Engineering topics

Aikin, Arthur C.

Publications and source records attributed to Aikin, Arthur C..

10 records

NASA NTRS2001

In Situ Measurements of Meteoric Ions

Metal ions found in the atmosphere above 60 km are the result of incoming meteoroid atmospheric ablation. Layers of metal ions are detected by sounding rocket in situ mass spectrometric sampling in the 80 to 130 km region, which coincides with the altitude region where meteors are observed. Enhancements of metal ion concentrations occur during meteor showers. Even outside of shower periods, the metal ion altitude profiles vary from measurement to measurement. Double layers are frequent at middle latitudes. More than 40 different meteoric atomic and molecular ions, including isotopes, have been detected. Atmospheric metal ions on average have an abundance that matches chrondritic material, the same composition as the early solar system. However there are frequently local departures from this composition due to differential ablation, species dependent chemistry and mass dependent ion transport. Metal ions react with atmospheric O2, O, O3, H2O and H2O2 to form oxygenated and hydrogenated ionic compounds. Metal atomic ions at high altitudes have long lifetimes. As a result, these ions, in the presence of Earth's magnetic field, are transported over long distances by upper atmospheric winds and ionospheric electric fields. Satellite measurements have detected metal ions as high as, approximately 1000 km and have revealed circulation of the ions on a global scale.

Grebowsky, Joseph M.↗

NASA NTRS2000

Atmospheric Effects of Biomass Burning in Madagascar

Simultaneous tropospheric ozone and aerosols observed using the TOMS satellite instrument are reported for Madagascar during the 1979 through 1999 time period Ozone observations made using the TOMS tropospheric ozone convective-cloud differential method show that the tropospheric ozone amount associated with Madagascar has an average monthly value of 30 DU (Dobson units). The average value is enhanced by 10 to 15 DU in October This maximum coincides with the time of maximum biomass area burning in Madagascar and parts of southern Africa. The aerosol index derived from TOMS is examined for correlation with biomass burning in Madagascar and southern Africa. There is good correlation between a satellite observation derived fire index for different parts of Madagascar, tropospheric ozone and the TOMS aerosol index in the same geographical area. Aerosols from fires were found to reach their peak in November and to persist over Madagascar until sometime in December.

Aikin, Arthur C.↗

NASA NTRS1994

Energetic particle-induced enhancements of stratospheric nitric acid

Inclusion of complete ion chemistry in the calculation of minor species production during energetic particle deposition events leads to significant enhancement in the calculated nitric acid concentration during precipitation. An ionization rate of 1.2 x 10(exp 3)/cu cm/s imposed for 1 day increases HNO3 from 3 x 10(exp 5) to 6 x 10(exp 7)/cu cm at 50 km. With an ionization rate of 600 cu cm/s, the maximum HNO3 is 3 x 10(exp 7)/cu cm. Calculations which neglect negative ions predict the nitric acid will fall during precipitation events. The decay time for converting HNO3 into odd nitrogen and hydrogen is more than 1 day for equinoctial periods at 70 deg latitude. Examination of nitric acid data should yield important information on the magnitude and frequency of charged particle events.

Aikin, Arthur C.↗

NASA NTRS1994

A search for relativistic electron induced stratospheric ozone depletion

Possible ozone changes at 1 mb associated with the time variation and precipitation of relativistic electrons are investigated by examining the NIMBUS 7 SBUV ozone data set and corresponding temperatures derived from NMC data. No ozone depletion was observed in high-latitude summer when temperature fluctuations are small. In winter more variation in ozone occurs, but large temperature changes make it difficult to identify specific ozone decreases as being the result of relativistic electron precipitation.

Aikin, Arthur C.↗

NASA NTRS1992

Stratospheric evidence of relativistic electron precipitation

The hypothesis of Thorne (1977, 1980) and Baker et al. (1986, 1987) that the precipitation of energetic electrons is modifying the high-latitude ozone distribution in the Southern Hemisphere is tested by comparing electron density data from a ground-based partial reflection sounder with simultaneous satellite data on ozone mixing ratios taken at the 40 to 50 km altitude. The results do not support the theory that large electron densities coincide with ozone destruction. There is no evidence, for instance, that the January 15, 1984 ionization event had an associated ozone loss. Further experiments for investigating the relationship between the precipitating electrons and ozone depletion are suggested.

Aikin, Arthur C.↗

NASA NTRS1992

Spring polar ozone behavior

Understanding of the springtime behavior of polar stratospheric ozone as of mid 1990 is summarized. Heterogeneous reactions on polar stratospheric clouds as hypothesis for ozone loss are considered and a simplified description of the behavior of Antarctic ozone in winter and spring is given. Evidence that the situation is more complicated than described by the theory is produced. Many unresolved scientific issues remain and some of the most important problems are identified. Ozone changes each spring since 1979 have clearly established for the first time that man made chlorine compounds influence stratospheric ozone. Long before important advances in satellite and in situ investigations, it was Dobson's decision to place a total ozone measuring spectrometer at Halley Bay in Antarctica during the International Geophysical Year and subsequent continuous monitoring which led to the discovery that ozone was being destroyed each spring by chlorine processed by polar stratospheric clouds.

Aikin, Arthur C.↗

NASA NTRS1990

Variations of mesospheric equatorial ozone as observed by the Solar Maximum Mission

Tropical lower mesospheric ozone concentrations determined from UV sunset occultations demonstrate latitude dependent variations from 1985 through 1988. The annual and semiannual ozone behavior is caused primarily by equatorial temperature waves. Secular changes are the result of variations in mesospheric temperature, solar flux, and trace constituents which are involved in the ozone chemistry. The variation with latitude of the observed ozone trends between 1985 and 1989 is different from predictions of some models which simulate stratospheric and lower mesospheric ozone behavior over a sunspot cycle. This is the result of differences between the actual temperature structure of the atmosphere and that adopted in the models.

Aikin, Arthur C.↗

NASA NTRS1989

Ozone minimum occurs in Antarctica in the springtime

Observations on the formation of the Antarctic ozone hole in the upper atmosphere are summarized, and the mechanism responsible for the ozone depletion in the spring is examined. It is shown that the sequence of events begins with the absorption of H2O, N2O5, HCl, and ClONO2 on the cloud ice particles in the winter and chemical reactions among absorbed chemicals which release (HNO3)s, Cl2, HOCl, and ClNO2. With the return of sunlight in the spring, the clouds evaporate, and the Cl2, HOCl, and ClONO2 molecules are destroyed by sunlight to form Cl atoms. These attack ozone, producing a reduction of ozone that accounts for the bulk of the ozone decrease observed by the ground-based ozone monitors. Data on the ozone concentration for the period between 1957 through 1987 indicate that the southern ozone hole has been intensifying since 1975 as the amount of man-made chlorine increases.

Aikin, Arthur C.↗

NASA NTRS1988

Polar Ozone Workshop. Abstracts

Results of the proceedings of the Polar Ozone Workshop held in Snowmass, CO, on May 9 to 13, 1988 are given. Topics covered include ozone depletion, ozonometry, polar meteorology, polar stratospheric clouds, remote sensing of trace gases, atmospheric chemistry and dynamical simulations.

Aikin, Arthur C.↗

NASA NTRS1988

The threee-dimensional morphology of the Antarctic ozone hole

The three-dimensional morphology of the spring antarctic ozone distribution as determined by the Nimbus 7 Solar Backscatter Ultraviolet (SBUV) spectrometer instrument is presented for the period 1 to 11 October in 1986. The data show that a clearly defined minimum in ozone relative to the local ozone field extends throughout the stratosphere from the tropopause to above 50 km, though decreasing in intensity with altitude. Near 18 km ozone in the ozone hole is 50 percent less than the average surrounding ozone. But even at 50 km the ozone is 20 percent less than the surrounding ozone field. The ozone minimum in the upper stratosphere is displaced about 6 degrees toward the equator so that observations at a fixed station may provide the illusion that the ozone minimum is restricted only to low altitudes. While the ozone minimum is spatially coherent throughout the stratosphere, there are differences in the behavior of ozone at different altitudes that suggest the existence of at least three distinct altitude domains. Below 30 km ozone is characterized by classic ozone hole behavior. Between 33 and 43 km ozone is more stable, actually increasing during September and October. Above 43 km ozone has always decreased during September to a minimum in October, but it has suffered a long term decrease of 7 to 12 percent since 1979 similar to that seen at low altitudes.

Aikin, Arthur C.↗