-length near-surface tiltmeters. It was found that the signals for static strain changes recorded by the long-base-length strain meters and tiltmeters are in good quantitative agreement with the deformation calculated for a dislocation in an elastic half-space. In contrast, colocated short-base-length tiltmeters produced spurious results, with signals much larger than the theoretical coseismic deformations computed using the U.S. Geological Survey/CalTech network; these signals correlated well with peak site acceleration.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 7923-794
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  • 62
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    Correlation of interannual length-of-day variation with El Nino/Southern Oscillation, 1972-1986 (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Correlation between interannual length-of-day (LOD) changes and an index representation of El Nino/Southern Oscillation (ENSO) for the period of 1972-1986 was examined in two ways: as the cross-correlation function in the time domain and as the complex coherence spectrum in the frequency domain. The ENSO representation was derived from barometric measurements from the Tahiti and Darwin, Australia, meteorological stations, as the difference of the sea-level pressure between the two locations. The cross correlation between this ENSO representation and LOD variation on the interannual time scale was found to have a maximum value of 0.68 and the LOD phase lag of 2 months, indicating that most of the interannual LOD variation is caused by ENSO, and that the transfer of ENSO's axial angular momentum to the solid earth lags behind the Tahiti-Darwin pressure variation by about 2 months. The corresponding coherence spectrum showed minimum correlation around biennial periods, indicating an influence of the stratospheric quasi-biennial oscillation on LOD variations.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 7709-771
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    Geomagnetic activity during the passage of the earth through Halley's tail in 1910 (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The magnetic disturbance expected when the earth passed through the center of Comet Halley's tail in 1910 apparently occurred 12 hr too early. A detailed study of the records reveals that the discrepancy is due to a change in the convention for determining the start of the day. The magnetic disturbance did in fact arrive at the expected time and no unusual aberration of the solar wind need be invoked to explain the timing. The disturbance consisted of two troughs in the horizontal component of the earth's magnetic field, separated by about 14 hr, presumably associated with wakes in the solar wind momentum flux on either side of the ion tail. The disturbance was independent of latitude, indicating that the responsible current system flowed far above the earth's surface. After the comet's passage the magnetosphere was left in a mildly disturbed condition, with a weak ring current present.
    Keywords: GEOPHYSICS
    Type: Nature (ISSN 0028-0836); 333; 338-340
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    Ionospheric wave and irregularity measurements using passive radio astronomy techniques (1988)
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    Publication Date: 2011-08-19
    Description: The observation of midlatitude structures using passive radio astronomy techniques is discussed, with particular attention being given to the low-frequency radio telescope at the Clark Lake Radio Observatory. The present telescope operates in the 10-125-MHz frequency range. Observations of the ionosphere at separations of a few kilometers to a few hundreds of kilometers by the lines of sight to sources are possible, allowing the determination of the amplitude, wavelength, direction of propagation, and propagation speed of ionospheric waves. Data are considered on large-scale ionospheric gradients and the two-dimensional shapes and sizes of ionospheric irregularities.
    Keywords: GEOPHYSICS
    Type: Radio Science (ISSN 0048-6604); 23; 273-282
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    Satellite observations of current and waves in space plasmas (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Plasma processes occurring in the magnetosphere are examined in the light of recent observations of currents and waves with satellite-born magnetic experiments. In particular, results from the Viking and AMPTE/CCE satellites indicate that geomagnetic field lines that guide stationary Birkland currents can also support resonant Alfven waves. The relationship of these waves to the current systems and their source in the magnetosphere is still under investigation. It is emphasized that Birkland currents and Alfven waves are fundamental to an understanding of the earth's plasma environment.
    Keywords: GEOPHYSICS
    Type: Laser and Particle Beams (ISSN 0263-0346); 6; 503-511
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    Exceptional preservation of fossils in an Upper Proterozoic shale (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: An exceptionally well-preserved and distinctive assemblage of Late Proterozoic fossils from subtidal marine shales is reported. In addition to the spheromorphic acritarchs and cyanobacteria sheaths routinely preserved in Proterozoic rocks, this assemblage includes multicellular algae, a diverse assortment of morphologically complex protistan vesicles, and probable heterotrophic bacteria. Thus, it provides one of the clearest and most taxonomically varied views of Proterozoic life yet reported.
    Keywords: GEOPHYSICS
    Type: Nature (ISSN 0028-0836); 334; 424-427
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    Methane line parameters from 3700 to 4136/cm (1988)
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    Publication Date: 2011-08-19
    Description: The positions and strengths of about 1900 absorption lines of methane between 3700 and 4136/cm were measured experimentally to provide a reference line list for the identification of weak CH4 features in planetary spectra. The line parameters were obtained at room temperature with accuracies of 0.0002-0.003/cm for positions and + or - 3-40 percent for strengths using spectra recorded at 0.011/cm resolution (unapodized) with a Fourier transform spectrometer at Kitt Peak National Observatory/National Solar Observatory. Individual line strengths range from 0.00002-0.013/sq cm per atm at room temperature, and the sum of the observed strengths is 1.42/sq cm per atm at 297 K. All measurements are reported in natural isotopic abundance.
    Keywords: GEOPHYSICS
    Type: Applied Optics (ISSN 0003-6935); 27; 3275-327
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    Antarctic measurements of ozone by SAGE II in the spring of 1985, 1986, and 1987 (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: This paper presents a three-year (1985, 1986, and 1987) comparison of ozone profiles within the southern polar vortex for September and October, using data obtained by the Stratospheric Aerosol and Gas Experiment II. It was found that, by the first half of October 1986, daily minima in total ozone showed a moderate recovery of 5-7 percent relative to 1985, whereas in 1987, a significant drop of 15 percent from the 1985 minima was observed. The interannual variability of total ozone, temperature, and temperature area or vortex size were found to display a quasi-biennial oscillation (QBO) signal similar to that established by Garcia and Solomon (1987) for Antarctica. Since the 1985 and 1987 years displayed the same QBO phase (westerly) and the 1987 depletion was greater than that of 1985, it is concluded that the long-term secular ozone trend continues to be downward.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 15; 907-910
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  • 69
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    Heterogeneous reactions of N2O5 with H2O and HCl on ice surfaces - Implications for Antarctic ozone depletion (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: This paper reports on the measurements of reaction probabilities for heterogeneous reaction of N2O5 with H2O and HCl on ice surfaces at 195 K, using a fast-flow reactor coupled with a quadrupole mass spectrometer. The reaction probability for N2O5 on pure-water ice was found to be 0.028 + or - 0.011, with nitric acid in the solid phase as the sole product. In the presence of HCl in ice, the probability of N2O5 reaction was enhanced (to 0.037); the reaction produced, besides solid-phase nitric acid, ClNO2 and ClONO which were released into the gas phase within a few milliseconds. The latter two compounds can be readily photolyzed in the austral spring to form active chlorine which would remove stratospheric ozone. It is suggested that, since the polar stratospheric clouds are believed to contain HCl-ice mixture on the surface, the reactions of N2O5 on H2O/HCl particles is a major factor in the Antarctic springtime ozone depletion.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 15; 851-854
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    Comment on 'Interplanetary protons (EP = 1 MEV) 1973-1986 and out to 22.4 AU' (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 15; 840
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  • 71
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    ClO and O3 stratospheric profiles - Balloon microwave measurements (1988)
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    Publication Date: 2011-08-19
    Description: Stratospheric ClO and O3 vertical profiles were measured at 32-deg N in May 1985 and October 1986. The ClO profiles and diurnal variation are in general agreement with theory, but have somewhat less midday ClO near 34 km. Measured 35-45 km O3 is larger than theoretical, and no stratospheric O3 diurnal variation was observed, as expected. HNO3 was detected, and an H2O2 upper limit was obtained.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 15; 780-783
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    A comparison of ozone trends from SME and SBUV satellite observations and model calculations (1988)
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    Publication Date: 2011-08-19
    Description: Data on monthly ozone abundance trends near the stratopause, observed by the Ultraviolet Spectrometer (UVS) on the SME and by the Solar Backscatter Ultraviolet Instrument (SBUV) on NIMBUS-7 are presented for June, September, and January of the years 1982-1986. Globally averaged trends determined from the SME data (-0.5 + or - 1.3 percent/yr) were found to fall within model calculations by Rusch and Clancy (1988); the SBUV trends, on the other hand, were found to exceed maximum predicted ozone decreases by a factor of 3 or more. Detailed comparison of the two data sets indicated that an absolute offset of 3 percent/yr accounts for much of the difference between the two trends; the offset is considered to be due to incomplete characterization of the SBUV calibration drift. Both the UVS and SBUV data exhibited similar seasonal and latitudinal variations in ozone trends, which were reproduced by photochemical model calculations that included latitude-dependent NMC temperature trends over the 1982-1986 period.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 15; 776-779
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    Cross-B convection of artificially created, negative-ion clouds and plasma depressions - Low-speed flow (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A negative-ion, positive-ion plasma produced by the release of an electron attachment chemical into the F region becomes electrically polarized by collisions with neutrals moving across magnetic field lines. The resulting electric field causes E x B drift of the two ion species and the residual electrons. The cross-field flow of the modified ionosphere is computed using a two-dimensional numerical simulation which includes electron attachment and mutual neutralization chemistry, self-consistent electric fields, and three-species plasma transport. The velocity of the plasma is initially in the direction of the neutral wind because the negative-ion cloud is a Pedersen conductivity enhancement. As the positive and negative ions react, the Pedersen conductivity becomes depressed below the ambient value and the velocity of the plasma reverses direction. A plasma hole remains after the positive and negative ions have mutually neutralized. The E x B gradient drift instability produces irregularities on the upwind edge of the hole.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 8696-870
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  • 74
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    An assessment of the long-term drift in TOMS total ozone data, based on comparison with the Dobson network (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Seven years of total ozone data derived from the TOMS instrument on Nimbus-7 are compared with results from 41 Dobson stations. In this study, a significant improvement in fit from previous studies is obtained using a model which assumes a change in the rate of drift between TOMS and Dobson around the middle of 1982. Results indicate that the TOMS measurements have drifted relative to the Dobson stations with a two-part linear trend of -0.25 + or - 0.17 percent per year during the period from launch to 6/30/82, and -0.51 + or - 0.21 percent per year during 7/1/82 - 10/31/85. The causes of this drift cannot be definitively separated between residual uncorrected drift in the TOMS instrument (a similar drift is apparent in the SBUV-Dobson comparisons), limited sensitivity of the TOMS to increases in tropospheric ozone, and the effect of local increases in pollution levels on individual Dobson stations.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 15; 1133-113
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    Definitive IGRF models for 1945, 1950, 1955, and 1960 (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Definitive internal geomagnetic field models are obtained for the epochs 1945, 1950, 1955, and 1960, with the solution including local biases for the fixed observatories. In order to derive a priori models for the epochs, the International Geomagnetic Reference Field (12/83) model (based on Magsat data) was projected backward in time using a spline fit to annual secular-variation models. An uncertainty model was developed which included estimates of the effects of crustal and core fields not represented by the model. Differences between biases from year to year are found to be within the predicted bounds.
    Keywords: GEOPHYSICS
    Type: Journal of Geomagnetism and Geoelectricity (ISSN 0022-1392); 40; 6, 19
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    On the persistence of unstable bump-on-tail electron velocity distributions in the earth's foreshock (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: This paper presents further evidence for the persistence of bump-on-tail unstable reduced velocity distributions in the earth's electron foreshock, which contradicts the understanding of quasi-linear saturation of the bump-on-tail instability. A modified theory for the saturation of the bump-on-tail instability in the earth's foreshock is proposed to explain the mechanism of this persistence, and the predictions are compared to the results of a numerical simulation of the electron plasma in the foreshock. The results support the thesis that quasi-linear saturation of the bump-on-tail instability is modified in the foreshock, due to the driven nature of the region, so that at saturation the stabilized velocity distribution still appears bump-on-tail unstable to linear plasma analysis.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 9628-964
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    Retrieval of constituent mixing ratios from limb thermal emission spectra (1988)
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    Publication Date: 2011-08-19
    Description: An onion-peeling iterative, least-squares relaxation method to retrieve mixing ratio profiles from limb thermal emission spectra is presented. The method has been tested on synthetic data, containing various amounts of added random noise for O3, HNO3, and N2O. The retrieval method is used to obtain O3 and HNO3 mixing ratio profiles from high-resolution thermal emission spectra. Results of the retrievals compare favorably with those obtained previously.
    Keywords: GEOPHYSICS
    Type: Applied Optics (ISSN 0003-6935); 27; 3482-349
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    Simulations of plasma structure evolution in the high-latitude ionosphere (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The Naval Research Laboratory has recently developed a two-dimensional inertial, electrostatic code which has been successfully applied to the development and evolution of ionospheric structure driven by plasma instabilities. This code models the ionosphere and magnetosphere as a set of horizontal two-dimensional layers which are coupled by the vertical magnetic field lines at high latitudes. It is shown that the development of instability-generated structure can be strongly dependent on this coupling. For example, the influence of magnetospheric coupling on the E x B gradient drift instability is to retard the instability's growth and to isotropize density irregularities. The influence of ionospheric coupling on the Kelvin-Helmholtz instability is to retard its growth and to suppress vortex formation. This paper presents the results of numerical simulations of these instabilities and discusses their application to high-latitude ionospheric structure.
    Keywords: GEOPHYSICS
    Type: Radio Science (ISSN 0048-6604); 23; 503-512
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    A comparison of mapped and measured total ionospheric electron content using global positioning system and beacon satellite observations (1988)
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    Publication Date: 2011-08-19
    Description: Total ionospheric electron contents (TEC) were measured by global positioning system (GPS) dual-frequency receivers developed by the Jet Propulsion Laboratory. The measurements included P-code (precise ranging code) and carrier phase data for six GPS satellites during multiple five-hour observing sessions. A set of these GPS TEC measurements were mapped from the GPS lines of sight to the line of sight of a Faraday beacon satellite by statistically fitting the TEC data to a simple model of the ionosphere. The mapped GPS TEC values were compared with the Faraday rotation measurements. Because GPS transmitter offsets are different for each satellite and because some GPS receiver offsets were uncalibrated, the sums of the satellite and receiver offsets were estimated simultaneously with the TEC in a least squares procedure. The accuracy of this estimation procedure is evaluated indicating that the error of the GPS-determined line of sight TEC can be at or below 1 x 10 to the 16th el/sq cm. Consequently, the current level of accuracy is comparable to the Faraday rotation technique; however, GPS provides superior sky coverage.
    Keywords: GEOPHYSICS
    Type: Radio Science (ISSN 0048-6604); 23; 483-492
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    Plasma instabilities stimulated by HF transmitters in space (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Diffuse incoherent signal returns are often observed on Alouette and ISIS topside ionograms in addition to coherent echoes of electromagnetic and electrostatic waves. These diffuse signals, which at times can be the dominant features on topside ionograms, have been attributed to sounder-induced temperature anisotropies which drive the Harris instability. Previous theoretical investigations were based on the electrostatic approximation to the dispersion equation. The present paper will present calculations indicating that when the electromagnetic terms are retained in the dispersion equation and when the sounder-stimulated perpendicular electron temperature approaches 1 keV, then the whistler mode can have a temporal growth rate larger than the electrostatic electron cyclotron harmonic wave mode central to the diffuse resonance problem. Present sounders lack the power and antenna lengths to generate whistler mode waves in this manner. In addition, such waves would have large group velocities and would quickly leave the vicinity of the sounder. Experiments to investigate the wave growth, propagation, and damping of such stimulated waves are planned for the 1990s using a highly flexible sounder on the Space Shuttle and a receiver on a subsatellite.
    Keywords: GEOPHYSICS
    Type: Radio Science (ISSN 0048-6604); 23; 585-590
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    Volcanic winters (1988)
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    Publication Date: 2011-08-19
    Description: The impact of volcanic eruptions on weather and climate is considered. The data from nineteenth-century eruptions is examined, showing the importance of sulfur volatiles for climate change. Information obtained from ice cores is discussed, and the contrasts between the eruptions of Mt. St. Helens and El Chichon are pointed out. The atmospheric effects of the greatest historic eruptions are recalled. The potential for the occurrence of 'volcanic winters' and the possible role of volcanism in mass extinctions are considered.
    Keywords: GEOPHYSICS
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    Birkeland currents in the earth's magnetosphere (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Satellite observations of the large-scale patterns, flow directions, and intensities of Birkeland currents in the auroral and polar regions and their relationship to the orientation and magnitude of the IMF are reviewed. Viking and AMPTE/CCE observations have provided evidence for resonant Alfven waves on the same geomagnetic field lines that guide stationary Birkeland currents. The observations suggest that Birkeland currents play an important role in the coupling of energy between the interplanetary medium and the lower ionosphere and atmosphere.
    Keywords: GEOPHYSICS
    Type: Astrophysics and Space Science (ISSN 0004-640X); 144; 1-2,; 155-169
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    Evaluation of the international reference ionosphere with the large AE-C and DE2 data bases (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Empirical models such as the International Reference Ionosphere (IRI) are synthesized from large data bases. They can be viewed as analytical tools to facilitate accessing information stored in the data banks. However, in establishing the models, one has to apply smoothing and averaging procedures that in effect reduce the original information content. This study evaluates the agreement between the data base and the model at two opposite extremes of time resolution. Electron densities and temperatures in the altitude range of 300 to 400 km predicted by the IRI and measured by the AE-C and DE 2 satellites on the level of individual orbits as well as on the level of mission averages are compared. Whereas the averages show excellent agreement, the comparison for individual measurements indicates the limitations of empirical models.
    Keywords: GEOPHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 8; 4, 19
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    The terrestrial plasma source - A new perspective in solar-terrestrial processes from Dynamics Explorer (1988)
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    Publication Date: 2011-08-19
    Description: The geospace environment has been viewed as a mixing bowl for plasmas of both solar and terrestrial origin. The present perspective on the nature of the supply mechanisms has undergone a radical evolution over the past decade, particularly during the five years of the Dynamics Explorer mission. During this period, the terrestrial source has increased in importance in both magnitude and character of ionospheric outflow. These outflows include the classical polar wind, the cleft ion fountain, the auroral ion fountain, and the polar cap. The earth can be envisioned as a multifaceted fountain which ejects particles from different spatial locations spread around the globe. These particles exhibit a range of masses from 1 to 32 amu and a range of energies from 1 eV to 10 keV. The total flux of this ionospheric outflow is very large: adequate to supply the entire magnetospheric particle population. And the implications of the outflow are significant across a broad spectrum of solar-terrestrial processes ranging from sources of magnetospheric plasmas, to influences on ionospheric density and temperature structure, to energy transfer in phenomena such as stable auroral red arcs. The Dynamics Explorer mission has made a major contribution in the characterization of the terrestrial plasma source.
    Keywords: GEOPHYSICS
    Type: Reviews of Geophysics (ISSN 8755-1209); 26; 229-248
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    A new laboratory source of ozone and its potential atmospheric implications (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Although 248-nm radiation falls 0.12 eV short of the energy needed to dissociate O2, large densities of ozone (O3) can be produced from unfocused 248-nm KrF excimer laser irradiation of pure O2. As soon as any O3 is present, it strongly absorbs the 248-nanometer radiation and dissociates to vibrationally excited ground state O2 (among other products), with a quantum yield of 0.1 to 0.15. During the laser pulse, a portion of these molecules absorb a photon and dissociate, which results in the production of three oxygen atoms for one O3 molecule destroyed. Recombination then converts these atoms to O3, and thus O3 production in the system is autocatalytic. A deficiency exists in current models of O3 photochemistry in the upper stratosphere and mesosphere, in that more O3 is found than can be explained. A detailed analysis of the system as it applies to the upper atmosphere is not yet possible, but with reasonable assumptions about O2 vibrational distributions resulting from O3 photodissociation and about relaxation rates of vibrationally excited O2, a case can be made for the importance of including this mechanism in the models.
    Keywords: GEOPHYSICS
    Type: Science (ISSN 0036-8075); 241; 945-950
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  • 86
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    Flood basalt volcanism during the past 250 million years (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A chronology of the initiation dates of major continental flood basalt volcanism is established from published potassium-argon (K-Ar) and argon-argon (Ar-Ar) ages of basaltic rocks and related basic intrusions. The dating is therefore independent of the biostratigraphic and paleomagnetic time scales. Estimated errors of the initiation dates of the volcanic episodes determined from the distributions of the radiometric ages are, approximately, + or - 4 percent. There were 11 distinct episodes during the past 250 million years. Sometimes appearing in pairs, the episodes have occurred quasi-periodically with a mean cycle time of 32 + or - 1 (estimated error of the mean) million years. The initiation dates of the episodes are close to the estimated dates of mass extinctions of marine organisms. Showers of impacting comets may be the cause.
    Keywords: GEOPHYSICS
    Type: Science (ISSN 0036-8075); 241; 663-668
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  • 87
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    Numerical simulations of thermal-chemical instabilities at the core-mantle boundary (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Numerical simulations of thermal-chemical instabilities in the D-double-prime layer at the core-mantle boundary are presented which show that strong lateral heterogeneities in the composition and density fields can be initiated and maintained dynamically if there is continuous replenishment of material from subduced slabs coming from the upper mantle. These chemical instabilities have a tendency to migrate laterally and may help to support core-mantle boundary topography with short and long wavelengths. The thermal-chemical flows produce a relatively stagnant D-double-prime layer with strong lateral and temporal variations in basal heat flux, which gives rise to thermal core-mantle interactions influencing the geodynamo.
    Keywords: GEOPHYSICS
    Type: Nature (ISSN 0028-0836); 334; 237-240
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  • 88
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    Laboratory studies of the nitric acid trihydrate - Implications for the south polar stratosphere (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Vapor pressures of HNO3 and H2O have been measured over the trihydrate crystal, formed by vapor deposit on a glass surface. In the temperature range 190 to 205 K the two phase-equilibrium trihydrate/vapor was studied by adding and removing H2O. Coexistence equilibria vapor pressures of trihydrate/solid solutions of HNO3 in ice and of mono-/trihydrate were also measured. Results show that for typical mixing ratios of H2O and HNO3 found in the lower stratosphere (3 ppm H2O, 5 ppb HNO3) the trihydrate would start to form at temperatures about 7 K higher than the ice point. The pressure of atmospheric HNO3 would rapidly decrease as the atmosphere cools without large changes in partial pressures of H2O. These laboratory results provide information on the formation of polar stratospheric clouds containing H2O and HNO3.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 15; 855-858
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  • 89
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    Watching a disappearing shield (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The remote-sensing techniques used to monitor atmospheric ozone levels are reviewed, and recent results are discussed. The importance of the ozone layer as a shield for UV radiation is stressed, and the impact of human activities generating ozone-destroying compounds is considered. Ground-based, airborne, balloon-borne, and satellite remote-sensing methods are shown to complement each other to provide both global coverage and detailed structural information. Data obtained with the Nimbus-7 TOMS and solar-backscatter UV instruments are presented in graphs and briefly characterized.
    Keywords: GEOPHYSICS
    Type: Aerospace America (ISSN 0740-722X); 26; 32-35
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  • 90
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    Atomic oxygen modeling in the upper thermosphere (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Empirical models of atomic oxygen in the earth's thermosphere are discussed, and calibration problems in satellite drag and in situ mass spectrometer measurements are reviewed. Models based on drag data and mass spectrometer data are found to agree on average to within 15 percent, suggesting that the absolute values are reasonably well known in the upper thermosphere. Comparison of different models with various data sources show residuals of at least 15 percent which are the results of unmodeled magnetic storm, EUV, and geographical variations and smaller scale variations caused by gravity waves.
    Keywords: GEOPHYSICS
    Type: Planetary and Space Science (ISSN 0032-0633); 36; 907-920
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  • 91
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    Observed velocity fluctuations on a major Antarctic ice stream (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Recent ice velocity measurements on the major Antarctic Ice Stream B are compared with those collected 10 years ago. The results show that the ice flow in the mouth of Ice Stream B has decelerated by about 20 percent. The possible causes of this deceleration are discussed on the basis of present knowledge of current regional dynamics, and the possible effects of this deceleration on future ice stream behavior are examined.
    Keywords: GEOPHYSICS
    Type: Nature (ISSN 0028-0836); 334; 695-697
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  • 92
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    Global fire at the Cretaceous-Tertiary boundary (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Cretaceous-Tertiary boundary clays rich in iridium from five sites in Europe and New Zealand were investigated. The clays are found to be 100-10,000-fold-enriched in elemental carbon (mainly soot), which is isotopically uniform and apparently comes from a single global fire. The soot layer coincides with the iridium layer, suggesting that the fire was triggered by meteorite impact and began before the ejecta had settled.
    Keywords: GEOPHYSICS
    Type: Nature (ISSN 0028-0836); 334; 665-669
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  • 93
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    A multidimensional model for aerosols - Description of computational analogs (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The numerical algorithms used to simulate the advection, diffusion, sedimentation, coagulation, and condensational growth of atmospheric aerosols are described. The model can be used in one, two, or three spatial dimensions. The continuity equation in a generalized horizontal and vertical coordinate system is developed, which allows the model to be quickly adapted to a wide variety of dynamical models of global or regional scale. Algorithms are developed to treat the various physical processes, and the results of simulations are presented, which show the strengths and weaknesses of these algorithms. Although the emphasis is on the modeling of aerosols, the work is also applicable to the simulations of the transport of gases.
    Keywords: GEOPHYSICS
    Type: Journal of the Atmospheric Sciences (ISSN 0022-4928); 45; 2123-214
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  • 94
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    Global surface-water-induced seasonal variations in the earth's rotation and gravitational field (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The effects of seasonal changes in continental surface-water storage on the low-degree gravitational-field coefficients (J), the annual wobble excitation (Psi), and the seasonal length-of-day (LOD) variations are investigated by means of numerical simulations based on compiled meteorological data (Willmott et al., 1985) and satellite snow-load estimates (Chao et al., 1987). The formulation of the model equations and the overall characteristics of the data sets are discussed in detail, and the computation results are presented in tables and graphs. The effect on Psi is found to be relatively small due to longitudinal cancellation, but those on LOD and J are considered significant.
    Keywords: GEOPHYSICS
    Type: Geophysical Journal (ISSN 0952-4592); 94; 263-270
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  • 95
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    Thermochemical stabilities and vibrational spectra of isomers of the chlorine oxide dimer (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Molecular orbital calculations were performed to determine the relative thermochemical stabilities and IR vibrational spectra of isomers of the ClO dimer. Two straight-chain isomers (ClOOCl and ClOClO) and one branched species (ClClO2) were identified as energy minima on the Cl2O2 potential surface. It is shown that ClOOCl and ClClO2 are comparable in terms of stability, while ClOClO is about 11 kcal/mol higher in energy. The IR spectra obtained by Molina and Molina (1987) as a result of the reaction of chlorine atoms with ClO precursors are consistent with the production of the two most stable forms of Cl2O2.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 15; 883-886
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  • 96
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    Overview of the polar ozone issue (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The causes of the Antarctic ozone depletion are discussed together with the role of the polar stratospheric clouds (PSCs, which are ice clouds that form towards spring over Antarctica in the altitude range of 10-20 km) in the process of ozone depletion. Evidence is presented suggesting that heterogeneous chemical reactions occurring on the surfaces of the PSCs could dramatically deplete the abundances of reactive nitrogen compounds and enhance those of reactive chlorine species which are responsible for ozone depletion. It was also shown that the surface reactions are not limited to ice clouds but can also take place on the liquid sulfuric acid aerosols present at lower latitudes, indicating that heterogeneous chemistry may take place to some extent on a global scale. Finaly, observations of low-abundance NO2 in north polar regions suggests that heterogeneous removal of reactive nitrogen may well be occurring in the Arctic, with possible attendant applications for Arctic ozone.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 15; 845
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  • 97
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    Causes of rapid motions of the earth's pole (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Analysis of new, highly accurate geodetic data reveals rapid motions of the earth's pole, with peak-to-peak variations of about 0.002 to 0.020 seconds of arc, fluctuating on timescales between two weeks and several months. Comparison with meteorological excitation estimates shows that these motions are at least partially driven by surface air pressure changes as modified by the response of sea level to atmospheric loading. Such geodetic measurements thus potentially provide a novel means of observing the dynamics of the atmosphere and oceans at very low spatial wavenumbers.
    Keywords: GEOPHYSICS
    Type: Nature (ISSN 0028-0836); 334; 115-119
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  • 98
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    Kinetics and product studies of the BrO + ClO reaction - Implications for Antarctic chemistry (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Discharge flow-mass spectrometry and flash photolysis-UV spectrometry were used to investigate the reaction of ClO with BrO over the temperature range of 220-400 K and the pressure range of 1-760 Torr. Rate constants were determined for: (1) Br + ClOO, (2) Br + OClO, and (3) BrCl + O2. It is found that the rate constants for the overall reaction and each reaction branch are inversely dependent on temperature and independent of pressure. For temperatures found in the Antarctic stratosphere, the rate coefficients for the channels yielding ClOO and OClO are a factor of 2-3 larger than previously estimated.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 15; 887-890
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  • 99
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    Observations of a gradual transition between Ps 6 activity with auroral torches and surgelike pulsations during strong geomagnetic disturbances (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: This paper describes a long-lasting large-amplitude pulsation event, which occurred on January 10, 1983 in the ionosphere and magnetosphere and was characterized by Steen and Rees (1983). Over the 4-h period (0200-0600 UT), the characteristics of the pulsations in the ionosphere changed from being Ps 6 auroral torches toward substorms and back to Ps 6. At GEO, the corresponding characteristics were a modulation of the high-energy particle intensity and plasma dropouts. Based on the ideas presented by Rostoker and Samson (1984), an interpretation of the event is offered, according to which the pulsations are caused by the Kelvin-Helmholtz instability during an interval of strong magnetospheric convection. On the basis of this explanation, a new interpretation of the substorm time sequence is proposed.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 8713-873
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  • 100
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    Effect of wet tropospheric path delays on estimation of geodetic baselines in the Gulf of California using the Global Positioning System (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Surface Meteorological (SM) and Water Vapor Radiometer (WVR) measurements are used to provide an independent means of calibrating the GPS signal for the wet tropospheric path delay in a study of geodetic baseline measurements in the Gulf of California using GPS in which high tropospheric water vapor content yielded wet path delays in excess of 20 cm at zenith. Residual wet delays at zenith are estimated as constants and as first-order exponentially correlated stochastic processes. Calibration with WVR data is found to yield the best repeatabilities, with improved results possible if combined carrier phase and pseudorange data are used. Although SM measurements can introduce significant errors in baseline solutions if used with a simple atmospheric model and estimation of residual zenith delays as constants, SM calibration and stochastic estimation for residual zenith wet delays may be adequate for precise estimation of GPS baselines. For dry locations, WVRs may not be required to accurately model tropospheric effects on GPS baselines.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 6545-655
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