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At least 991 records · Page 55
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NASA NTRS1985

Atmospheric Tides Between 80 Km and 120 Km

The structure and variability of tides in the 80 to 120 km height region are reviewed. Particulary emphasized are seasonal-latitudinal variations in the vertical structure of diurnal and semidiurnal winds between 70 to 110 km as measured by meteor and partial reflection drift radars, and tidal temperatures determined by incoherent scatter radars between 100 and 140 km. Variations in tidal structures with longitude, from day to day, and during equinoctial transition periods are also addressed. A brief summary of the current status of atmospheric tidal modelling is provided.

Forbes, J. M.↗
NASA NTRS1985

Mean Winds and Tides over Urbana, Illinois During November 16-22, 1981

The Urbana Meteor Radar uses a high power pulse transmitter to achieve high echo rates, and an interferometer to spatially locate the individual echoes. The irregularly spaced observations of range, radial velocity, and direction cosines are reduced to a rectangular grid, evenly spaced in time and height, of estimates of the zonal and meridional wind. This is accomplished using the method of GROVES whereby a constant horizontal wind is fitted, using least squares, to all echoes occurring within a fixed time/height interval. This interpolation region is then stepped in time and height. the size of the interpolation region is 2 hours by 5 km, the time step is approximately 11 minutes, and the height step is 2 km. The filtering of high temporal and spatial frequencies is somewhat reduced by weighting the echoes according to their distance from the center of the interpolation box.

Tetenbaum, D.↗
NASA NTRS1986

Mass loading of the Earth's magnetosphere by micron size lunar ejecta. 1: Ejecta production and orbital dynamics in cislunar space

Particulate matter possessing lunar escape velocity sufficient to enhance the cislunar meteroid flux was investigated. While the interplanetary flux was extensively studied, lunar ejecta created by the impact of this material on the lunar surface is only now being studied. Two recently reported flux models are employed to calculate the total mass impacting the lunar surface due to sporadic meteor flux. There is ample evidence to support the contention that the sporadic interplanetary meteoroid flux enhances the meteroid flux of cislunar space through the creation of micron and submicron lunar ejecta with lunar escape velocity.

Alexander, W. M.↗
NASA NTRS1986

Initial results of the Global Thermospheric Mapping Study (GTMS)

The Global Thermospheric Mapping Study (GTMS) is a multi-technique experimental study of the thermosphere designed to map simultaneously its spatial and temporal morphology with a thoroughness and diversity of measurement techniques heretofore unachieved. The GTMS is designed around the Incoherent Scatter Radar Chain in the western hemisphere. The European incoherent scatter radars and the worldwide communities of Fabry-Perot interferometers, meteor wind radars, partial reflection drifts radars, MST radars, and satellite probes are included to extend the spatial coverage and types of measurements available. Theoretical and modeling support in the areas of thermospheric and ionospheric structure, tides, and electric fields are included to aid in program planning and data interpretation. Solar activity was low on the three observation days (F10.7 = 97, 98, 96) and magnetic conditions were unsettled to active (A = 10, 12, 20). All six incoherent scatter radar facilities collected data. Each collected F region data day and night while Saint Santin and Millstone Hill additionally collected E region data during daylight hours. Initial results from Sondrestrom and Millstone Hill are presented. Good quality Fabry Perot data were collected at Fritz Peak and San Jose dos Campos. Weather conditions produced poor results at Arequipa and Arecibo. Initial results from Fritz Peak are presented. Mesosphere/lower-thermosphere observations were conducted under the ATMAP organization. The magnetometer chains also were operational during this campaign. Initial thermospheric general circulation model predictions were made for assumed solar-geophysical conditions, and selected results are presented.

Oliver, W. L.↗
NASA NTRS1985

The microbial community at Laguna Figueroa, Baja California Mexico - From miles to microns

The changes in the composition of the stratified microbial community in the sediments at Laguna Figeroa following floods are studied. The laguna which is located on the Pacific coast of the Baja California peninsula 200 km south of the Mexican-U.S. border is comprised of an evaporite flat and a salt marsh. Data collected from 1979-1983 using Landsat imagery, Skylab photographs, and light and transmission electron microscopy are presented. The flood conditions, which included 1-3 m of meteoric water covering the area and a remanent of 5-10 cm of siliciclastic and clay sediment, are described. The composition of the community prior to the flooding consisted of Microcoleus, Phormidium sp., a coccoid cynanobacteria, Phloroflexus, Ectothiorhodospira, Chloroflexus, Thiocapsa sp., and Chromatium. Following the floods Thiocapsa, Chromatium, Oscillatora sp., Spirulina sp., and Microcoleus are observed in the sediments.

Stolz, J. F.↗
NASA NTRS1986

Cometary particles - Thin sectioning and electron beam analysis

Thin sections (500 to 1000 angstroms thick) of individual micrometeorites (5 to 15 micrometers) have been prepared with an ultramicrotome equipped with a diamond knife. Electron microscope examination of these sections has revealed the internal structures of chondritic micrometeorites, and a subset of highly porous, fragile particles has been identified. Delicate meteoritic materials such as these are characteristic of debris from cometary meteors.

Bradley, J. P.↗
NASA NTRS1986

A continued program of planetary study at the University of Texas McDonald Observatory

The beginning of eclipses of the Pluto-Charon system was detected. The onset of coma formation of P/Halley at 5.4 au was detected and evidence of sublimation at 4.8 au when CN emission was detected. Extensive spatial maps of the gas in the comae of comets Halley and Giacobini-Zinner were obtained in fall 1985. Halley was time variable, and Giacobini-Zinner was depleted in C2 and C3 relative to CN. Comet Kopff was shown to have a pre-perihelion brightness maximum of its gas, consistent with mantle development if the comet is a high obliquity object. New Haser model scale lengths for CN, C3, and C2 were determined using results from the Faint Comet Survey. Spectra of 12 asteroids in unusual orbits showed no evidence of any comet-like emission features. In particular, 3200 Phaethon (1983 TB) has no gas or dust coma, in spite of the similarity of its orbit with the Geminid meteor stream. Data were analyzed on Saturn's H2 and CH4 bands for the recent southern summer using a Tomasko-Doose type of haze distribution. This haze model fits the data moderately well, giving a CH4 mixing ratio of (4.2 + or 0.4)x003. Simple functions were found to approximate the collision-induced rotation-translation thermal opacity of H2.

Smith, H. J.↗
NASA NTRS1986

Oblique impact - A process for obtaining meteorite samples from other planets

Cratering flow calculations for a series of oblique to normal impacts of silicate projectiles onto a silicate halfspace were carried out to determine whether the gas produced upon shock vaporizing both projectile and planetary material could entrain and accelerate surface rocks and thus provide a mechanism for propelling SNC meteorites from the Martian surface. The difficult constraints that the impact origin hypothesis for SNC meteorities has to satisfy are that these meteorites are lightly to moderately shocked and yet were accelerated to speeds in excess of the Martian escape velocity. Two dimensional finite difference calculations demonstrate that at highly probable impact velocities, vapor plume jets are produced at oblique impact angles of 25 deg to 60 deg and have speeds as great as 20 km/sec. These plumes flow nearly parallel to the planetary surface. It is shown that upon impact of projectiles having radii of 0.1 to 1 km, the resulting vapor jets have densities of 0.1 to 1 g/cu cm. These jets can entrain Martian surface rocks and accelerate them to velocities 5 km/sec. It is suggested that this mechanism launches SNC meteorites to earth.

Okeefe, John D.↗
NASA NTRS1987

Comment on the paper 'On the influx of small comets into the earth's upper atmosphere'

The possibility that comets containing up to 100 tons of ice encounter the earth's atmosphere at a rate of one every 20 min is discussed. Cometary 'hail storms' were proposed to explain observed regular transient decreases in the atmospheric UV dayglow intensity. The decreases take the form of dark 'holes' up to 50 km across. The probability that clouds of objects assumed to be as dark as the nucleus of Comet Halley between the earth and moon would be detectable by ground-based electrooptical deep space telescopes is considered. Conflicting projections of the number of objects which would be detected per hour are examined. High correlations are noted between cometary passages (Comets Encke, Tuttle, Tempel) and intervals of meteor showers (Taurids, Leonids, Geminis, etc.). The holes, however, are not correlated or coincident with the showers. It is suggested that dedicated searches for the unclassified dark objects be carried out in November, when cometary fluxes are high.

Soter, Steven↗
NASA NTRS1986

The chemical composition of comets and possible contribution to planet composition and evolution

The theory of cold aggregation of interstellar dust into comets is shown to support the ideas that comets provided not only a substantial part of the earth's water but also of its complex organic surface material. Comparison of the density of interstellar dust with meteor densities leads to the conclusion that comets are very fluffy bodies whose solid matter occupies no more than 2/5 of the total volume and possibly substantially less. This implies an extremely low comet albedo of about 0.05 in the visual even for slightly absorbing individual components.

Greenberg, J. Mayo↗
NASA NTRS1987

Optical flash background rates

Flash background rates are measured from August 18-September 5, 1985 using the Lowell 0.61-m telescope at CTIO and the 28-cm f/10 Schmidt-Cassegrain telescope at ESO. During 230.1 hours of observing 40 flash events were detected, and it was observed that the background events were dominated by meteors and satellites passing through the field-of-view. The measured flash rate is compared with that of Pedersen et al. (1984), and it is determined that the background flash rate that is applicable to the data of Pedersen et al. for February 8, 1984 is 0.023 events/hr. The morphology of that flash, which appears to be controlled by a gamma-ray burster, is examined.

Schaefer, B. E.↗
NASA NTRS1987

Middle Atmosphere Program. Handbook for MAP, volume 25

GLOBMET (the Global Meteor Observation System) was first proposed by the Soviet Geophysical Committee and was accepted by the Middle Atmosphere Program Steering Committee in 1982. While the atmospheric dynamics data from the system are of primary interest to MAP, GLOBMET also encompasses the astronomical radio and optical observations of meteoroids, and the physics of their interaction with the Earth's atmosphere. These astronomical observations and interactional physics with the Earth's atmosphere are discussed in detail.

Roper, R. G.↗
NASA NTRS1987

Long-period variations of wind parameters in the mesopause region and the solar cycle dependence

The solar cycle dependence of wind parameters below 100 km on the basis of long term continuous ionospheric drift measurements in the low frequency range is discussed. For the meridional prevailing wind no significant variation was found. The same comparison as for winter was done for summer where the previous investigations gave no correlation. Now the radar meteor wind measurement values, too, showed a significant negative correlation of the zonal prevailing wind with solar activity for the years 1976 to 1983. The ionospheric drift measurement results of Collm have the same tendency but a larger dispersion due to the lower accuracy of the harmonic analysis because of the shorter daily measuring interval in summer. Continuous wind observations in the upper mesopause region over more than 20 years revealed distinct long term variations, the origin of which cannot be explained with the present knowledge.

Greisiger, K. M.↗
NASA NTRS1987

Circulation in the mesosphere and lower thermosphere during the MAP (Middle Atmosphere Program)/WINE (Winter in the Northern Europe) period

One of the scientific programs in the MAP project, Winter in the Northern Europe (WINE) 1983 to 1984 involved an analysis of circulation processes in the middle atmosphere which characterized that winter period. Rocket soundings were conducted at many stations. In order to investigate deviations of the mean winds for the MAP/WINE period from the circulation conditions of other winters and from the climatic norm, rocket sounding data of Churchill and Barrow stations was well as the Pressure Modulated Radiometer channel 3000 data enabled the compilation of geopotential fields and the calculation of winds in the geostrophic approximation for comparison with the meteor winds. The large scale processes of the winter which determined the circulation in the period of the experiment were analyzed briefly. The analysis and results are discussed.

Tarasenko, D. A.↗
NASA NTRS1987

Characteristics of atmospheric disturbances with a quasi-two day period

In 1968 the Soviet equatorial meteor expedition measured, at an altitude of 80 to 105 km, wind velocity disturbances in the equatorial atmosphere with a quasi-two day period. An example of such disturbances is provided which shows time series of wind velocity in the meridional and zonal directions. The results of the time series analysis are discussed.

Kalchenko, B. V.↗
NASA NTRS1987

A study of the mechanism of internal gravity wave generation by quasigeostrophic meteorological motions

Numerous experiments on the detection of atmospheric waves in the frequency range from acoustic to planetary at meteor heights have revealed that important wave sources are meteorological processes in the troposphere (cyclones, atmospheric fronts, jet streams, etc.). A dynamical theory based on the others work include describing the adaptation of meteorological fields to the geostropic equilibrium state. According to this theory, wave motions appear as a result of constant competition between the maladjustment of the wind and pressure fields due to nonlinear effects and the tendency of the atmosphere to establish a quasi-geostrophic equilibrium of these fields. These meteorological fields are discussed.

Medvedev, A. S.↗
NASA NTRS1987

On the dependence of the lower thermospheric wind regime on the solar cycle

The lower thermosphere occupies the intermediate position between the overlying thermospheric layers, for which direct correlation of its parameters with solar variety variations is well established, and the underlying ones, where this correlation is mainly of an indirect character. Therefore, for understanding the mechanism of solar terrestrial correlation it is important to investigate the dependence of different atmospheric parameters in the lower troposphere, and of wind regime parameters in particular, on the solar activity. Several series of observations were used which include the results of meteor radar wind velocity measurements carried out in Obninsk complemented by the data obtained using the same technique at Jodrell Bank from 1953 to 1958 and in Kharkov from 1960 to 1963. The interannual variations of values averaged over these periods for prevailing wind velocities and semidiurnal harmonic amplitudes and also results for some months are presented. These results are discussed.

Djachenko, V. A.↗
NASA NTRS1987

Lower thermosphere wind regime according to radiometeor measurements in Kazan

Research in dynamic processes in the lower thermosphere has been carried out in Kazan using the meteor radar facilities of the Kazan State University under the MAP-GLOBMET international program. Presented is experimental data on seasonal dependences of the wind for anomalous winter circulation periods, spring and autumn reconstructions and stable summer circulation from observations conducted in 1978 to 1984. Prevailing wind parameters are shown: zonal and meridional component amplitudes and A sub 0 and azimuth of the prevailing wind vector. The values are also presented for semidiurnal zonal and meridional tidal components, their correlation coefficient and zonal component amplitude maximum time.

Sidorov, V. V.↗