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Klein, M. J.

Publications and source records attributed to Klein, M. J..

At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Interagency Array Study Report

The interagency array study that was convened in early 1982 to determine which of the world's large radio reception facilities might be feasibly and beneficially enlisted to help support the Voyager encounters at Uranus (1986) and Neptune (1989), and also to examine the future for such similar events and options as might appear is discussed. A similar but more specific study of the Parkes Radio Telescope at Uranus Encounter was just then being completed with a strong positive recommendation, and formed the foundation of the broader study. The approach, driving considerations, and outcome of the interagency array study are discussed. The recommendations of the study team concentrated upon the Voyager Encounters are: specifically to develop Parkes for the Uranus Encounter, while pursuing related Advanced Systems development work with the Owens Valley Radio Observatory, and to seek support for the Neptune Encounter from Parkes, the Very Large Array near Socorro, Mexico, and the Japanese institute of Space and Astronautical Sciences 64 meter station.

Wayland, J. W.↗
NASA NTRS1983

Uranus - Variability of the microwave spectrum

Radio astronomical observations of Uranus show that the radio emission spectrum is evolving in time. Ammonia vapor must be depleted in the Uranian atmosphere as Gulkis et al. (1978) previously suggested. Since 1965, ammonia either has been decreasing in time or is a decreasing function of latitude, or both, provided that the radio emission is atmospheric in origin. If Uranus has an observable low-emissivity 'surface', these trends may be reversed. The microwave observations made in 1965, at the time when the spin axis of Uranus was nearly perpendicular to the sun-Uranus line, are consistent with an atmospheric opacity profile that would be produced by saturated ammonia vapor in a predominantly hydrogen atmosphere. At the present time, when the spin axis of Uranus is nearly aligned with the sun-Uranus line, the measurements require an opacity that would be produced by saturated water vapor. A large thermal gradient between the pole and equator is ruled out.

Gulkis, S.↗
NASA NTRS1982

Sensitive ammonia observations in the southern hemisphere

The 64-m spacecraft communication antenna of the NASA-JPL Deep Space Network has been equipped for spectral line observations at K band (18-25 GHz). To demonstrate the potential of this system, preliminary observations of the (1, 1) transition of ammonia are reported for a selection of eight southern molecular clouds. Estimates of gas density and ammonia column density are reported for six sources.

Dickinson, D. F.↗
NASA NTRS1981

Constraints on the composition of the Venus atmosphere from microwave measurements near 1.35 cm wavelength

The determination of the brightness temperature of Venus near 1.35 cm wavelength is reviewed. The observed brightness temperature is compared with models for the microwave emission based on the physical and chemical structure of the atmosphere as obtained from spacecraft. Upper limits are set on the concentrations of microwave-absorbing minor constituents. In particular, upper limits are determined for SO2 (180 ppm) and H2O (0.3%) for a mixing-ratio profile that is uniformly mixed up to the cloud bottom at 50 km and is rapidly depleted (scale height, approximately 1 km) at higher altitudes. The total optical depth of the cloud region at or above 50 km is less than 0.17 at 1.35 cm wavelength. The SO2 upper limit is only in marginal agreement with the spacecraft results, and it may be that the latter have been overestimated, or that the distribution of SO2 is more complex than given by the uniform mixing model.

Janssen, M. A.↗
NASA NTRS1981

Venus. I - Carbon monoxide distribution and molecular-line searches

An observational program to study variations of the vertical distribution of CO in the Venus atmosphere is presented. Measurements of the J = 0 - 1 absorption line at 2.6 mm wavelength are reported for two phase angles in 1977, one near eastern elongation (February) and the other near inferior conjunction (April). The two spectra are significantly different, with the April absorption line being narrower and deeper. The results of numerical inversion calculations show that the CO mixing ratio increases by a factor of approximately 100 between 78 and 100 km and that the CO abundance above approximately 100 km is greatest on the night-side hemisphere. These conclusions are in qualitative agreement with theoretical models. In addition to the CO observations, a search for other molecules was made to provide further information on the composition of the Venus middle atmosphere. The J = 0 - 1 transition of (C-13)O was detected and upper limits were derived for nine other molecules.

Wilson, W. J.↗
NASA NTRS1981

Precision flux density measurements of the giant planets at 8420 MHz

Precision measurements of the 3.56 cm flux densities of Jupiter, Saturn, Uranus, and Neptune are reported. The results are compared with previously published measurements as a means of: (1) remotely sensing long-term changes in the microwave emission from the atmospheres of these planets; (2) measuring the effects of Saturn's rings on the disk temperature as observed from earth at different ring inclination angles.

Turegano, J. A.↗
NASA NTRS1981

Precision flux density measurements of the giant planets at 8420 MHz

Precision measurements of the 3.56 cm flux densities of Jupiter, Saturn, Uranus, and Neptune are reported. The results are compared with previously published measurements as a means of: remotely sensing long-term changes in the microwave emission from the atmospheres of these planets and measuring the effects of Saturn's rings on the disk temperature as observed from earth at different ring inclination angles.

Turegano, J. A.↗
NASA NTRS1980

The position angle of Jupiter's linearly polarized synchrotron emission Observations extending over 16 years

Parkes, Owens Valley and Goldstone measurements are presented, showing the variation with central meridian longitude of the position angle of Jupiter's linearly polarized synchrotron emission at wavelengths of 21, 13, 11 and 6 cm; the observations span a total time interval greater than one Jovian orbital period. The form of the position angle versus longitude curve shows a slight dependence on wavelength and epoch. The epoch dependence appears to reflect Jupiter's changing aspect with respect to the earth. The observations yield a Jovian rotation period agreeing to within about 0.02 s with that derived from the decametric burst measurements, implying a highly stable inner magnetic field configuration.

Komesaroff, M. M.↗
NASA NTRS1978

Saturn's microwave spectrum: Implications for the atmosphere and the rings

Measurements of Saturn's disk temperature are compiled to determine the planet's microwave spectrum from 1 mm to 100 cm wavelength. The data were adjusted to conform with a common flux density scale. A model of Saturn's rings is used to remove the effects of the rings from the atmospheric component at centimeter and decimeter wavelengths. Theoretical spectra for a number of convective atmospheric models were computed and compared with the observed spectrum. Radiative-convective models with approximately solar composition and with an effective temperature of approximately 89 K are in good agreement with the observations. The agreement between the observed and theoretical spectra is a strong indication that gaseous ammonia is present in Saturn's atmosphere. A good fit to the data is obtained with an ammonia mixing ratio of approximately 5 x 10,0001. A comparison of the millimeter wavelength data with the best-fitting atmospheric spectrum indicates that the thermal component of the ring brightness temperature near 1 mm wavelength is approximately 25 k.

Klein, M. J.↗
NASA NTRS1978

Evidence of an increase in the microwave brightness temperature of Uranus

Measurements are reported which indicate that the microwave brightness temperature of Uranus near 3 cm wavelength has increased by about 35% in the past decade. It is suggested that changes of this magnitude could be caused by seasonal or latitudinal variations of the microwave opacity of the Uranus atmosphere. The data appear to be inconsistent with models of synchrotron emission from a trapped radiation belt.

Klein, M. J.↗
NASA NTRS1978

Jupiter's atmosphere - Observations and interpretation of the microwave spectrum near 1.25-cm wavelength

Measurements of Jupiter's disk-temperature spectrum in the 20- to 24-GHz (1.5 cm less than lambda less than 1.25 cm) region are reported. These data are combined with previously published data to produce a uniformly calibrated thermal spectrum of Jupiter in the wavelength interval 0.85 to 2.1 cm. Model studies are carried out to determine optimum pressure-temperature profiles for an assumed radiative-convective temperature structure. It is found that the temperature at the 1-bar total effective pressure level is between 140 and 165 K, with a most probable value of 153 K, provided that NH3 is uniformly saturated in the clouds on a global scale. We show that the temperature profile for the microwave model is approximately 20 K cooler than the profiles derived from infrared data. An explanation of this discrepancy is discussed in terms of a model which invokes different NH3 distributions in the belts and zones.

Klein, M. J.↗
NASA NTRS1978

Venus - Detection of variations in stratospheric carbon monoxide

The reported observations of the J = 0-1 rotational transition (115271.2 MHz) of carbon monoxide in the Venusian atmosphere indicate that the distribution of stratospheric CO is variable. Observations were obtained with a 11-m antenna on several days in February 1977, when Venus was near maximum eastern elongation (k approximately 0.4), and in April 1977 during inferior conjunction (k approximately 0.01). Differences in the line intensities and shapes for the two data sets are described. The results are interpreted to suggest that on the nightside of Venus there is relatively more CO at higher altitudes and relatively less CO at lower altitudes than on the dayside of the planet.

Gulkis, S.↗
NASA NTRS1976

The variability of the total flux density and polarization of Jupiter's decimetric radio emission

Results are presented for a continuing program to monitor the Jovian 13-cm flux at weekly intervals and for an observational program to measure the linear polarization on an annual basis. The initial results of these programs are compared with existing data. Some implications about the radiation belts are discussed. When the new data are combined with previously published 11- and 21-cm measurements, it is found that the nature of the time variations during the past 13 years is similar but not identical at these wavelengths and that there is no convincing evidence that the variations are correlated with either solar activity or Jupiter's distance from the sun. The peak degree of polarization of the synchrotron has not changed more than 1% from the mean value of 24.5% during the 12-year interval considered.

Klein, M. J.↗
NASA NTRS1976

A search for radio emission from ionized hydrogen in M15

A sensitive search at 3.6 cm for thermal emission from ionized gas in the globular cluster M15 (NGC 7078) reveals no emission greater than the experimental error, which is 0.003 Jy. Based on this flux-density limit, the mass of ionized gas within 3 pc of the cluster center is less than 26 solar masses. This result suggests that the ionized-gas content of M15, which contains an intense X-ray source, is not greatly enhanced compared with similar globular clusters without known X-ray sources. This mass limit is an order of magnitude greater than the amount of gas required to produce the X-ray flux by accretion onto massive black holes.

Klein, M. J.↗
NASA NTRS1975

Recent increase in Jupiter's decimetric radio emission

Observations of the linear polarization properties of Jupiter's decimetric radioemission showed the planet's total intensity to increase between late summer 1973 and July 1974. Measurements were made with the NASA 64-m parabolic antenna operating at a wavelength of 13.1 cm. Data were plotted as a function of the longitude of the central meridian. Both data sets showed similar periodic intensity variation with longitude. However, the 1974 data points were consistently above the corresponding 1973 values. The flux density difference was attributed to the increase in the planet's decimetric radio emission. Measured at wavelengths of 21 cm and 11 to 13 cm the average peak flux densities were plotted as a function of the epoch of each observation.

Klein, M. J.↗