Monitoring of the behavior of naturally pulsating galactic radio sources, or pulsars, through regularly spaced measurements of pulse arrival times, has been conducted by several laboratories. A tabular presentation is here made of pulse arrival time measurements from the NASA Deep Space Network between late 1968 and early 1981. By expressing the measurements in ephemeris time, and referring them to the geocenter, usable tables of results have been generated for each pulsar listed in the first of the tables given. The considerations addressed by the tables are: (1) a necessary step in the study of pulsar dynamics is the reduction of topocentric arrival times to the barycenter of the solar system; (2) the tabulated data are accessible to all opinions as to the procedures to be used in interpreting arrival time data; and (3) different observing programs can usually be combined to produce an improvement in the total data set.

The structure and variability of the middle atmosphere of Venus (60 to 140 km) were studied from the Pioneer Venus orbiter by using an infrared remote sensing instrument developed from those on terrestrial weather satellites. The wavelengths observed were selected to allow the vertical temperature profile, the albedo, the cloud opacity profile, and the far infrared opacity due to water vapor to be inferred from the data. The measured temperature field has been used to model the dynamics of the region, and the thermal and solar fluxes have been used to compute the planetary radiation budget. The results for the diurnal variation of temperature at a given height show fairly small amplitudes up to an altitude of about 95 km, above which the day to night contrast increases rapidly with height. At the equator the dependence of temperature in the stratosphere (65 to 95 km) on solar longitude is dominated by a wave number 2 solar tide with an amplitude of about 10 K. Transient features including traveling waves are also present on a wide range of scales. The equator to pole gradients are larger than expected, and the stratosphere is typically 15 to 20 K warmer at the pole than at the equator. Nightside temperatures in the mesosphere (95 to 140 km) are generally low except for a local maximum near the antisolar point, and breakdown of local thermodynamic equilibrium is evident above about 120 km. The winds forced by the measured temperature field in a diagnostic circulation model show the ‘4‐day’ zonal wind decreasing rapidly with height above the clouds and becoming very small by 80 or 90 km. altitude. The mean meridional component reverses at about the same altitude and pole‐to‐equator winds as high as 100 m s −1 are produced above 100 km. The most significant discovery concerning the cloud morphology is a dramatic ‘dipole’ structure, consisting of two clearings in the cloud at locations straddling the pole and rotating around it every 2.7 days. The clearings are thought to be evidence for subsidence of the atmosphere at the center of a polar vortex. The absence of corresponding evidence for descending motions elsewhere suggests that a single large circulation cell may fill the northern hemisphere at levels near the cloud tops. A crescent‐shaped ‘collar’ region, consisting of anomalous and variable temperature and cloud structure, surrounds the pole at about 70°N and rises perhaps 15 km above the mean cloud top elevation; it has a solar‐fixed component and sometimes contains spiral streaks. This feature, and the double vortex eye, are large, persistent deviations from the mean circulation due to planetary‐scale waves of unknown origin. No explanation is offered at present for the dominance of wave number 2 structures at equatorial and polar latitudes, while the mid‐latitudes are dominated by a wave number 1 feature (the polar collar). A thin, ubiquitous haze is found covering the northern hemisphere, including the polar features. The far‐infrared opacity of the atmosphere is greater in the afternoon than at any other local time and also tends to increase at high latitudes; the most likely cause is a small but variable amount of water vapor. The angular dependence of the intensity of scattered sunlight fits a cloud model consisting of 1‐µm droplets. The observed angular and planetographic distribution of total reflected solar energy and emitted thermal flux, when integrated over the northern hemisphere of Venus, are consistent with radiative balance to within the accuracy of a preliminary calculation.

Orbiter infrared measurements of the Venus atmosphere in the 60- to 140-kilometer region show very small diurnal temperature differences near the cloud tops, increasing somewhat at higher levels. The seasonal (that is, equator to pole) contrasts are an order of magnitude larger, and the temperatures unexpectedly increase with increasing latitude below 80 kilometers. An isothermal layer at least two scale heights in vertical extent is found near the 100-kilometer altitude, where the temperature is about 175 K. Structure is present in the cloud temperature maps on a range of spatial scales. The most striking is at high latitude, where contrasts of nearly 50 K are observed between a cold circumpolar band and the region near the pole itself.

The Goldstone radar system was operated at wavelengths of 3.5 and 12.6 cm to probe the Martian surface during the 1975 opposition. Regions studied in detail by range-Doppler techniques are Syrtis Major, Sinus Meridiani, and the crater Schiaparelli. Average rms slopes of 1.6° and 1.1° were measured in Syrtis Major at 3.5 and 12.6 cm, respectively, while the average reflectivity was 0.064 ± 0.02 at both wavelengths. No wavelength dependence of surface roughness was seen in Sinus Meridiani, where rms surface slopes averaged 1.8° and the reflectivity was 0.08 ± 0.02. The regions around Schiaparelli were probed at a 12.6-cm wavelength. The echo from the bottom of the crater was undetectable. Hence ρ0C < 25, where ρ0 is the reflectivity and C is the Hagfors roughness parameter. Operating at 3.5 cm during May and June of 1976, 149 continous-wave echo spectra were obtained near latitude 18°, sampling most longitudes including the early Viking landing sites A1 and A2. The average total radar cross section is 4.8% of the geometrical cross section. The diffuse component was estimated to be 1.9%, leaving 2.9% to the average quasi-specular component. The average rms slope is 4.1°. Six spectra obtained at site A1 indicate that rms slopes are 5 to 9° between latitudes 17 and 19°. Three spectra obtained at s site A2 indicate an rms slope of 3.9°.

The Goldstone radar system was used at a wavelength of 12.6 cm to probe the Martian surface during the 1973 opposition. Measurements of range and reflected power were made at least weekly between July 12 and November 24. Surface cells isolated by the radar system were 8 km E-W × 110 km N-S. Altitudes were calculated from signal time delays measured relative to a triaxial ellipsoid and were combined with altitudes measured during the 1971 opposition. Contours of constant altitude were calculated at 200 m intervals between latitudes −14° and −22°. These contours are presented in conjunction with Mars charts derived from Mariner 9 television pictures. Reflected power was measured at angles of incidence between −5° and +5°. These measurements were combined with those obtained during the 1971 opposition. Predictions of the reflected power versus the angle of incidence were calculated from the exponential surface model of Hagfors. The predictions were fit to the data in a least-squares sense, using a nonlinear iterative procedure, to yield estimates of surface roughness and reflectivity. The smoother regions exhibit a typical reflectivity of 8.2%. A tendency for the reflectivity to decrease with increasing roughness was observed.

Eleven pulsars were observed and five were detected at 15.1 GHz. Several exhibit strong scintillations at 8.4 GHz. Estimates are made of the spectral indices of five pulsars. Average pulse shapes are presented for the stronger signals.

Taking advantage of the favorable opposition of 1971, the Goldstone radar system, operating at 2388MHz, was used to scan the Martian surface. Measurements of altitude and reflected power were taken approximately every 3 days. Each measurement represents an area 8km E-W × 80km N-S, the highest resolution attained to date. Altitude measurements obtained on different observing days were combined to produce altitude profiles for three complete rotations, each at different latitudes. Large-scale variations in altitudes cover a range of 14km. Altitude changes of 5 in 30km of longitude were observed. The altitude profiles show the heavy cratering of the surface, and several large craters (50–100km) 1–2 km deep are easily seen. Reflected power for different angles of incidence was measured, yielding the scattering properties of the surface as a function of longitude. Correlation was found between the peak intensity of the reflected signal and the width of the scattering function. The average relationship between the intensity and the width suggests a power reflection coefficient of at least 0.064 ± 0.012. Departures from the average are interpreted as deviations in the reflection coefficient from the mean value. These variations are presented as a function of longitude for each of the three rotations.

THE first discontinuity in period of the Vela Pulsar (PSR 0833–45) occurred between February 24 and March 3, 1969 (refs. 1 and 2). The period decreased by 208 ns and the rate of change of period increased by 1 × 10−15 s s−1. A similar discontinuity occurred between August 21 and September 4, 1971. A preliminary analysis of the data shows that the period decreased by 179 ns and that the rate of change of period increased. A definitive analysis of the discontinuity will have to await more data because of the normally irregular behaviour of the period3.

view Abstract Citations (23) References (14) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Observations of Interstellar Scintillations of Pulsar Signals at 2388 MHz Downs, G. S. ; Reichley, P. E. Abstract The scintillation index and fading time have been measured at 2388 MHz. These measurements, together with low-frequency measurements, are interpreted in terms of the extended-medium theory of Uscinski. Typically we find a scale size of electron irregularities of 4 X 10 cm and an rms value of the electron density of 2 X 1(h . Failure to observe long-term variations suggests a second component of density fluctuations. Publication: The Astrophysical Journal Pub Date: January 1971 DOI: 10.1086/180657 Bibcode: 1971ApJ...163L..11D full text sources ADS | data products SIMBAD (8)