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At least 1,225 records · Page 68

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NASA NTRS1980

The behavior of the O/+/-H/+/ transition level at solar maximum

An examination of the transition level at which the ionospheric ions O(+) and H(+) are equal in concentration has been carried out by using the retarding potential analyzer data from the OGO 6 satellite. Between dip latitudes of 0 and 50 deg the transition level shows a much more pronounced latitude dependence during solar maximum than during solar minimum. The longitude dependence of the transition level features indicates the roles that zonal and meridional F region winds might play in the distribution of O(+) and H(+) in the low- and mid-latitude ionosphere.

Kutiev, I.↗

NASA NTRS1980

Longitudinal variability of methane and ammonia bands on Jupiter

Results of a quantitative study of the longitudinal variations of methane and ammonia absorption on Jupiter are presented. A total of 78 high signal-to-noise ratio photoelectric spectra in the range 6000 to 6600 A were obtained on two consecutive nights, with complete longitudinal equatorial coverage each night through 9-min exposures covering a total of over 9 h. Analysis of the equivalent widths of the CH4 6190 A and NH3 6450 A absorption bands by means of a blind, automated, self-consistent method of continuum determination reveals large equivalent widths in both bands near longitudes of 35 and 340 deg and small equivalent widths near 150 deg, with a high degree of correlation between the equivalent widths of the bands. Continuum molecular absorption is found to be slightly negatively correlated with band equivalent widths. Radiative transfer calculations based on the model of Sato and Hansen (1979) using a doubling and adding technique indicate that the observed longitudinal variables of equivalent widths and continuum reflectivity are the results of longitudinal variations in ammonia cloud altitude.

Cochran, W. D.↗

NASA NTRS1980

Solar wind ion injections in the morning auroral oval

Energy versus time dispersion of precipitating ion bursts was observed during two rocket flights in the morning auroral oval. Individual bursts lasted about 20 seconds and repeated on a time scale of 100 seconds. The dispersion is interpreted as energy-dependent time-of-flight delay which provides identification of ion charge-to-mass ratio as well as injection source distance. The data are consistent with injections of magnetosheath ions with injection distances ranging from 7 to 19 earth radii. Individual events extended over a regin of at least several degrees of magnetic longitude and 0.3 degrees of invariant latitude. It is suggested that these events are associated with turbulent plasma entry into the magnetospheric entry layer.

Carlson, C. W.↗

NASA NTRS1980

Interhemispheric transport induced by neutral zonal winds in the F region

Reliable measurements of the interhemispheric ion transport velocity have shown a large longitudinal variability at equinox. The roles of zonal and meridional F region neutral winds have been evaluated in a simple way to account for the observed longitude dependence. The magnetic declination and relative displacement of the geographic and geomagnetic equators are both important considerations. It is shown that the zonal wind makes a strong contribution to the observed interhemispheric transport velocities near equinox.

Heelis, R. A.↗

NASA NTRS1979

The effect of accuracy, conservation and filtering on numerical weather forecasting

Considerations leading to the numerical design of the GLAS fourth-order global atmospheric model are discussed, including changes recently introduced into the model. The computation time and memory requirements for the fourth-order model are similar to those of the present second-order GLAS model with the same 4 deg latitude, 5 deg longitude, and 9 vertical-level resolution. However, the fourth-order model forecast skill is significantly better than that of the current GLAS model, and after three days it is comparable to the 2.5 by 3 deg version of the GLAS model in the sea level pressure maps, and has less phase errors in the 500 mb maps.

Kalnay-Rivas, E.↗

NASA NTRS1980

The distribution of S II forbidden line emission around Jupiter

Forty-six low-dispersion spectra with high temporal resolution (about 2.5 minutes) are used to investigate the distribution and intensity of the nebular S II forbidden line emission at 6716 and 6731 A around Jupiter. The emission is found to be in the form of a ring in the vicinity of the Jovian magnetic equator with radial limits between four and seven Jovian radii. It is suggested that the ring thickness is quite variable, and that the variation found in intensity with longitude is caused by preferential plasma loading of field lines associated with the Io-induced Jovian decametric bursts.

Pilcher, C. B.↗

NASA NTRS1980

Comparison of near coincident LRIR and OAO-3 measurements of equatorial night ozone profiles

The Limb Radiance Inversion Radiometer (LRIR), the infrared limb scanner on Nimbus 6, obtained equatorial night ozone profiles on 25 and 28 July, 1975, at nearly the same longitudes as the UV stellar occultation measurements made from the OAO-3 Copernicus observatory on 26 July, 1975. The LRIR determinations agree with many other data sources, but average roughly a factor of 3 lower than the Copernicus results. The LRIR results do not support the suggestion that there are serious gaps in understanding the chemistry of mesospheric ozone.

Gille, J. C.↗

NASA NTRS1980

Midlatitude measurements of the ionospheric electric field during the ALADDIN programme

Three measurements of ionospheric electric field were made during the 24-h ALADDIN rocket program at Wallops Island on June 29-30, 1974. The first of these used a double probe instrument, flown at 1500 Local Solar Time, and the second and third measurements were made by barium cloud releases at evening and morning twilight. These three electric field vectors have been compared with the predictions of a number of models of electric field due to the dynamo effects of various atmospheric tides, and also of a possible magnetospheric origin. On the assumption that the measurements were made at a location equatorward of the afternoon convergence and poleward of the morning divergence in the electric field patterns related to the Sq current system, Stening's (1973) model of the diurnal variation of the electric field induced by the (1, -2) tidal model at the time of the summer solstice correctly predicts the directions of the observed electric field. Forbes and Lindzen's (1976, 1977) model, incorporating the three major propagating tidal modes as well as the evanescent (1, -2) mode, also bears an acceptable relationship to the ALADDIN electric field directions. The ALADDIN E-field magnitudes are comparable with those obtained by ground-based observations from Millstone Hill and from Saint Santin but are about half of Stening's model values, and three times those of Forbes and Lindzen. Saint Santin E-field directions, at the same latitude but 75 deg difference in longitude, are distinctly different from ALADDIN, implying that longitudinal differences are significant.

Rees, D.↗

NASA NTRS1980

The behavior of ozone near the stratopause from two years of BUC observations

Two years of Nimbus 4 backscattered ultraviolet data have been recalibrated and reprocessed. A Laplace transform inversion was applied to radiances at 2876 A and below for 560,000 individual scans for the period April 1970-May 1972. The behavior of ozone near 50 km as a function of time, latitude, and longitude is presented. The high-latitude 1-mbar ozone mixing ratio is maximum at the winter solstice, about 10 microgram/g and is minimum at the summer solstice, about 4 microgram/g. Below 30 deg latitude the ozone is fairly constant at 4 microgram/g. Ozone variability is large in winter and spring and small in summer and fall.

Mcpeters, R. D.↗

NASA NTRS1980

21 cm maps of Jupiter's radiation belts from all rotational aspects

Two-dimensional maps of the radio emission from Jupiter were made in December 1977 at a frequency of 1,412 MHz using the Westerbork telescope. Pictures in all four Stokes parameters have been obtained every 15 deg in longitude, each smeared over 15 deg of the planet's rotation. The maps have an E-W resolution of about 1/3 of the diameter of the disk and a N-S resolution 3 times less. The total intensity and linear polarization maps are accurate to 0.5% and the circularly polarized maps to 0.1% of the maximum intensities in I. The whole set of maps clearly shows the existence of higher order terms in the magnetic field of Jupiter.

De Pater, I.↗

NASA NTRS1980

The occurrence rate, polarization character, and intensity of broadband Jovian kilometric radiation

The paper describes the major observational features of one new component of Jupiter's radio emission spectrum, the broadband kilometer wavelength radiation, or bKOM. This study, using the Voyager Planetary Radio Astronomy (PRA) experiments, reveals that the overall occurrence morphology, dynamic spectra, and polarization character of bKOM are strong functions of the latitude and/or local time geometry of the observations. The postencounter data show a decline in the mean occurrence rates and power level of bKOM and, in particular, a depletion in the occurrence rate at those same longitudes where the detection rate is a maximum before encounter. Additionally, the polarization sense undergoes a permanent reversal in sign after encounter, whereas the time-averaged wave axial ratio and degree of polarization remain relatively unchanged. Finally, no evidence of any control by Io is found. The strong dependence of the morphology on local time suggests a source whose beam is nearly fixed relative to the Jupiter-sun line

Desch, M. D.↗

NASA NTRS1980

Satellite-inferred morning-to-evening cloudiness changes

Outgoing infrared radiation values inferred from radiance measurements in the water vapor window taken at approximately 0900 and 2100 LT by scanning radiometers aboard the polar orbiting NOAA satellites are compared in order to determine whether a significant diurnal variation exists. Data with a resolution of 2.5 deg in latitude and longitude are mapped for latitudes between 50 deg N and 50 deg S for two seasons, June-August 1975 and December 1975-February 1976. Over land regions and coastal waters it is found that the 12-h differences in outgoing IR are dominated by middle and high clouds, likely of convective origin. Over the tropical oceans there is evidence of a morning bias in high cloudiness (possibly of convective origin) and low cloudiness (stratus, stratocumulus and trade wind cumulus), and an evening bias in middle cloudiness. Because of the compensation between these three cloud regimes the net morning to evening differences in outgoing IR are rather small except over the eastern oceans where the low cloud regime predominates and tends to produce a weak but statistically significant evening maximum.

Short, D. A.↗

NASA NTRS1980

Voyager image processing at the Image Processing Laboratory

This paper discusses new digital processing techniques as applied to the Voyager Imaging Subsystem and devised to explore atmospheric dynamics, spectral variations, and the morphology of Jupiter, Saturn and their satellites. Radiometric and geometric decalibration processes, the modulation transfer function, and processes to determine and remove photometric properties of the atmosphere and surface of Jupiter and its satellites are examined. It is exhibited that selected images can be processed into 'approach at constant longitude' time lapse movies which are useful in observing atmospheric changes of Jupiter. Photographs are included to illustrate various image processing techniques.

Jepsen, P. L.↗

NASA NTRS1980

Modelling of equatorial phase and amplitude scintillations from OGO-6 and AE irregularity data

The technique of modelling equatorial phase and amplitude scintillations from in-situ measurements of irregularity amplitude, ambient ionization density and irregularity power spectrum is outlined. The in-situ measurements do not directly provide information on irregularity layer thickness for which radar backscatter observations are utilized. The equatorial scintillation models developed from OGO-6 and AE-C in-situ measurements during the two solstices are presented. Considerable differences in the longitude variation of scintillations are predicted during the two solstices. The model estimates are in good agreement with the available ground based phase and amplitude measurements. Problems associated with the use of bottomside spread-F data for transionospheric propagation modelling at VHF/UHF are also discussed.

Basu, S.↗

NASA NTRS1980

Coordinates of features on the Galilean satellites

Control nets of the four Galilean satellites, established photogrammetrically from pictures taken by the two Voyager spacecraft during their flybys of Jupiter in 1979, are discussed. Coordinates of 504 points on Io, 112 points on Europa, 1547 points on Ganymede, and 439 points on Callisto are listed. Selected points are identified on maps of the satellites. Measurements of these points were made on 234 pictures of Io, 115 pictures of Europa, 282 pictures of Ganymede, and 200 pictures of Callisto. The systems of longitude were defined by craters on Europa, Ganymede, and Callisto. Preliminary solutions are found for the directions of the axes of rotation of the Galilean satellites. Mean radii are determined as 1815 + or - 5 km for Io, 1569 + or - 10 km for Europa, 2631 + or - km for Ganymede, and 2400 + or - 10 km for Callisto.

Merton, E. D.↗

NASA NTRS1980

Energetic particles in the pre-dawn magnetotail of Jupiter

A detailed account is given of the energetic electron and proton populations as observed with Voyagers 1 and 2 during their passes through the dawn magnetotail of Jupiter. The region between 20 and 150 R sub J is dominated by a thin plasma sheet, where trapped energetic electron and proton fluxes reach their maximum. Proton spectra can be represented by an exponential in rigidity with a characteristic energy of approximately 50 keV. Proton anisotropies were consistent with corotation even at 100 R sub J. A major proton acceleration event as well as several cases of field aligned proton streaming were observed. The flux of 0.4 MeV protons decreases by three orders of magnitude between 30 and 90 R sub J and then remains relatively constant to the magnetopause. Fine structure in the data indicate longitudinal asymmetries with respect to the dipole orientation. Electron spectra in the magnetosheath and interplanetary space are modulated by the Jovian longitude relative to the subsolar point.

Schardt, A. W.↗

NASA NTRS1981

Galactic X-ray emission from pulsars

The contribution of pulsars to the gamma-ray flux from the galactic plane is examined using data from the most recent pulsar surveys. It is assumed that pulsar gamma-rays are produced by curvature radiation from relativistic particles above the polar cap and attenuated by pair production in the strong magnetic and electric fields. Assuming that all pulsars produce gamma-rays in this way, their luminosities can be predicted as a function of period and magnetic field strength. Using the distribution of pulsars in the galaxy as determined from data on 328 pulsars detected in three surveys, the local gamma-ray production spectrum, the longitude profile, and the latitude profile of pulsar gamma-ray flux are calculated. The largest sources of uncertainty in the size of the pulsar contribution are the value of the mean interstellar electron density, the turnover in the pulsar radio luminosity function, and the average pulsar magnetic field strength. A present estimate is that pulsars contribute from 15 to 20 % of the total flux of gamma-rays from the galactic plane.

Harding, A. K.↗

NASA NTRS1981

Baseline mathematics and geodetics for tracking operations

Various geodetic and mapping algorithms are analyzed as they apply to radar tracking systems and tested in extended BASIC computer language for real time computer applications. Closed-form approaches to the solution of converting Earth centered coordinates to latitude, longitude, and altitude are compared with classical approximations. A simplified approach to atmospheric refractivity called gradient refraction is compared with conventional ray tracing processes. An extremely detailed set of documentation which provides the theory, derivations, and application of algorithms used in the programs is included. Validation methods are also presented for testing the accuracy of the algorithms.

James, R.↗