Showing papers on "Longitude published in 1981"

Voyager measurement of the rotation period of Saturn's magnetic field

Abstract: Saturn's radio rotation period was determined using measurements made by the planetary radio astronomy experiment onboard the Voyager spacecraft. The sidereal period deduced, 10 hr 39 min 24 sec ? 7 sec, is within the 10 hr to 11 hr range of optical periods derived from a century of atmospheric spot and Doppler spectroscopy observations. The radio rotation period is presumably that of the planet's magnetic field. A provisional Saturn longitude convention is proposed and equations are provided to compute a longitude ephemeris and to transform between the proposed system and the (10 hr 14 min) system used for the Pioneer 11/Saturn encounter. The degree of longitude smearing which could result over the long term from the merging of data sets organized in this system is evaluated. No evidence of control of the radio emission by any of Saturn's satellites was found.

Synoptic observations of Jupiter's radio emissions: average statistical properties observed by voyager

Abstract: Observations of Jupiter's low frequency radio emissions collected over one month intervals before and after each Voyager encounter were analyzed. Compilations of occurrence probability, average power flux density and average sense of circular polarization are presented as a function of central meridian longitude, phase of Io, and frequency. The results are compared with ground based observations. The necessary geometrical conditions are preferred polarization sense for Io-related decametric emission observed by Voyager from above both the dayside and nightside hemispheres are found to be essentially the same as are observed in Earth based studies. On the other hand, there is a clear local time dependence in the Io-independent decametric emission. Io appears to have an influence on average flux density of the emission down to below 2 MHz. The average power flux density spectrum of Jupiter's emission has a broad peak near 9MHz. Integration of the average spectrum over all frequencies gives a total radiated power for an isotropic source of 4 x 10 to the 11th power W.

Northern Hemisphere Airstream Regions

Abstract: Near-surface airstream source regions of the Northern Hemisphere have been identified using 16-year mean resultant winds from 3° latitude by 3° longitude grids. Tracing the airstreams back to their divergent centers reveals 19 different sources during various seasons of the year. Five of these sources(air originating over the North and South Pacific and Atlantic Oceans and air over Turkey) are resident in the Northern Hemisphere 12 months of the year. Another three (central Asian, Arctic and central East Asian air) exist for at least 11 months per year. The remaining 11 source regions are present from 1–9 months per year and their area of influence is much less than that of the 5 year-long sources. In the mean, there are several favored locations for frontal zones, e.g., a north–south band in Mexico (dividing Atlantic from Pacific air), a north–south band in northern South America, and two northeast–southwest trending bands over the cast coasts of Asia and North America, representing the mean lea...

Multi-spacecraft observations of heliographic latitude-longitude structure in the solar wind

Abstract: The heliographic latitude-longitude structure of high speed solar winds observed prior to the maximum of sunspot cycle 20 is investigated by multi-spacecraft comparisons. It is shown that differences in solar wind structures are due to two different kinds of spatial structures. One structure is found to be consistent with the simultaneous existence of a single, broad stream at latitudes above 7 deg N and a series of narrow streams at lower latitudes, while the other is consistent with the existence of a latitudinally sloping stream boundary near the solar equator. For latitude separations less than 3.5 deg, cross-correlations of Explorer-Mariner velocities show only previously reported systematic increases in velocity with latitude, and for latitude separations from 3.5 to 6.2 deg, differences in high speed streams shift in longitude and/or amplitude are also identified on a timescale of one solar rotation.

The North American Plate from the Arctic Archipelago to the Romanzof Mountains

Abstract: The part of the North American plate under consideration lies north of latitude 68°N and extends from the Coppermine Arch at longitude 120°W to the Romanzof Uplift at longitude 142°W. It embraces portions of Canada’s continental shelf, the Cordilleran Foldbelt, and the Interior Platform of mainland Canada and Banks Island of the Arctic Archipelago. The project area includes segments of several physiographic (after Bostock, 1970) and tectonic (after Norris, D. K., 1973) elements shown in Figs. 1 and 2, respectively.

Ocean mesoscale variability from repeat tracks of Geos‐3 altimeter data

Abstract: The Geos-3 satellite altimeter observed numerous sea surface profiles along nearly repeated tracks in the western North Atlantic during its 3.5-year lifetime, enabling observation of the variation of sea surface topography along these tracks. Analysis of 14 north-going and 13 south-going sets of repeated tracks has yielded the variability of the surface at a resolution of 1° from 25° to 41°N latitude and from 60° to 80°W longitude. The observed rms variation of surface topography ranges from about 8 cm in the Sargasso Sea to a maximum of 48 cm in the Gulf Stream meander region, in agreement with known mesoscale energetics of this region.

Simultaneous measurements of meteor winds and green line intensity variations: Gravity waves and planetary waves

Abstract: We provide evidence of the influence of planetary waves on the intensity variations of the 557.7-nm airglow emission. The comparison relies on simultaneous measurements at four different stations located between 37°N and 56°N in latitude, 36°E and 3°W in longitude: meteor wind observations in France and USSR and optical measurements at 557.7 nm in France and Spain, in July 1971. An oscillation of period near 2 days had been identified in the wind data; it is also apparent on the nightglow intensity variations. Its characteristics are well accounted for by the first symmetric mode of the 52- hour period planetary oscillation of horizontal wave number 3, described previously (Glass et al., 1975). A 4±1 hour period gravity wave apparently present in the data of the French stations is discussed.

Pre-encounter distributions of Saturn's low frequency radio emission

Abstract: An analysis of Voyager 1 pre-encounter data is presented in which one-month averages of flux density from Saturn are determined as functions of both central meridian longitude and frequency. Comparisons of corresponding distributions for two one-month intervals seven months apart yield information on their stability, and a redetermination of the magnetos-pheric rotation period.

Rocket measurements of the distribution of water vapor in the stratosphere at high latitudes

Abstract: Two measurements of the altitude distribution of stratospheric water vapor have been made with a rocket-borne infrared photometer, which measures long path atmospheric absorption of the solar beam in the 2.7-μm spectral region. The photometer was flown from Cape, Parry, Canada (latitude 70.2°N, longitude 124.6°W), on December 6, 1974, and from Kiruna, Sweden (latitude 67.9°N, longitude 21.1°E), on March 13, 1975, at sunset. These measurements indicate that the water vapor mixing ratio increases from approximately 1.5 ppmv at the tropopause to approximately 8 ppmv at 50 km and then decreases at higher altitudes. These features are consistent with current theoretical considerations of the stratospheric water vapor distribution and with the results of other experimental investigations. A source region from methane oxidation at higher altitudes and a sink near the tropopause are suggested. A computer simulation of laboratory measurements indicated that the wings of the water vapor lines in the 2.7-μm region are super-Lorentzian. This super-Lorentzian behavior of the line wings was incorporated in the analysis of the atmospheric measurements.

Recently increased tropical cyclone activity and inferences concerning coastal erosion and inland hydrological regimes in New Zealand and Eastern Australia

Abstract: For the area bounded by 0–35 °S latitude and 105 °E–105 °W longitude a significant increase of tropical cyclone frequency occurred about 1954–55 and this regime persisted throughout the 1960s and 1970s. Probably this frequency increase was accompanied by an increase of cyclonic storm intensity. It was related to an atmospheric pressure regime change over Australasia which commenced in early 1954.

IUE monitoring of the spatial distribution of the H Ly-alpha emission from Jupiter

Abstract: North-south spatial maps of the Jovian H Lyman-alpha emission observed with the IUE satellite support the identification of a marked longitudinal asymmetry in the equatorial brightness, with the peak around lambda III(1965) = 50-100 deg longitude, and show a weaker planet-wide equatorial brightening above the level predicted by a plane-parallel layer model. IUE observations made 18 months after the initial discovery of the localized emission bulge establish that it is fixed with respect to Jupiter's magnetic longitude (lambda III system) and not with respect to atmospheric longitude (lambda II system). In addition, a decrease in brightness of 20% in the region of the emission bulge has been observed over a one yr interval, while the rest of the planet remained roughly constant in brightness. This decrease is more than would be expected as a result of changes in the incident solar Lyman-alpha flux, indicating a real decrease in reflectivity in this region of Jupiter's upper atmosphere.

Positions of Sunspot Groups and Solar Rotation

Abstract: The question is studied whether the one-year solar oscillation found by V. F. Chistyakov for the years 1965–1973 can be traced in the observations of sunspots of 1874–1971 published by Greenwich Observatory. The result is negative. But the study leads to the following two conclusions: (1) The average observable centres of gravity of spot groups are variably displaced towards the central meridian or towards the limb, the time scale of this variability being of the order of 70 years. Thus the angular velocity should be determined from recurrent groups in transit of the central meridian only. (2) The angular velocity will be smaller when determined from older spots.

Large amplitude stationary Rossby waves in the Southern Hemisphere

Abstract: Large Amplitude stationary waves downstream of South America, and in the lee of Australia were investigated using Tiros N photographs. These waves appear to be Rossby lee waves associated with anomalous poleward flow over the Andes and by continental heating over Australia. The waves have a maximum amplitude near 300 mb between 20 and 40 deg S and correlate well with observed precipitation bands in the Atlantic and Pacific Oceans. The orientation of these waves is such that they transfer zonal momentum to the roaring forties latitudes. Stationary Rossby waves, in the Northern Hemisphere, have a characteristic wavelength of the order of 120 deg longitude. In January the observed stationary wavelengths have a wavelength of less than 60 deg longitude with an amplitude in the upper tropospheric meridional wind of more than 15 m sec E-1.

Large-scale sea-surface temperature anomalies in the northeast pacific ocean

Abstract: Slow-developing, long-lasting perturbations of sea-surface temperature in the eastern North Pacific are revealed by anomaly patterns representing monthly deviations from the mean seasonal cycle. These patterns are typically defined by a central core of anoma!ously warm (or cold) water located approximately between latitudes 30"-45"N, and west of longitude 140"W, which is partially surrounded by anomalously cold (or warm) water to the north, east, and south. They can persist up to qeveral years and then, in a relatively short time, un&ergo a pattern reversal in which warm anomalies are replaced by cold anomalies and vice versa. Some examples are presented that represent selected periods in the 1960s and 1970s. A coniparison of mean wind fields for January 1976 and January 1980, which were periods of sharply. contrasting sea-temperature anomaly patterns, suggest that air-sea interaction processes have an active role in forming and maintaining these patterns. RESUMEN

The Sun’s Rotation and Perturbations of Geopotential Height and Temperature Fields in the Stratosphere

Abstract: The morphology of a solar activity effect apparently connected with the Sun's rotation and showing up in 25-day and 13.6-day oscillations of stratospheric geopotential and temperature fields is analysed in this study. The used data cover the height range between roughly 20 and 30 km and a timespan from July 1965 to October 1971. Most prominent responses are found for zonal harmonic wave number 1 at the oscillation period of 25 days (solar rotation period modulated by seasonal changes) and for the zonally averaged meteorological quantities at the oscillation period of 13.6 days. Additional statistically significant effects show up in the zonal harmonics with wave number 1 and 3 at half the solar rotation period and in the zonal means with periodicities near 25–27 days. The results point towards a modulation of the quasistationary stratospheric planetary wave with a positive geopotential anomaly around roughly 180° longitude by solar activity changes. The direct physical mechanisms of this Sun-climate relationship are not yet clear, but it can be concluded that atmospheric dynamics is an important factor for its morphology and that downward propagation of such effects seems possible and should be investigated in future studies.

Multisatellite observations of geomagnetic pulsations

Abstract: The technique of using simultaneous data from more than one spacecraft to study hydromagnetic waves in space is proving to be a very powerful one which will undoubtedly become more widespread in the future. We review the results obtained using this technique thus far. All of the work has involved longer period (>20 s) pulsations and most of the data has come from near geostationary orbit. Attempts to measure the thickness of field line resonance regions have not so far been conclusive, but they suggest that values of about (l/2)R E are typical. Signals in the Pc3 and 4 bands in the morning are coherent over at least 20° of longitude while in the afternoon they are much more localized. One afternoon source is resonance with hot ions. Pi 2’s on the nightside can also be confined to small regions of longitude.